Positive selection of T cells, an in vitro view.

The thymus provides a unique set of cues for the effective selection and differentiation of CD4 and CD8 T-cells from a pool of immature thymocytes. Several approaches have been used to elucidate the complex set of intrathymic interactions that mediate these selection and differentiation events. Over the years, a number of different in vitro approaches have been developed and employed to assist in the identification of the cellular and molecular players that underpin thymic function. Here we provide an overview of the advances, which were obtained by in vitro approaches, to our understanding of the process of positive selection and CD4/CD8 lineage commitment.