P134 Antibodies to inter-locus shared DR11 and DP epitope: Characterization and analysis consideration

Abstract

Aim Antibodies (AB) to shared HLA epitopes can result in a single sensitizing event conferring incompatibility with a large percentage of donors. In addition, apparent AB strength on Luminex single antigen bead (SAB) assays can be artificially lowered, impacting virtual crossmatch (XM) assessment. ”DEE” and ”DED” epitopes at position 55–57 on DPB1 are known to be immunogenic. Our goal was to further characterize these AB in our patient population, with an interest in the ”DEE” epitope present at position 57–59 on DRB1. Methods Patients with DP AB to either DPB1∗04:02 (DEE) or DP14 (DED) were queried, and SAB results reviewed for reactivity to known immunogenic DP epitopes (DED - DP3, 6, 9, 14, 17, 20; DEE - DP2, 04:02, 10, 18, 28). AB to DR antigens were also noted, as well as patient HLA typing. To confirm AB cross-reactivity to shared sequence, a serum with AB to multiple DP epitopes (DPA1∗02/04, DED/DEE, and DEAV) was adsorbed using lymphocytes containing just the DEE epitope. Results Patients who lacked DED and DEE on their cells formed an AB of combined specificity: 35 to DED/DEE, and another 25 to DED/DEE plus other DP antigens. Of 8 patients with isolated DEE DP AB, typing identified DED epitope in 5 (no typing available for 2); of 7 patients with isolated DED DP AB, typing identified DEE epitope in 3 (no typing available for remaining 4). DR11 AB were co-present in 60 of 68 patients containing DEE DP AB (with or without other specificities); of the patients without DR11 AB for whom typing was available, all 6 typed as DR11. None of the 7 patients with isolated DED AB had DR11 AB, only 2 of whom typed as DR11. Eluate from the adsorption study reacted exclusively with DED and DEE DP antigens as well as DR11. Conclusions DED and DEE are immunogenic epitopes on HLA-DP, although specificity can be to either or both depending on self-antigens. DEE and combined DED/DEE antibodies (but not DED) cross-react with DR11 due to a shared epitope. However, if DR11 is a self-antigen it’s possible to form DP-exclusive DEE AB, confirming that DR-specific sequences outside the ”DEE” epitope are important. AB to shared epitopes are important to recognize because they can cause positive flow XM despite low MFI on SAB.