Contribution of the Major Histocompatibility Complex (MHC) B locus-based genetic resistance to multiple strains of infectious bursal disease virus

Seven lines of major histocompatibility complex (MHC)-B congenic specific pathogen free (SPF) chickens and two lines of non-B congenic SPF chickens with similar B haplotype but differing non-MHC genes were utilized to investigate the effect of the B locus on infectious bursal disease (IBD) development. In initial experiments, chickens were challenged at 28 days of age with the variant infectious bursal disease virus (IBDV) strain AL-2, classical IBDV strain STC, or very virulent (vv) IBDV strain rA. IBD severity was evaluated throughout the seven-day course of infection by assessing survivability and histopathological analysis of bursal lesion scores. Follow up studies investigated the effects of varying STC challenge doses on IBD development. Results demonstrated that the challenge strain of IBDV has a large impact on B locus-based genetic resistance. The most significant differences in survivability and bursal lesions were noted after challenge with the vvIBDV strain, with MHC-B congenic chicken lines B*13 and B*19 being the most susceptible. Based on survivability, the B*19 chicken line was also characterized as the most susceptible after challenge with high doses (105 EID50) of the STC strain. No differences in survivability were detected among the chicken lines when challenged with the variant strain AL-2. Based on the results with these chicken lines, B locus-based genetic resistance to IBDV is mainly associated with survival during the early stages of infection and has minimal association with bursal damage and bursal lymphocyte depletion. Non-B locus-based genetic differences also have a significant impact on survival during early IBDV infection.