Developmental Biology of Teleost Lymphocytes

After the precocious onset of innate immune mechanisms, teleosts progressively establish immunocompetence based on antigen-specific T and B lymphocytes. The thymus and the head kidney are the primary lymphoid organs from where mature naive lymphocytes migrate to secondary sites to encounter antigens and become activated. Although the teleost T and B lineages are not completely understood, a considerable amount of information has been accumulated from studies on a few model species, relevant for basic (zebra fish) and aquaculture applied investigation (rainbow trout, carp, European sea bass). The selection of mutants and gene expression analysis in particular allowed for a fairly accurate comprehension of molecular mechanisms regulating thymopoiesis and some aspects of lymphocyte development. The early appearance in mucosal tissues of “nonconventional” lymphocytes endowed with innate/regulatory activities requires further studies focused on their developmental pathways.