Immunomodulatory effects of Trichinella
spiralis-derived excretory–secretory
antigens
Ivana Radovic, Alisa GrudenMovsesijan, Natasa Ilic, Jelena
Cvetkovic, Slavko Mojsilovic, Marija
Devic & Ljiljana Sofronic-Milosavljevic
Immunologic Research
ISSN 0257-277X
Volume 61
Number 3
Immunol Res (2015) 61:312-325
DOI 10.1007/s12026-015-8626-4
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Immunol Res (2015) 61:312–325
DOI 10.1007/s12026-015-8626-4
Immunomodulatory effects of Trichinella spiralis-derived
excretory–secretory antigens
Ivana Radovic • Alisa Gruden-Movsesijan •
Natasa Ilic • Jelena Cvetkovic • Slavko Mojsilovic
Marija Devic • Ljiljana Sofronic-Milosavljevic
•
Published online: 25 January 2015
Ó Springer Science+Business Media New York 2015
Abstract Helminth-derived products, either released into
the circulation during the course of the infection or isolated
after in vitro cultivation of the parasite and applied by the
injection, are able to suppress the host immune response to
autoantigens and allergens, but mechanisms could differ.
Prophylactic application of Trichinella spiralis excretory–
secretory muscle larvae (ES L1) products ameliorates
experimental autoimmune encephalomyelitis (EAE) with
the same success as infection did. However, a shift to the
Th2-type response in the periphery and in the central nervous system, accompanied by activation of regulatory
mechanisms, had a striking, new feature of increased proportion of unconventional CD4?CD25-Foxp3? regulatory
cells both in the periphery and in the central nervous system of animals treated with ES L1 before the induction of
EAE.
Keywords Trichinella spiralis Excretory–secretory
antigens Experimental autoimmune encephalomyelitis
Introduction
Understanding the relationship between infectious agents
and autoimmunity still remains a key issue in immunology.
I. Radovic A. Gruden-Movsesijan N. Ilic J. Cvetkovic
M. Devic L. Sofronic-Milosavljevic (&)
Institute for the Application of Nuclear Energy – INEP,
University of Belgrade, Banatska 31b, 11080 Belgrade, Serbia
e-mail: sofronic@inep.co.rs
S. Mojsilovic
Institute for Medical Research, University of Belgrade,
Belgrade, Serbia
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Despite the large body of evidence supporting the contention that infections can cause autoimmunity, numerous
epidemiological and experimental studies have suggested
that exposure to pathogens early in life could ensure proper
development of immunoregulatory mechanisms and hence
decreases the risk of autoimmune diseases [1, 2].
Throughout evolution, the immune system has evolved in
the continuous presence of a vast number of microorganisms and those organisms became essential for its proper
development. The impact of pathogens made the immune
system capable of mounting appropriate defensive
responses, while the presence of organisms such as helminths or microbiota influenced the development of
immunoregulatory mechanisms essential for immune tolerance. Nowadays, in economically developed countries,
with a high level of health care and sanitation, the immune
system is deprived of contact with some organisms that
have shaped it during coevolution, which might cause
dysregulation leading to the development of inflammatory
disorders such as autoimmune diseases [3].
Infections with parasitic helminths usually are not life
threatening, and host ‘‘tolerates’’ the presence of parasites
in such way that clinical symptoms fade during the infection course and become either restricted or disappear.
During coevolution, both helminth parasites and their hosts
developed specific adaptations that enabled each participant in the complex relationship to survive. The key
adaptation mechanism is immunomodulation that is beneficial to both the host and the parasite, since this can protect
the host from unnecessary damage caused by excessive
inflammatory responses and at the same time protect the
parasites from elimination. This modulation of the host
immune response does not refer only to helminth antigens,
but to nonrelated antigens as well [4]. The beneficial effect
of helminth infections on the outcome of different
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Immunol Res (2015) 61:312–325
autoimmune diseases such as multiple sclerosis (MS) [5],
inflammatory bowel disease [6] and type 1 diabetes mellitus (T1D) [7] has been already demonstrated. Results
from experimental models led to a series of clinical trials
and studies of live parasitic infestations in patients with
Crohn’s disease, ulcerative colitis and MS [3, 8]. Parasitedriven protection from autoimmune diseases was associated with induction of a Th2 response and a network
consisting of regulatory T cells (Tregs) (either Foxp3? or
Foxp3-), CD8? Tregs, regulatory B cells, alternatively
activated macrophages and regulatory/anti-inflammatory
cytokines such as IL-10 and TGF-b [9]. Regulatory T cells
(Tregs) are, however, key components of the immune
regulatory network capable of suppressing not only the
specific response against the parasite but also toward
autoantigens [10].
Experimental autoimmune encephalomyelitis (EAE)
has been widely used as an animal model for the human
disease MS [11, 12]. The inflammatory process in both
MS and EAE has been considered to be a consequence of
activation of a Th1/Th17 cytokine cascade [13]. Th1 and
Th17 cells can be suppressed by Tregs but their activity
seems to be impaired in patients with MS [14]. Parasites,
especially helminths, might be very helpful in restoring
homeostasis, since they are able to promote normal
immune regulation and suppress immunopathology during autoimmune diseases [3, 15]. Experimental models
have shown that infection with Schistosoma mansoni
[16], Trypanosoma cruzi [17] or Trichinella spiralis (T.
spiralis) [18, 19] suppressed the development of EAE.
