T cell receptor diversity in alloreactive responses against HLA‐B27 (B*2705) is limited by multiple‐level restrictions in both α and β chains

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Abstract
The T cell receptors (TCR) in HLA‐B27 (B*2705) alloreactivity were analyzed in cytotoxic T lymphocytes (CTL) from two individuals. Non‐random usage was found in Vβ, N+Dβ, Vα, and Jα, but not in Jβ segments or Nα‐regions. Vβ segments from homology subgroup 4 were predominant and not associated to a particular donor or fine specificity, suggesting involvement in recognizing the HLA‐B27 molecule. In contrast, preferential Vα usage was associated with particular individuals and fine specificities, indicating distinct Vβ and Vα recruitment and contribution to allorecognition. Recurrent N+Dβ motifs and Jα segments, even from different donors, limited junctional diversity, suggesting that CDR3 usage was determined by the alloantigenic epitope independently of individuals. TCR were selected differently at various levels, as indicated by the following findings. Four clonotypes with similar fine specificity had identical β and unrelated α chains. Similar α were associated with unrelated β chains, and vice versa. CTL using Vβ subgroup 4 did not globally show concomitant predominance of other TCR elements. Vα7, one of the preferred Vα segments, was always associated with Vβ subgroups other than 4. Sometimes, a TCR showed homology in elements 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 selection of TCR elements by different epitopes, providing a key to the inner structure of allospecific TCR repertoires.