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Avian Pathology
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Chicken infectious anaemia vaccinal strain persists in
the spleen and thymus of young chicks and induces
thymic lymphoid cell disorders
Asaad Vaziry
a c
, Amer Silim
a
, Christ ian Bleau
b
, Diane Frenet t e
a
& Lucie Lamont agne
b
a
Départ ement de Pat hologie & Microbiologie, Facult é de Médecine Vét érinaire,
Universit é de Mont réal, Saint -Hyacint he, Québec, Canada
b
Départ ement des Sciences Biologiques, Universit é du Québec à Mont réal, C. P. 8888,
Succ. Cent re-Ville, Mont réal, Québec, Canada, H3P 3P8
c
Animal Science Depart ment , Facult y of Agricult ure, Universit y of Kurdist an, Sanandaj ,
Iran
Available online: 04 Aug 2011
To cite this article: Asaad Vaziry, Amer Silim, Christ ian Bleau, Diane Frenet t e & Lucie Lamont agne (2011): Chicken
inf ect ious anaemia vaccinal st rain persist s in t he spleen and t hymus of young chicks and induces t hymic lymphoid cell
disorders, Avian Pat hology, 40: 4, 377-385
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Avian Pathology (August 2011) 40(4), 377385
Chicken infectious anaemia vaccinal strain persists in the
spleen and thymus of young chicks and induces thymic
lymphoid cell disorders
Asaad Vaziry1,3, Amer Silim1, Christian Bleau2, Diane Frenette1 and Lucie Lamontagne2*
1
Downloaded by [Asaad Vaziry] at 08:08 07 October 2011
Département de Pathologie & Microbiologie, Faculté de Médecine Vétérinaire, Université de Montréal, Saint-Hyacinthe,
Québec, Canada, 2Département des Sciences Biologiques, Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville,
Montréal, Québec, Canada, H3P 3P8, and 3Animal Science Department, Faculty of Agriculture, University of Kurdistan,
Sanandaj, Iran
The chicken infectious anaemia virus (CIAV) infection may induce immunosuppression and persistent
infection. The use of vaccination in young chicks is still controversial due to its low immune efficiency. In
order to verify the viral persistency of a vaccinal strain of CIAV and its associated-lymphoid
cell disorders,
†
54 1-day-old specific pathogen free chicks were vaccinated (CIAV-VAC ; Intervet, Millsboro, Delaware,
USA) and haematologic examination, expression of viral VP3 gene, humoral response and phenotyping of
lymphoid cells were studied in lymphoid organs at various times post vaccination (p.v.). No clinical signs
were observed but light heteropaenia was detected in CIAV-vaccinated chicks. The VP3 gene of CIAV was
detected by polymerase chain reaction in the thymus and spleen from day 7 until 28 days p.v. Thymic larger
CD4CD8 cells increased only at 7 days p.v. while smaller CD4CD8 cells decreased after 14 and 28
days in CIAV-vaccinated birds. The CD4 expression, in contrast to that seen for CD8, decreased in
thymocytes from the CIAV-vaccinated group. In the spleen and bursa, the percentage of CD8 cells
increased at 7 and 28 days p.v. only, while CD4 cells decreased simultaneously. The vaccinated chicks also
exhibited a higher number of splenic CD3 CD8 cells (natural killer cells). The anti-CIAV antibody
responses, however, remained low in most vaccinated chicks and did not persist up to 18 days p.v. These
results suggest that the vaccinal virus strain is clinically attenuated but persists in the thymus and spleen in
some birds, inducing a low humoral immune response and altering thymopoiesis.
Introduction
Chicken infectious anaemia virus (CIAV) was first
isolated by Yuasa et al. (1983). The virus is a Gyrovirus
belonging to the family Circoviridae with a circular
single-stranded DNA genome (Gelderblom et al., 1989).
The genome encodes for three viral proteins designated
as VP1, VP2 and VP3. These viral proteins are expressed
in the infected cells, whereas only VP1*which is the
capsid polyprotein*is present in the purified virus
particles (Todd et al., 1990). The disease is transmitted
vertically and horizontally (Chettle et al., 1989; Hoop,
1992). It is characterized by aplastic anaemia, heterophil
decrease, generalized lymphoid atrophy, skin lesions,
haemorrhages, immunosuppression, enhancement of the
pathogenicity of secondary infectious agents, suboptimal
antibody responses and mortality in chicks younger than
3 weeks old (Taniguchi et al., 1982; Goryo et al., 1985;
McNulty et al., 1988; Vielitz & Landgraf, 1988; Jeurissen
et al., 1992; Otaki et al., 1992). In younger chicks,
extensive lesions occurred in thymus and bone marrow
between 10 and 17 days post infection (p.i.) (Kuscu &
Gurel, 2008).
The clinical or subclinical features result from virus
replication and apoptosis of haemacytoblasts in bone
marrow and T-cell precursors in the thymus of infected
chicks leading to the anaemia, intramuscular haemorrhages and granulocytopaenia, the reduction in size of
the thymic cortex and the immunosuppression (Noteborn et al., 1994; Noteborn, 2004; Kuscu & Gurel,
2008). In the thymus, it has been shown that the virus
replication and cell destruction occur in immature
cortical lymphocytes (Jeurissen et al., 1989; McNeilly
et al., 1991).
It has been reported that CIAV infection either destroys
cells expressing CD4, CD8, and CT1 molecules on their
surface or interferes with the expression of these molecules
on thymic cells (Hu et al., 1993a, b). In addition to the
infection of precursor T cells in the thymus, Adair et al.
