INVOLVEMENT OF CLASS-II BETA-CHAIN AMINO-ACID RESIDUE-85 AND RESIDUE-86 IN T-CELL ALLORECOGNITION

Alloreactive T-cell clones were derived by limiting dilution following priming to allogeneic cells during HLA-DR1 alloantigens. Clonal specificities were determined by extensive testing on a panel of allogeneic lymphoblastoid cell lines and by blocking studies with monoclonal antibodies specific for HLA-DR, -DQ, and -DP class II molecules. Out of nine DR1-positive cell lines, three failed to stimulate a subset of the T-cell clones in conventional proliferation assays. Proliferation by all of the clones was blocked by anti-DR antibodies, not by anti-DQ or anti-DP, which was consistent with the conclusion that the HLA-DR molecule was recognized. This DR1-associated polymorphism has been identified as Dw20 by the Tenth International Histocompatibility Workshop. The molecular basis for this altered recognition of the DR1 molecule was determined by allele-specific oligonucleotide hybridization and by DNA sequencing studies. The first, second, and third hypervariable regions of all nine DR1-positive cell lines were identical. Valine and glycine were found at positions 85 and 86 of the DR1β1 chain in DR1 molecules from six of the nine lymphoblastoid cell lines, whereas alanine and valine were found in the three variant (Dw20) DR1-positive cells. By analogy with class I structure, residues 85 and 86 would be located at the extreme C-terminal end of the β-chain α helix. Together or separately, these amino acid differences may define a T-cell recognition element on the DR1 molecule serving to contact allospecific T-cell receptors. Alternatively, if allorecognition involves recognition of a self peptide complexed with an allogenic MHC molecule, then it is possible that the differences T cells recognize on DR1 class II proteins arise from peptide-specific interactions with residues 85 and 86. © 1990.