HLA Class II reactive sera from kidney allograft recipients: detection of antibodies specific for epitops of DQ and DP alpha/beta chains

Aim: All preformed HLA antibodies have a deleterious impact on kidney graft outcome. Alpha and beta chains of DQ and DP molecules can elicit a humoral immune response. Methods: In 191 HLA class II-positive renal transplant recipients we investigated the incidence of DQ and DP alloantibodies by Single antigen beads coated with 29 DQA1/DQB1 and 24 DPA1/DPB1 heterodimers (One Lambda Inc). We also analyzed the putative epitopes for antibody formation by analysis of amino acid sequences of molecules corresponding to detected specificities. All patients were DQA1/DQB1 and/or DPA1/ DPB1 typed by SSP assays. Results: Anti-DQ antibodies were detected in 126 patients. Ninety-four (75%) had had a previous transplant; 14 of these only developed anti-DQ antibodies. Seventy-one percent of patients had anti-DQB1 antibodies, 2% had anti-DQA1 and the remaining 29% had both. As for the epitopes that might determine antibody-patterns development, 28 epitopes were identified (11 for DQA1 and 17 for DQB1); 7 epitopes had not been reported yet (DQA1: 41K/130A0103; 50L02, 03; 52R03, 04, 05, 06; 69T04, 06; 75I01, 02, 03, 04, 06; 160D0302, 0303. DQB1: 87Y05, 0604/05/07/09). Anti-DP antibodies were detected in 64 patients. Fifty-one (80%) had had a previous transplant; 6 of these only developed anti-DP antibodies. Eightyone percent of patients had anti-DPB1 antibodies, 3% had anti-DPA1 and the remaining 16% had both. As for the putative epitopes, we identified 1 epitope characteristic of DPA1 and 10 epitopes characteristic of DPB1 molecules. Nine DPB1 epitopes were located in the 6 hypervariable regions of exon 2 of the DPB1 alleles, while one epitope (96R:*02, 04, 17, 23, 28) was outside of these regions. Conclusions: These data show that both alpha and beta chain epitopes of DQ and DP molecules are immunogenic and indicate the importance of epitope-identification studies.