Functional and molecular characterization of teleost leukocytes

The coupling of immunologically relevant in vitro assay systems, cell separ ation techniques, and the development of distinct clonal leukocyte Lines ha s established the existence of T, B, natural killer, and accessory cell equ ivalents in teleosts. B cells are directly defined by monoclonal antibodies to teleost immunoglobulin (Ig) and identification of Ig H and L chain gene s. As in mammals, fish B cells show Ig H-chain gene rearrangements, allelic exclusion, produce both membrane-bound and secreted forms of Ig, and trans duce intracellular proliferative signals upon anti-Ig cross-linking. It has also been found that some fish B cells express a unique chimeric Ig chain with sequence homology to mammalian Ig delta. Teleost T cells are still ind irectly defined as sIg(-) lymphocytes due to a lack of definitive surface m arkers. These mIg(-) lymphocytes are the responding cells in mixed leukocyt e cultures, proliferate specifically to autologously processed and presente d antigen, provide helper function for in vitro antibody responses, and pro duce interleukin-like factors upon activation. Recent identification of tel eost T-cell receptor alpha and beta genes has now permitted the unequivocal genetic demonstration that some of these mig cells are bona fide T cells. It is anticipated that such long-term clonal cell lines will be indispensab le tools for dissecting the physiology, biochemistry and molecular biology of teleost immune responses.