However, since treatment with live worms carries certain
risks, investigations have focused on identifying helminth-derived molecules with immunomodulatory
capacities that could be safely administered to patients
[20]. One of the most studied helminth-derived products
is ES-62, a molecule from Acantocheilonema viteae that
possesses the capacity to modulate both Th1- and Th2mediated diseases [21]. Excretory–secretory products (ES
L1) released from T. spiralis muscle larvae during the
chronic phase of the infection are most likely to be
important for communication with the host organism.
Besides their participation in establishing parasitism [22],
these molecules are undoubtedly involved in the modulation of the host immune response, thereby creating an
environment suitable for the survival of both the parasite
and the host organism. Here, we investigated the potential
of T. spiralis ES L1 products to promote immune regulation and control the development of EAE. We have
provided evidence for the immunomodulatory capacity of
T. spiralis muscle larvae ES L1 products, represented by
their beneficial effect on the outcome of EAE. We also
explored mechanisms by which ES L1 acts to alleviate
the disease.
313
Materials and methods
Animals
Dark Agouti (DA) rats were bred and housed at the Military Medical Academy in Belgrade. Animals were used at
12–14 weeks of age, and they had free access to food and
water. All animal experiments were performed according
to institutional guidelines and were approved by the local
Institutional Animal Care and Use Committee.
Antigen preparation
Trichinella spiralis strain (ISS 161) was maintained and
recovered from muscles of infected Wistar rats by digestion of the carcasses in prewarmed gastric juice [23].
Muscle larvae were kept under controlled conditions
(37 °C, 5 % CO2) in complete Dulbecco’s modified
Eagle’s medium (DMEM) (Sigma, St Louis, MO), for 18 h
[24]. Excretory–secretory products of the muscle larvae
(ES L1) were obtained by dialysis and concentration of
culture supernatants and were kept at -20 °C until further
use.
EAE induction and evaluation
EAE was induced in DA rats by a single intradermal
injection (0.1 ml), in the right hind footpad, with an encephalitogenic emulsion prepared by mixing rat spinal cord
(SC) tissue homogenate (50 % w/v in saline) emulsified in
an equal amount of complete Freund’s adjuvant (CFA;
Difco, Detroit, MI) containing 4 mg/ml Mycobacterium
tuberculosis (Difco). Starting from day 8 postimmunization
(pi), rats were weighed and assessed for signs of the disease
daily as follows: 0 = no clinical signs; 1 = flaccid tail;
2 = hind limb paresis; 3 = complete bilateral hind limb
paralysis often associated with incontinence; and
4 = moribund state or death. Intermediate scores were
assigned if neurological signs were of lower severity than
observed typically. Several disease parameters were
examined to evaluate the severity of EAE: incidence, mean
day of onset, duration of illness, mean maximal severity
score (the mean of the maximal clinical score that each rat
in a group developed over the course of the experiment)
and cumulative disease index (the sum of the daily mean
clinical scores for a group over a given number of days).
Animals were observed for 25 days after the immunization.
In vivo treatment with ES L1 antigens
DA rats were divided into five groups (5 animals/group),
and each group was subjected to EAE induction. Prior to
this, the control group (marked EAE) received a PBS
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Fig. 1 ES L1 ameliorates EAE in DA rats. Groups designated ES L1/
150 ? EAE and ES L1/250 ? EAE were injected once i.p. with 150
and 250 lg of ES L1, respectively, 7 days before EAE induction.
Groups marked ES L1/2x150 ? EAE and ES L1/2x250 ? EAE were
injected i.p. with the indicated amounts of ES L1 antigens twice, 14
and 7 days before EAE induction. Animals treated with PBS at the
same times as indicated for ES L1 treatment were used as the control
group. Clinical score on each day of the disease if the 150-lg ES L1
dose was applied once or twice before EAE induction (a); clinical
score on each day of the disease if the 250-lg ES L1 dose was applied
once or twice before EAE induction (b); parameters of illness:
incidence, mean day of onset, duration of illness, and mean maximal
clinical score (c); cumulative index of the disease for each group (d).
Data represent the mean ± SD of results from two independent
experiments. *p \ 0.05; **p \ 0.01
injection, while the experimental groups were injected
intraperitoneally (i.p.) with different amounts of T. spiralis
ES L1 products in PBS: Dose of 150 lg was administered
once (ES L1/150) 7 days before EAE induction, or twice
(ES L1/2x150) 14 and 7 days before EAE induction;
250 lg dose was administered once (ES L1/250) 7 days
before EAE induction, or twice (ES L1/2x250) 14 and
7 days before EAE induction.
For the analyses of cytokine production and the presence
of regulatory T cells at different phases of EAE development, ES L1-treated or untreated EAE-induced animals
were killed during the inductive (day 8 pi), effector (day 15
pi) and recovery phases (day 25 pi) and cells were harvested from spleens and CNS.
