1
Latent Tuberculosis:
Advances in Diagnosis and Treatment
Dimitrios Basoulis, Georgia Vrioni, Violetta Kapsimali,
Aristeidis Vaiopoulos and Athanasios Tsakris
Medical School of the National and Kapodistrian University of Athens
Greece
1. Introduction
Tuberculosis (TB) is one of the oldest diseases known to affect humans. It is caused by
bacteria belonging to the Mycobacterium tuberculosis complex and strains of these bacteria
have been found in human bones dated from the Neolithic era. It was known to the ancient
Greeks, Indians and the Inca, making it a disease with a global distribution even from
ancient times. Latent tuberculosis infection refers to a time period where the host has been
exposed and infected by the bacteria yet does not exhibit any signs or symptoms of
infection. It is estimated that one third of the world, almost 2 billion people suffer from
latent tuberculosis infection.
2. Epidemiology
Tuberculosis is a multisystemic infection with myriad presentations and manifestations.
According to the World Health Organization (WHO) it is estimated that one third of the
world's population is currently infected by the bacillus and out of those people 5-10% will
exhibit symptoms at some point during their life. WHO estimates that the largest number of
new TB cases in 2008 occurred in the South-East Asia Region, which accounted for 35% of
incident cases globally. However, the estimated incidence rate in sub-Saharan Africa is
nearly twice that of the South-East Asia Region with over 350 cases per 100 000 population
(WHO, 2011). Tuberculosis remains the most common cause of infectious disease related
mortality worldwide. It is evident by this alone that latent tuberculosis is a serious public
health problem, not only due to the possibility of the patients themselves eventually
developing active tuberculosis, but also because of the public health risk that they impose.
M. tuberculosis is most commonly transmitted from a patient with infectious pulmonary
tuberculosis via droplet nuclei, aerosolised by coughing, sneezing or even speaking. The
tiny droplets dry rapidly, but the smallest of them (<10μm in diameter) can remain
suspended in the atmosphere for several hours. When inhaled, these droplets can reach the
terminal airspaces of the lung. Risk factors for transmission include the proximity of contact,
the duration of contact, the degree of infectiousness of the case and the shared environment
of the contact. It needs to be noted that patients that have sputum smear negative and
culture positive tuberculosis are less infectious, whereas patients with culture negative
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Pulmonary Infection
sputum pose essentially no risk for transmission. It is estimated that up to 20 people can be
infected by a single patient before tuberculosis can be identified in high prevalence
countries. Transmission is more common in tightly packed populations (i.e. overpopulated
areas, military personnel etc.) in countries with a higher incidence.
It has been demonstrated that large clusters of TB are associated with an increased number
of tuberculin skin test-positive contacts, even after adjusting for other risk factors for
transmission. The number of positive contacts was significantly lower for cases with
isoniazid-resistant TB compared with cases with fully-susceptible TB. This result has been
interpreted to imply some connection between isoniazid resistance and mycobacterial
virulence (Verhagen et al., 2011).
After exposure to the bacteria, the patient has a 5-10% chance of developing active
tuberculosis. Risk factors that determine this progression include age, the individual's innate
susceptibility to disease and level of function of cell-mediated immunity. Clinical illness
directly following infection is classified as primary tuberculosis and is more common in
children. The majority of patients infected will develop disease within a year while the rest
will develop latent tuberculosis. Activation of tuberculosis bacilli at any point thereafter is
termed secondary tuberculosis. Several diseases predispose the patient to develop active
tuberculosis with chief amongst them HIV co-infection. It is estimated that nearly all of
infected individuals that are HIV positive will at some point develop active tuberculosis;
this risk depends on the level of immunosuppression and the CD4+ cell count of the
infected patient. Patients with diabetes have 2-5 times increased risk for developing active
disease, whereas the relative risk for patients with chronic renal failure climbs to 10-25.
3. Pathophysiology of tuberculosis infection
Two models for the pathophysiology of tuberculosis infection and the formation of
granulomas have been suggested. The first one is the static model and it is considered to be
the traditional one. The second was suggested a few years ago and it is the dynamic model
of infection.
3.1 The static model
Mycobacteria belong to the family Mycobacteriaceae and the order Actinomycetales. The
most important member of the Mycobacterium tuberculosis complex is the namesake
organism, Mycobacterium tuberculosis. The complex also includes M. bovis (the bovine
tubercle bacillus), M. africanum (isolated from cases in West, Central and East Africa), M.
microti (a less virulent rarer bacillus), M. pinnipedii and M. canettii (very rare isolates). M.
tuberculosis is a slow-growing, obligate aerobe and obligate pathogen. Most often, it is
neutral on Gram's staining, however, once stained, the bacilli cannot be de-colorised by acid
alcohol, hence the characterization as acid-fast and the reason they are best seen using the
Ziehl-Neelsen stain. This ability of mycobacteria is derived from the high content of mycolic
acids, long chain fatty acids and other lipids found in abundance in the cell wall of
mycobacteria (Harada, 1976; Harada et al, 1977). In the mycobacterial cell wall, lipids are
linked to underlying arabinolactan and peptidoglycan, which confers a high resistance to
antibiotics due to low permeability of this structure. Another element of the cell wall
structure is the lipoarabinomannan which is crucial to the mycobacterium's survival within
Latent Tuberculosis: Advances in Diagnosis and Treatment
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the host's macrophages. All of these proteins, characteristic of M. tuberculosis are included in
the purified protein derivative (PPD, a precipitate of non-species-specific antigens obtained
from filtrates of heat-sterilised, concentrated broth cultures.
The majority of inhaled bacilli are trapped at the level of the upper airways and expelled. A
small fraction (<10%) will descend further down the bronchial tree. When the inhaled
droplet nuclei reach the terminal airspaces of the lung, the bacilli, transported with the
droplets, begin to grow for 2-12 weeks before any immune response from the host can be
elicited. The host's immune system responds when the bacillary load reaches 1000-10,000
cells. Non-specifically activated alveolar macrophages will eventually begin to ingest the
bacilli and sequester them from the host.
Phagocytes have 2 methods of dealing with the mycobacteria. Fusing the phagosomes
containing the mycobacteria with lysosomes they create phagolysosomes. Phagolysosomes
are the product of a fusion-fission process between the lysosomes, the phagosomes and
other intracellular vesicles. The Ca+2 signalling pathway and recruitment of vacuolar-proton
transporting ATPase (vH+-ATPase) lead to a decrease in the pH of the phagolysosome, that
in turn allows acid hydrolases to function efficiently for their microbicidal effect. Another
way that phagocytes deal with the mycobacteria is through ubiquitination of mycobacterial
cell wall and membrane components, which in turn leads to increased susceptibility to nitric
oxide produced by the phagocytes. This process leads to phagocyte apoptosis (Beisiegel et al
2009; Bermudez & Goodman, 1996; Chan & Flynn, 2004; Cooper, 2009; Pieters, 2008; Ahmad,
2010).
This form of defence, however, proves inefficient as the bacilli have the ability to survive
inside the macrophages by modulating the behaviour of its phagosome, preventing its
fusion with acidic, hydrolytically-active lysosomes (Pieters, 2008; Russel et al 2009) The
escape of M. tuberculosis from macrophage destruction is dependent on the 6-kDa early
secreted antigenic target (ESAT-6) protein and ESX-1 protein secretion system encoded by
the region of difference 1 (RD1). The ESAT-6 protein associates with liposomes containing
dimyristoylphosphatidylcholine and cholesterol and causes destabilization and lysis of
liposomes. It can also infiltrate the phagosome's membrane and cause lysis of the
phagosome, enabling the mycobacteria to escape (Brodin et al, 2004; de Jonge et al, 2007;
Derrick & Morris, 2007; Kinhikar et al, 2010).
In this initial stage of interaction, either the macrophages manage to contain the bacillary
reproduction through sequestration and production of cytokines and proteolytic enzymes,
or the bacilli manage to survive and multiply, leading to macrophage lysis. Through
chemotaxis, monocytes arrive at the site of infection to ingest the bacilli after the
macrophage lysis. Either through lysis or apoptosis the mycobacterial antigens are exposed
and presented to T lymphocytes that will carry out the burden of the host's immune
response orchestration.
Following these events, the host's immune system activates two more mechanisms to battle
the invading bacteria: a tissue damaging response and a macrophage activating response.
The tissue damaging response is a delayed-type hypersensitivity reaction to bacillary
antigens leading to the destruction of “infected” macrophages. The macrophage activation
focuses on activating specific macrophages to ingest and destroy the bacteria. Local
macrophages are activated when the non-specific macrophages present bacillary antigens to
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Pulmonary Infection
T lymphocytes, stimulating them to release lymphokines. Depending on which one of the
two mechanisms is predominant, the subsequent form of tuberculosis is determined.
