Case report: binding of a clinically relevant human leukocyte antigen-DQα-specific antibody in a kidney graft recipient is inhibited by donor-type human leukocyte antigen-DQβ chain.

In this case report, we have found what may be an immunization with donor-specific human leukocyte antigen (HLA)-DQα in combination with recipient-specific HLA-DQβ. A renal allograft recipient who did not comply with immunosuppressive therapy during pregnancy had graft failure 23 months posttransplantation with biopsy-proven humoral and cellular rejection. Sera were tested in a Luminex-based single-antigen bead assay. We compared Luminex reactivity with the degree of eplet mismatching between the recipient's own HLA-DQ chains and the HLA-DQ chains bound to the Luminex beads. Eplet calculations were done with the HLAMatchmaker. HLA-DQ similarities were compared further by dissimilarity scoring in HistoCheck. We observed that Luminex beads with donor-type HLA-DQα and HLA-DQβ bound less antibody than beads with donor-type HLA-DQα combined with recipient HLA-DQβ. In HLAMatchmaker, we identified all eplet mismatches between donor and recipient HLA-DQ. Next, we counted how many of these eplets were represented on the various Luminex beads. We found that antibody binding to the bead increased with the number of such mismatches for HLA-DQα. Surprisingly, antibody binding decreased as the number of eplet mismatches for HLA-DQβ increased, from a mean fluorescence intensity (MFI) value of 18,800 for no mismatched eplets to approximately 10,000 for 12 mismatched eplets. These findings were confirmed by comparing antibody binding with the structural dissimilarity score between the recipient HLA-DQ type and the HLA-DQ bound to the Luminex beads. In this patient, clinically relevant antibodies bound strongly to donor-like HLA-DQα chains when combined with recipient-like HLA-DQβ. HLA-DQβ chains more similar to those of the donor reduced the binding of donor- specific HLA-DQα antibody.