(1993) demonstrated that mature T lymphocytes in the
spleen are also affected by CIAV. In many experimental
studies, a greater destruction of CD8 cells than CD4
cells was observed (Cloud et al., 1992; Adair et al., 1993),
while in some other studies no selective decrease in
cytotoxic T lymphocytes (CTL) was detected by flow
cytometric analysis of CD4 and CD8 subpopulations
(Hu et al., 1993b). However, impairment of CTL activity
has also been reported (Cloud et al., 1992; Bounos et al.,
*To whom correspondence should be addressed. Tel: 514 987 3000, ext. 3184. Fax: 514 987 4647. E-mail: lamontagne.lucie@uqam.ca
Received 27 February 2011
ISSN 0307-9457 (print)/ISSN 1465-3338 (online)/11/040377-09 # 2011 Houghton Trust Ltd
DOI: 10.1080/03079457.2011.586330
Downloaded by [Asaad Vaziry] at 08:08 07 October 2011
378
A. Vaziry et al.
1995). VP3 gene presence in CIAV-infected cells is shown
to induce apoptosis in chicken lymphoblastoid T cells and
myeloid cells, which are susceptible to the infection, but
not in chicken embryo fibroblasts, which are not susceptible to CIAV (Noteborn et al., 1994).). The B cells are not
susceptible to the infection (Markowski-Grimsrud &
Schat, 2001). After infection with CIAV, antibodies are
produced in immunologically mature chickens that prevent lesion development. Therefore, the age-related resistance to CIAV is antibody mediated since older birds can
develop lesions or persistent viraemia when the antibody
system is compromised by embryonal bursectomy (Hu
et al., 1993a). In addition, it was proposed that CIAV can
persist as a latent virus in spite of occurrence of neutralizing antibodies (McNulty, 1991; Miller & Schat, 2004).
Considering the ubiquitous and contagious nature of
CIAV, some attenuated viral strains have been studied or
used as vaccine strains. It was demonstrated that
attenuated viral strains may induce lower T-cell depletion in the thymus and reduced severity of lesions in
1-day-old chicks than those induced by a pathogenic
viral strain (McKenna et al., 2003). However, the current
vaccines cannot be used for younger birds because of the
age-dependent susceptibility to CIAV (Miller & Schat,
2004). No information is available on viral persistency of
vaccinal strains in younger birds.
In the present study, the viral persistency of CIAVVAC† vaccine virus (Intervet, Millsboro, Delaware,
USA) and T-cell disorders were investigated in 1-dayold specific pathogen free (SPF) chicks.
Materials and Methods
Chicken and experimental design. Embryonated SPF eggs were obtained
from the Veterinary Laboratories Agency (Nepean, Ontario, Canada)
and incubated, hatched and reared in the Faculty of Veterinary
Medicine facilities (St-Hyacinthe, Québec, Canada). All procedures
were approved by the Université de Montréal animal care committee.
Thirty-six 1-day-old SPF chicks were divided in two groups and housed
separately in isolators for chickens under sterile condition in room
under negative pressure. Eighteen chicks of the vaccinated group
received intraperitoneally (i.p.) 5 ml CIA vaccine (CIAV-VAC† ) while
18 chicks in the control group were inoculated with phosphate-buffered
saline. At 7, 14 and 28 days post vaccination (p.v.), six chicks from each
group were weighed, blood-sampled by cardiac puncture and euthanized by CO2 chamber. Eighteen more chicks were vaccinated by i.p.
injection, as indicated above, kept under the same conditions and
euthanized at 18, 21 and 28 days p.v. for additional antibody assay and
virus genome detection by polymerase chain reaction (PCR).
Sampling and cell extraction. The blood samples were collected directly
into heparinized microhaematocrit tubes for packed cell volume
(PCV) determinations and also for white blood cell counts (WBC)
and differential analysis. The thymus, spleen, bone marrow and bursa
were collected under sterile conditions and subjected to the lymphocyte extraction procedure. Samples of sera and caecal tonsils were
also collected and kept frozen until tested. Isolation of lymphocytes
from the spleen, thymus and bursa was conducted by mincing each
tissue into fragments in RPMI 1640 media (GIBCO Laboratories,
Grand Island, New York, USA) supplemented with 20% foetal bovine
serum (FBS) and antibiotic-antimycotic solution (GIBCO Laboratories), and then pushing it through a 70 mm cell strainer (Falcon
Scientific Co., Montreal, Québec, Canada). Lymphocytes from the
spleen and thymus cell suspensions were further enriched by
centrifugation at 1000 g for 20 min on a Lymphoprep gradient
(Cedarlane, Hornby, Ontario, Canada). The recovered lymphocyte
layer from the spleen and thymus and the original cell suspension
from bursa samples were washed in fresh media by centrifugation at
500 g for 10 min. Bone marrow cells were collected from the femur
in RPMI 1640 with 5% FBS after cutting the two epiphyses and
pushing the media through the medular cavity using a 1-ml insulin
syringe. The suspensions were placed on an FBS cushion and
incubated on ice for 10 min to remove the debris. The top layer
from each bone marrow cell suspension was recovered in a fresh tube.
The cell suspensions of the thymus, spleen, bursa and bone marrow
suspensions have been enumerated in a haemacytometer with trypan
blue (Fischer Scientific, Montréal, Québec, Canada), adjusted at 106
viable cells per 1 ml and used for different assays.
Haematology. Peripheral leukocyte analyses such as PCV, WBC and
differential percentages of heterophils, monocytes, lymphocytes, eosinophils, and basophils were performed by MayGrunwald staining and
light microscopic examination.
Immunolabelling of lymphocyte subsets. The phenotype of lymphocyte
subpopulations such as CD4CD8 , CD4 CD8, CD4CD8,
CD3 CD8, CD3 IgM, CD3TCRgd cells was determined by
double-immunolabelling (CD4 and CD8, CD3 and CD8, CD3 and
IgM, or CD3 and TCRgd markers) using fluorescein isothiocyanate
(FITC)-conjugated anti-CD4, anti-IgM, anti-CD3 or anti-TCRgd, and
phycoerythrine (PE)-conjugated anti-CD8a or anti-CD3 monoclonal
antibodies (Southern Biotech, Anaheim, California, USA). For doublestaining, 1106 cells from thymic, splenic or bursal lymphocyte
suspensions were incubated with 1 mg anti-chicken monoclonal antibodies labelled with FITC or PE for 30 min at 48C. Cells were then
washed gently three times in RPMI 1640 and cells were fixed overnight
at 48C in phosphate-buffered saline, pH 7.2, containing 1% formaldehyde (Fischer Scientific). Cytofluorometric analysis of positive FITCstained and PE-stained cells was performed on a FACScan cytofluorometer (Becton Dickinson, Mountain View, California, USA) using
CellQuest software (Becton Dickinson, San Jose, California, USA).