Bone marrow-derived DCs (BMDCs) were generated
from male DA rats 16–18 weeks old according to the
procedure described previously [25]. DCs were obtained
by culturing bone marrow cells from DA rats in RPMI1640 supplemented with 10 % FCS, 2 mM L-glutamine,
1 mM Na-pyruvate, 10 mMHepes, 50 lM 2-ME (Sigma),
50 U/ml gentamycin (Galenika, Belgrade, Serbia) and
growth factors: 25 ng/ml GM-CSF, 25 ng/ml IL-4 and
25 ng/ml Flt-3 ligand (all from Biosource Invitrogen,
Camarillo, CA). Cells were maintained at 37 °C in a
humidified CO2 incubator, and fresh medium was added on
days 3 and 6. On day 8, BMDCs (5 9 106cells/well) were
pulsed for 48 h with T. spiralis ES L1 antigens (50 lg/ml),
myelin oligodendrocyte glycoprotein (MOG)63–87 peptide
(10 lg/ml) (a kind gift from Prof Dr M. Lukic, Center for
Molecular Medicine and Stem Cell Research, Faculty of
Medical Sciences, University of Kragujevac, Serbia) and
the combination of MOG peptide and ES L1 (except that
ES L1 was added for the final 24 h), or left unstimulated by
cultivation in medium alone. At day 10, supernatants were
collected for measuring cytokine levels, while unstimulated and stimulated DCs were co-cultured with T
lymphocytes.
T lymphocytes were isolated from popliteal draining
lymph nodes (DLN) of EAE-immunized animals on day 8
pi, using Pan T isolation microbeads on a MiniMACS
Cells
Spinal-cord-infiltrating cells were obtained from the SC of
rats perfused with sterile PBS. They were homogenized,
adjusted to 30 % Percoll (Sigma) and overlaid on a 40 %/
70 % Percoll gradient. Following centrifugation at 7009g
for 20 min, mononuclear cells were recovered from the 40/
70 % Percoll interface and washed in RPMI medium
(Sigma). The cells obtained from spleens and SC were used
for assessment of cytokine production and stained for
markers of Tregs, CD4, CD25 and Foxp3.
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Fig. 2 Course of EAE in ES L1-treated and untreated DA rats used
for in vitro examination. Rats injected i.p. with 250 lg of ES L1
antigens or PBS twice, 14 and 7 days before EAE induction, were
divided into groups (5 animals/group) and killed at the indicated time
points (arrows). The presented results concern groups analyzed at the
end of the observation period (day 25 pi, recovery phase). The
following parameters were monitored: clinical score on each day of
the disease (a), cumulative index of the disease (b) and incidence,
mean day of onset, duration of illness, mean maximal clinical score
(c). Data represent the mean ± SD of results from two independent
experiments. *p \ 0.05; **p \ 0.01
separation column (Miltenuyi Biotech, Auburn, CA)
according to the manufacturer’s instructions.
Culture supernatants were collected and stored at -20 °C
for cytokine analyses.
Cell cultures
Cytokine ELISAs
Spleen cells were seeded in 24-well plates (2 9 106/well)
and cultivated at 5 % CO2 and 37 °C in RPMI-1640 medium
(PAA Laboratories, Pasching, Austria) supplemented with
antibiotics (Galenika, Belgrade, Serbia), 5 % FCS and in the
presence of concanavalin A (2.5 lg/ml) (ConA, INEP,
Belgrade, Serbia) or in medium alone for 48 h.
SC-infiltrating cells were cultured in 96-well plates
(5 9 105/ml) at 5 % CO2 and 37 °C in RPMI-1640 medium supplemented with antibiotics, 2 % rat serum, without
stimulation, for 72 h.
Culture supernatants from spleens and SC were collected and analyzed for cytokines.
Purified T cells obtained from DLN of EAE-immunized
animals were plated in round-bottomed 96-well plates at
1 9 105/well, and for determination of proliferation
capacity, cells were co-cultivated with unstimulated and
stimulated DCs (1 9 104, 0.5 9 104, 0.25 9 104/well) for
2 days. In some DC/T cell co-cultures, T cells were stimulated with MOG peptide (10 lg/ml). They were pulsed
with 1 lCi/well 3H thymidine (Amersham, Amersham,
UK) for an additional 18 h and measured for 3H thymidine
incorporation. For determination of cytokine production,
purified T cells (2.5 9 106/well) were co-cultivated with
stimulated or unstimulated DCs (5 9 105/well) in 24-well
plates in a final volume of 1 ml for 48 h. Again, in some
DC/T cell co-cultures, T cells from EAE-immunized animals were stimulated with MOG peptide (10 lg/ml).
Cytokines (IL-12p70, IL-4, IL-10, IL-17, IFN-c and TGFb) were measured in culture supernatants using commercially available ELISA kits (for IL-4, IL-10, IFN-c BD
Biosciences, San Jose, CA; for IL-12p70 and IL-17 PeproTech, Rocky Hill, NJ; for TGF-b R&D Systems, Minneapolis, MN). Cell culture supernatants were analyzed
according to the manufacturer’s instructions.
Flow cytometry analysis
Spleen and SC cells from each animal were prepared for
phenotype analysis and intracellular staining. For surface
antigen staining, cells were incubated with the following antirat antibodies: FITC-labeled anti-CD4 and PE-labeled antiCD25 (both purchased from eBioscience, San Diego, CA).
After washing, intracellular staining was performed using a
Foxp3 Staining Buffer Set and PECy5-labeled anti-rat Foxp3
antibody according to the manufacturer’s protocol (eBioscience). Stained cells were analyzed using the CyFlowCL
(Partec, Munster, Germany). For characterization of lymphocytes, at least 10 000 events were collected. Data were
analyzed with FlowJo software (TreeStar, Ashland, OR).
