Selection of dual Valpha T cells.
Incomplete allelic exclusion of TCRa gene rearrangement permits the generation of dual Valpha T cells, though the issues of their frequency and whether both alphabeta 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 rearranged TCRa genes, as background controls. The data presented show that both the frequency of dual Valpha T cells and the relative expression levels of co-expressed Valpha chains are variable and are determined by thymic selection. Possession of a Valpha chain which is inefficiently positively selected appears to increase the likelihood that a second Valpha chain will be co-expressed, whilst the relative cell surface levels of a given pair of Valpha chains differ between CD4 and CD8 subsets. Further, for some but not all Valpha pairs, dual Valpha T cells appear to express elevated levels of surface TCR. Finally, contrary to previous claims, dual Valpha T cells do not appear to be relatively frequent amongst immature thymocytes.
Transplantation Biology Group, MRC Clinical Sciences Centre, Imperial College School of Medicine, Hammersmith Hospital, London, GB. jielliot@rpms.ac.uk
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Elliott
D000818:Animals; D015704:CD4 Antigens / Q000032:analysis; D016827:CD8 Antigens / Q000032:analysis; D015332:Gene Rearrangement, alpha-Chain T-Cell Antigen Receptor; D051379:Mice; D008810:Mice, Inbred C57BL; D016688:Mice, Inbred NOD; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000032:analysis*; D013601:T-Lymphocytes / Q000276:immunology*
D015704:CD4 Antigens; D016827:CD8 Antigens; D016693:Receptors, Antigen, T-Cell, alpha-beta