DR-restricted T-cell reactivities associated with the Dw19 specificity can be directed against the products of either locus DRB3 (DRw52c) or locus DRB1.

HLA-Dw 19 antigen presenting cells express two different DR beta chains encoded respectively by DRB1 and DRB3 genes. In the present study we determined which of these two DR beta chains is recognized by DR-restricted T-cell clones. First we selected influenza-specific, DR-restricted T-cell clones of which restriction is strictly associated with the Dw19 specificity. Then we characterized by oligonucleotide typing one antigen presenting cell (HC12M) which exhibits a new haplotype associating a DRB1 gene highly related or identical to that from Dw 18 haplotypes with a DRB3 gene highly related or identical to that from Dw19 haplotypes. Finally, by testing the reactivity of the selected T-cell clones against Dw18, Dw19, and HC12M antigen presenting cells, we show that these DR-restricted "Dw19-specific" effectors can recognize either the DRB1-encoded chain present only on Dw19 antigen presenting cell or the DRB3-encoded chain shared by Dw19 and HC12M antigen presenting cells. Interestingly, our results show that DRB1 chains from Dw19 and Dw18 which differ by a single amino acid substitution at position 86 may be distinguished by T cells, implicating that this residue plays a role in T-cell recognition of HLA-DR-antigen complex. The implication of our results with regard to the new nomenclature of HLA specificities defined by T-cell clones will be discussed.