Bursal immunopathology responses of specific?pathogen?freechickens and red jungle fowl infected with very virulent infectiousbursal disease virus

AbstractVery virulent infectious bursal disease virus (vvIBDV) targets B lymphocytes in the bursa of Fabricius (BF), causingimmunosuppression and increased mortality rates in young birds. There have been few studies on the host immune responsefollowing vvIBDV infection at different inoculum doses in chickens with different genetic backgrounds. In this study, wecharacterized the immune responses of specific-pathogen-free (SPF) chickens and Malaysian red jungle fowl followinginfection with vvIBDV strain UPM0081 at 103.8and 106.8times the 50% embryo infectious dose (EID50). The viral burden,histopathological changes, immune cell populations, and expression of immune-related genes were measured and comparedbetween infected and uninfected bursa at specific intervals. The populations of KUL1+,CD3+CD4+ and CD3+CD8+ cellswere significantly increased in both types of chickens at 3 dpi, and there was significant early depletion of IgM+B cells at1 dpi in the red jungle fowl. vvIBDV infection also induced differential expression of genes that are involved in Th1 and proinflammatoryresponses, with groups receiving the higher dose (106.8 EID50)showing earlier expression of IFNG, IL12B,IL15, IL6, CXCLi2, IL28B, and TLR3 at 1 dpi. Although both chicken types showed equal susceptibility to infection, thered jungle fowl were clinically healthier than the SPF chickens despite showing more depletion of IgM+B cells and failureto induce IFNB activation. In conclusion, high-dose vvIBDV infection caused an intense early host immune response in theinfected bursa, with depletion of IgM+B cells, bursal lesions, and cytokine expression as a response to mitigate the severityof the infection