Analysis was done on 10,000 events and discrete viable lymphoid cell
populations were gated according to forward scatter versus 908 angle
scatter parameters. Percentages of different lymphoid cell subpopulations in the thymus, spleen and bursa were determined by multiparametric analysis.
Viral VP3 DNA of CIAV detection by nested PCR. Total DNA was
extracted from the thymus, spleen and bursa, caecal tonsils, bone
marrow and liver using Trizol_LS Reagent (Life Technologies, Grand
Island, New York, USA) according to the manufacturer’s procedure.
Bursa tissues were homogenized by beads previous to Trizol extraction. To detect the viral genome in the samples, fragments of 374
base pairs (bp) situated between nucleotides 472 and 846, and of 203
bp situated between nucleotides 588 and 791, were targeted to be
amplified in conventional and nested PCR, respectively. A set of
primers were designed and used as follow: forward (5?-CTCTCCAAG
AAGATACTCCAC-3?), reverse (5?-GCTCGTCTTGCCATCTTA-3?),
forward nested (5?-ATCACTCTATCGCTGTGTGG-3?) and reverse
nested (5?-GGAGTAGTGGTAATCAAGC-3?). The PCR program
consisted of an initial denaturation at 948C for 5 min, and 35 cycles
of 948C for 35 sec, 588C for 55 sec, and 728C for 1 min followed by a
final extension at 728C for 5 min. PCR products were analysed by
electrophoresis on 1.4% agarose gel in TAE buffer (40 mM Tris and
2 mM ethylenediamine tetraacetic acid, pH 8.0) containing 0.5 mg/ml
ethidium bromide for 60 min at 100 V and visualized under an
ultraviolet light transilluminator.
Specific anti-CIAV antibodies. Specific anti-CIAV antibodies were
quantified in serum by enzyme-linked immunosorbent assay (ELISA)
using the IDEXX FlockChek* CIAV test Kit (IDEXX Laboratories,
Inc., Westbrook, Massachusetts, USA) according to the manufacturer’s procedure.
Statistical analysis. The percentages of blood cells and lymphocytes
subsets in lymphoid organs from CIAV-vaccinated young birds were
compared with those from sham birds using Student’s t test. Values of
P 50.05 were considered significant.
Persistence of CIAV vaccinal strain 379
Results
Persistency of CIAV vaccinal strain in lymphoid organs.
The presence of the viral VP3 gene of the CIAV vaccinal
strain was detected by PCR in the thymus, spleen, bursa,
and caecal tonsils. As shown in Table 1, viral VP3 gene
was expressed in the thymus of five (out of six)
vaccinated birds at day 7 p.v. There were no viral VP3positive cases in the thymus samples at 14, 18 and 21
days p.v., whereas the presence of viral genome in the
thymus was revealed at 28 days p.v. in two of the 12
tested vaccinated chicks. In the spleen, the vaccine virus
was detected in one chick at 7 days p.v. and persisted in
some vaccinated birds until 28 days p.v. All other
specimens collected from the bursa and caecal tonsils
remained negative for viral DNA. In addition, the bone
marrow, sera and liver were also negative in the nested
PCR (results not shown).
Analysis of thymic cell subpopulations. To verify whether
the viral persistency of the CIAV genome of the vaccinal
strain in the thymus induces disorders in lymphoid cell
(a)
Ctrl
Vac. CAV
PCV
35
30
25
20
%
15
10
5
0
WBC
(b)
Nb. cells (x103)/mm3
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Haematologic evaluation of CIAV-vaccinated SPF chicks.
Thirty-six 1-day-old CIAV-vaccinated SPF birds or controls were euthanized at 7, 14 and 28 days p.v. Birds in both
the CIAV-vaccinated and control groups did not show any
clinical signs or anaemia following vaccination. No
weight losses were observed in the vaccinated and control
groups. No thymic atrophy, as revealed by gross examination, was observed in vaccinated chicks at various times.
The PCV, WBC and percentages of lymphocytes in blood
of CIAV-vaccinated birds did not show any significant
variations up to 28 days p.v. when compared with chicks in
the control group (Figure 1a,b,d). However, the percentage of blood heterophils slightly decreased at 14 days p.v.
only in vaccinated chicks (P B0.05) (Figure 1c). Bone
marrow cell numbers were not altered in these chicks
(results not shown).
populations, the percentages of the different lymphoid
subsets in the thymus from CIAV-vaccinated chicks were
compared with those from control group birds at various
times p.v. The lymphoid cells were isolated from the
thymus and double-immunolabelled with fluorescent
antibodies against CD4, CD8, CD3, TCRgd and IgM,
and were analysed using cytofluorometry by comparing
the co-expression of markers among the gated cells.
As shown in Figure 2, percentages of thymic
CD4CD8 , CD4 CD8 or TCRgd cells were not
altered in vaccinated chicks and the values were similar to
those from control birds (Figure 2a,b,d). The percentages
of CD4CD8 thymic cells, however, slightly decreased
after 14 and 28 days in the CIAV-vaccinated group
(P B0.05)(Figure 2c). No significant modification in the
percentages of thymic CD3 CD8, corresponding to
natural killer (NK) cells, was detected in vaccinated
chicks (results not shown).
To verify whether the thymopoiesis was altered by
CIAV vaccination, thymocytes were analysed according
to forward scatter/908 angle scatter parameters. Thymocytes were separated into smaller (G1) and larger
(G2) cells, as shown in Figure 3. The G1/G2 ratio of
thymic cells did not significantly differ between CIAVvaccinated or control birds (results not shown). The
multiparametric analysis of cells within the G1 region
revealed the presence of CD4CD8 , CD4CD8
and CD4 CD8 cell subsets (Figure 3Ib,e), whereas
the cells located in the G2 area were mostly doublepositive (CD4CD8) (Figure 3Ic,f). Percentages of
small CD4CD8 cells (in the G1 area) decreased at
14 and 28 days p.v. in the thymus of CIAV-vaccinated
birds (P B0.05) (Figure 3IIa), whereas the large
CD4CD8 cells increased only at 7 days p.v.
