Meaning of HLA Antibodies Frequently Detected by Single Antigen Bead Assay

Abstract

Introduction: Single Antigen Bead (SAB) assay to detect HLA antibodies is the highly sensitive and specific technique. Nowadays, almost patients awaiting a transplantation performed SAB assay to determine unacceptable HLA antigens, and waiting time for transplantation from deceased donors was considered. Because of inherent limitation of SAB kits, which use recombinant technology, false reactivity to denatured antigens could happen. False reactivity affects donor selection and waiting transplantation time. We investigated SAB data to examine false reactive results. Methods: We tested 155 pre-transplanted and 45 post-transplanted sera for anti-HLA antibodies using panel kit and SAB kit (LABScreen Luminex kits, One Lambda, Canoga Park, CA, USA). Negative Control Beads (NC) value was below 500 mean fluorescent intensity (MFI) and Positive Control Beads (PC) value was over 5000 MFI in all results. Results: In panel kit analysis, 27% of patients were positive for HLA antibodies. Sixty-four percent of patients were positive at least one HLA antibodies on SAB assay even negative in panel kit analysis. MFI of detected HLA antibodies, which were from sera for negative in panel kit and positive in SAB kit, was under 3000 in 70.9% and between 3000 and 10000 in 25.6% in Class I SAB assay, and under 3000 in 80.7% and between 3000 and 10000 in 17.1% in Class II SAB assay. Comparison with allele frequencies from our laboratory HLA typing (n = 785), three-times high frequent HLA antibodies were HLA-A*11:02 (6%), A*80:01 (4.5%), B*15:12 (10.5%), C*17:01 (18.5%), C*18:02 (4.5%), DRB1*04:04 (6.5%), DRB1*16:01 (6.5%), DRB1*16:02 (5.0%), DQ2 (A1*05:01/B*02:01; 15.5%), DQ7 (A1*05:03/B1*03:01; 6.5%, A1*05:05/B1*03:01; 7.5%, A1*06:01/B1*03:01; 4.5%), DQ8 (A1*03:02/B1*03:02; 7.5%), DQ9 (A1*03:02/B1*03:03; 6.5%), DP1 (A1*01:03/B1*01:01; 8.5%, A1*02:01/B1*01:01; 5.0%), and DP5 (A1*02:02/B1*05:01; 7.5%). Conclusion: HLA antibody with higher detection frequency than allele frequency of population was considered false reactive antibody, because a possibility of exposure would be very low. Most of false reactive HLA antibodies showed under 3000 MFI. Erroneous interpretation about HLA antibodies for patients awaiting transplantation impact on donor selection and waiting time calculation. Studying for frequently seen false reactive HLA antibody could help relevant SAB results.