Antibodies to private and public HLA class I epitopes in platelet recipients

BACKGROUND: Transfusions or pregnancies can cause immunization against priv ate HLA determinants and public epitopes shared by more than one private HL A antigen. HLA antibodies are correlated with febrile transfusion reactions , lower platelet response following platelet transfusion, and an increased rate of renal transplant rejection. Until now, antibody specificities in al loantisera from platelet recipients have been poorly characterized. STUDY DESIGN AND METHODS: Consecutive serum screens from platelet recipient s were analyzed for antibodies against private HLA class I antigens and pub lic HLA epitopes using a serum analysis program based on the 2 x 2 table an alysis of correlations. Serum screens of highly immunized patients and of p atients with new alloimmunization events were reviewed separately. RESULTS: Of the serum screens from 566 platelet recipients, 1577 indicated alloimmunization (panel-reactive antibodies >5%). The program assigned a sp ecificity in 1024 of these screens (64.9%) and at least once in 522 of 566 patients (92.2%). In 267 patients, antibodies detecting public epitopes in the combined A- or B-locus cross-reacting groups were found; other public m arkers were detected in 39 patients. Patterns of reactivity were remarkably less stable than in patient groups previously studied. In many patients, a ntibodies with apparent private epitope specificity preceded the identifica tion of antibodies against a shared marker of the same cross-reactive group . However, the disappearance of antibodies (whether or not this was followe d by a new antibody against a private or public marker belonging to another cross-reacting group) was also observed. CONCLUSION: The computerized analysis of microlymphocytotoxicity tests enha nces the rate of antibody specification in sera from platelet recipients wi th lymphocytotoxic antibodies. The identified antibodies should be taken in to account in the selection of platelet donors. The data confirm and extend previous observations on HLA class I antibodies and elucidate new alloimmu nization events.