Characterization of HLA class I specific antibodies by ELISA using solubilized antigen targets: II. Clinical relevance.

Until recently, the nature of humoral sensitization to HLA has been characterized by data from lymphocyte-based assays, predominantly cytotoxicity tests. We have examined the characteristics, determined by enzyme-linked immunosorbent assay (ELISA), of sera from 191 subjects known to have produced HLA-specific antibody. We found that ELISA detected higher frequencies compared with cytotoxicity of many (74.5%), but not all, HLA-specific antibodies; in many cases (42.6%) the frequencies of these antibodies were higher than predicted from population frequencies whereas some antibodies (23.4%) occurred with lower than expected frequencies. Some of the increase in frequencies can be accounted for by crossreactivity, i.e., sensitization to epitopes shared among two or more allelic products. The presence of epitopes shared between a recipient's antigen and a mismatched antigen in a donor also tended to narrow the specificity of antibody produced. However the data also indicate differences in immunogenicity among different antigens suggesting that crossreactive group matching would be beneficial in some but not all cases. Finally, we present case studies to illustrate the value of ELISA in predicting humoral rejection episodes and in monitoring the efficacy of rejection therapies.