If the macrophage activation predominates, large numbers of activated macrophages arrive
at the site of infection and granulomatous lesions begin to form. During this early stage and
under the influence of a vascular endothelial growth factor (VEGF), the granuloma becomes
highly vascularised which in turn will provide the pathway for the lymphocytes and
macrophages to arrive at the site (Alatas F et al, 2004) Once there, the macrophages will
further differentiate into different cells such as multi-nucleated giant cells, epitheliod cells
and foamy macrophages. These cells will form the outer wall of the granuloma, now dubbed
tubercle. The structure becomes much more stratified and a fibrous cuff forms outside the
macrophage layer. Lymphocytes move away from the centre and aggregate outside this
fibrous layer (Cáceres et al 2009).
The tissue damaging response on the other hand leads to destruction of macrophages that
fail to contain the bacilli and in turn creates a necrotic area at the centre of the tubercle with
dead macrophages. Due to low oxygen, presence of nitric oxide, nutrient deficiency and
very acidic pH the mycobacteria cannot continue to multiply inside the tubercle centres, yet
they can survive and remain dormant (Ahmad, 2010; Ohno et al, 2003; Voskuil et al, 2003).
The central necrotic region resembles cheese in texture and has granted the name caseous
necrosis to this process. At this point, some of the tubercles calcify and heal while others
evolve further.
Two distinct types of granulomas have been identified. The classic caseous granulomas are
composed of epithelial macrophages, neutrophils, and other immune cells surrounded by
fibroblasts. M. tuberculosis resides inside macrophages in the central caseous necrotic region.
The second type of granulomas (fibrotic lesions) is composed of mainly fibroblasts and
contains very few macrophages. The exact location of viable M. tuberculosis in these lesions
is not known (Barry et al, 2009). It needs to be noted that even the healed, fibrotic tubercles
can still contain mycobacteria in a dormant state.
It has been suggested that the caseating centre of the granuloma is not the site where the
host's immune response is organized and maintained, but rather that site is at the outer
layers of the tubercle, where the macrophages can present their antigens to the lymphocytic
population of the tubercle. This formation resembles a secondary lymphoid organ and is
theorised to be better suited to orchestrate the host's immune response, as suggested by the
high proliferative activity only observed in peripheral follicle-like structures (Ulrichs et al,
2004).
If the tissue damaging response predominates, due to a week response from the
macrophages, the initial lesion cannot be contained and continues to grow at the expense of
the surrounding tissue. Bronchial walls and blood vessels are destroyed in this process
(hence why haemoptysis is a chief symptom in rampant tuberculosis) and cavities are
gradually formed (Zvi et al, 2008).
The mycobacterial cell wall components are recognized by host receptors that include tolllike receptors (TLRs), nucleotide-binding oligomerisation domain (NOD)-like receptors
(NLRs), and C-type lectins, including mannose receptor (MR), the dendritic cell-specific
intercellular adhesion molecule grabbing nonintegrin (DC-SIGN), macrophage inducible Ctype lectin (Mincle) and dendritic cell-associated C-type lectin-1 (Dectin-1). The TLR
Latent Tuberculosis: Advances in Diagnosis and Treatment
5
signalling is the main arm of the innate immune response and M. tuberculosis phagocyted
through different receptors may have a different fate (Harding & Boom, 2010; Ishikawa E et
al, 2009; Jo, 2008; Jo et al, 2007; Noss et al, 2001).
Cell mediated immunity, more specifically macrophages and CD4+ T lymphocytes, plays a
very important role in the above process. The infected macrophages produce a host of
cytokines: Interleukin 1 (IL1) which leads to the development of fever, interleukin 6 (IL6)
which leads to hyperglobulinemia and tumour necrosis factor (TNF- ) that contributes to
the killing of mycobacteria, the formation of caseating granulomas, fever and weight loss.
As mentioned earlier, non-specific macrophages are also responsible for presenting the
bacillary antigens to the T cells and eliciting their response (Khader & Cooper, 2008; Kursar
et al 2007). Activated T helper Type 1 lymphocytes participate in the destruction of infected
cells through an MHC class II restricted process. They also produce interferon (IFN- ) and
interleukin 2 (IL2) and promote cell-mediated immunity. Once the bacillary growth is
stabilized, the presence of CD8+ T cells appears to gain importance, both for the production
of IFN- and an increase in the cytotoxic activity. This is a period of stalemate where the
bacillary load remains relatively constant and the infection is in a state of latency (Bodnar et
al, 2001; Russel et al, 2009).
More recently, it was demonstrated that IL1-beta, a subset of interleukin 1, which plays an
important part as mediator in the host’s immune response, is induced when ESAT-6 is
secreted from the bacilli. IL1-beta is activated through the inflammasome, a caspase
activating protein complex. Caspases are cysteine-aspartic proteases that play a part in
inflammation response and apoptosis. Mycobacteria have developed the ability to halt the
inflammasome’s formation by secreting a Zn+2 metalloprotease, encoded by the zmp1 gene.
Mycobacteria genetically modified for zmp1 deletion and through the secretion of ESAT-6
lead to IL1-beta activation and elicit a stronger immune response from the host leading to
improved mycobacterial clearance by macrophages, and lower bacterial burden in the lungs
of aerosol-infected mice (Danelishvili, 2010; Lalor, 2011; Master 2008; Mishra, 2010).
Mycobacteria secrete their own enzymes (Rv3654c and Rv3655c) within the macrophage
cytoplasm with the ability to cleave caspase-8. In this manner, the bacilli prevent
macrophage apoptosis by preventing the inflammasome’s formation and promote cellular
lysis (Danelishvili, 2010). It has been demonstrated that it is more beneficial to bacterial
growth if the macrophages are steered towards lysis as opposed to apoptosis. Necrosis was
correlated with Caspase 3 activity and bacterial growth, whereas activation of calcium, TNFalpha and Caspase 8 was associated with apoptosis and decreased bacterial load (Arcila et
al, 2007).
Humoral immunity seems to play a much lesser role if any. The evidence that B-cells and M.
tuberculosis-specific antibodies can mediate protection against extracellular M. tuberculosis
is highly controversial as their contribution is probably of minor importance (TBNET, 2009).
The host's immune response can eventually cause more problems through tissue destruction
and uncontrolled activation of macrophages and lymphocytes. For this reason there is a
negative feedback mechanism in place, to control the extent of the response. A family of
receptor tyrosine kinases provide this negative feedback mechanism to both, TLR-mediated
and cytokine-driven proinflammatory immune responses (Liew, 2005). Again, the
mycobacteria have developed mechanisms to take advantage of this process in order to halt
the immune response to their benefit. Several M. tuberculosis cell wall components or protein
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Pulmonary Infection
products such as 19-kDa lipoprotein, glycolipids (particularly Man-LAM), trehalose
dimycolate (cord factor) can modulate antigen-processing pathways by MHC class I, MHC
class II and CD1 molecules, phagolysosome formation and other macrophage intracellular
signalling pathways (Ahmad, 2010; Bowdish et al, 2009; Gehring et al, 2004; Harding &
Boom, 2010; Jo et al, 2007; Nigou et al, 2001; Noss et al, 2001; Pecora et al; 2006). This results
in a subset of macrophages that are unable to present mycobacterial antigens to T
lymphocytes
It is hypothesized that the infection sustains itself not through replicating bacilli forming
equilibrium with those being destroyed by the host's immune system, but through a
population of non-replicating bacilli that can withstand the immune response. The
evidence to this is indirect, suggested by the lack of cellular debris in the granuloma
centres of infected mice (Rees & Hart, 1961). It is believed that the host's immune response
is driven by antigens produced during active multiplication of the bacilli and thus, those
that remain dormant would not sustain that response to its maximum potential
(Andersen, 1997).
3.2 The dynamic model
More recently a dynamic model of infection was proposed able to give some logical
explanations to some short-comings of the static model. The first question posed was how it
is possible for the mycobacteria to remain dormant in the tubercle environment when the
host is trying to re-structure the damaged tissues. The alveolar macrophages have a lifespan
of 3 months, yet according to the static model, they exist in stalemate with the mycobacteria
for a much longer period of time, whether as part of the middle layer of the granuloma or as
part of the caseous centre having phagocyted bacilli and sustaining them in their dormant
state (Cardona, 2009).
The second question was how did the bacilli reactivate themselves from their dormant state,
as it has been demonstrated that the resuscitation factors necessary for this are only
produced by active bacilli (Cardona, 2009; Shleeva et al, 2002).
The third question posed seeks an explanation based on a physiological model regarding the
ability of isoniazid to treat latent tuberculosis when it is known that isoniazid can only take
effect on actively multiplying bacilli (Cardona, 2009; TBNET, 2009).
