Sequential immunopathological studies on infectious bursal disease vaccines in broiler chickens
Abstract
The present study was conducted to delineate the sequential immunopathological changes in broiler chickens
vaccinated with intermediate plus IBD vaccines P and Q, which are currently used in Haryana. A total of 108 day old
chickens were divided into different groups viz. Group A chickens received no vaccine and served as control, chickens
vaccinated with vaccine P and Q at 17 days of age were designated as group B1 and group C1, respectively while chickens
which were given primary dose of vaccine at 17 days of age with vaccines P and Q, then subsequently on 24 days of age
received booster dose of these vaccine were designated as group B2 and C2, respectively. No pathological lesions were
observed in group A at different time interval i.e. 7, 14, 21 and 28 days post vaccination (DPV). Bursa of Fabricius (BF)
showed congestion and oedema, vascular changes such as congestion and haemorrhages in other organs at 7 DPV. The
severity of lesions was more evident at 14 and 21 DPV. However, lesions started to resolve at 28 DPV. Microscopically,
BF from vaccinated groups revealed congestion, haemorrhages and depletion of lymphocytes. However, mild to
moderate vascular changes were observed in thymus, caecal tonsils, liver, kidneys, lungs, proventriculus, intestine and
heart. Overall average GLS and HLS was significantly (p≤0.05) higher in booster vaccinated group B2 (vaccine P) and
group C2 (vaccine Q) as compared to single vaccinated group B1 (vaccine P) and group C1 (vaccine Q). Vaccine Q
produced more severe histopathological lesions both in booster as well as in single vaccine groups as compared to
vaccine P. Group D, comprised of IBD suspected field cases from 14 different poultry flocks of Haryana with most of
flocks reported to be vaccinated with B2K, Georgia and intermediate plus hot strain vaccines at different ages (12-15 days
of age). Grossly, petechial and ecchymotic haemorrhages were observed in pectoral, thigh and leg muscles. BF revealed
oedema, fibrinous exudate and severe haemorrhages. However, other organs revealed congestion and haemorrhages.
Microscopically, BF showed severe congestion, haemorrhages, marked depletion and necrosis of lymphocytes, fibrous
connective tissue proliferation in inter-follicular areas along with heterophilic infiltration. Thymus, spleen and caecal
tonsils revealed severe congestion, marked haemorrhages, mild depletion and necrosis of lymphocytes, while vascular
changes in other organs. To ascertain the role of T cells with pathological lesion observed in BF of chickens vaccinated
with P and Q vaccines as well as in IBD affected filed cases, expression of CD8+ and CD4+ T cells were studied by
immunohistochemistry. Vaccine Q produced more immunohistochemical expression for CD8+ and CD4+ T cells both in
single as well as in booster vaccinated group as compared to the respective groups of vaccine P. In IBD affected field
cases, immunopositive CD8+T cells were diffusely present in cortico-medullary portion throughout the bursal follicles.
Widely scattered CD4+T cells were present in follicles beneath bursal epithelium, inter-follicular and cortico-medullary
region of BF. But the numbers of immunopositive cells were less in comparison to CD8+ T cells. The relative mRNA
expression of cytokine genes i.e. IFN-γ, IL-1β and IL-6 in vaccinated chickens by real time PCR when compared with β-
actin gene at different time intervals showed an up-regulation at 14 and 21 DPV in all vaccinated groups as compared to
control group. From the present study, it can be concluded that both types of intermediate plus vaccine produced
immunosuppression as evidenced by the different degree of lesions in BF. In single as well as booster vaccination, the
vaccine Q produced more lesions in BF as compared to vaccine P. Lesions were also evidenced by upregulated
expression of cytokine genes such as IFN-γ, IL-1β and IL-6 and significant increase in CD8+ T cells in the BF. These
responses were more pronounced with vaccine Q in single as well as booster vaccination as compared to the respective
groups of vaccine P. From the present study, it can be concluded that both types of intermediate plus vaccine produced
immunosuppression as evidenced by the different degree of lesions in BF. In single as well as booster vaccination, the
vaccine Q produced more lesions in BF as compared to vaccine P. Lesions were also evidenced by upregulated
expression of cytokine genes such as IFN-γ, IL-1β and IL-6 and significant increase in CD8+ T cells in the BF. These
responses were more pronounced with vaccine Q in single as well as booster vaccination as compared to the respective
group of vaccine P.
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