The T-cell receptor V beta 6 gene usage in alloreactive T-cell responses.
To analyze the role of TCR V beta gene elements in allorecognition, we have determined frequencies of the TCR V beta 6 elements expressed by allospecific T cells as compared to randomly activated T cells. Limiting dilution analysis was applied to estimate the usage of TCR V beta elements in CD4+ T cells polyclonally stimulated by immobilized anti-CD3 or specifically activated with HLA-DR disparate allotargets. In a focused alloresponse of HLA-DRB1*0401+ responders to HLA-DRB1*0404+ stimulator cells, V beta 6+ T cells were preferentially recruited. To map the functional domain of allogeneic HLA-DR molecules involved in the recruitment of V beta 6+ T-cell specificities, CD4+ T cells from HLA-DRB1*0401+ donors were activated with allogeneic stimulators sharing either the first and second or the third HVR of the HLA-DRB1 gene. Stimulation with allotargets sharing the sequence of the HVR3 caused a twofold to fourfold enrichment of V beta 6+ CD4+ T cells, while sequence variations in the HVR3 was sufficient to abrogate the preferential usage of V beta 6+ T cells. These data suggest that sequence variations mapped to the alpha-helical loop of the HLA-DR beta chain impose structural constraints that shape the alloreactive TCR V beta repertoire.