Antibodies to crossreactive HLA antigens. Evaluation by cytotoxicity, flow cytometry, and inhibition of monoclonal antibody binding.

Broadly sensitized patients have antibodies that react with cells from most individuals except those having HLA antigens similar to their own. In this work we addressed the question of whether crossreactive antigens could also be considered compatible. Broadly reactive sera were tested in multiple experiments against lymphocytes selectively mismatched for only one HLA-A, B antigen. Antibodies, measured by cytotoxicity and flow cytometry, were detected in most cases, and their prevalence was the same, regardless of whether the mismatched HLA antigen was crossreactive with the patient's. There were several patients bearing one of the A2, B5, or B7 crossreactive group antigens with antibodies against another antigen of the group. Anti-HLA-A2 reactivity was further evaluated by testing the inhibitory effect of broadly reactive sera on the binding of an anti-HLA-A2 monoclonal antibody. Anti-A2 reactivity measured in this assay was detected in A28-positive patients as frequently as in A28-negative patients. These results suggest that antigens of several crossreactive antigen groups are significantly immunogenic and elicit antibodies as often as noncrossreactive antigens. Further studies are necessary to evaluate other less-frequent antigen combinations.