Distribution of T cell subsets in chicken lymphoid tissues

The distributions of T cell subsets in chicken lymphoid tissues were investigated immunohistochemically using monoclonal antibodies (Lc-6, Lc-4) with specificity for chicken CD4 and CD8, respectively. In thymic tissues, CD8+ cells were found only in the cortex, while CD4+ cells were detected not only in the cortex but also in the medulla. The cortex just below the capsule demonstrated no immunoreactivity to either antibody. In the cecal tonsile, CD8+ cells were found restrictly in the subepithelial lamina propria. It was noted that the germinal centers were clearly surrounded with many CD4+ cells in the mid and deep portions of the lamina propria. In the spleen, clusters of CD8+ cells were observed only in the red pulp. Most lymphocytes in the periarteriolar lymphatic tissue and perivenous lymphatic tissue showed a CD4-positive reaction. No lymphocyte in the germinal centers reacted with these two monoclonal antibodies. No immunoreactivity for either CD8 or CD4 was detected anywhere else in the bone marrow or bursa of Fabricius. In the case of exposure to the protein antigen (alum-precipitated bovine serum albumin), CD4+ cells were demonstrated in some germinal centers, which were increased in size, while the areas expressing CD8 in the red pulp were decreased in size. These results suggest that the preferential distributions of T cell subsets are inherent in chicken lymphoid tissues.