According to the dynamic model that has been suggested, the granulomas are not static
formations but rather, inside the granuloma, there exists a balance between inactive
dormant bacilli, rapidly multiplicating ones, dying bacilli and cellular debris constantly
being removed from the site (TBNET, 2009). The exact nature of the metabolic state of
mycobacteria within the macrophages in the granuloma is a matter of great debate and
investigation.
The size of the actively multiplicating mycobacterial load in the granuloma determines the
antigen-specific re-stimulation of memory T lymphocytes. On the other hand, if the
mycobacteria are mostly contained within macrophages in their dormant state, it is more
likely that T cell immunity will begin to decline. This in turn would explain why a
tuberculin skin test can revert to negative after exposure at a rate of about 5% per year
(TBNET, 2009).
Latent Tuberculosis: Advances in Diagnosis and Treatment
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Perhaps the most important element in this proposed model is the role of the foamy cell, i.e.
alveolar macrophages at the end of their life cycle and filled with lipids, due to phagocytosis
of extracellular debris, mostly consisting of lipid-rich cellular membrane remains. The
mycobacteria phagocyted by these cells can survive through the mechanisms explained
earlier. The dynamic model suggests that the mycobacteria can continue to grow albeit at
very slow rates instead of becoming dormant. The slower metabolic rate provides resistance
to stress and reduces the nutritional needs of the bacilli, thus allowing their survival
(Cardona, 2009; Muñoz-Elias et al, 2005). It has not been fully researched but evidence
suggests that mycobacteria can escape the phagosomes of the foamy cells and reach the
bronchial tree and become aerosolised.
Foamy cells provide a stressful environment that conditions the bacilli to become more
resistant. This in turn, confers them the ability to better survive in the open air and
according to some studies explains why they are more virulent. Moreover, the high lipid
content of the foamy cells also provides triglycerides to the bacilli that will in turn provide
them with nutrients in new infection sites in the event of starvation. In fact the highly
aggressive Beijing strains have also been found to contain large amounts of lipids, which
would at least partly account for the greater virulence (Garton et al, 2002; Neyrolles et al,
2006; Peyron et al, 2008). Finally the high lipid content of foamy cells when exposed to the
alveolar spaces will contribute to increased surfactant concentration and thus will make
aerosolisation of the bacteria easier (Cardona, 2009).
Growing bacteria are easy to combat since they cannot survive in stressful environments.
The dynamic model offers a different explanation of the mechanism, with which the host's
immune system focuses on the non-replicating bacteria. The phagocyted bacilli, as explained
in the static model, will eventually lead to lysis or apoptosis of the macrophages. This
cellular debris and the extracellular bacteria will form the population of the non-replicating
bacteria at the caseous centre. The attraction of specific macrophages and neutrophils will
provide a new breeding ground for the active bacteria and also material for the formation of
the foamy cells, as they will phagocyte cellular membrane remnants to clear the debris from
the caseous centre of the granuloma. The bacilli, inside the foamy cells, under these
circumstances, will eventually find themselves within the bronchial spaces and after they
are aerosolised they will reinfect the host at new sites. Due to their higher virulence they
will manage to overcome the initial immune response and form a new granuloma to repeat
the same sequence of events (Cardona, 2009). At the new site of infection the bacilli are
actively multiplying again and thus are susceptible to isoniazid. This would explain why a
single-drug nine month treatment is effective in most cases of latent tuberculosis.
4. Latent tuberculosis and reactivation
Mycobacteria are completely eradicated only in about 10% of the cases, while in the
remaining, the bacilli survive for years to come, through the processes explained. This state
has been termed latent tuberculosis infection. In any event where the host's immune
response dwindles, there is a risk for the bacilli to reactivate themselves and lead to active
tuberculosis infection. Most of the new cases of tuberculosis in low incidence countries are
the result of such reactivation of latent tuberculosis infections. It is of interest to note that
expression of DosR-regulated dormancy antigens continues even in this latent stage of
infection, providing a promising new target for vaccines that would help battle latent TB
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Pulmonary Infection
infections in the future (Leyten et al, 2006; Lin & Ottenhoff, 2008). It is also probable that M.
tuberculosis, during the latent stage of infection can form spore-like structures, typically seen
with other mycobacteria, in response to prolonged stationary phase or nutrient starvation,
for its survival (Ghosh et al, 2009).
The reactivation of latent infection requires M. tuberculosis to exit dormancy. This is mainly
achieved through the effects of a family of five proteins, dubbed resuscitation promoting
factors (Rpfs), that have the effect of a lytic transglycosylase. These molecules were found to
be able to cause degradation to cell wall components of the mycobacteria. It is not exactly
known how this activity relates to the resuscitation process, it is however theorised that the
end result of this enzymatic activity is changes to the mycobacterial cell-wall, overcoming
the environmental restraints to the bacterial multiplication. Another theory states that the
changes brought to the cell wall, lead to production and secretion of peptidoglycans with
the ability to modulate the environment and the host's immune response (Hett et al, 2007;
Tufariello et al, 2006). It needs be noted that M. tuberculosis bacilli found in the sputum of
patients with latent infection and after deletion of the Rpfs encoding genes, can only be
cultured when Rpfs are introduced to the growth material and thus resuscitation is possible
(Mukamolova et al, 2010), however for non-dormant mycobacteria it seems that the Rpfs are
not important for their multiplication (Kana et al, 2008).
Exposure of subjects to droplet nuclei from a source
case of sputum smears positive pulmonary TB
Host defence
Duration and proximity of contact
No infection
Onset of Infection
Strong immune response
Weak immune response
Limited bacterial growth
Primary TB
Host factors
Bacterial factors
Pathogen elimination
Latent TB
Immune response persists
Clearance of latent infection
Reactivation of TB infection
Fig. 1. Natural progression of tuberculosis, adapted from Ahmad, 2010
Latent Tuberculosis: Advances in Diagnosis and Treatment
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It has also been demonstrated that amongst the Rpfs, those that seem to be the most
important are RpfA and RpfB. Infected mice with strains of mycobacteria with deletion of
the genes encoding these specific Rpfs, were found to be more resistant to TB reactivation
and also their macrophages were found to produce larger quantities of TNF- and IL6
(Russel-Goldman et al, 2008). These resuscitation factors are another possible target for
future vaccines against latent TB (Zvi et al, 2008).
5. Latent tuberculosis diagnosis
Diagnosis of latent tuberculosis is a matter of active current research due to the difficulties
presented in identifying patients with latent infection. There is no question that controlling
contacts and identifying people who are carrying the bacilli would be the best prevention
plan. However, due to the lack of any physical signs or symptoms and the fact that all or
most of the bacilli during this state remain dormant, it is very difficult to elicit an immune
system response that would be evident to the observer. This in turn means that it is difficult
to identify individuals with latent infection. An ideal test for latent tuberculosis infection
diagnosis should meet the following criteria:
High sensitivity in all populations at risk.
High specificity regardless of BCG vaccination and infection with environmental
mycobacteria.
Reliability and stability over time.
Objective criteria for positive result, affordability and easy administration.
Ability to distinguish recently infected individuals with increased risk of progression to
active tuberculosis.
There are currently two groups of tests for latent tuberculosis infection diagnosis: tuberculin
skin tests (TST) and interferon- release assays (IGRA).
5.1 The tuberculin skin test
Historically, the most accurate method for detecting if an individual had come in contact
with M. tuberculosis was the tuberculin skin test (TST). This test measures the hosts' in vivo
immune response in the form of a cell-mediated delayed hypersensitivity reaction to a
mixture of more than 200 M. tuberculosis antigens, termed as purified protein derivative
(PPD). The PPD is a crude mixture of antigens, not specific to M. tuberculosis, but also
found in other mycobacteria such as the BCG bacillus, M. bovis and even non-tuberculous
mycobacteria. This mixture is intradermally injected, usually at the inner side of the forearm
and the test result is read as an induration on the site of injection after 48-72 hours (Huebner
et al 1993). This reaction may last for up to 1 month, depending on the quality and quantity
of the initial reaction. Strong reactions may result in tissue necrosis, which is the only
absolute contraindication to the TST (TBNET, 2009). The induration is caused due to the
introduction of the antigens that causes non-specific neutrophils and antigen-specific T
lymphocytes to arrive at the site and sparkle an inflammatory cascade of cytokine
production. The migration of immune cells to the site seems to have a biphasic distribution:
an initial nonspecific infiltration where the neutrophils arrive at the site, taking place in the
first 4-6 hours and which is an event that also occurs in nonsensitised subjects and a second
specific peak, where the specific T cells arrive at the site (Kenney et al, 1987; Platt et al, 1983;
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Pulmonary Infection
Poulter et al, 1982; TBNET, 2009). The lymphocyte population is a mix of CD4+ and CD8+
cells with the former being always greater in number (Gibbs et al, 1984). The lymphocytic
infiltration is at first perivascular and under the influence of early cytokines, such as IFN- ,
TNF- and TNF- , the endothelium is stimulating into expressing adhesion molecules (Eselectin), increasing the permeability of the vascular walls and enabling the cells to migrate
to the dermis. Regulatory T-cells influence the size of the induration of the tuberculin skin
test. Cutaneous CD4 T-cells accumulating after tuberculin PPD stimulation in the skin are
predominantly of a CD45 RO memory phenotype (Sarrazin et al, 2009). The criteria for the
test's interpretation vary considerably and depend on the nature of the population being
tested. They are arbitrary and the result of international consensus.
