Microenvironmental regulation of T cell development in the thymus.

T cell development in the thymus occurs through a series of events beginning with thymic colonization by migrant precursors and ending with the emigration of functionally competent CD4+ and CD8+ T cells to the periphery. It is well accepted that signals through the pre-T cell receptor (pre-TCR) and alpha-beta TCR (alphabetaTCR) complex play pivotal roles in the maturation of CD4-8- and CD4+8+ thymocytes, respectively. It is clear that stromal cells constituting the thymic microenvironment provide non-TCR-mediated interactions which are essential for several developmental events. Examples of such will be discussed here in relation to early and late events in T cell development.