OR28: DISCREPANT HLA-DQ EPITOPE EXPRESSION ON SINGLE ANTIGEN BEADS VERSUS B CELLS CARRYING THE SAME HLA-DQA1∗/DQB1∗ ALLELES

Abstract

Aim Predicting virtual crossmatch (XM) results for patients with DQ antibodies has been challenging and a number of explanations have been set forth including structural variations of the DQA/DQB heterodimers, non-native epitopes among solid phase beads, and level of expression of HLA-DQ molecules on donor cells. We compared reactivity of anti-DQ antibodies using Luminex bead assays to reactivity with B cells using flow cytometry. Methods The reactivity of 4 anti-DQ specific sera (Table 1) were evaluated by Luminex Single Antigen (LSA) and phenotype-panel beads, and flow cytometry. Results Serum TE reacted strongly with beads carrying DQ4, 5, and 6 specificities. In contrast its reactivity with B cells carrying these specificities varied significantly based on the DQA/DQB allele combinations (Table 2). Strikingly, cell# 8, 9, 10, and 11 carrying the DQB1∗05:01, DQA1∗01:01 alleles were not reactive with serum TE (Table 2) despite a high level of surface expression of these molecules on these cells as assessed by serum AT (Table 3). Serum AA also failed to react with a DQB1∗05:01, DQA1∗01:01 cell (Table 3). Conclusion The expression of HLA-DQ epitopes on SA beads is not always concordant with that of B cells carrying the same DQA1∗/DQB1∗ alleles. Thus, reactivity of anti-DQ antibodies with SA beads does not always accurately predict their reactivity with B cells expressing the same alleles.