Intestinal T cells of Dicentrarchus labrax (L.): Gene expression and functional studies.

Cellular and molecular data have evidenced a gut-associated lymphoid tissue in a variety of teleost species, abundantly containing T cells, whose origin, selection and functions are still unclear. This study reports CD4, CD8-a, MHCI-a, MHCII-b, rag-1 and TCR-b gene transcription along the intestine (anterior, middle and posterior segments) and in the thymus of one year-old Dicentrarchus labrax (L.). Real-time PCR findings depicted a main role of the thymus in T-cell development, but also rag-1 and CD8-a transcripts are detected in the intestine, having significant expression in the posterior segment. In the whole intestine TCR-b and CD8-a exceeded CD4 transcripts. RNA ISH confirmed these data and detailed that mucosal CD8-a + cells were especially numerous in the epithelium and in aggregates in the lamina propria. Regional differences in T-cell-specific gene expressions are first described in the intestine of a bony fish. High non-specific cytotoxic activity against xenogeneic and allogeneic cells was found in lymphocytes purified from the intestinal mucosa, providing further insight into their local defence roles.