In the United States, according to the Center for Disease Control (CDC), 5 tuberculin units
(TUs) are used and a test is considered positive for the general population with no known
TB contacts when the induration measures 15mm or more. An induration of 10 or more
millimetres is considered positive in recent immigrants (< 5 years) from high-prevalence
countries, injection drug users, residents and employees of high-risk congregate settings,
mycobacteriology laboratory personnel, persons with clinical conditions that place them at
high risk, children < 4 years of age, infants, children, and adolescents exposed to adults in
high-risk categories. Finally, an induration of 5 or more millimetres is considered positive in
HIV-infected persons, a recent contact of a person with TB disease, persons with fibrotic
changes on chest radiograph consistent with prior TB, patients with organ transplants,
persons who are immunosuppressed for other reasons (e.g., taking the equivalent of >15
mg/day of prednisone for 1 month or longer, taking TNF- antagonists, etc.) (CDC, 2011).
In Europe, the situation differs from country to country depending on the incidence and
prevalence of TB. In countries with high incidence, such as former Soviet Union countries, a
10mm induration is considered positive. In most European countries 2 TUs are used and
interpretation of the results follows the same guidelines as in the US (ECDC, 2011).
As with every screening test, TST has a chance of false positive and false negative results.
Possible false positive reactions are caused due to infections with non-tuberculous
mycobacteria, previous vaccination with BCG, incorrect method of TST administration
(including wrong amount of PPD injected as well as injecting it subcutaneously rather than
intradermally), incorrect interpretation of reaction (more often than many would assume,
doctors and/or nurses measure the erythema caused by the immune response rather than
the induration leading to overestimation of the reaction caused), incorrect bottle of antigen
used. False negative results are caused by cutaneous anergy (anergy is the inability to react
to skin tests because of a weakened immune system, such as in HIV patients or patients
under immunosuppression, particularly those taking anti-TNFmedications for
autoimmune conditions), recent TB infection (within 8-10 weeks of exposure), very old TB
infection (many years), very young age (less than 6 months old), recent live-virus
vaccination (e.g., measles and smallpox), overwhelming TB disease (tuberculosis by itself is
thought to cause a degree of immunosuppression to the host in these advanced cases), some
viral illnesses (e.g., measles and chicken pox), incorrect method of TST administration,
incorrect interpretation of reaction (ECDC, 2011; CDC, 2011).
Of special consideration is the so-called booster effect after TST testing. In certain people,
who have been exposed to M. tuberculosis, the ability of their immune system to react to the
PPD antigens might have diminished over the course of time. These patients when tested
Latent Tuberculosis: Advances in Diagnosis and Treatment
11
with the TST would have a negative reading. However, reintroducing the tuberculosis
antigens to their immune system by the test itself stimulates their immune system to react
more fiercely to these antigens. Subsequent tests in these individuals would result as
positive even though they haven't been exposed to the bacilli in the time between the two
tests. In a sense, the first TST “boosted” the results of the second one. In certain populations,
the CDC suggests performing a two-step test in order to identify possible false negative first
tests and prevent unnecessary treatment. Such populations include health-care workers,
doctors, nurses or nursing home residents, whose status with regards to tuberculosis
exposure and/or infection is important to know.
It is evident that the TST has several limitations to its use, which in turn sparked the interest
in developing new diagnostic tools such as the IGRAs. Such limitations include a high
proportion of false positive and false negative results, difficulty in separating true infection
from the effects of BCG vaccination and NTM infection, technical problems in
administration, immune response boosting after repeated TST, complicated and subjective
interpretation and a need for a second visit for the interpretation of the test's result.
5.2 The interferon-γ release assays
Interferon- release assay kit tests were developed the past decade as an alternative to the
TST. They are whole-blood tests that can aid in diagnosing M. tuberculosis infection,
including both latent tuberculosis infection and active disease. They are indirect in vitro, ex
vivo tests that measure the production of interferon- by a patient's T lymphocytes after the
latter are incubated with specific M. tuberculosis antigens in vitro (Andersen et al, 2000;
Harboe et al, 1996; Mahairas et al, 1996). To conduct the test, fresh blood sample from the
patient is mixed with the antigens and the response is measured either by measuring the
produced interferon through enzyme-linked immunosorbent assay (ELISA), rapid enzymelinked immunospot assay or by measuring the number of activated T cells through flow
cytometry. The difference in method used is what distinguishes the two commercially
available kits. QuantiFERON-TB Gold In-Tube (QFT-GIT, by Cellestis Limited, Carnegie,
Victoria, Australia) uses the ELISA method and the T-SPOT (by Oxford Immunotec Limited,
Abingdon, UK) uses the ELISPOT. It is interesting to mention that initially IGRAs would use
the PPD as antigen but still follow the same principle and in an interesting twist of fate, it
has been suggested to use the specific IGRA antigens for TST, as these antigens have been
found to elicit a distinctive immune response with induration on animals. IGRAs are
performed on fresh blood specimens.
The antigens used in these methods are peptides derived from ESAT-6, CFP-10 and for the
Quantiferon method TB7.7 proteins of the mycobacteria. The first two are encoded at the
region of difference (RD) 1 genetic locum whereas the third at the RD11, regions that are
deleted from the M. bovis BCG genome and are absent in most environmental mycobacteria,
with the exception of M. kansasii, M. szulgai and M. marinum (TBNET, 2009). During earlier
stages of the method's development, the entire protein product was used. The early
secretory antigenic target (ESAT) is a 6kDa protein and the culture filtrate protein (CFP-10)
is a 10kDa protein. Together they form an heterodimeric complex and depend on each other
for stability. They are secreted through the ESX1 secretion system and are considered to be
an indication of virulence. Their role is not fully understood but they seem to induce lysis
through integration on the macrophage cellular membrane (Brodin et al, 2004; de Jonge et al,
12
Pulmonary Infection
2007; Derrick & Morris, 2007; Kinhikar et al, 2010; Renshaw et al, 2005). Even less is known
regarding TB7.7. IGRA techniques support the dynamic model for latent TB since they
detect IFN- produced by T cells, with a short lifespan that have been activated by
macrophages that presented to them the tuberculosis antigens (Cardona, 2009).
For the QFT-GIT (Table 1), 1 ml of blood is drawn into one of each of three special testing
tubes. These are precoated and heparinised by the manufacturer. Within 16 hours the tubes
must be incubated for another 16 to 24 hours at 37 °C. After centrifugation, the plasma is
harvested to be further processed. QFT-GIT collection tubes contain a gel plug that separates
the plasma from the cells when centrifuged. The plasma can be used immediately or at a
later point in time. Results are interpreted according to the manufacturer’s
recommendations (ECDC, 2011).
Result
IFN- concentration (International Units per ml, IU/ml)
M. tuberculosis antigens
Nil
PHA
Positive
≥ 0.35 IU/ml and ≥ 25% over nil
≤ 8.0 IU/ml
Any
Negative
< 0.35 IU/ml or < 25% over nil
≤ 8.0 IU/ml
≥ 0.5 IU/ml
< 0.35 IU/ml or < 25% over nil
≤ 8.0 IU/ml
< 0.5 IU/ml
Any
> 8.0 IU/ml
Any
Indeterminate
Table 1. Quantiferon results interpretation, adapted from ECDC, 2011
For the T-SPOT assay (Table 2), 8 ml of blood are required and the assay must be performed
within eight hours of blood collection. Alternatively, the manufacturer also provides a
reagent (T-Cell Xtend) which extends processing time to 32 hours after blood collection. The
T-cell-containing peripheral blood mononuclear cell fraction is separated from whole blood
and distributed to the microtitre plate wells (250,000 cells/well) provided in the assay kit.
Following 16 to 20 hours incubation, the number of IFN- -secreting T-cells (represented as
spot-forming units) can be detected by ELISPOT assay. As with QFT-GIT the test's results
are interpreted according to the manufacturer's recommendations (ECDC, 2011).
Spot count
Result
M. tuberculosis antigens
ESAT-6
CFP-10
Nil
PHA
Positive
≥ 6 over nil
and/or
≥ 6 over nil
≤ 10
Any
Negative
≤ 5 over nil
and/or
≤ 5 over nil
≤ 10
≥ 20
< 10
≥ 20
≤ 10
< 20
> 10
Any
Borderline
Indeterminate
If for any antigen highest is 5 - 7 over nil
≤ 6 over nil
and
≤ 6 over nil
Any
Table 2. T-Spot results interpretation, adapted from ECDC, 2011
Latent Tuberculosis: Advances in Diagnosis and Treatment
13
The presence of negative and positive controls ensures that IGRAs are correctly performed.
