An antiviral T-cell clone defines a functional supertypic specificity shared by different HLA-DR molecules from DR2-short, DRw11, and DRw13 haplotypes

A novel T-cell-defined HLA-DR polymorphism not predicted from the linear amino acid sequence

Recent investigations have shown that alloreactive T cells are capable of responding to structures defined by specific linear amino acid sequences on class II molecules. In the present study we show that also a polymorphism can be recognized that is not defined by such linear amino acid sequences. Two human T-cell clones, sensitized to DRw13 haplotypes, are described. The description of clone c50 serves to exemplify the first model. This DRB1-specific clone responds to stimulator cells that carry DR molecules, different in their DRB1 first and second hypervariable regions (HV1 and HV2) but identical in their HV3 regions (i.e., DRw13,Dw18; DRw13,Dw19; DR4,Dw10; and DRw11,LDVII). The second clone, c1443, behaves nonconventionally. It responds to DRw13,Dw18; DRw13,Dw19; and DR4,Dw4 stimulator cells, although no specific amino acid sequence is shared between these specificities. The latter pattern of reactivity suggests the existence of a novel polymorphism recognized by alloreactive T cells. This particular polymorphism may also be biologically significant.

Both HLA-DR and HLA-DQ determinants contribute to HLA-Dw typing

The respective contribution of HLA-DR and HLA-DQ gene products in the induction of allogeneic proliferative responses in primary mixed lymphocyte reaction and, therefore, in HLA-Dw typing, is still unclear or controversial. This is in part due to a strong linkage disequilibrium between HLA-DR and -DQ genes. We used DR- or DQ-restricted influenza-specific T-cell clones to define DR and DQ products on a large panel of allogeneic antigen presenting cells. With this functional screening assay, we identified two haplotypes with unusual DR/DQ associations. Cells of these haplotypes were then used as responder cells in mixed lymphocyte culture and stimulated by homozygous typing cells displaying DR or DQ incompatibilities. Our results indicate that DR or DQ incompatibilities alone can give rise, in both cases, to strong T-cell proliferation in a mixed lymphocyte reaction. This was further verified by blocking experiments of secondary mixed lymphocyte reactions by HLA-specific monoclonal antibodies. Anti-DQ, but not anti-DR, antibodies inhibited DQ-incompatible responses. Conversely, anti-DR, but not anti-DQ, antibodies could block DR-incompatible mixed lymphocyte reactions. Together, the results suggest that both HLA-DR and DQ gene products can be involved in HLA-Dw typing. Finally, in dual DR- and DQ-incompatible mixed lymphocyte reaction combinations, HLA-DR molecules seem to have an immunodominant effect, because the response is mostly inhibited by anti-DR antibodies. Immunodominance of HLA-DR allodeterminants may, at least in part, explain some of the controversial conclusions reported by others concerning the role of HLA-DQ molecules in HLA-Dw typing.