(P B0.05) (Figure 3IIb). Percentages of small
CD4 CD8 cells increased at 14 and 28 days p.v. in
CIAV-vaccinated chicks (P B0.05) (Figure 3IIa). Large
CD4CD8 cells transiently decreased at 7 days p.v.
(P B0.05) (Figure 3IIb).
25
20
15
10
5
0
7
7
14
28
Time post vaccination (days)
Heterophils
(c)
14
28
Time post vaccination (days)
Lymphocytes
(d)
60
50
*
40
% 30
20
10
0
7
14
Time post vaccination (days)
28
70
60
50
40
%
30
20
10
0
7
14
Time post vaccination (days)
28
Figure 1. Haematological examination of blood from CIAV-vaccinated SPF chicks at hatch. (1a) Haematocrit (PCV), (1b) WBC,
(1c) percentages of heterophils and (1d) lymphocytes in the blood of CIAV-vaccinated birds (j) and control birds (I) were determined
at 7, 14 and 28 days p.v. The mean of each value for vaccinated and control birds (n 6) was calculated and compared. *P50.05.
380
A. Vaziry et al.
Table 1. Detection of CIAV vaccinal virus genome in the thymus, spleen, bursa of Fabricius and caecal tonsils in CIAV-vaccinated and
control groups of chicks at 7 to 28 days p.v.
7 days
Organ
Thymus
Spleen
Bursa
Caecal tonsils
Time p.v.
18 days
14 days
21 days
28 days
Control CIAV vaccine Control CIAV vaccine Control CIAV vaccine Control CIAV vaccine Control CIAV vaccine
0/6b
0/6
0/6
0/6
5/6
1/6
0/6
0/6
0/6
0/6
0/6
0/6
0/6
1/6
0/6
0/6
0/6
0/6
0/6
0/6
0/6
2/6
0/6
0/6
0/6
0/6
0/6
0/6
0/6
3/6
0/6
0/6
0/6
0/6
0/6
0/6
2/12
3/12
0/12
0/12
†
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Groups of six chicks were inoculated by CIAV-VAC or phosphate-buffered saline at hatch, euthanized at various times p.v. and
organs were sampled. VP3 gene expression was detected by PCR. Data presented as number positive/number tested.
The intensity of CD4 or CD8 expression in thymocytes
may reflect their maturation level. Cytofluorometric
analysis of CD4 and CD8 expression on thymocytes is
presented in Figure 4. It revealed that the CD4 expression
on thymocytes increased at 7 days p.v. (P B0.001) while it
decreased at 28 days p.v. (P B 0.05) (Figure 4a,c). The
CD8 expression on the thymocyte surface, however,
strongly increased in the CIAV-vaccinated group at 7
days p.v. (P B0.01) and remained variable until 28 days
p.v. in the group of CIAV-vaccinated chicks (Figure 4b,d).
at 28 days p.v., the number of NK cells increased less in
CIAV-vaccinated birds than that of the control group
(PB0.05) (Figure 5e) in spite of the fact that NK cells
increased in older control birds.
In the bursa of Fabricius, percentages of CD4 CD8
cells increased at 7 and 28 days p.v. (P B0.05) (Figure 6a)
whereas percentages of CD4CD8 cells simultaneously
decreased (P B0.05) (Figure 6b). The number of doublepositive (CD4CD8) bursal cells were slightly lowered
in the CIAV-vaccinated group only at 28 days p.v.
(PB0.05) (Figure 6c). Percentages of IgM bursal
lymphocytes were relatively steady until day 28, when
the percentage of these cells was lower in CIAVvaccinated chicks (P B0.05) (Figure 6d).
Analysis of splenic and bursal lymphocyte subpopulations.
In the spleen, the percentage of CD4 CD8 cells
increased at 28 days p.v. only (P B0.05) (Figure 5a)
while CD4CD8 cells decreased simultaneously
(P B0.05) (Figure 5b) in CIAV-vaccinated chicks. The
subpopulation of CD4CD8 spleen cells exhibited a
paramount elevation only 7 days after vaccination
(P B0.05) (Figure 5c). The splenic IgM B cells as
well as TCRgd cells were not significantly altered
following CIAV vaccination (Figure 5d,f). The vaccinated chicks, however, exhibited a higher number of
CD3 CD8 cells (corresponding to NK cells) in the
spleen at 7 days p.v. (P B0.05) (Figure 5e). Nevertheless,
Thymic CD4+CD8-
(a)
Humoral immune response. The efficiency of the vaccine
virus to induce anti-CIAV antibodies in 1-day-old SPF
chicks was monitored using ELISA. As shown in
Figure 7, vaccination with CIAV-VAC† did not
produce a notable humoral response in the majority
of the vaccinated chicks when administered at hatch.
Among the 30 vaccinated birds sampled at five
different times p.i., the anti-CIAV titres were detected
in one chick, three chicks and one chick at 7, 14 and
(b)
25
20
20
%
Control
CIAV-vaccinated
15
15
%
10
10
5
5
0
Thymic CD4-CD8+
25
7
14
0
28
7
Time post vaccination (days)
Thymic CD4+CD8+
(c)
100
80
%
*
60
40
20
0
7
14
28
Time post vaccination (days)
Thymic TCRγδ cells
(d)
*
35
30
25
20
%
15
10
5
0
14
28
Time post vaccination (days)
7
14
28
Time post vaccination (days)
Figure 2. Percentages of lymphocyte subpopulations in thymus of SPF chicks at 7, 14 and 28 days following CIAV vaccination at hatch.
