Surface markers of fish T-cells

Two immunological reactions against foreign antigens can be distinguished: (1) the humoral immune response, involving the production of immunoglobulin s by plasma cells; (2) the cell-mediated immune responses, mediated by thym us-derived cells. All jawed vertebrates show these two immunological pathwa ys. In lower vertebrates, the existence of cell-mediated immunity has been shown by transplantation experiments resulting in allograft rejection. The basic phenomena observed are similar to those in mammals. Lymphocyte hetero geneity, particularly the participation of T-like lymphocytes in fish immun ity, is now well established. T-like cells were defined as sIg(-) cells whi ch proliferate in the presence of specific mitogens for mammalian T lymphoc ytes (Con A and PHA). The mixed leucocyte reaction (MLR) has been demonstra ted in all vertebrates, from shark to mammals. The in vitro antihapten anti body response to a T-dependent antigen requires the participation of sIg(+) and sIg(-) cells and monocytes. In addition, fish sIg(-) lymphocytes speci fically proliferate in the presence of processed and presented antigen, rem iniscent of the mammalian classical T-cell/B-cell/APC collaboration. Hither to, only a few attempts to generate antibodies, reacting exlusively with fi sh T-cell markers, have been successful. The use of molecular tehniques suc h as PCR and library screening has allowed the identification of cDNA clone s encoding TCR-alpha and -beta chains in several fish species. TCR delta-li ke chains not yet detected in teleosts have been isolated in shark, suggest ing that TCR gamma delta-like receptors should exist in all gnathostomes. W hereas the teleost TCR beta locus shows a translocon organisation comparabl e to that of its mammalian counterpart, elasmobranch TCR beta genes are arr anged in multiple clusters. As in mammals, the TCR repertoire in fish speci es appears to be considerable. (C) 1999 Academic Press.