Normal T lymphocytes can express two different T cell receptor β chains: Implications for the mechanism of allelic exclusion

We have examined the extent of allelic exclusion at the T cell receptor (TCR) β locus using monoclonal antibodies specific for Vβ products. A small proportion (~1%) of human peripheral blood T cells express two Vβ as determined by flow cytometric analysis, isolation of representative clones, and sequencing of the corresponding Vβ chains. Dual β T cells are present in both the CD45R0⁺ and CD45R0^- subset. These results indicate that dual β expression is compatible with both central and peripheral selection. They also suggest that the substantial degree of TCRβ allelic exclusion is dependent only on asynchronous rearrangements at the β locus, whereas the role of the pre-TCR is limited to signaling the presence of at least one functional β protein.