NORMAL T-LYMPHOCYTES CAN EXPRESS 2 DIFFERENT T-CELL RECEPTOR BETA-CHAINS - IMPLICATIONS FOR THE MECHANISM OF ALLELIC EXCLUSION

We have examined the extent of allelic exclusion at the T cell recepto r (TCR) beta locus using monoclonal antibodies specific for V beta pro ducts. A small proportion (similar to 1%) of human peripheral blood T cells express two V beta as determined by flow cytometric analysis, is olation of representative clones, and sequencing of the corresponding V beta chains. Dual beta T cells are present in both the CD45R0(+) and CD45R0(-) subset. These results indicate that dual beta expression is compatible with both central and peripheral selection. They also sugg est that the substantial degree of TCR beta allelic exclusion is depen dent only on asynchronous rearrangements at the beta locus, whereas th e role of the pre-TCR is limited to signaling the presence of at least one functional beta protein.