The three testing tubes contain the mycobacteria antigens (Mtb), no antigens (Nil) and
phytohaemagglutinin A (PHA), a T-cell activating mitogen. The Nil vial serves as the
negative control for the process whereas the PHA as the positive one. If there is IFNproduction in the Mtb tube, none in the Nil and any amount in the PHA, it means that the
result is a positive one because it would imply that the sample's lymphocytes reacted to the
antigens as expected and did not react to any other antigens that might have contaminated
the sample. If on the other hand there is no IFN- production in the Mtb tube and the Nil
tube but there is in the PHA one, it implies that the lymphocytes react normally to the PHA
antigen yet they do not react when exposed to the bacilli antigens and therefore these
lymphocytes haven't met these antigens before. Finally, the results are indeterminate if at
any point there is IFN- production in the Nil tube, which might imply contamination or
there is increased baseline interferon production or if there is no sufficient production in the
PHA tube, which might imply anergy. Technical factors (sample collection, storage and
transportation) might also contribute to returning indeterminate results (ECDC, 2011).
There is a lot of debate on whether IGRAs are indeed more reliable than the traditional TST.
In Germany, Denmark and Switzerland, IGRAs have substituted TST when screening
populations receiving anti-TNF- therapies. The US, Australia, France and Denmark use
either TST or IGRAs, whereas Canada, the United Kingdom, Italy, Spain, Australia and
Slovakia to name a few, support a 2-step approach using both TST and IGRAs in an attempt
to increase sensitivity and specificity of both methods. The two-step approach seems to be
the most favoured strategy for IGRA use, especially in BCG vaccinated contacts.
IGRAs have some distinct advantages over TST with regards to diagnosing latent
tuberculosis infection. IGRA testing requires a single patient visit to conduct the test and
results can be available within the day. Moreover there is no “booster” effect associated with
IGRAs since they are ex vivo, in vitro tests. Finally, due to the specificity of the M. tuberculosis
antigens used, BCG vaccination does not cause false positive results. Due to the positive
control, IGRAs are able to differentiate between immunocompromised hosts and negative
results with more accuracy. In the TBNET/ECDC systematic review and meta-analysis
(Sester et al. 2010) IGRAs were also found to have greater sensitivity in diagnosing active TB
infection compared to the TST, 80% for QFT-GIT, 81% for T-Spot compared to only 65% for
the TST. In the same review, specificity was found to be 79% (75-82%) for QFT-GIT, 59% (5662%) for T-spot and 75% (72-78%) for TST. Sensitivity to diagnose latent TB infection was
found 67%, 87% and 71% for QFT-GTI, T-Spot and TST respectively, whereas specificity for
latent TB infection was 99%, 98% and 88% respectively (Diel et al, 2011; Menzies et al, 2007;
Pai et al, 2008; Sester et al, 2010).
Current consensus amongst the European countries is that IGRAs can be included in
screening for latent TB infection, albeit there is not enough evidence yet to provide a clear
picture. Nonetheless it can provide an extra step in establishing a diagnosis. On the other
hand, due to their high negative predictive value for immunocompetent patients, negative
IGRA results can safely exclude progression to active disease, albeit it does not rule out the
possibility of latent infection (Diel et al, 2011). Applying the IGRAs to specimens from
possible infection sites (i.e. Bronchoalveolar Lavage) as opposed to blood samples,
especially in immunodeficient individuals can help distinguish between active and latent TB
(Jafari et al, 2009). In diagnosing active tuberculosis we mention for completeness, that
14
Pulmonary Infection
current consensus is that IGRAs do not have a place in routine screening, yet in certain cases
when there is a strong clinical suspicion yet no laboratory proof, they can contribute.
Neither IGRAs nor TST can replace the standard laboratory tools for diagnosing active
tuberculosis (ECDC, 2011).
As with the TST, IGRAs also have some shortcomings. Perhaps most importantly IGRAs,
just like TST are unable to distinguish between latent and active infection when limited to
blood testing. Moreover, blood samples need to be processed within 8-30 hours after
collection; otherwise the white blood cells will gradually become non-responsive to the
antigenic stimulation. Errors in collecting or transporting blood specimens or in running
and interpreting the assay can decrease the accuracy of IGRAs. Since these techniques are
relatively new, there is still limited data on the use of IGRAs in certain population groups
such as children younger than 5 years of age, HIV patients, anti-TNF- treated patients or in
general immunocompromised patients. Finally there is a significant cost to this process as
opposed to the fairly cheap TST method.
Finally, another method is being developed for use that employs flow cytometry for the
detection of interferon producing lymphocytes. This method is not yet commercially
available and due to the high cost of the process it is not known yet if it will contribute to
latent tuberculosis diagnosis (Fuhrmann et all 2008). There are experimental methods
detecting antibodies against tuberculosis antigens, but as mentioned already humoral
immunity plays a small part in tuberculosis if any at all and thus these methods so far have
no clinical application (El-Shazly, 2007). Most recently the WHO issued a statement asking
countries to ban antibodies based tests for the diagnosis of tuberculosis (WHO, 2011).
6. Latent tuberculosis treatment
Individuals with known contacts with patients suffering from active tuberculosis and who
test positive with the aforementioned methods are considered, given reasonable clinical
suspicion, to have latent infection. They are eligible to receive treatment in order to prevent
them from developing an active infection. In some cases (i.e. children, HIV patients) even
without TST or IGRAs supporting, clinical suspicion alone is enough to start treatment and
re-test the patient at a later time to verify the result of the diagnostic tests. Treatment for
latent tuberculosis is less expensive than for active and preventing the disease provides
overall a great economic benefit for the health-care system.
Current guidelines (American Thoracic Society & CDC, 2000, revised 2005) in the US,
suggest a 9-month daily treatment with isoniazid (INH) 5mg/kg up to 300mg. This can be
reduced to only 6 months, for adults seronegative for HIV co-infection. In most cases the 9
month treatment plan is followed since it has been show to achieve better results (70%
complete remission vs. 60% for the 6 month regimen). In very few cases a 12-month regimen
is recommended, particularly for populations with a higher incidence of active tuberculosis
(TBNET, 2009).
As is the problem with most tuberculosis therapies there is a high amount of non-compliant
patients contributing to failure of treatment. One solution would be to enforce Directly
Observed Treatment (DOT) for patients taking isoniazid for latent tuberculosis, but such a
decision comes with a high financial cost. Under these circumstances, treatment can be
modified to a 2/week regimen at a dose of 15mg/kg up to 900mg. Isoniazid side-effects
Latent Tuberculosis: Advances in Diagnosis and Treatment
15
include polyneuropathy, preventable with administration of B6 vitamin and hepatic toxicity
that remains a prime reason for discontinuation of treatment. Studies have shown that 1020% of patients will have an increase in liver transaminases and about 2% will have
clinically significant hepatitis, with that percentage increasing in the present of co-morbidity
factors (Nolan et al, 1999).
Due to these problems the ATS and CDC have suggested alternative treatment options. One
such option is a daily dose of rifampicin (RMP) 4-month single-drug regimen or a daily dose
of pyrazinamide (PZA)-rifampicin 4-month regimen. The RMP treatment is not
recommended for HIV positive patients due to interactions with HAART treatment, but
otherwise it has shown promising results for patients intolerant of INH or for those cases
where INH resistance is verified or suspected. Benefits of this shorter regimen include a
lower cost and also higher degrees of compliance (Jasmer et al, 2002; Menzies et al, 2004,
2008; Polesky et al, 1996; Reichman et al, 2004; Villarino et al, 1997).
Initially the PZA-RMP regimen was designed to be administered for 2 months, but due to
adverse effects (serious hepatotoxicity and death) it is no longer recommended, but for some
rare cases (CDC, 2001; Lecoeur, 1989; Gao, 2006) Other possible regimens that are under
evaluation include a 3 month daily treatment with INH-RMP and a 3 month weekly INHrifapentin regimen. The former has been tested in the UK and exhibits satisfactory results in
terms of adverse effects and success of treatment (Ena & Valls, 2005). The latter is under
study in the US, the CDC recently made public that patients on this regimen have higher
compliance, satisfactory remission results compared to INH but it seems that they have
increased adverse effects and also the cost of treatment is higher than the RMP regimen.
7. Conclusion
Latent tuberculosis is a field of great scientific interest and research possibilities. We have
investigated the granuloma and its formation and 2 theories exist, a lot of the secrets still
remain hidden and more evidence is needed to support either theory. In the field of
diagnosis new tools are available and it remains to be seen how they will fare when tested
against special populations (i.e. HIV patients which is the field of our own research as well).
