DIFFERENTIAL USAGE OF T-CELL RECEPTOR V-GENE SEGMENTS IN CD4+ AND CD8+ SUBSETS OF LYMPHOCYTES-T IN MONOZYGOTIC TWINS

The TCR confers immunity by the specific recognition of foreign Ag peptides in the context of self-MHC molecules. The mechanisms controlling TCR selection and repertoire generation are not clearly understood and seem to occur in an apparently random, (self) Ag-driven manner. To address the question to what extent the TCR repertoire is randomly shaped or genetically predetermined, we have analyzed the alphabeta TCR repertoire of the CD4+ and CD8+ subsets of peripheral blood lymphocyte cultures of monozygotic twins by using the polymerase chain reaction technique with TCR V region gene family-specific oligonucleotide primers. Our studies demonstrate that there is high concordance in the overall patterns of V gene usage within a pair of twins, particularly in Vbeta usage (mean Vbeta CD4+ R2 = 0.869 and CD8+ R2 = 0.833) and to a lesser extent Valpha usage (mean Valpha CD4+ R2 = 0.621 and CD8+ R2 = 0.627); whereas the patterns between unrelated individuals show more variability. This study has also demonstrated that the Valpha and Vbeta genes are not randomly used within the CD4+ and CD8+ subsets. We observed significant preferential skewing of several Valpha or Vbeta gene families to either the CD4+ or CD8+ subset in the majority of individuals analyzed (p-value range = 0.0476 to < 0.001). In particular, Valpha11, 17, 22, and Vbeta3, 9, 12,18 were skewed to the CD4+ subset; whereas Valpha2, 6,12,15, 20 and Vbeta7, 14, 17 were skewed to the CD8+ subset. Furthermore, a number of the V genes showed patterns of skewing consistent only within a pair of twins. In three pairs of twins, Vbeta2 was skewed to the CD4+ subset, whereas the fourth pair used almost equal frequencies of Vbeta2 in both subsets. This observation was made for the Vbeta2, 4, 5, 6, 8, 19 and Valpha7, 16, 18, 21 families. Finally, the ratio of the relative V gene usage frequency that could be observed within an individual was conserved within the sets of twins; for instance, the relative amount of Vbeta2 to that of Vbeta3 was higher in both individuals of one set of twins, whereas it was lower in all of the other three sets. Together these observations suggest that the predominant influence shaping the TCR repertoire is genetically predetermined, of which, HLA-predicted selection mechanisms exerted during thymic maturation might be contributing factors.