Threshold of pre-T-cell-receptor surface expression is associated with αβ T-cell lineage commitment

Results: We have used a sensitive immunofluorescence technique to reveal the surface-expression profile of the pre-TCR on immature thymocyte subsets. We show that early pre-T cells (CD25+CD44–) can be subdivided on the basis of the level of surface pre-TCR expression. Detectable surface pre-TCR expression identified a rapidly cycling population of early pre-T cells which had successfully undergone β-selection and been rescued from programmed cell death. Late pre-T cells (CD25–CD44–), which had traversed the β-selection checkpoint, expressed surprisingly heterogeneous surface levels of the pre-TCR: high levels of surface pre-TCR expression were associated with commitment to the αβ T-cell lineage, whereas late pre-T cells with lower levels of surface pre-TCR could develop along both the αβ or γδ T-cell lineages.