Statistical analysis
Statistical comparisons between groups were made using the
Student’s unpaired or paired t test and the Mann–Whitney
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Fig. 3 Effect of in vivo ES L1 treatment on cytokine production by
SC-infiltrating cells during EAE. Cytokine production by SCinfiltrating cells was measured in the inductive (8 day pi), effector
(15 day pi) and recovery (25 day pi) phase during EAE from ES L1
(EAE/ES L1)-treated and control (EAE) animals. Data represent the
mean ± SD of results from two independent experiments. *p \ 0.05;
**p \ 0.01; ***p \ 0.001
test. The results are presented as mean ± SD. Differences
with probability (p) values less than 0.05 were considered
statistically significant.
not altered, but the duration of illness was significantly
shorter in all ES L1-treated animals than in control rats
(Fig. 1c). Moreover, according to the obtained results, the
dose that showed the most convincing effect on the course
of EAE was 250 lg given twice at weekly intervals, i.e.,
14 and 7 days before EAE induction. This dose was
applied in further studies related to the mechanisms
underlying the observed immunomodulation. Rats injected twice i.p. with 250 lg of ES L1 antigens or PBS were
subjected to EAE induction and analyzed for T cell
response at different time points during the course of
EAE, i.e., at induction (day 8 pi), effector (day 15 pi) and
recovery phase (day 25 pi) of the disease. The groups of
ES L1-treated and untreated, EAE-immunized DA rats
that were intended to be analyzed in the recovery phase
were also monitored for disease course. EAE was reduced
in severity in animals treated with ES L1 antigens prior to
EAE induction (Fig. 2). The cumulative index for the ES
L1-treated group was 0.32 ± 0.08, while for the control
group, it was 0.97 ± 0.18 (Fig. 2b). The difference
clearly shows that treatment with ES L1, performed as
described above, had a significant impact on disease
development.
Results
Application of ES L1 antigens ameliorates EAE
Previously Sofronic et al. [26] demonstrated that T. spiralis ES L1 antigens, acting via DCs, possess immunomodulatory capacity, which was indicated by alleviation
of EAE in DA rats. This study was focused on the
investigation whether direct application of isolated ES L1
to DA rats could ameliorate EAE. The first task was to
determine whether chosen doses of ES L1 in applied time
intervals influence the course of the disease. Groups of
DA rats injected with ES L1 as indicated in Materials and
Methods, as well as the control PBS-injected group, were
subjected to EAE induction and further monitored for the
development of clinical signs and body weight loss. The
changes in average body weight were not significantly
different between the groups injected with ES L1 or PBS
(data not shown). DA rats that had received ES L1 antigens exhibited milder signs of EAE compared to the
control EAE group (Fig. 1a, b), with reduced clinical
parameters (except maximal clinical score for ES L1/
2x150, Fig. 1c) and significantly lower cumulative indices
(except for ES L1/150, Fig. 1d). The onset of disease was
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Production of cytokines by SC-infiltrating cells
SC-infiltrating cells were isolated in the inductive (8 day
pi), effector (15 day pi) and recovery (25 day pi) phase
during EAE from ES L1-treated and control animals. The
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Fig. 4 Effect of in vivo ES L1 treatment on cytokine production by
spleen cells during EAE. Cytokine production by spleen cells was
measured in the inductive (8 day pi), effector (15 day p.) and
recovery (25 day pi) phase during EAE from ES L1 (EAE/ES L1)-
treated and control (EAE) animals. Data represent the mean ± SD of
results from two independent experiments. *p \ 0.05; **p \ 0.01;
***p \ 0.001
production of cytokines IL-4, IL-10, IL-17, IFN-c and
TGF-b was determined in cells cultivated in medium alone.
The release of IFN-c by SC-infiltrating cells from treated
animals was lower than in control groups during all phases
of EAE but the difference reached statistical significance
only in the inductive phase of the disease (Fig. 3a). IL-17
production presented the same profile as IFN-c, characterized by diminished production throughout the disease in
ES L1-treated animals. Significantly lower levels of IL-17
were detected in the inductive and recovery phase of EAE,
but not at the peak of the disease (Fig. 3b). During the
course of EAE, release of Th2 and regulatory cytokines
was higher in treated animals compared to control rats.
Thus, IL-4 release was significantly elevated in ES L1treated rats with values almost twice as high as in EAE
animals (Fig. 3c). IL-10 production could not be detected
in the inductive phase of the disease in the culture supernatants of SC-infiltrating cells. Nevertheless, release of this
cytokine was greatly enhanced as the disease progressed
and peaked in the effector phase, with reduced, but still
significantly elevated levels in the recovery phase
(Fig. 3d). On the other hand, there was no significant difference in the production of TGF-b between ES L1-treated
and untreated groups during the inductive and effector
phases (Fig. 3e). Only in the recovery phase of EAE, did
production of TGF-b by SC-infiltrating cells from ES L1treated animals attain a significant increase when compared
to the control.
