FALSE POSITIVE REACTION AGAINST 73ID EPLET IN SINGLE ANTIGEN BEAD ASSAY

The purpose of this study was to investigate possible false-positive reactions against HLA-A*31:01, -A*33:01, and -A*33:03 beads in One Lambda single antigen bead assay (OL-SAB) solely explained by the 73ID eplet (73ID profile). As this eplet is also present in A*02:11, not represented in the OL-SAB panel, the reactivity with HLA-A31, -A33 has been used as surrogate for A*02:11 antibodies. The study included sera from seven patients with the 73ID profile that were tested with untreated and acid-treated OL-SAB, adsorption/elution (A/E) experiment and flow cytometry crossmatch (FCXM). The results showed increased MFI in acid treated beads, lack of antibody recovery in A/E assays, negative FCXM with all cells. These data indicate that the 73ID eplet is only accessible in denatured HLA molecules. Therefore, the reactivities solely against HLA-A31, -A33 in the OL-SAB are likely false-positive and are not reliable surrogate markers for A*02:11 antibodies.