Thymocytes from CIAV-vaccinated (j) and control birds (I) were double-labelled with anti-CD4, anti-CD8, anti-TCRgd conjugated to
FITC or PE and analysed by cytofluorometry. The mean percentage of thymic (2a) CD4CD8 , (2b) CD4 CD8, (2c) CD4CD8
and (2d) TCRg^ subpopulations for CIAV-vaccinated and control groups (n6) were calculated and compared. *P50.05.
Persistence of CIAV vaccinal strain 381
A
I
C
B
10.76
1.96
67.5
90.19
Control
4.33
6.47
F
E
D
8.69
0.55
70.30
95.99
CIAVVaccinated
2.42
8.42
Small thymic cells
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(a)
100
80
%
Large thymic cells
(b)
CD4-CD8+
CD4+CD8+
100
CD4+CD8-
*
*
80
60
60
40
40
%
*
20
*
0
Control
CIAVvaccinated
7 days
*
Control
CIAVvaccinated
14 days
Control
CIAVvaccinated
28 days
20
*
0
–20
Control
CIAVvaccinated
7 days
Control
CIAVvaccinated
14 days
Control
CIAVvaccinated
28 days
Figure 3. Analysis of small and large lymphocyte subpopulations in thymus of SPF chicks at 7, 14 and 28 days following CIAV
vaccination at hatch. Thymocytes from CIAV-vaccinated (j) and control birds (I) were double-labelled with anti-CD4, anti-CD8, antiTCRgd conjugated to FITC or PE and analysed by cytofluorometry. (3I) Thymocytes were separated into small (G1 area) and large (G2
area) cells according to forward scatter/908 angle scatter parameters: (3Ia) control and (3Id) CIAV-vaccinated groups of birds;
multiparametric analysis of CD4/CD8 (3Ib, 3Ie) small and (3Ic, 3If) larger thymocytes. (3II) Percentages of (3IIa) small and (3IIb)
large cell subpopulations in the thymus from control and CIAV-vaccinated groups at various days p.v. *P 50.05.
18 days p.i., respectively. The anti-CIAV antibodies did
not persist up to 18 days p.v. in seropositive chicks.
Discussion
In the present work, we report that a commercial CIAV
vaccinal strain induces a subclinical infection in 1-dayold chicks associated with viral persistence in the spleen
and thymus, transient humoral response and alterations
in thymopoiesis.
Clinical signs of CIAV infection in very young chicken
are characterized by anorexia, depression, pallor, and
decrease of weight gain, haematocrit and WBC, especially blood lymphocytes and heterophils. Pale bone
marrow and atrophy of the thymus, spleen and bursal
reflect depletion of T cells and B cells, predisposing the
birds to secondary infections (reviewed in Todd, 2004).
CIAV infection in 1-day-old SPF chicks rendered them
anaemic with depleted bone marrow and thymus at 14
days p.i. (Yuasa & Imai, 1986).
The attenuated CIAV strains are commercially used as
vaccines but some technical and practical problems affect
the widespread use of these vaccines (reviewed in Schat,
2009). In the present work, we addressed whether a
commercial vaccinal strain may retain the ability to
induce disorders in percentages of thymus and spleen
cells and on thymopoiesis as the pathogenic CIAV strain.
We have shown that a commercial attenuated vaccine
(CIAV-VAC† ) did not induce clinical signs in 1-day-old
chicks, did not significantly decrease total WBC in spite of
low significant decrease of heterophil percentage at 14
days only, and induced no significant cell depletion in the
thymus, spleen, bursa and bone marrow. The transient
decrease in the percentage of heterophils may reflect
either cell recruitment in infected organs or a low decrease
in myelopoiesis. However, the absence of anaemia and no
bone marrow cell depletion do not support the second
hypothesis. These observations are in agreement with
those reported by McKenna et al. (2003), who have shown
that some attenuated CIAV strains may induce subclinical
infection with no anaemia and no or low mild lesions.
Replication of the vaccinal viral strain tested in our
work was detected in the thymus in most of vaccinated
chicks, at 7 days p.v. only, indicating that viral
replication was rapidly aborted in the thymus, reflecting
the attenuation of this viral strain. Kaffashi et al.
(2006) have demonstrated that pathogenic CIAV can
replicate in many organs, both in 1-day-old and 6-weekold infected chicks, up to day 18 p.i., and reach a peak
in the thymus, spleen and liver at 18 or 20 days p.i. At
28 days p.v., however, the VP3 gene was still observed
382
A. Vaziry et al.
(a)
(b)
Control
Vac CAV
81.06
115.21
Control
183.15
Vac CAV
436.19
Thymic CD4+ cells
180
160
140
120
100
80
60
40
20
0
**
*
600
500
**
400
300
200
100
0
7
Downloaded by [Asaad Vaziry] at 08:08 07 October 2011
Thymic CD8+ cells
(d)
Relative expression
of CD8
Relative expression of
CD4
(c)
7
14
28
Time post vaccination (days)
14
28
Tim e post vaccination (days)
Figure 4. Analysis of relative expression of CD4 and CD8 molecules on thymocytes from CIAV-vaccinated and control groups at various
times p.v. Lines illustrate the intensity of (4a) CD4 or (4b) CD8 molecules on thymocytes of one control bird and one CIAV-vaccinated
bird. Thymocytes from CIAV-vaccinated (j) and control birds (I) were double-labelled with anti-CD4 and anti-CD8, conjugated to
FITC and PE, and analysed by cytofluorometry. The relative expression levels of (4c) CD4 and (4d) CD8 were compared on thymocytes
from each group (n6) of birds at 7, 14 and 28 days p.v. *P50.05,**P50.01.
