IMMUNOCYTOCHEMICAL STUDY OF PEYERS-PATCHES FOLLICULAR-ASSOCIATED EPITHELIUM IN THE MARSUPIAL, DIDELPHIS-ALBIVENTRIS

The lack of probes defining leukocyte subpopulations has restricted on togenetic studies of the opossum gut. We report for the first time the organization of the gut cellular immune components using species cros s-reactive antibodies. Mouse monoclonal antibodies against human HLA-D R were used together with immunocytochemistry to demonstrate MHC class II-like antigens in the opossum Peyer's patches (PP). Positive staini ng was obtained in the M cell and enterocytes comprising the follicula r-associated epithelium (FAE). Rabbit polyclonal antibody against huma n CD3 stained opossum thymocytes and T-cell dependent areas of spleen, lymph node, and PP interfollicular zones, but failed to stain intraep ithelial lymphocytes in the FAE. In contrast rabbit polyclonal antibod y against human IgA stained B-cell immunocytes and plasma cells presen t in the M-cell lateral invaginations. It is surmised that B-cell acti vation could occur in the opossum M-cell niches by thymus independent antigens, bypassing T-helper-cell function.