A competent immune system requires that mature T cells express TCR and CD4/CD8 coreceptors with matching MHC specificities. Such matching of TCR and coreceptor specificity is induced in the thymus at the CD4(+)8(+)stage of development and is referred to as lineage commitment. The process by which immature CD4(+)8(+)thymocytes are signaled to undergo lineage commitment continues to be the subject of intense investigation and discussion. Here, we review the major models by which lineage commitment is thought to occur and discuss the experimental results on which they were based.
Copyright 1999 Academic Press.