False-positive reactions against HLA class II molecules detected in Luminex single-antigen bead assays

Anti-donor HLA-specific antibodies (DSA) are associated with poor graft outcomes in renal transplantations [1, 2]. Panel reac- tive antibody (PRA) assays using the Luminex platform are commonly used to detect DSA. PRA assays are performed by using three different panels: 1) pooled antigen panels that use bead populations coated in affinity-purified HLA molecules ob- tained from multiple cell lines, which are used as screening tests; 2) phenotype panels that use bead populations bearing HLA proteins from a cell line derived from a single individual; and 3) single-antigen bead (SAB) assays that use beads coated in molecules representing a single cloned allelic HLA antigen [3]. Each bead population in phenotype panels features more than one type of HLA molecule, thus requiring expertise to inter- pret the results, whereas SAB assays provide accurate identifi- cation of HLA antibodies [3]. However, cloned HLA antigens are not in their native state. Purification and bead coating can lead to conformational changes that could cause binding of clinically irrelevant antibodies [4-9]. Here, we report a case with sus- pected false reactions against denatured HLA class II molecules in SAB assays. KCI Citation Count: 4