Production of cytokines by spleen cells
Spleen cells harvested at the indicated time points
throughout the disease were cultivated in medium alone or
stimulated with T cell mitogen ConA. Supernatants were
analyzed for cytokine content as an indicator of the
immune response at the systemic level during the course of
EAE. Figure 4 displays production of cytokines by
splenocytes from treated and untreated, EAE-induced rats
cultivated in medium alone. Production of IFN-c in ES L1treated animals was reduced compared to untreated EAE
animals, during the course of the disease, but the difference
reached statistical significance only in the inductive and
recovery phases (Fig. 4a). Release of IL-17 declined
throughout the disease in animals treated with ES L1, when
compared to controls also leading to a statistically significant difference in the inductive and recovery phases of
EAE (Fig. 4b). Thus, ES L1 treatment of DA rats markedly
suppressed the release of IFN-c and IL-17, mediators of
disease induction and progression. On the other hand,
splenocytes from ES L1-treated, EAE-immunized animals
produced greatly elevated levels of the Th2 cytokine IL-4
in the inductive and effector phases of EAE, when compared to control EAE rats (Fig. 4c). Production of the
regulatory cytokines IL-10 and TGF-b was hardly affected
by treatment with ES L1. Only at the peak of the disease
did spleen cells from ES L1-treated animals release
somewhat more IL-10 than controls, but without statistical
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Fig. 5 Foxp3? expression in SC-infiltrating cells during the course of
EAE. Representative plots for each time point from one of two
experiments present CD25 versus Foxp3, gated on CD4? T cells (a);
the percentage of different T regulatory cell populations,
CD4?CD25?Foxp3? (left panel) and CD4?CD25-Foxp3? (right
panel) in the inductive (8 day pi), effector (15 day pi) and recovery
(25 day pi) phase during EAE from ES L1 (EAE/ES L1)-treated and
control (EAE) animals (b). Data represent the mean ± SD of results
from two independent experiments. *p \ 0.05; ***p \ 0.001
significance (Fig. 4d), while levels of TGF-b were slightly
higher in treated than in untreated animals in all EAE
phases, especially during recovery, but the differences
were not statistically significant (Fig. 4e). ConA stimulation provoked higher levels of all secreted cytokines but
did not change the pattern of release (data not shown).
Quantification of Foxp3? T cells in SC-infiltrating cells
and spleen
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SC-infiltrating and spleen cells were analyzed for the presence
of CD4?CD25?Foxp3? cells during the course of EAE, at day
8, 15 and 25 pi. Flow cytometric analysis of SC-infiltrating cells
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Fig. 6 Foxp3? expression in spleen cells during the course of EAE.
Representative plots for each time point from one of two experiments
show CD25 versus Foxp3, gated on CD4? T cells (a); the percentage
of different T regulatory cell populations, CD4?CD25?Foxp3? (left
panel) and CD4?CD25-Foxp3? (right panel) in the inductive (8 day
pi), effector (15 day pi) and recovery (25 day pi) phase during EAE
from ES L1 (EAE/ES L1)-treated and control (EAE) animals (b).
Data represent the mean ± SD of results from two independent
experiments. *p \ 0.05; ***p \ 0.001
revealed that the percentage of CD4?CD25?Foxp3? T cells
was higher in the ES L1-treated, EAE-immunized group than in
controls throughout the disease, and the difference reached
statistical significance during the inductive and the recovery
phases of EAE (Fig. 5b). Surprisingly, a very high percentage of
CD4? Foxp3? cells that did not express CD25 were
found among SC-infiltrating cells from ES L1-treated animals, on day 15 pi (Fig. 5b). An increased proportion of
CD4?CD25-Foxp3? cells were still present on 25 day pi in ES
L1-treated compared with untreated, EAE-induced animals.
The number of CD4?CD25-Foxp3? cells was low in the control EAE-immunized group throughout the disease (Fig. 5b).
Spleen cells were also analyzed for the presence of Foxp3?
T cells during the course of EAE. At day 8 pi, the percentage of
CD4?CD25?Foxp3? cells was low in both ES L1-treated and
untreated animals (Fig. 6b). CD4?CD25?Foxp3? T cells
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Fig. 7 Induction of CD4?CD25-Foxp3? cells in healthy rats treated with
ES L1. Percentage of CD4?CD25?Foxp3? (a) and CD4?CD25-Foxp3?
(b) at different time points corresponding with EAE induction (day 0), and
days 8, 15 and 25 pi. PBS-treated animals served as controls. Data represent
the mean ± SD of results from two independent experiments. **p \ 0.01;
***p \ 0.001
showed expansion at the effector and the recovery phases in
ES L1-treated, EAE-induced rats, but when compared to
controls, the increase was significant only on day 15 pi, in the
effector phase of the disease (Fig. 6b). In the control EAE
group, the number of CD4?CD25?Foxp3? cells was low in
the inductive and effector phases of the disease, and only
started to rise in the recovery phase (Fig. 6b). Again, the
striking feature of ES L1 treatment was the appearance of
CD4?CD25-Foxp3?cells among spleen cells isolated these
EAE-immunized rats (Fig. 6b). This cell population could
only be seen at day 15 pi, in a number that greatly exceeded
that found in control animals. Unlike the situation with SCinfiltrating cells, CD4?CD25-Foxp3? cells could not be
detected among spleen cells from ES L1-treated animals in the
recovery phase.
persisted thereafter (Fig. 7a). CD4?CD25-Foxp3? cells
were detected at day 8 (time that corresponds to day 8 after
EAE induction), in a number five times greater than the
control value (Fig. 7b). The relative number of these cells
slowly declined till the end of the observation period, but
remained significantly higher than in the controls.
Induction of CD4?CD25-Foxp3? cells in healthy rats
treated with ES L1
It was obvious that application of ES L1 antigens before
EAE induction provoked a significant expansion of
CD4?CD25-Foxp3? cells at the periphery and in the target
organ, since these cells were absent from the spleen and SC
infiltrates in untreated animals. Support to this finding was
provided by the results obtained when healthy DA rats were
injected with the same amount of ES L1 antigens at the same
time intervals and were analyzed for the presence of
CD4?CD25-Foxp3? and CD4?CD25?Foxp3? among
spleen cells obtained at different time points corresponding
with EAE induction (day 0), and days 8, 15 and 25 pi.
