Abstract
Infectious bursal disease (IBD) is an important immunosuppressive disease of chickens. The causative agent, infectious bursal disease virus (IBDV), consists of two serotypes, 1 and 2. Serotype 1 consists of classic IBDV (cIBDV) and variant IBDV (vIBDV). Both of these strains vary in antigenicity and pathogenesis. The goal of this study was to compare the immunopathogenesis of cIBDV and vIBDV. Three-week-old specific pathogen free chickens were inoculated intraocularly with standard challenge strain (STC) (cIBDV) and a variant strain Indiana (IN) (vIBDV). The cIBDV produced more pronounced bursal damage, inflammatory response and infiltration of T cells as compared to vIBDV. There were significant differences in the expression of innate (IFN-α and IFN-β), proinflammatory cytokine and mediator (IL-6 and iNOS) in cIBDV- and vIBDV-infected bursas. The expression of chemokines genes, IL-8 and MIP-α was also higher in cIBDV-infected chickens during the early phase of infection. The expression of Toll like receptor 3 (TLR3) was downregulated at post inoculation days (PIDs) 3, 5, and 7 in the bursas of vIBDV-infected chickens whereas TLR3 was upregulated at PIDs 3 and 5 in cIBDV-infected bursas. In vIBDV-infected bursa, TLR7 expression was downregulated at PIDs 3 and 5 and upregulated at PID 7. However, TLR7 was upregulated at PIDs 3 and 7 in cIBDV-infected bursas. The expression of MyD88 was downregulated whereas TRIF gene expression was upregulated in cIBDV- and vIBDV-infected bursa. These findings demonstrate the critical differences in bursal lesions, infiltration of T cells, expression of cytokines, chemokines and TLRs in the bursa of cIBDV-and vIBDV-infected chickens.
Highlights
Infectious bursal disease (IBD) is one of the most important naturally occurring viral diseases of commercial chickens worldwide [1]
All of the chickens inoculated with classic IBDV (cIBDV) showed morbidity and 8% mortality whereas chickens infected with variant IBDV (vIBDV) appeared healthy and no morbidity or mortality was noted in this group
While comparing the pathogenesis of cIBDV and vIBDV, we noted that cIBDV produced more pronounced bursal damage as compared to vIBDV during early stages of the infection
Summary
Infectious bursal disease (IBD) is one of the most important naturally occurring viral diseases of commercial chickens worldwide [1]. The causative agent, IBD virus (IBDV) belongs to the family Birnaviridae. The virus causes an acute, highly contagious and immunosuppressive disease in chickens [1]. The virus infects and destroys actively dividing IgM-bearing B cells in the bursa of fabricius [2,3]. IBDV exists in different antigenic and pathogenic forms [4]. Initial isolates designated as classical strains (cIBDV) of the serotype 1 viruses were considered to be a single antigenic type. In the early 1980s, antigenic variants (vIBDV) of the virus were identified in the United
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