Relevance Of MICA Alleles And MICA Antibodies And Posttransplant Rejection In Clinical Organ Transplantations

IntroductionThe HLA matching rate between donors and recipients is correlated withposttransplantation rejection and survival, and rejection can often be attributed toHLA mismatch. However, studies have also shown that transplant failure can occurin HLA-identical living-related donor (LRD) transplantations, suggesting the needto identify non-HLA antigens that lead to graft failure. Successive studies haveindicated that non-HLA antigens contribute substantially to transplant failure inHLA-identical donor transplants.MHC class–related chain A (MICA) is a non-classical Class gene with67MICA alleles found in the major histocompatibility complex (MHC) in tightlinkage disequilibrium with the human leukocyte antigen-B gene locus (HLA-B).Unlike classical class molecules, the MICA protein without β2-microglobulinbinding is expressed on the cell surface of endothelial cells, which makes thispolymorphic molecule a target for both cellular and humoral immune responses.MICA has many alleles and its diversity resides in different races and ethnicgroups. The polymorphic MICA gene can inducing graft versus host reaction(GVHR) or host versus graft reaction (HVGR) in transplantation, and a series ofstudies have shown that antibodies to this highly polymorphic molecule have beendetected in patients who have undergone transplantations. Moreover,allograft-induced MICA antibodies have been implicated in transplant failure. Frequently, patients who have experienced posttransplant rejection had more HLAand MICA antibodies than those with functioning grafts.Presently, there are no reports of MICA alleles matching prior to LRDtransplantations. Therefore, the MICA matching rates between recipients anddonors we studied to evaluate their potential impact on posttransplant rejection inHLA-identical LRD organ transplantations.ObjectiveIn order to investigate the correlation between matching rate of MICA allelesand posttransplant rejection in clinical living related donor transplantation (LRD),blood samples were detected for HLA and MICA matching through polymerasechain reaction with sequence specific primers. Our further purpose was to find theevidence of MICA taking part in organ transplantations, excluding the influence ofHLA and HLA Abs. With the detection results of Abs to MICA in selectedrecipients after transplantations, we would demonstrate the relevance betweenMICA matching rate, Abs against doners’ MICA antigen and posttransplantoutcome. Finally, we could offer an dependable prognostic index for LRDtransplantation, with reasonable theory of MICA mathching before transplantaionsby experimental result to avoid posttransplant rejection as possible.Methods1. Extracted whole blood samples were collected from donors and recipients ofliving-related transplantion including4cases small bowel transplantation,6casesof liver transplantion and10cases of kidney transplantion. DNA of all cases wasextracted from whole blood or pathological sections using HLA-MorgantmABDRSSP Kit (Texas BioGene, Inc) according to the manufacturers’ instructions. HLAtyping between recipients and donors (all alleles of HLA-A, HLA-B, HLA-DR)were performed by sequence-specific primers (PCR/SSP) and analisis of gel electrophoresis.2. To design synthetic primer of most frequent MICA genetype in northernChinese Han population, we looked up literature repeatedly. Finally, we selectedthe highest8frequent MICA genotypes. MICA alleles matching rate betweenrecipients and donors were determinated by polymerase chain reaction based onsequence-specific primers (PCR-SSP) and analisis of gel electrophoresis.3. Selected18living patients’ sera was collected at2,4,6,8,10,12monthesafter transplantations. Abs to MICA alleles were determined using LABScreenassay by Luminex Technology, according to the manufacturer’s specifications(One Lambda, Canoga Park, CA) using96-well filter plates. Serum samples ofsubjects were tested at1:3dilution for Abs against a panel of10MICA alleles(MICA*001,*002,*004,*007,*009,*012,*017,*018,*019, and*027). Themean fluorescent signal was measured using LABScan and analyzed byHLA-VisualTM.4. All selected recipients’ histopathology slides from2weeks to6months afterthe transplantations were diagnosed independently by two permanent pathologistsunder light microscopy. Biopsy samples were divided into three different levelswith Banff standard.5. All selected allografts survival was recorded, binding clinical condition andimmunosuppressive therapy.6. Statistic analysis was performed for HLA/MICA matching rate, pathologicallevel and grafts survival depending on acquired data.Results1. HLA matching results of the20blood samples from the donors–recipientpairs were all half-matching (Figure1). Almost all HLA-A, HLA-B, and HLA-DRalleles (including those newly published from1996to2004) were detected by96 series of primer amplifications. The samples were considered HLA half-matchingbased on computer software analysis and interpretation.2. In spite of the same benchmark for HLA half-matching, the matching rate ofMICA between recipients and donors was irregular among the different LDRtransplantations. The PCR-SSP results between donors and recipients of the8frequent MICA genotypes which include13alleles in LRD organ transplantationsare shown in Figure2. Our research indicates that better MICA matching ratesbetween recipients and doners correspond relatively to less posttransplant rejectionand longer survival. Otherwise then opposite.3. Detection results of Abs level to MICA showed the same tendency withMICA matching rate, wich means the high detection rate in recipients withposttransplant rejection. We found that the lower MICA matching rate with themore episode of rejection, the higher intensity of MICA-PRA antibodies. Based onthe result of mean fluorescent signal (MFI), we propose that MICA-PRAantibodies have an effect on acute and chronic rejection.4. In conclusion, we have demonstrated the relationship of MICA matching rateand posttransplant outcomes from the standpoint of pretransplant matching. Ourresearch indicates that better MICA matching rates correspond relatively to lessposttransplant rejection and longer survival; therefore, the poor graft survival inour series of HLA-identical LRD organ transplantations could be explained byMICA incompatibility between recipients and donors. Based on our results,detection of MICA matching rates between donors and recipients before clinicaltransplantations could be used for prognostication of posttransplant outcomes.Closer MICA matching needs to be considered to improve graft outcomes amongsensitized recipients.