Control rats were treated with PBS. The percentage of both
CD4?CD25-Foxp3? and CD4?CD25?Foxp3? cells in
control rats was very low (Fig. 7a,b). However, ES L1
treatment provoked expansion of both types of cells
(Fig. 7a,b). The significant increase of CD4?CD25?Foxp3?
cells was detected as soon as 7 days after antigen application
(time that corresponds to day 0 of EAE induction) and
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The impact of ES L1 products on DC and T cell activity
in vitro
Results presented in this paper point out that ES L1, applied
before EAE induction, could successfully alleviate this autoimmune disease. The impact of ES L1, applied intraperitoneally, is most likely mediated through DCs, key cells for
initiation, progression and regulation of the immune response.
It was already shown that stimulation of DCs with ES L1
antigens in vitro provoked the release of IL-10 and lowered
that of IL12p70 from DCs [27]. Here, we are proving that ES
L1 could alter the existing phenotype of DCs that had already
been in contact with encephalitogenic antigens, like MOG
peptide. DCs stimulated with MOG peptide (DC/MOG), ES
L1 antigens (DC/ES L1) and a combination of MOG and ES
L1 (DC/48hMOG24hESL1) were examined for cytokine
production. It was observed that ES L1, added to the culture of
MOG-pulsed DCs, significantly reduced the release of IL12p70 and increased that of IL-10, compared to DC/MOG
alone (Fig. 8a). It can be concluded that ES L1 products
possess the capacity to modify cytokine secretion from DCs
already primed with MOG.
To explore whether ES L1-provoked change in DC
activation is reflected on autoreactive T cells, stimulated
and unstimulated DCs were co-cultivated with T cells
isolated from DLN of EAE-immunized animals. T cells,
cultivated in vitro with DC/MOG, produced elevated levels
of IL-17 compared to DC/med (Fig. 8b). ES L1-stimulated
MOG-pulsed DCs altered the cytokine profile of T cells by
causing significant reduction in IL-17 secretion and to a
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Immunol Res (2015) 61:312–325
321
b Fig. 8 Impact of ES L1 on DC and T cells in vitro. DCs were
stimulated with ES L1 (DC/ES L1), MOG (DC/MOG), MOG for the
whole 48 h and ES L1 for the final 24 h (DC/48hMOG/24hES L1) or
were cultivated in medium alone (unstimulated; DC/med). The
production of IL-10 and IL-12p70 from DCs (a); cytokine profile of
encephalitogenic T cells isolated from DLN of EAE-induced animals
and co-cultivated with stimulated or unstimulated DCs (b); the impact
of ES L1-stimulated DCs on cytokine production of encephalitogenic
T cells restimulated with MOG (c). Data represent the mean ± SD of
results from two independent experiments. #Statistical significance
obtained when results were compared with DC/MOG. ###p \ 0.001.
*Statistical significance obtained when results were compared to DC/
med *p \ 0.05; **p \ 0.01; ***p \ 0.001
(3.375 ± 177 for DC/48hMOG24h ESL1 vs. 5.823 ± 183
for DC/MOG, p \ 0.001).
The influence of ES L1 products on the activity of T cells
in EAE-induced rats was assessed by co-cultivation of ES
L1-stimulated DCs with autoreactive T cells, restimulated
with MOG. ES L1-stimulated DCs significantly suppressed
the production of IL-17 and IFN-c (Fig. 8c), compared with
T cells cultivated with unstimulated DCs (DC/med). On the
other hand, DC/ES L1 provoked eightfold greater release of
IL-4 from autoreactive T cells stimulated with MOG,
accompanied by increased levels of IL-10 and TGF-b, in
comparison with T cells co-cultivated with DC/med. ES L1stimulated DCs affected cell proliferation as well, significantly reducing the proliferative potential of T cells originated from EAE-induced rats (2.750 ± 196 for DC/ES L1
vs. 4.918 ± 167 for DC/med, p \ 0.001).
Discussion
lesser extent IFN-c in comparison with DC/MOG
(Fig. 8b). On the other hand, the presence of ES L1-stimulated MOG-pulsed DCs provoked strong release of IL-4
and IL-10 from T cells, compared to DC/MOG. The impact
of ES L1 on MOG-pulsed DCs was also confirmed by
reduced proliferation of T cells isolated from EAE-immunized animals compared to co-cultures with DC/MOG
The causal relationship between the incidence of inflammatory disorders, such as autoimmune diseases, and helminth infections, as explained by the ‘‘Hygiene
hypothesis,’’ ranks these organisms among those important
for the proper development of the immune system [6].
Many studies are focused on understanding the complex
cellular and molecular mechanisms that regulate the host
immune response during parasitic infections, especially
those that strive to define the nature and role of parasitederived products responsible for protection from immunopathology. Among other helminthes, T. spiralis demonstrated capacity to improve the outcome of EAE. Namely,
chronic infection with this parasite significantly ameliorated EAE [19]. The chronic phase of the infection is
characterized by the presence of encapsulated larvae
(cysts) in infected muscles that continually communicate
with the host through ES L1 products, which influence the
host immune system. Therefore, amelioration of EAE by T.
