Preferential TCR V usage in rat repertoire selection: V alpha 8 imparts both positive thymic selection by and alloreactivity to RT1f.

Using a panel of newly developed mAb to two rat TCR V alpha and four TCR V beta segments, TCR V usage in CD4 and CD8 T cells of eight RT1 congenic strains sharing the LEW background was analyzed by flow cytometry. While no striking effects on V beta 8.2 and 8.5 usage were observed, a 3- to 4-fold over-representation of V beta 10 in the CD4 as compared with the CD8 subset in all strains suggested a preference of V beta 10 for MHC class II products. The degree of 'overselection' was mapped to the RT1.B/D region. In addition, an allele-specific overselection of V alpha 4+ CD4 T cells was mapped to RT1.B/Du and of V beta 16+ CD8 T cells to RT1.Au. Finally, a dramatic overselection of V alpha 8+ CD8 T cells by RT1f (14% in RT1f versus 1-2% in other haplotypes) provides the most striking case yet for an intrinsic affinity of a TCR V segment for an MHC product. V alpha 8+ CD8 T cells are not only overselected by RT1f in the thymus, but also during the alloreactive response of peripheral CD8 T cells to RT1f. The implications of these findings for the contribution of TCR V segments to TCR-MHC interactions in repertoire selection and alloreactivity are discussed.