New guidelines for treatment are issued and those are under evaluation. Latent tuberculosis
is an important public health issue, an insidious infection that can persist for years; above
all, clinical suspicion is paramount for its diagnosis.
8. References
Ahmad S. (2010) New approaches in the diagnosis and treatment of latent tuberculosis
infection Respir Res. Vol 11 No 1 Dec 2010 pp169
Alatas F, Alatas O, Metintas M, Ozarslan A, Erginel S & Yildirim H.(2004) Vascular
endothelial growth factor levels in active pulmonary tuberculosis. Chest. Vol 125
No 6 Jun 2004 pp2156-9
American Thoracic Society, Centers for Disease Control and Prevention. (2000) Targeted
tuberculin testing and treatment of latent tuberculosis infection. Am J Respir Crit
Care Med. Vol 161 No 4 pt2 Apr 2000 pp221–247
Andersen P, Munk ME, Pollock JM, Doherty TM (2000) Specific immune-based diagnosis of
tuberculosis. Lancet Vol 356 No 9235 Sep 2000 pp1099-104
16
Pulmonary Infection
Andersen P. (1997) Host responses and antigens involved in protective immunity to
Mycobacterium tuberculosis. Scand J Immunol. Vol 45 No 2 Feb 1997 pp115-31
Arcila ML, Sánchez MD, Ortiz B, Barrera LF, García LF, Rojas M (2007) Activation of
apoptosis, but not necrosis, during Mycobacterium tuberculosis infection correlated
with decreased bacterial growth: role of TNF-alpha, IL-10, caspases and
phospholipase A2. Cell Immunol. Vol 249 No 2 Oct 2007 pp80-93
Barry CE 3rd, Boshoff HI, Dartois V, Dick T, Ehrt S, Flynn J, Schnappinger D, Wilkinson RJ
& Young D. (2009) The spectrum of latent tuberculosis: rethinking the biology and
intervention strategies. Nat Rev Microbiol. Vol 7 No 12 Dec 2009 pp845-55
Beisiegel M, Mollenkopf HJ, Hahnke K, Koch M, Dietrich I, Reece ST, Kaufmann SH (2009)
Combination of host susceptibility and Mycobacterium tuberculosis virulence
define gene expression profile in the host Eur J Immunol. Vol 39 No 12 Dec 2009
pp3369-84
Bermudez LE, Goodman J (1996) Mycobacterium tuberculosis invades and replicates within
type II alveolar cells Infect Immun. Vol 64 No 4 Apr 1996 pp1400-6
Bodnar KA, Serbina NV, Flynn JL (2001) Fate of Mycobacterium tuberculosis within murine
dendritic cells. Infect Immun. Vol 69 No 2 Feb 2001 pp800-9
Bowdish DM, Sakamoto K, Kim MJ, Kroos M, Mukhopadhyay S, Leifer CA, Tryggvason K,
Gordon S, Russell DG (2009) MARCO, TLR2, and CD14 are required for
macrophage cytokine responses to mycobacterial trehalose dimycolate and
Mycobacterium tuberculosis. PLoS Pathog.Vol 5 No 6 Jun 2009
Brodin P, Rosenkrands I, Andersen P, Cole ST & Brosch R. (2004) ESAT-6 proteins:
protective antigens and virulence factors? Trends Microbiol. Vol 12 No11 Nov 2004
pp500-8
Cáceres N, Tapia G, Ojanguren I, Altare F, Gil O, Pinto S, Vilaplana C & Cardona PJ. (2009)
Evolution of foamy macrophages in the pulmonary granulomas of experimental
tuberculosis models. Tuberculosis (Edinb). Vol 89 No 2 Mar 2009 pp175-82
Cardona PJ. (2009) A dynamic reinfection hypothesis of latent tuberculosis infection.
Infection. Vol 37 No 2 Apr 2009 pp80-6 Review
CDC (2001) Update: Fatal and severe liver injuries associated with rifampin and
pyrazinamide for latent tuberculosis infection, and revisions in American Thoracic
Society/CDC recommendations--United States, 2001. MMWR Morb Mortal Wkly
Rep. Vol 50 No 34 Aug 2001 pp733-5
Center for Disease Control TB fact-sheet (n.d)
http://www.cdc.gov/tb/publications/factsheets/testing/skintesting.htm
Chan J & Flynn J. The immunological aspects of latency in tuberculosis. (2004) Clin Immunol.
Vol 110 No 1 Jan 2004 pp2-12
Cooper AM Cell-mediated immune responses in tuberculosis. Annu Rev Immunol. Vol 27
2009 pp393-422
Danelishvili L, Yamazaki Y, Selker J, Bermudez LE (2010) Secreted Mycobacterium
tuberculosis Rv3654c and Rv3655c proteins participate in the suppression of
macrophage apoptosis. PLoS One Vol 5 No 5 May 2010
de Jonge MI, Pehau-Arnaudet G, Fretz MM, Romain F, Bottai D, Brodin P, Honoré N,
Marchal G, Jiskoot W, England P, Cole ST & Brosch R.J (2007) ESAT-6 from M.
tuberculosis dissociates from its putative chaperone CFP-10 under acidic conditions
and exhibits membrane-lysing activity. Bacteriol. Vol 189 No 16 Aug 2007 pp6028-34
Latent Tuberculosis: Advances in Diagnosis and Treatment
17
Derrick SC, Morris SL (2007) The ESAT6 protein of Mycobacterium tuberculosis induces
apoptosis of macrophages by activating caspase expression. Cell Microbiol. Vol 9 No
6 Jun 2007 pp1547-55
Diel R, Goletti D, Ferrara G, Bothamley G, Cirillo D, Kampmann B, Lange C, Losi M,
Markova R, Migliori GB, Nienhaus A, Ruhwald M, Wagner D, Zellweger JP,
Huitric E, Sandgren A, Manissero D (2011) Interferon- release assays in the
diagnosis of latent M. tuberculosis infection. Eur Respir J Vol37 No1Jan2011 pp88-99
ECDC (2011) Guidance Use of interferon-gamma release assays in support of TB diagnosis
http://ecdc.europa.eu/en/publications/Publications/1103_GUI_IGRA.pdf
ECDC (2011) Mastering the basics of TB control – Development of a handbook on TB
diagnostic methods
http://ecdc.europa.eu/en/publications/Publications/1105_TER_Basics_TB_contr
ol.pdf
El-Shazly S, Mustafa AS, Ahmad S & Al-Attiyah R. (2007) Utility of three mammalian cellentry proteins of Mycobacterium tuberculosis in the serodiagnosis of tuberculosis.
Int J Tuberc Lung Dis. Vol 11 No 6 Jun 2007 pp676–682
Ena J & Valls V (2005) Short-course therapy with rifampin plus isoniazid, compared with
standard therapy with isoniazid, for latent tuberculosis infection: a meta-analysis.
