Cross-reactive T cell clones from unrelated individuals reveal similarities in peptide presentation between HLA-B27 and HLA-DR2.

HLA-B27- responder cells were stimulated in vitro with B2705+ lymphoblastoid cell lines and alloreactive CTL clones were obtained by limiting dilution. Of the CD3+ CD4-CD8+ HLA-B27-specific CTL clones obtained, two of them, possessing the same TCR, cross-reacted with HLA-DR2. The fine specificity of these CTL was established with HLA-B27 and HLA-DR2 subtypes. They recognized the B2701 to B2706 subtypes, but only DR2Dw2. Lysis of DR2+ target cells was specifically inhibited by anti-CD3, anti-class II, and anti-DR mAb, but not with an anti-CD8 antibody. The monoclonal nature of the cross-reaction was established by the mutual inhibition of HLA-B27 and DR2Dw2 cells in cold target competition experiments. The DR2 protein involved in the cross-reaction was the heterodimer carrying the B50101 product, as shown by using L cell transfectants expressing each of the two molecules encoded in the DR2Dw2 haplotype. A correlation between the fine specificity of these CTL clones and the amino acid sequences of HLA-B27 and HLA-DR2 subtypes revealed a shared structural motif between HLA-B27 and the DR2 B5*0101 chain, which could be related to the observed cross-reaction. This motif was contributed for by several residues located in adjacent beta strands, at the floor of the peptide-binding site. The contribution of two of these residues, as well as other beta-pleated sheet residues to HLA-B27 allorecognition by the cross-reactive CTL clones was directly demonstrated with site-directed mutants. These results suggest that the dual reactivity pattern reflects presentation of identical or structurally related peptide by HLA-B27 and HLA-DR2Dw2. As T cell cross-reactivity between HLA-B27 and HLA-DR2 was previously found in cells from an unrelated individual the results reported here are likely to reflect an intrinsic property of HLA-B27, rather than the fortuitous finding of a rare clonal reaction pattern. We speculate on the potential implications of these results for the pathogeny of HLA-B27-associated spondyloarthropathies.