spiralis infection could be ascribed to these products, but
the direct impact of ES L1 on the disease course has not
been explored so far. Our research was set up to investigate
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322
the immunomodulatory capacities of T. spiralis ES L1
antigens prophylactically applied to animals before EAE
induction. ES L1 antigens provided significant amelioration from EAE, as reflected in the lower maximal clinical
score and cumulative index and reduced duration of illness
in ES L1-treated animals. This indicated that the applied
parasite antigens could influence the course of CNS autoimmunity. The capacity of T. spiralis ES L1 antigens to
modulate the immune response in EAE-induced animals
was demonstrated by a shift to the Th2-type response in the
periphery and CNS and activation of regulatory mechanisms. Kuijk et al. [28] demonstrated successful amelioration of EAE using worm antigens, but unlike us they
applied soluble extracts of T. suis and T. spiralis larvae,
without addressing mechanisms underlying observed phenomenon. Motomura and coworkers [29] also used T.
spiralis larval crude muscle antigens for prophylactic
treatment of experimentally induced colitis in mice. The
results were satisfactory, since the severity of the disease
and mortality rate were significantly reduced. Our results
also correlate with the study on treatment with Shistosoma
egg antigen (SEA) antigens from Shistosoma japonicum
before EAE induction or during the preclinical phase. This
treatment resulted in amelioration of the severity and
progression of EAE [30]. Moreover, exposure to the
phosphorylcholine containing glycoprotein ES-62, secreted
by the filarial nematode, Acanthochelionema vitae, prevented initiation and progression of collagen-induced
arthritis in a murine model [31].
The effect of ES L1 was most prominent on the production of the Th2-type cytokine IL-4, both at the
periphery and in the target organ, which could suppress the
release of Th1 cytokines such as IFN-c. Indeed, significant
reduction in the levels of IFN-c and IL-17, cytokines crucial for the induction and progression of the disease, was
observed in EAE animals treated with ES L1. This treatment resulted in high-level production of IL-4 throughout
the disease. We assume that the ES L1-induced switch of
the immune response to Th2 type and downregulation of
the Th1/Th17 response was partly responsible for mitigation of the severity of EAE. The suppressive effect of ES
L1 antigens on pro-inflammatory cytokines could also be
explained through impact of the anti-inflammatory cytokine IL-10, abundantly produced in the CNS during the
course of EAE in ES L1-treated animals. The influence of
ES L1 on TGF-b production of was negligible, indicating
that immunomodulation provoked by ES L1 is not dependent of TGF-b. Prophylactic treatment with ES L1 antigens
creates a cytokine milieu that prevents the disease from
developing to the extent seen in untreated EAE rats. In a
model of EAE treatment with S. japonicum egg antigens
amelioration of the disease was accompanied by downmodulation of IFN-c production and the induction of IL-4
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Immunol Res (2015) 61:312–325
[30]. Moreover, intraperitoneal injection of soluble proteins isolated from Schistosoma mansoni eggs (SEA)
inhibited the development of type 1 diabetes (T1D) in
NOD mice by inducing Th2/regulatory type of response
[32]. On the other hand, ES-62 reduced the severity of
developing collagen-induced arthritis by suppression of
antigen-specific T helper (Th)1-type cytokine production
and collagen-specific immunoglobulin levels, with no
increase in Th2 responses [21]. It is clear that the impact of
helminth infections or their products on the development of
various inflammatory disorders differs, depending on the
helminth species, the nature of their products and on the
host organism.
ES L1 antigens may also act on autoreactive T cells
through local DCs, altering their maturation status.
Recently published results demonstrated that DCs are
rendered tolerant by exposure to T. spiralis ES L1 antigens,
suggesting that the observed suppression could be promoted by DCs/ES L1 [27]. Indeed, DC/ES L1 revealed
suppressive activity on the response of T cells from EAEimmunized animals stimulated with MOG peptide, which
was manifested in reduced cell proliferation and IFN-c and
IL-17 secretion. On the other hand, DC/ES L1 provoked
abundant production of IL-4 and increased secretion of
anti-inflammatory cytokines from T cells originating from
EAE-induced rats, which could indicate their capacity to
modify the function of existing autoreactive T cells. ES L1
antigens could also act by altering the maturation status of
already existing DCs in EAE-induced animals. We have
demonstrated that ES L1 possess the capacity to modulate
cytokine production of DCs previously pulsed with MOG
(DC/48hMOG24hESL1), by suppressing IL-12 and
enhancing IL-10 release. DCs treated this way had the
potential to modify the pattern of cytokine secretion of T
cells from EAE-induced animals, when compared to cocultures with DC/MOG. These results, although obtained
in vitro, are promising, since they could indicate the
potential of ES L1 antigens to change the course of an
autoimmune disease by modulating the activity of existing
immune cells, both innate and adaptive in nature.
ES L1 also facilitated induction/expansion of
CD4CD25Foxp3-positive T cells, which persisted in
increased proportions in both the CNS and spleen of treated
rats throughout the disease. The enhanced presence of these
cells in the spinal cord of DC/ES L1 recipients correlated
with significant reduction in EAE severity. It was already
emphasized that Treg cells are actively involved in
diminishing the severity and in resolution of the disease
[33]. Depletion of Treg cells prior to active immunization
increased the severity of EAE, accompanied by enhanced
IFN-c and IL-17 production, indicating the importance of
Tregs in restraining inflammatory responses and autoreactive effector cells [34, 35]. Key mediators of Treg
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Immunol Res (2015) 61:312–325
suppressive activity are IL-10 and TGF-b [36]; IL-10 being
recognized as a crucial component in Treg mediated suppression of EAE [37]. Evidence from investigations with
different parasite antigens revealed that they promote the
host regulatory network and stimulate activation of regulatory CD4?CD25?Foxp3? T cells responsible for suppression of autoreactive effector T cells [38–40]. What was
intriguing about our findings was the large proportion of
unconventional CD4? T cells in the spleen and spinal cords
of EAE-induced rats that received ES L1 treatment. These
cells were CD25 negative but they expressed the transcriptional factor Foxp3. Neither infection with T. spiralis
[19] nor treatment with ES L1-stimulated DCs [25, 27]
gave rise to the population of CD4?CD25-Foxp3?cells, so
we assumed that this phenomenon must be the consequence of application of isolated ES L1 antigens. When we
assessed the percentage of CD4?CD25?Foxp3? and
CD4?CD25-Foxp3? T cells in spleens of DA rats treated
with ES L1 antigens, we found increased numbers of both
subtypes, with dominance of CD4?CD25-Foxp3?T cells.
