Abstract
Cartilaginous and bony fish are the most primitive vertebrates with a thymus, and possess T cells equivalent to those in mammals. There are a number of studies in fish demonstrating that the thymus is the essential organ for development of T lymphocytes from early thymocyte progenitors to functionally competent T cells. A high number of T cells in the intestine and gills has been reported in several fish species. Involvement of CD4+ and CD8α+ T cells in allograft rejection and graft-versus-host reaction (GVHR) has been demonstrated using monoclonal antibodies. Conservation of CD4+ helper T cell functions among teleost fishes has been suggested in a number studies employing mixed leukocyte culture (MLC) and hapten/carrier effect. Alloantigen- and virus-specific cytotoxicity has also been demonstrated in ginbuna and rainbow trout. Furthermore, the important role of cell-mediated immunity rather than humoral immunity has been reported in the protection against intracellular bacterial infection. Recently, the direct antibacterial activity of CD8α+, CD4+ T-cells and sIgM+ cells in fish has been reported. In this review, we summarize the recent progress in T cell research focusing on the tissue distribution and function of fish T cells.
Highlights
T cells play important roles in the adaptive immune system
Mammalian T cell receptor (TCR) comes mainly in two forms: A heterodimer of TCRα and TCRβ chains is found on the surface of conventional circulating αβ-T cells, and a heterodimer of TCRγ and TCRδ chains is found on the “more primitive” mucosa-associated γδ-T cells. αβ-T cells are the more abundant T cell type found in lymphoid organs and blood in mammals
The pesence of CTLs and Th cells in fish has been suggested in a number of functional studies, and recently CTLs and Th have been identified as CD8+ and CD4+ cells, respectively using monoclonal antibodies
Summary
T cells play important roles in the adaptive immune system. All T cells possess a T cell receptor (TCR) by which they recognize peptide presented by MHC, along with CD3 and co-stimulatory. Mammalian TCR comes mainly in two forms: A heterodimer of TCRα and TCRβ chains is found on the surface of conventional circulating αβ-T cells, and a heterodimer of TCRγ and TCRδ chains is found on the “more primitive” mucosa-associated γδ-T cells. CTLs express CD8 molecules involved in the interaction with MHC class I, while helper T cells express CD4 that interacts with MHC class II. In humans and mice, helper T cells are further divided into several populations, Th1, Th2, Th17 and Tregs which play different roles in immune responses. T cell associated genes and their encoded proteins with T cell activity, e.g., surface markers, cytokines and transcriptional factors, have been well documented (reviewed by [3,4]). We summarize the recent progress in T cell research focusing on the tissue distribution and function of fish
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