Surface expression of TCR dimers by cells synthesizing three or four distinct types of receptor chains was analyzed. Cells containing intact gamma, alpha, and beta chains had only gamma delta dimers on the cell surface. In human PEER cells, addition of a functional alpha chain led to the loss of gamma delta dimer expression and expression of only alpha beta dimers. This result was not due to transcriptional down-regulation of the gamma or delta loci. In murine cells expressing all four chains, both gamma delta and alpha beta dimers could be demonstrated on a single cell. No other chain combinations (alpha gamma, alpha delta, beta gamma, or beta delta) were detected. Thus, there is stringent control of assembly and/or transport of TCR heterodimers, such that functional receptors consist only of alpha beta and gamma delta pairs, and no additional repertoire diversity is generated by cross pairing.

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