T-CELL RECEPTOR DIVERSITY IN ALLOREACTIVE RESPONSES AGAINST HLA-B27 (B-ASTERISK-2705) IS LIMITED BY MULTIPLE-LEVEL RESTRICTIONS IN BOTH ALPHA-CHAINS AND BETA-CHAINS

The T cell receptors (TCR) in HLA-B27 (B2705) alloreactivity were ana lyzed in cytotoxic T lymphocytes (CTL) from two individuals. Non-rando m usage was found in V beta, N+D beta, V alpha, and J alpha, but not i n J beta segments or N alpha-regions. V beta segments from homology su bgroup 4 were predominant and not associated to a particular donor or fine specificity, suggesting involvement in recognizing the HLA-B27 mo lecule. In contrast, preferential V alpha usage was associated with pa rticular individuals and fine specificities, indicating distinct V bet a and V alpha recruitment and contribution to allorecognition. Recurre nt N+D beta motifs and J alpha segments, even from different donors, l imited junctional diversity suggesting that CDR3 usage was determined by the alloantigenic epitope independently of individuals. TCR were se lected differently at various levels, as indicated by the following fi ndings. Four clonotypes with similar fine specificity had identical be ta and unrelated alpha chains. Similar alpha were associated with unre lated beta chains, and vice versa. CTL using V beta subgroup 4 did not globally show concomitant predominance of other TCR elements. V alpha 7, one of the preferred V alpha segments, was always associated with V beta subgroups other than 4. Sometimes, a TCR showed homology in ele ments of one chain to a second TCR or group of TCR, and to another in the other chain. These results are best explained by differential sele ction of TCR elements by different epitopes: providing a key to the in ner structure of allospecific TCR repertoires.