Fowlpox virus infection causes a lymphoproliferative response in chickens

While attenuated fowlpox virus (FPV) strains are widely used for vaccination of chickens and turkeys for prevention of fowlpox, recombinant FPV expressing various foreign genes have been evaluated for their ability to offer protection against various diseases in poultry as well as mammals. Little is known regarding the cell-mediated immune responses to FPV infection. In this study, immune response in chickens infected with a virulent and a vaccine strain of FPV were compared by a lymphoproliferation assay. Interestingly, a lymphoproliferative response was seen during 2-4 weeks post-infection irrespective of the FPV strain used in this study. Analyses of the buffy coat cultures with (35)S-methionine pulse labeling revealed an elevated protein of approximately 48-50 kDa in the culture supernatants. Furthermore, those supernatants could stimulate naive, non-adherent cells of the buffy coat cultures, in a dose dependant manner, suggestive of stimulatory cytokines. FPV, a complex virus presumably stimulates a variety of cytokines in vivo causing a proliferative cellular response. Knowledge of those cytokines or a better understanding of the proliferative responses is pivotal in evaluation of FPV vaccines and in the design of FPV-based recombinant vaccines.