Natural soluble human leukocyte antigen class I in donor serum neutralizes donorspecific HLA alloantibodies in recipient serum
Dong Il Won1, Nan Young Lee1, Jeong-Hoon Lim2, Young Seok Han3, Chan-Duck Kim2, Seung Huh3
1Department of Clinical Pathology, 2Department of Internal Medicine, 3Department of Surgery, School of Medicine, Kyungpook National University, Daegu, Korea
Correspondence to: Dong Il Won, M.D., Ph.D.
Department of Laboratory Medicine, Kyungpook National University Hospital, 130 Dongdeok-ro, Jung-gu, Daegu 41944, Korea
E-mail: wondi@knu.ac.kr
Published online: May 20, 2020.
© The Korean Journal of Hematology. All rights reserved.

Abstract
Background: Human leukocyte antigen (HLA) molecules are cell-bound but can be identified in a soluble form. These soluble HLA (sHLA) molecules have an immunomodulatory function. We investigated whether natural sHLA in donor serum can neutralize donor-specific HLA alloantibodies (DSAs) in recipient serum.
Methods: Neutralizing effects of donor serum on DSAs in recipient serum were measured using inhibition assay principle of flow cytometric crossmatch (FCXM), performed using sera from 143 kidney transplant recipients and their donors. The adding of donor serum to recipient serum yielded lower mean fluorescence intensity (MFI) ratios (test/control) than when diluent was added [Roswell Park Memorial Institute (RPMI) or third-party serum]; presuming it was caused by neutralizing effects of sHLA.
Results: In the recipient group with class I DSAs alone (N=14), donor serum addition to recipient serum resulted in lower T cell MFI ratios [2.25 (1.31–32.51)] than those observed on RPMI addition [3.04 (1.33–125.39), P<0.05]. In the recipient group with class II DSAs alone (N=27), donor serum addition showed no significant difference in B cell MFI ratios [5.03 (1.41–103.53)] compared to diluent addition: RPMI [4.50 (1.34–145.98)] or third-party serum [5.08 (1.44–138.47)], P>0.05 for both.
Conclusions: Using inhibition FCXM, we verified that natural sHLA class I in donor serum neutralizes DSAs in recipient serum. However, no neutralizing effects of sHLA class II were revealed in this study. These potentially beneficial effects of sHLA infused via blood-derived products should be considered when desensitizing highly HLA-sensitized patients.
Keywords: Soluble HLA, Donor-specific HLA alloantibody, Neutralization, Flow cytometric crossmatch


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