in the thymus of some birds, indicating viral persistence. Hu et al. (1993a) showed that persistent viraemia
occurs in CIAV-infected birds in the absence of anti-
(a) 40
30
Splenic CD4-CD8+
Control
CIAV-vaccinated
*
body production. The viral persistence of pathogenic
CIAV was confirmed by Imai et al. (1999), who
suggested that CIAV can induce persistent infection in
Splenic CD4+CD8-
(b) 40
30
% 20
% 20
10
10
0
7
14
Time post vaccination (days)
0
28
7
Splenic CD4+CD8+
(c) 60
7
14
50
40
% 30
20
10
0
28
7
Time post vaccination (days)
*
14
28
Time post vaccination (days)
Splenic TCRγδ cells
25
20
15
*
15
%
% 10
10
5
0
(f)
Splenic CD3-CD8+cells
(e) 20
14
28
Time post vaccination (days)
Splenic IgM+ cells
(d) 60
*
50
40
% 30
20
10
0
*
5
0
7
14
28
Time post vaccination (days)
7
14
28
Time post vaccination (days)
Figure 5. Percentages of lymphocyte subpopulations in the spleen of SPF chicks at 7, 14 and 28 days following CIAV vaccination at
hatch. Splenic cells from CIAV-vaccinated (j) and control birds (I) were double-labelled with anti-CD4, anti-CD8, anti-TCRgd, antiIgM, and anti-CD3 conjugated to FITC or PE and analysed by cytofluorometry. The mean percentage of splenic (5a) CD4 CD8, (5b)
CD4CD8 , (5c) CD4CD8, (5d) IgM, (5e) CD3 CD8, and (5f) TCRg^ subpopulations for CIAV-vaccinated and control
groups (n6) were calculated and compared. *P50.05.
Persistence of CIAV vaccinal strain 383
(a)
Bursal CD4-CD8+
Control
CIAV-vaccinated
**
8
%
(b)
10
6
40
%
20
2
10
**
0
0
7
14
Time post vaccination (days)
7
28
Bursal CD4+CD8+
(c)
(d)
14
Time post vaccination (days)
28
Bursal IgM+ cells
100
80
%
*
60
40
*
20
7
0
14
28
Time post vaccination (days)
7
14
28
Time post vaccination (days)
Figure 6. Percentages of lymphocyte subpopulations in the bursa of Fabricius of SPF chicks at 7, 14 and 28 days following CIAV
vaccination at hatch. Lymphoid cells from CIAV-vaccinated (j) and control birds (I) were double-labelled with anti-CD4, anti-CD8,
anti-IgM conjugated to FITC or PE and analysed by cytofluorometry. The mean percentage of bursal (6a) CD4 CD8, (6b)
CD4CD8 , (6c) CD4CD8 and (6d) IgM subpopulations for CIAV-vaccinated and control groups (n 6) were calculated and
compared. *P50.05, **P 50.01.
infected birds. The detection of the VP3 gene in total
DNA cannot permit one to clearly distinguish between
viral replication or integrated viral DNA in cellular
genome. However, porcine circoviruses can persist in
infected cells but they are not endogenous as retroviruses (Victoria et al., 2010).
The replication of vaccinal strain in the thymus and its
persistence in some birds suggest the occurrence of
thymopoiesis disorders, as previously reported in the
thymus of pathogenic CIAV-infected birds (Jeurissen
et al., 1989; Kuscu & Gurel, 2008). The cytofluorometric
analysis of thymocyte subsets from CIAV-vaccinated
birds revealed that larger CD4CD8 thymic cells
transiently increased but that was followed by a relative
decrease of CD4CD8 cells in spite of no significant
decrease in total thymic cells. This observation suggests
that replication of vaccinal strain slightly alters the
thymocyte maturation process or that mature antiviral
CD4CD8 and CD4 CD8 cells are recruited into the
thymus from the blood and spleen. The absence of
significant changes in percentages of CD4CD8 or
TCRgd cells and the slight increase of CD4 CD8 cells
do not support the second hypothesis. On the other
hand, the discrimination between dividing cells and
resting cells by the forward scatter/908 angle scatter
ELISA units (OD 650 nm)
Downloaded by [Asaad Vaziry] at 08:08 07 October 2011
*
30
*
4
14
12
10
8
%
6
4
2
0
Bursal CD4+CD8-
50
2500
2000
1500
1000
500
0
0
5
10
15
20
Time post vaccination (days)
25
30
Figure 7. Anti-CIAV antibody titres after vaccination of 1-day†
old SPF chicks by CIAV-VAC . Serum samples from the CIAVvaccinated and control groups were tested for anti-CIAV
antibodies at 7, 14, 18, 21 and 28 days p.v. by ELISA test. Each
point represents the ELISA titre of one chick tested. The line
corresponds to the negative threshold.
parameters revealed that smaller thymic CD4CD8
cells were depleted in vaccinated chicks, suggesting that
viral infection can block cell mitosis. Infection of the Tcell precursor in the thymus and inhibition of anaphasepromoting complex/cyclosome by the viral apoptin,
which leads to G2/M arrest and apoptosis, has already
been reported in pathogenic CIAV infection (Teodoro
et al., 2004).
The analysis of the expression intensity of CD4 and
CD8 markers revealed that CD4 expression, but not
CD8 expression, was diminished in thymocytes*suggesting that a vaccinal strain of CIAV may specifically
interfere with CD4 expression, leading to a decrease in
percentage of small CD4CD8 cells. The specific
decrease of CD4 expression on thymocytes by CIAV
viral infection has never been reported. However, the Thelper subset is known to be a target cell in the spleen for
CIAV (Adair et al., 1993). Hu et al. (1993b) demonstrated that percentages of both CD4 and CD8
thymic cells similarly decreased in the thymus of 1-dayold chicks infected with the pathogenic CIAV (CIA-1
strain) due to cell destruction by viral infection or
interference with CD4 and CD8 expression. The
CD4CD8 cell subset, however, represents the most
important population in the thymus, and a decrease of
CD4 cells would involve also a decrease in CD8 cells.
