Appearance of T cells in the bursa of Fabricius and cecal tonsils during the acute phase of infectious bursal disease virus infection in chickens.

Groups of 3-wk-old specific-pathogen-free chickens were inoculated intraocularly with two virulent and one vaccine strain of infectious bursal disease virus (IBDV). During the acute phase of infection, the bursa of Fabricius and cecal tonsil were examined by immunohistochemistry for IBDV antigen and T cell. With all three viruses examined, the infection resulted in the appearance of viral antigen in the bursa accompanied by the presence of CD3+ cells. The CD3+ cells were predominantly TCR2+ and appeared at the site where viral antigens were present. The CD3+ cells continued to persist in the bursa after most of the IgM+ cells and IBDV antigen-positive cells had disappeared. Similar appearance of CD3+ cells was noted following viral antigen accumulation in the germinal centers of cecal tonsils in virulent IBDV-infected chickens. These results demonstrated that infection with IBDV resulted in extensive viral replication in the bursa and the cecal tonsils with an associated accumulation of T cells. The role these T cells may play in the pathogenesis of IBDV infection remains to be established.