Why these cells are induced with purified antigens and not
by live infection or by DCs stimulated with the same
product remains to be investigated. What should be
emphasized at this point is that, albeit application of isolated ES L1 products exerted a beneficial effect on the
outcome of EAE, it did not provoke the same immune
response as live infection. Although attempts to replace
live infection with more appropriate treatments are
understandable and most welcome, it is possible that isolated products could not replace the evolutionarily created
relationship between the host and the parasite. However,
administered in a right amount, time and route, maybe they
could generate immunomodulation sufficient to overcome
this kind of disease, and this is why these products and their
effects are extensively investigated.
Based on present knowledge, suppressor activity is not
confined to CD25? T cells, and those within the
CD4?CD25- T cell population, CD8? cells and natural
killer (NK) T cells have also been shown to exert an
immunosuppressive function in vitro and in vivo [41–43].
CD4?CD25-Foxp3? T cells were found in both rodents
and humans, and it was shown that they possess suppressive activity [44, 45]. Fontenot and coworkers [44] even
concluded that Foxp3 expression, and not CD25 expression, is essential for Treg activity in a mice model. The
regulatory function of CD25- cells was demonstrated in a
study of the protective effect of various populations of
CD4? T cells on diabetes development [46]. Other authors
have confirmed the existence of CD4? regulatory T cells
that do not express CD25 and their regulatory function in
animal models of autoimmune encephalomyelitis [47, 48],
and inflammatory bowel disease [49]. In another model
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system of bacterial superantigen-induced tolerance,
CD4?CD25- T cells exerted their regulatory activity by
suppressing staphylococcal enterotoxin B responsiveness
[50]. The suppression was mediated by large amounts of
secreted IL-10. In our model, spinal-cord-infiltrating cells
from ES L1-injected animals produced significantly more
IL-10 than cells from untreated EAE animals, and the level
of this cytokine correlated with the relative number of
CD4?CD25-Foxp3? T cells within spinal cord infiltrates
of these animals. Whether IL-10 originated from
CD4?CD25-Foxp3? T cells or not remains to be elucidated. Immunoregulatory role of CD4?CD25-Foxp3? T
cells was demonstrated in mice infected with Bordetella
pertussis [51]. The authors found that this type of cell is
the dominant Treg population in the lung, gut and liver and
that they act through IL-10 to control the immune response
to infective agents and to mediate tolerance. It has been
proposed that CD4?CD25-Foxp3? T cells represent a
peripheral reservoir of CD4?CD25?Foxp3? Treg cells,
which could be recruited when needed, e.g., in autoimmune diseases [52]. Several groups have reported
increased proportions of CD4?CD25-Foxp3? T cells in
the blood of patients with systemic lupus erythematosus
[53, 54]. In a study of multiple sclerosis, patients in
remission were shown to have normal levels of
CD4?CD25?Foxp3? Treg cells, but relapsing patients had
an increased proportion of systemic CD4?CD25-Foxp3?
Treg cells, and these Treg cells were able to suppress
effector T cells in vitro [55].
In conclusion, we have shown that ES L1 antigens
possess the capacity to modulate the outcome of the
autoimmune disease, EAE, by prophylactic administration.
Modulation of EAE with these antigens was achieved by
triggering and maintaining a Th2 and anti-inflammatory
response and presumably by the induction of Tregs that do
not express CD25. Furthermore, it was shown that ES L1
antigens, in vitro, provoked bias in the response of T cells
isolated from EAE-induced rats from Th1/Th17 toward the
Th2/regulatory type. These antigens also possess the
capacity to modulate the function of MOG-stimulated DCs.
The results obtained from in vitro experiments gave us only
a hint of what effects ES L1 might have if they were
applied after EAE induction. This represents a great challenge and sets the task for the future to explore the full
immunomodulatory potential of ES L1 antigens in a model
of autoimmune disease.
Acknowledgments We wish to thank Prof Dr Marija MostaricaStojkovic (Institute of Microbiology and Immunology, School of
Medicine, University of Belgrade) for critical reading and valuable
suggestions during the preparation of this manuscript. This work was
supported by the Ministry of Education, Science and Technological
Development, Republic of Serbia (Project 173047).
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324
Conflict of interest Authors: Ivana Radovic, Alisa Gruden-Movsesijan, Natasa Ilic, Jelena Cvetkovic, Slavko Mojsilovic, Marija
Devic and Ljiljana Sofronic-Milosavljevic declare that they have no
conflict of interest.
Immunol Res (2015) 61:312–325
19.
Ethical standard All applicable international, national and/or
institutional guidelines for the care and use of animals were followed.
20.
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