Virulent avian influenza A viruses: their effect on avian lymphocytes and macrophages in vivo and in vitro.

To investigate the pathogenesis of virulent avian influenza A viruses, the effect of A/turkey/Ont/7732/66 (H5N9) (Ty/Ont), A/tern/South Africa/1961 (H5N3) (Tern/S.A.) and A/chicken/Pennsylvania/1370/83 (H5N2) (Ck/Penn) on avian lymphoid cell populations was examined in vivo. Previous studies have shown that infection of chickens with Ty/Ont resulted in the extensive destruction of lymphoid tissues. In this study, other virulent avian H5 influenza viruses, Tern/S.A. or Ck/Penn, had little or no effect on lymphoid tissues of infected chickens. Therefore the effect of Ty/Ont on lymphoid tissue is a specific activity of this virus only and not of other virulent avian H5 influenza strains. To examine the role of viral replication in the destruction of lymphocytes, in vitro cultures of avian macrophages and lymphocytes were inoculated with Ty/Ont. Macrophages supported the synthesis of viral proteins whereas lymphocytes produced small, but detectable amounts of viral protein; however, infectious virus was not produced by either cell type. Furthermore inoculation of chicken spleen cells with Ty/Ont in vivo and in vitro had a profound effect on the proliferative response of lymphocytes to concanavalin A. These results suggest that Ty/Ont infects macrophages as well as lymphocytes in the chicken, and the effects of the virus on both cell types may well contribute to lymphoid necrosis.