Tracing an Orphan's Genealogy

摘要

In mammals, the essential site of T cell production is the thymus Most T cells bear receptor's (TCRs) composed of alpha and beta chains; the remainder bear TCRs composed of gamma and delta chains. Immature alpha beta T cells are subject to a strict education Called double-positive (DP) thymocytes because they bear both CD4 coreceptors and CD8 alpha beta coreceptors, they express a rearranged TCR beta chain and are in the process of rearranging their TCR a chains, The final TCRs are selected accordingto precise rules of recognition [of antigenic peptides presented by major histocompati-bility complex (MHC) class I and II molecules] and high-affinity binding to ligand (high enough to allow positive selection of TCR-bearing cells, but not so high as to nrevent negative selection and death). Mature T cells emerging from this pathway beat either CD4 or CD8alpha beta coreceptors and ate described as single positive (SP). These cells leave the thymus to colonize the secondary lymphoid organs of the body, including lymph nodes, spleen, and Peyer's patches of the gut.