The decrease of CD4 expression only in thymic cells
induced by the attenuated vaccinal CIAV strain rather
revealed a discrimination between the thymocyte subsets
expressing CD4 and/or CD8. It is well known that
the thymic CD4 CD8 cell subset occurs earlier than
the CD4CD8 or CD4CD8 cell subsets during the
avian thymopoiesis (Davidson & Boyd, 1992). As a
result, the lower expression of CD4 in presence of
higher expression of CD8 may reflect the accumulation
of CD4 CD8 cells rather than a differential decrease in
CD4-expressing thymocytes. The decreases in
CD4CD8 cells observed at 14 and 28 days p.v.
indicate that thymocyte precursors can support the
replication of the CIAV vaccinal strain, as confirmed
by VP3 gene presence in the thymus of some birds at 28
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384
A. Vaziry et al.
days p.v., such as seen with pathogenic CIAV (reviewed
in Schat, 2009).
Contrary to that seen in the thymus, the VP3 gene was
gradually expressed in the spleen of vaccinated 1-day-old
chicks with time. The percentage of splenic CD4 CD8
cells increased while CD4CD8 cells decreased at 28
days p.v. only, such as seen in the thymus, suggesting the
occurrence of a delayed CTL immune response. However, the CTL responses may not lead to viral elimination. Markowski-Grimsrud & Schat (2003) have
demonstrated that CIAV-infected chicks without antiCIAV maternal antibodies have lost the ability to mount
a CTL response at 7 days p.i. against secondary viral
infections, suggesting that CIAV can impair the CTL
functions. Adair et al. (1991) have shown that interferong production decreased after up to 43 days p.i. in CIAV
infection, indicating suppression of CTL responses. We
have not observed any increase in the interferon-g
production in CIAV-vaccinated chicks (results not
shown), suggesting that CD8-dependent cytotoxic
function is not strongly stimulated by viral vaccination.
In addition, no significant stimulation of lymphocytes to
Concanavalin A (ConA) has been detected in thymic or
splenic cells from CIAV-vaccinated chicks (results not
shown), supporting the hypothesis that vaccination did
not strongly stimulate lymphocyte activities. Depressed
responsiveness of lymphocytes to mitogens following
CIAV infection has been well documented (Otaki et al.,
1988; Adair et al., 1991; McConnell et al., 1993;
Bounous et al., 1995).
Transient increase of CD3 CD8 (NK cells) suggests
the occurrence of an innate antiviral immune response. It
was previously demonstrated that pathogenic CIAV did
not alter the NK cell activity (Markowsi-Grimsrud &
Schat, 2001).
Finally, the percentage increases of CD4 CD8 cells
in the bursa of Fabricius correlated with concurrent
decreases of CD4CD8 cells, suggesting that these
modifications reflect the thymus disorders rather than a
specific viral replication. No VP3 gene was detected in
the bursa or caecal tonsils. However, the late decrease of
immune
IgM cells and low and transient humoral
†
responses following the CIAV-VAC administration
suggest disorders in B-cell-dependent immunity. It is
well known that the infection with pathogenic CIAV
strain triggers antibody production in immunologically
mature chickens, which mediates the age-related resistance to the virus. It was previously reported that
pathogenic CIAV was recovered from blood cells or
lymphoid organs of infected birds at different days p.i.
even in the presence of low or high viral-neutralizing
antibodies (Yuasa et al., 1983; Imai et al., 1999). We can
hypothesize that the incompetent immune system of the
very young chicks favours a decrease of the CD4 cells
in the thymus and spleen, a decrease in the percentage of
IgM B cells, low antibody response and persistence of
vaccinal strain in the thymus and spleen.
The virus persistence and the lymphoid disorders
induced by the CIAV vaccine virus in very young birds
lead to practical consequences and may potentially play
an important role in the subclinical infections and
decreased responsiveness to other avian pathogens in
the poultry industry.
Work is in progress to determine the effects of
infection with vaccinal CIAV strain on the efficiency of
bursal viral disease vaccination in young chicks.
References
Adair, B.M., McNeilly, F., McConnell, C.D. & McNulty, M.S. (1993).
Characterization of surface markers present on cells infected by
chicken anemia virus in experimentally infected chickens. Avian
Diseases, 37, 943950.
Adair, B.M., McNeilly, F., McConnell, C.D.G., Todd, D., Nelson, R.T.
& McNulty, M.S. (1991). Effects of chicken anemia agent on
lymphokine production and lymphocyte transformation in experimentally infected chickens. Avian Diseases, 35, 783792.
Bounous, D.I., Goodwin, M.A., Brooks, R.L., Lamichhane, C.M.,
Campagnoli, R.P., Brown, J. & Snyder, D.B. (1995). Immunosuppression and intracellular calcium signaling in splenocytes from chicks
infected with chicken anemia virus, CL-1 isolate. Avian Diseases, 39,
135140.
Chettle, N.J., Eddy, R.K., Wyeth, P.J. & Lister, S.A. (1989). An outbreak
of disease due to chicken anaemia agent in broiler chickens in
England. The Veterinary Record, 124, 211215.
Cloud, S.S., Lillehoj, H.S. & Rosenberger, J.K. (1992). Immune
dysfunction following infection with chicken anemia agent and
infectious bursal disease virus. I. Kinetic alterations of avian
lymphocyte
subpopulations.
Veterinary
Immunology
&
Immunopathology, 34, 337352.
Davidson, N.J. & Boyd, R.L. (1992). Delineation of chicken thymocytes
by CD3TCR complex, CD4 and CD8 antigen expression reveals
phylogenically conserved and novel thymocyte subsets. International
Immunology, 4, 11751182.
Gelderblom, H., Kling, S., Lurz, R., Tiseher, I. & Von Bulow, V. (1989).
Morphological characterization of chicken anaemia agent (CAA).
Archives of Virology, 109, 115120.
Goryo, M., Sugimura, H., Matsumoto, S., Umemura, T. & Itakura, C.
(1985). Isolation of an agent inducing chicken anaemia. Avian
Pathology, 14, 483496.
Hoop, R.K. (1992). Persistence and vertical transmission of chicken
anaemia agent in experimentally infected laying hens. Avian
Pathology, 21, 493501.
Hu, L.B., Lucio, B. & Schat, K.A. (1993a). Abrogation of age-related
resistance to chicken infectious anemia by embryonal bursectomy.
Avian Diseases, 37, 157169.
