Pathogenic avian adenovirus type II induces apoptosis in turkey spleen cells

Wild-type mammalian adenoviruses are known to inhibit programmed cells death in infected cells. This study demonstrated for the first time that an avian type II adenovirus, the hemorrhagic enteritis virus (HEV) of turkeys, induced apoptosis in turkey spleen cells at 3 and 4 days post infection. The increased apoptosis rate in spleens of HEV-infected turkeys was associated with increased virus replication. Increased apoptosis preceded extensive virus-induced cellular necrosis. At 3 days post infection, spleen cells from HEV-infected turkeys released tumor necrosis like factor and nitric oxide inducing factors after ex vivo stimulation with concanavalin A. Spleen cells from HEV-exposed turkeys also secreted an interleukin 6-like factor when cultured in vitro. These cytokines may have contributed to HEV-pathogenesis and HEV-induced apoptosis and necrosis in the spleen. Induction of apoptosis by an avian adenovirus but not by wild-type mammalian adenoviruses indicates that evolutionarily distant adenoviruses may have different pathogenic mechanisms.