Clin Infect Dis. Vol 40 No 5 Mar 2005 pp670-6
Fuhrmann S, Streitz M & Kern F. (2008) How flow cytometry is changing the study of TB
immunology and clinical diagnosis. Cytometry A. Vol 73 No11 Nov 2008 pp1100-6
Gao XF, Wang L, Liu GJ, Wen J, Sun X, Xie Y, Li YP (2006) Rifampicin plus pyrazinamide
versus isoniazid for treating latent tuberculosis infection: a meta-analysis. Int J
Tuberc Lung Dis. Vol 10 No10 Oct 2006 pp1080-90
Garton NJ, Christensen H, Minnikin DE, Adegbola RA, Barer MR (2002) Intracellular
lipophilic inclusions of mycobacteria in vitro and in sputum. Microbiology Vol 148
No 10 Oct 2002 pp2951-8
Gehring AJ, Dobos KM, Belisle JT, Harding CV, Boom WH (2004) Mycobacterium
tuberculosis LprG (Rv1411c): a novel TLR-2 ligand that inhibits human
macrophage class II MHC antigen processing. J Immunol. Vol 15 No 173(4) Aug
2004 pp2660-8
Ghosh J, Larsson P, Singh B, Pettersson BM, Islam NM, Sarkar SN, Dasgupta S & Kirsebom
LA (2009) Sporulation in mycobacteria. Proc Natl Acad Sci U S A. Vol 106 No 26
Jun 2009 pp10781-6
Gibbs JH, Ferguson J, Brown RA, Kenicer KJ, Potts RC, Coghill G, Swanson Beck J (1984)
Histometric study of the localisation of lymphocyte subsets and accessory cells in
human Mantoux reactions. J Clin Pathol Vol 37 No 11 Nov 1984 pp1227–1234
Harada K (1977) Staining mycobacteria with periodic acid-carbol-pararosanilin: principle
and practice of the method. Microsc Acta. Vol 79 No 3 May 1977 pp224-36
Harada K, Gidoh S, Tsutsumi S (1976) Staining mycobacteria with carbolfuchsin: properties
of solutions prepared with different samples of basic fuchsin. Microsc Acta. Vol 78
No 1 Mar 1976 pp21-27
Harboe M, Oettinger T, Wiker HG, Rosenkrands I, Andersen P (1996) Evidence for
occurrence of the ESAT-6 protein in Mycobacterium tuberculosis and virulent
Mycobacterium bovis and for its absence in Mycobacterium bovis BCG. Infect
Immun Vol 64 No 1 Jan 1996 pp16-22
18
Pulmonary Infection
Harding CV, Boom WH (2010) Regulation of antigen presentation by M. tuberculosis: a role
for Toll-like receptors. Nat Rev Microbiol. Vol 8 No 4 Apr 2010 pp296-307
Hett EC, Chao MC, Steyn AJ, Fortune SM, Deng LL & Rubin EJ (2007) A partner for the
resuscitation-promoting factors of Mycobacterium tuberculosis. Mol Microbiol. Vol
66 No 3 Nov 2007 pp658-68
Huebner RE, Schein MF & Bass JB Jr The tuberculin skin test. Clin Infect Dis. Vol 17 No 6 Dec
1993 pp968-75
Ishikawa E, Ishikawa T, Morita YS, Toyonaga K, Yamada H, Takeuchi O, Kinoshita T, Akira
S, Yoshikai Y, Yamasaki S (2009) Direct recognition of the mycobacterial glycolipid,
trehalose dimycolate, by C-type lectin Mincle. J Exp Med. Vol 206 No 13 Dec 2009
pp2879-88
Jafari C, Thijsen S, Sotgiu G, Goletti D, Domínguez Benítez JA, Losi M, Eberhardt R, Kirsten
D, Kalsdorf B, Bossink A, Latorre I, Migliori GB, Strassburg A, Winteroll S, Greinert
U, Richeldi L, Ernst M & Lange C, Tuberculosis Network European Trialsgroup
(2009) Bronchoalveolar lavage enzyme-linked immunospot for a rapid diagnosis of
tuberculosis: a Tuberculosis Network European Trialsgroup study. Am J Respir Crit
Care Med. Vol 180 No 7 Oct 2009 pp666-73
Jasmer RM, Nahid P & Hopewell PC (2002) Latent Tuberculosis Infection N Engl J Med Vol
347 No 23 Dec 2002 pp1860-1866
Jo EK (2008) Mycobacterial interaction with innate receptors: TLRs, C-type lectins, and
NLRs. Curr Opin Infect Dis. Vol 21 No 3 Jun 2008 pp279-86
Jo EK, Yang CS, Choi CH, Harding CV (2007) Intracellular signalling cascades regulating
innate immune responses to Mycobacteria: branching out from Toll-like receptors.
Cell Microbiol. Vol 9 N 5 May 2007 pp1087-98
Kana BD, Gordhan BG, Downing KJ, Sung N, Vostroktunova G, Machowski EE, Tsenova L,
Young M, Kaprelyants A, Kaplan G & Mizrahi V. (2008) The resuscitationpromoting factors of Mycobacterium tuberculosis are required for virulence and
resuscitation from dormancy but are collectively dispensable for growth in vitro.
Mol Microbiol. Vol 67 No 3 Feb 2008 pp672-84
Kenney RT, Rangdaeng S, Scollard DM (1987) Skin blister immunocytology. A new method
to quantify cellular kinetics in vivo. J Immunol Methods Vol 97 No1 Feb 1987 pp101–
110
Khader SA, Cooper AM (2008) IL-23 and IL-17 in tuberculosis. Cytokine Vol 41 No 2 Feb 2008
pp79–83
Kinhikar AG, Verma I, Chandra D, Singh KK, Weldingh K, Andersen P, Hsu T, Jacobs WR Jr
& Laal S (2010) Potential role for ESAT6 in dissemination of M. tuberculosis via
human lung epithelial cells. Mol Microbiol. Vol 75 No 1 Jan 2010 pp92–106
Kinhikar AG, Verma I, Chandra D, Singh KK, Weldingh K, Andersen P, Hsu T, Jacobs WR
Jr, Laal S (2010) Potential role for ESAT6 in dissemination of M. tuberculosis via
human lung epithelial cells. Mol Microbiol. Vol 75 No 1 Jan 2010 pp92-106
Kursar M, Koch M, Mittrucker HW, Nouailles G, Bonhagen K, Kamradt T, Kaufmann SH
(2007) Cutting Edge: Regulatory T cells prevent efficient clearance of
Mycobacterium tuberculosis. J Immunol Vol 178 No 5 Mar 2007 pp2661–2665
Lalor SJ, Dungan LS, Sutton CE, Basdeo SA, Fletcher JM, Mills KH (2011) Caspase-1processed cytokines IL-1beta and IL-18 promote IL-17 production by gammadelta
Latent Tuberculosis: Advances in Diagnosis and Treatment
19
and CD4 T cells that mediate autoimmunity. J Immunol. Vol 186 No 10 May 2011
pp5738-48
Lecoeur HF, Truffot-Pernot C, Grosset JH (1989) Experimental short-course preventive
therapy of tuberculosis with rifampin and pyrazinamide. Am Rev Respir Dis. Vol
140 No 5 Nov 1989 pp1189-93
Leyten EM, Lin MY, Franken KL, Friggen AH, Prins C, van Meijgaarden KE, Voskuil MI,
Weldingh K, Andersen P, Schoolnik GK, Arend SM, Ottenhoff TH, Klein MR (2006)
Human T-cell responses to 25 novel antigens encoded by genes of the dormancy
regulon of Mycobacterium tuberculosis. Microbes Infect Vol 8 No 8 Jul 2006 pp2052–
2060
Liew FY, Xu D, Brint EK & O'Neill LA (2005) Negative regulation of toll-like receptormediated immune responses Nat Rev Immunol. Vol 5 No 6 Jul 2005 pp446-58
Lin MY & Ottenhoff TH. (2008) Not to wake a sleeping giant: new insights into hostpathogen interactions identify new targets for vaccination against latent M.
tuberculosis infection. Biol Chem. Vol 389 No 5 May 2008 pp497-511
Mahairas GG, Sabo PJ, Hickey MJ, Singh DC, Stover CK (1996) Molecular analysis of genetic
differences between Mycobacterium bovis BCG and virulent M. bovis. J Bacteriol
Vol 178 No 5 Mar 1996 pp1274-82
Master SS, Rampini SK, Davis AS, Keller C, Ehlers S, Springer B, Timmins GS, Sander P,
Deretic V (2008) Mycobacterium tuberculosis prevents inflammasome activation.
Cell Host Microbe. Vol3 No4 Apr 2008 pp224-32
Menzies D, Dion MJ, Rabinovitch B, Mannix S, Brassard P & Schwartzman K (2004)
Treatment completion and costs of a randomized trial of rifampin for 4 months
versus isoniazid for 9 months. Am J Respir Crit Care Med. Vol 170 No4 Mar 2004
pp445-9
Menzies D, Long R, Trajman A, Dion MJ, Yang J, Al Jahdali H, Memish Z, Khan K, Gardam
M, Hoeppner V, Benedetti A & Schwartzman K (2008) Adverse events with 4
months of rifampin therapy or 9 months of isoniazid therapy for latent tuberculosis
infection: a randomized trial. Ann Intern Med. Vol 149 No 10 Nov 2008 pp689-97
Menzies D, Pai M, Comstock G (2007) Meta-analysis: new tests in the diagnosis of latent
tuberculosis infection: areas of uncertainty and recommendations for research. Ann
Intern Med Vol 146 No 5 Mar 2007 pp340-54
Mishra BB, Moura-Alves P, Sonawane A, Hacohen N, Griffiths G, Moita LF, Anes E (2010)
Mycobacterium tuberculosis protein ESAT-6 is a potent activator of the
NLRP3/ASC inflammasome. Cell Microbiol. Vol 12 No 8 Aug 2010 pp1046-63
Mukamolova GV, Turapov O, Malkin J, Woltmann G & Barer MR (2010) Resuscitationpromoting factors reveal an occult population of tubercle Bacilli in Sputum. Am J
Respir Crit Care Med. Vol 181 No 2 Jan 2010 pp174-80
Muñoz-Elias EJ, Timm J, Botha T, Chan WT, Gomez JE & McKinney JD (2005) Replication
dynamics of Mycobacterium tuberculosis in chronically infected mice. Infect Immun
Vol 73 No 1 Jan 2005 pp546–551
Neyrolles O, Hernández-Pando R, Pietri-Rouxel F, Fornes P, Tailleux L, Barris Payan JA,
Pivert E, Bordat Y, Aguilar D, Prévost M-C, Petit C & Gicquel B (2006) Is adipose
tissue a place for Mycobacterium tuberculosis persistence? Pub Lib of Sci One Vol 1
Dec 2006 pp1–9
20
Pulmonary Infection
Nigou J, Zelle-Rieser C, Gilleron M, Thurnher M, Puzo G (2001) Mannosylated
lipoarabinomannans inhibit IL-12 production by human dendritic cells: evidence
for a negative signal delivered through the mannose receptor. J Immunol. Vol 166
No 12 Jun 2001 pp7477-85.