Hu, L.B., Lucio, B. & Schat, K.A. (1993b). Depletion of CD4 and
CD8 T lymphocyte subpopulations by CIA-1, a chicken infectious
anemia virus. Avian Diseases, 37, 492500.
Imai, K., Mase, M., Tsukamoto, K., Hihara, H. & Yuasa, N. (1999).
Persistent infection with chicken anaemia virus and some effects of
highly virulent infectious bursal disease virus infection on its
persistency. Research in Veterinary Science, 67, 233238.
Jeurissen, S.H., Janse, M.E., Van Roozelaar, D.J., Koch, G. & De Boer,
G.F. (1992). Susceptibility of thymocytes for infection by chicken
anemia virus is related to pre- and posthatching development.
Developmental Immunology, 2, 123129.
Jeurissen, S.H., Pol, J.M. & De Boer, G.F. (1989). Transient depletion of
cortical thymocytes induced by chicken anaemia agent. Thymus, 14,
115123.
Kaffashi, A., Noormohammadi, A.J., Allott, M.L. & Browning, G.F.
(2006). Virus load in 1-day-old and 6-week-old chickens infected with
chicken anaemia virus by the intraocular route. Avian Pathology, 35,
471474.
Kuscu, B. & Gurel, A. (2008). Lesions in the thymus and bone marrow
in chicks with experimentally induced chicken infectious anemia
disease. Journal of Veterinary Science, 9, 1523.
Markowski-Grimsrud, C.J. & Schat, K.A. (2001). Impairment of cellmediated immune responses during chicken infectious anemia virus
infection. In Proceedings of the 2nd International Symposium on
Infectious Bursal Disease and Chicken Infectious Anaemia (pp. 395
402). Rauischholzhausen, Germany.
Markowski-Grimsrud, C.J. & Schat, K.A. (2003). Infection with
chicken anemia virus impairs the generation of antigen-specific
cytotoxic T lymphocytes. Immunology, 109, 283294.
McConnell, C.D., Adair, B.M. & McNulty, M.S. (1993). Effects of
chicken anemia virus on cell-mediated immune function in
chickens exposed to the virus by a natural route. Avian Diseases,
37, 366374.
Downloaded by [Asaad Vaziry] at 08:08 07 October 2011
Persistence of CIAV vaccinal strain 385
McKenna, G.F., Todd, D., Borghmans, B.J., Welsh, M.D. & Adair, B.M.
(2003). Immunopathologic investigations with an attenuated chicken
anemia virus in day-old chickens. Avian Diseases, 47, 13391345.
McNeilly, F., Allan, G.M., Moffat, D.A. & McNulty, M.S. (1991).
Detection of chicken anaemia agent in chickens by immunofluorescence and immunoperoxidase staining. Avian Pathology, 20, 125132.
McNulty, M.S. (1991). Chicken anemia agent: a review. Avian
Pathology, 20, 187203.
McNulty, M.S., Connor, T.J., Mcneilly, F., Kirkpatrick, K.S. &
Mcferran, J.B. (1988). A serological survey of domestic poultry in
the United Kingdom for antibody to chicken anaemia agent. Avian
Pathology, 17, 315324.
Miller, M.M. & Schat, K.A. (2004). Chicken infectious anemia virus: an
example of the ultimate host-parasite relationship. Avian Diseases, 48,
734745.
Noteborn, M.H. (2004). Chicken anemia virus induced apoptosis:
underlying molecular mechanisms. Veterinary Microbiology, 98, 8994.
Noteborn, M.H., Todd, D., Verschueren, C.A., de Gauw, H.W., Curran,
W.L., Veldkamp, S., et al. (1994). A single chicken anemia virus
protein induces apoptosis. Journal of Virology, 68, 346351.
Otaki, Y., Nunoya, T., Tajima, M., Kato, A. & Nomura, Y. (1988).
Depression of vaccinal immunity to Marek’s disease by infection with
chicken anaemia agent. Avian Pathology, 17, 333347.
Otaki, Y., Saito, K., Tajima, M. & Nomura, Y. (1992). Persistence of
maternal antibody to chicken anaemia agent and its effect on the
susceptibility of young chickens. Avian Pathology, 21, 147151.
Schat, K.A. (2009). Chicken anemia virus. Current Topics of Microbiology and Immunology, 331, 151183.
Taniguchi, T, Yuasa, N., Maeda, M. & Horiuchi, T. (1982). Hematopathological changes in dead and moribund chicks induced by
chicken anemia agent. National Institute of Animal Health Quarterly
(Tokyo), 22, 6169.
Teodoro, J.G., Heilman, D.W., Parker, A.E. & Green, M.R. (2004). The
viral protein apoptin associates with the anaphase-promoting complex to induce G2/M arrest and apoptosis in the absence of p53.
Genes Development, 18, 19521957.
Todd, D. (2004). Avian circovirus diseases: lessons for the study of
PMWS. Veterinary Microbiology, 98, 169174.
Todd, D., Creelan, J.L., Mackie, D.P., Rixon, F. & McNulty, M.S.
(1990). Purification and biochemical characterisation of chicken
anaemia agent. Journal of General Virology, 71, 819823.
Victoria, J.G., Wang, C., Jones, A.S., Jaing, C., McLoughlin, K.,
Gardner, S. & Delwart, E.L. (2010). Viral nucleic acids in liveattenuated vaccines: detection of minority variants and an adventitious virus. Journal of Virology, 84, 60336040.
Vielitz, E. & Landgraf, H. (1988). Anaemia-dermatitis of broilers: field
observations on its occurence, transmission and prevention. Avian
Pathology, 17, 113120.
Yuasa, N. & Imai, K. (1986). Pathogenicity and antigenicity of eleven
isolates of chicken anaemia agent (CAA). Avian Pathology, 15, 639
645.
Yuasa, N., Taniguchi, T., Imada, T. & Hihara, H. (1983). Distribution
of chicken anemia agent (CAV) and detection of neutralizing
antibody in chicks experimentally inoculated with CAA. National
Institute of Animal Health Quarterly (Tokyo), 23, 7881.