Detection of HLA-C and HLA-DP antibodies in Hong Kong renal patients with antibody-mediated rejection

Abstract

Background: Apart from cell-mediated rejection, antibody-mediated rejection (AMR) also poses serious challenge to successful renal transplantation with detrimental consequences. Human leucocyte antigen (HLA) has been widely recognized as a major target antigen of antibodies eliciting immune responses against the graft. Due to low expression level on renal endothelial cells and lack of reliable assays in detecting HLA-C and –DP antibodies in the past, the clinical impact of these antibodies on graft rejection has long been overlooked and remains poorly understood. With the invention of single antigen bead assays that have been proven to be sensitive and specific for detecting HLA antibodies, the role of HLA-C and –DP antibodies in graft rejection can be extensively explored. Reports and clinical studies have emerged manifesting the significance of HLA-C and –DP antibodies in AMR in the past decade. The impact of HLA-C antibodies on graft survival has been less studied than that related to HLA-DP antibodies.

Aim: To analyze the incidence of HLA-C and -DP antibodies in both AMR and non-AMR renal patients before and after transplantation and investigate the relationship between the presence of donor-specific antibodies (DSA) and the occurrence of AMR in both HLA-C and -DP loci.

Methods: A total of 269 and 285 post-transplant serum samples were tested for the presence of HLA-C and –DP antibodies respectively using LIFECODES Single Antigen (LSA) assay. 34 and 46 patients positive for HLA-C and –DP antibodies respectively were selected and pre-transplant sera were screened for the presence of any pre-existing antibodies by LSA assay. The corresponding donors of patients positive for HLA-C or HLA-DP antibodies were investigated further to determine if the antibodies were donor-specific. Deoxyribonucleic acid (DNA) was extracted from the donors’ buffy coats by in-house extraction method. 23 and 21 donors were typed for HLA-C and HLA-DP respectively by Polymerase Chain Reaction-Sequence -Specific Oligonucleotide (PCR-SSO) assay.

Results: HLA-C antibodies were detected at a higher frequency in the rejected group (21.3%) than in the functioning group (10.8%) while HLA-DP antibodies were detected at a slightly higher frequency in the AMR group (22.4%) than in the non-AMR group (14.5%). The overall frequencies of detecting HLA-C antibodies and -DP antibodies in post-transplant renal patients were 12.6% and 16.1% respectively. The results showed correlation between the occurrence of AMR and the presence of HLA-C antibodies (p = 0.0498), but such association was not observed in HLA-DP antibodies (p = 0.146). In over 80% patients, HLA-C and –DP antibodies were found to be newly formed after transplantation. The percentage of detecting HLA-C DSAs in AMR patients (57.1%) was significantly higher than that in non-AMR patients (12.5%). In contrast, the percentage of detecting HLA-DP DSAs in patients with AMR (25%) was slightly lower than that found in non-AMR patients (30.8%). The findings showed that the occurrence of AMR was associated with the presence of HLA-C DSAs (p = 0.045), but HLA-DP DSAs did not appear to be directly related to AMR. (p = 1).

Conclusion: HLA-C and -DP antibodies were detected at a higher frequency in the rejected group, but the difference was only statistically significant for HLA-C antibodies. Both HLA-C and -DP antibodies were found to be newly formed after transplantation in most patients. HLA-C DSAs was found to be related to the occurrence of AMR, but such association was not observed in HLA-DP DSAs.