Majority of TcRβ+ T-lymphocytes located in thymus and midgut of the bony fish, Dicentrarchus labrax (L.)

Abstract

Real-time polymerase chain reaction (PCR) and in situ hybridization analyses were performed to investigate the occurrence and distribution of T-lymphocytes expressing TcRβ in intestine and lymphoid tissues of the bony fish, Dicentrarchus labrax (sea bass). Immunohistochemistry with the monoclonal antibody DLT15 (pan-T-cell marker) was carried out to compare the cytology, distribution and number of T-cells and TcRβ+ cells in the various sampled lymphoid organs. The highest TcRβ expression was revealed by real-time PCR in the thymus, with high levels also being found in the gut. In the thymus, DLT15+ and TcRβ+ cell populations were concentrated in the cortex and TcRβ+ cells were notably reactive at the cortical-medullary border, suggesting a specialized role of this region in thymocyte selection. The density of DLT15+ T-cells increased from the anterior to posterior intestine, whereas TcRβ+ lymphocytes were more numerous in the middle intestine compared with other segments. The existence, in fish thymus, of a medulla and a cortex comparable with those of mammals is revealed by this study. The concentration of TcRβ+ cells in the sea bass midgut also strongly suggests a special role of this intestinal segment in antigen-specific cellular immunity. The large population of TcRβ-/DLT15+ T-cells in the posterior gut can probably be ascribed to the TcRγδ phenotype fraction.