Selection of dual Vα T cells

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Abstract
Incomplete allelic exclusion of TCRa gene rearrangement permits the generation of dual Vα T cells, though the issues of their frequency and whether both α β pairs participate in thymic selection have not been resolved. Both questions have been investigated using lymphocytes from mice hemizygous at the TCRa locus and consequently unable to express two rear ranged TCRa genes, as background controls. The data presented show that both the frequency of dual Vα T cells and the relative expression levels of co-expressed Vα chains are variable and are determined by thymic selection. Possession of a Vα chain which is inefficiently positively selected appears to increase the likelihood that a second Vα chain will be co-expressed, whilst the relative cell surface levels of a given pair of Vα chains differbetween CD4 and CD8 subsets. Further, for some but not all Vα pairs, dual Vα T cells appear to express elevated levels of surface TCR. Finally, contrary to previous claims, dual Vα T cells do not appear to be relatively frequent amongst immature thymocytes.