Nolan CM, Goldberg SV & Buskin SE (1999) Hepatotoxicity associated with isoniazid
preventive therapy: a 7-year survey from a public health tuberculosis clinic. JAMA
Vol 281 No 11 Mar 1999 pp1014-8
Noss EH, Pai RK, Sellati TJ, Radolf JD, Belisle J, Golenbock DT, Boom WH, Harding CV
(2001) Toll-like receptor 2-dependent inhibition of macrophage class II MHC
expression and antigen processing by 19-kDa lipoprotein of Mycobacterium
tuberculosis. J Immunol. Vol 167 No 2 Jul 2001 pp910-8.
Ohno H, Zhu G, Mohan VP, Chu D, Kohno S, Jacobs WR Jr, Chan J (2003) The effects of
reactive nitrogen intermediates on gene expression in Mycobacterium tuberculosis.
Cell Microbiol. Vol 5 No 9 Sep 2003 pp637-48.
Pai M, Zwerling A & Menzies D (2008) Systematic review: T-cell-based assays for the
diagnosis of LTBI: an update. Ann Intern Med. Vol 149 No 3 Aug 2008 pp177-84
Pecora ND, Gehring AJ, Canaday DH, Boom WH, Harding CV (2006) Mycobacterium
tuberculosis LprA is a lipoprotein agonist of TLR2 that regulates innate immunity
and APC function. J Immunol. Vol 177 No 1 Jul 2006 pp422-9.
Peyron P, Vaubourgeix J, Poquet Y, Levillain F, Botanch C, Bardou F, Daffé M, Emile JF,
Marchou B, Cardona PJ, de Chastellier C, Altare F (2008) Foamy macrophages from
tuberculous patients' granulomas constitute a nutrient-rich reservoir for M.
tuberculosispersistence. PLoS Pathog. Vol 4 No 11 Nov 2008
Pieters J (2008) Mycobacterium tuberculosis and the macrophage: maintaining a balance.
Cell Host Microbe. Vol 3 No6 Jul 2008 pp399-407
Platt JL, Grant BW, Eddy AA, Michael AF (1983) Immune cell populations in cutaneous
delayed-type hypersensitivity. J Exp Med Vol 158 No 4 Oct 1983 pp1227–1242.
Polesky A, Farber HW, Gottlieb DJ, Park H, Levinson S, O'Connell JJ, McInnis B, Nieves RL,
Bernardo J (1996) Rifampin preventive therapy for tuberculosis in Boston's
homeless. Am J Respir Crit Care Med. Vol 154 No 5 Nov 1996 pp1473-7
Poulter LW, Seymour GJ, Duke O, Janossy G, Panayi G (1982) Immunohistological analysis
of delayed-type hypersensitivity in man. Cell Immunol Vol74 No2 Dec1982 pp358–
369
Rees RJ & Hart PD (1961) Analysis of the host-parasite equilibrium in chronic murine TB by
total and viable bacillary counts. Br J Exp Pathol. Vol 42 Feb 1961 pp83-8.
Reichman LB, Lardizabal A & Hayden CH (2004) Considering the role of four months of
rifampin in the treatment of latent tuberculosis infection. Am J Respir Crit Care Med.
Vol 170 No 8 Oct 2004 pp832-5
Renshaw PS, Lightbody KL, Veverka V, Muskett FW, Kelly G, Frenkiel TA, Gordon SV,
Hewinson RG, Burke B, Norman J, Williamson RA & Carr MD (2005). Structure
and function of the complex formed by the tuberculosis virulence factors CFP-10
and ESAT-6 EMBO J. Vol 24 No 14 Jul 2005 pp2491–8.
Russell DG, Cardona PJ, Kim MJ, Allain S & Altare F (2009) Foamy macrophages and the
progression of the human tuberculosis granuloma. Nat Immunol. Vol 10 No 9 Sep
2009 pp943–948
Latent Tuberculosis: Advances in Diagnosis and Treatment
21
Russell-Goldman E, Xu J, Wang X, Chan J & Tufariello JM (2008) A Mycobacterium
tuberculosis Rpf double-knockout strain exhibits profound defects in reactivation
from chronic tuberculosis and innate immunity phenotypes. Infect Immun. Vol 76
No 9 Sep 2008 pp4269-81.
Sarrazin H, Wilkinson KA & Andersson J.Rangaka MX, Radler L, van Veen K, Lange C &
Wilkinson RJ (2009) Association between tuberculin skin test reactivity, the
memory CD4 cell subset, and circulating FoxP3-expressing cells in HIV-infected
persons. J Infect Dis Vol 199 No 5 Mar 2009 pp702–71
Sester M, Sotgiu G, Lange C, Giehl C, Girardi E, Migliori GB, Bossink A, Dheda K, Diel R,
Dominguez J, Lipman M, Nemeth J, Ravn P, Winkler S, Huitric E, Sandgren A &
Manissero D (2011) Interferon- release assays in the diagnosis of active TB: A
systematic review and meta-analysis. Eur Respir J Vol 37 No 1 Jan 2011 pp100-11.
Shleeva MO, Bagramyan K, Telkov MV, Mukamolova GV, Young M, Kell DB & Kaprelyants
AS (2002) Formation and resuscitation of ‘‘non-culturable’’ cells of Rhodococcus
rhodochrous and Mycobacterium tuberculosis in prolonged stationary phase.
Microbiology Vol 148 No 5 May 2002 pp1581–1591
TBNET Mack U, Migliori GB, Sester M, Rieder HL, Ehlers S, Goletti D, Bossink A, Magdorf
K, Hölscher C, Kampmann B, Arend SM, Detjen A, Bothamley G, Zellweger JP,
Milburn H, Diel R, Ravn P, Cobelens F, Cardona PJ, Kan B, Solovic J, Duarte R,
Cirillo DM, & Lange C for the TBNET (2009) LTBI: latent tuberculosis infection or
lasting immune responses to M. tuberculosis? A TBNET consensus statement Eur
Respir J Vol 33 No5 May 200 pp956-973
Tufariello JM, Mi K, Xu J, Manabe YC, Kesavan AK, Drumm J, Tanaka K, Jacobs WR Jr &
Chan J (2006) Deletion of the Mycobacterium tuberculosis resuscitation-promoting
factor Rv1009 gene results in delayed reactivation from chronic tuberculosis. Infect
Immun. Vol 74 No 5 May 2006 pp2985-95.
Ulrichs T, Kosmiadi GA, Trusov V, Jörg S, Pradl L, Titukhina M, Mishenko V, Gushina N &
Kaufmann SH. (2004) Human tuberculous granulomas induce peripheral lymphoid
follicle-like structures to orchestrate local host defence in the lung. J Pathol. Vol 204
No 2 Oct 2004 pp217-28.
Verhagen LM, van den Hof S, van Deutekom H, Hermans PW, Kremer K, Borgdorff MW &
van Soolingen D (2011) Mycobacterial factors relevant for transmission of
tuberculosis. J Infect Dis. Vol 203 No 9 May 2011 pp1249-55
Villarino ME, Ridzon R, Weismuller PC, Elcock M, Maxwell RM, Meador J, Smith PJ, Carson
ML, Geiter LJ (1997) Rifampin preventive therapy for tuberculosis infection:
experience with 157 adolescents. Am J Respir Crit Care Med. Vol 155 No 5 May 1997
pp1735-8
Voskuil MI, Schnappinger D, Visconti KC, Harrell MI, Dolganov GM, Sherman DR,
Schoolnik GK (2003) Inhibition of respiration by nitric oxide induces a
Mycobacterium tuberculosis dormancy program. J Exp Med. Vol 198 No 5 Sep 2003
pp 705-13.
WHO (2001) WHO warns against the use of inaccurate blood tests for active tuberculosis
http://www.who.int/mediacentre/news/releases/2011/tb_20110720/en/index.h
tml
World Health Organization Tuberculosis Fact-sheet
http://www.who.int/mediacentre/factsheets/fs104/en/index.html
22
Pulmonary Infection
Zvi A, Ariel N, Fulkerson J, Sadoff JC & Shafferman A. (2008) Whole genome identification
of Mycobacterium tuberculosis vaccine candidates by comprehensive data mining
and bioinformatic analyses. BMC Med Genomics. Vol 1 May 2008 pp18