Trede, N.S. and Zon, L.I. (1998) Development of T-cells during fish embryogenesis. Developmental and comparative immunology. 22:253-263.
The common denominator of the vertebrate immune system includes the antigen receptors (immunoglobulins and TCR), the MHC molecules and the recombination activating genes (Rag-1 and Rag-2) . In most vertebrates, lymphoid ontogeny proceeds within specific organs such as the thymus for T-cell development and Bursa equivalents for B-cell development. Jawless fish do not have a thymus, and the most primitive vertebrate taxon in which the common denominator is found in the cartilagenous fish. Although the presence of thymic tissue in fish was documented almost a century ago , the genes that encode the four chains composing the T-cell receptor have only recently been cloned in several fish species [3, 4, 5, 6]. This review discusses recent developments in the field of fish immunology, particularly focusing on T-cell development in the thymus of cartilagenous and bony fish. The zebrafish is as a new developmental and genetic model system that will facilitate the study of T-cell development. Our recent studies on the immune system of this new model organism demonstrate conservation of the lymphoid program throughout gnathostome vertebrates. The relative ease with which zebrafish larvae can be studied, the powerful genetics and the increasing number of molecular tools available will be instrumental for elucidating early events in vertebrate lymphoid ontogeny.