High resolution molecular phototyping of MICA and MICB alleles using sequence specific primers

Major Histocompatibility Complex Class I Chain-Related A and B (MICA and MICB) Gene, Allele, and Haplotype Associations With Dengue Infections in Ethnic Thais

BACKGROUND

Major histocompatibility complex class I chain-related (MIC) A and B (MICA and MICB) are polymorphic stress molecules recognized by natural killer cells. This study was performed to analyze MIC gene profiles in hospitalized Thai children with acute dengue illness.

METHODS

MIC allele profiles were determined in a discovery cohort of patients with dengue fever or dengue hemorrhagic fever (DHF) (n = 166) and controls (n = 149). A replication cohort of patients with dengue (n = 222) was used to confirm specific MICB associations with disease.

RESULTS

MICA*045 and MICB*004 associated with susceptibility to DHF in secondary dengue virus (DENV) infections (odds ratio [OR], 3.22; [95% confidence interval (CI), 1.18-8.84] and 1.99 [1.07-2.13], respectively), and MICB*002 with protection from DHF in secondary DENV infections (OR, 0.41; 95% CI, .21-.68). The protective effect of MICB*002 against secondary DHF was confirmed in the replication cohort (OR, 0.43; 95% CI, .22-.82) and was stronger when MICB*002 is present in individuals also carrying HLA-B*18, B*40, and B*44 alleles which form the B44 supertype of functionally related alleles (0.29, 95% CI, .14-.60).

CONCLUSIONS

Given that MICB*002 is a low expresser of soluble proteins, these data indicate that surface expression of MICB*002 with B44 supertype alleles on DENV-infected cells confer a protective advantage in controlling DENV infection using natural killer cells.

Prognostic value of MICA/B in cancers: a systematic review and meta-analysis

Purpose

MHC class I chain related-proteins A (MICA) and B (MICB) are natural killer group 2D ligands that mediate tumor surveillance. Several studies have suggested that MICA/B levels predict clinical outcomes in patients with cancer; however, this remains contentious. Here, we present a systematic review and meta-analysis of available studies of the prognostic value of MICA/B in cancer.

Materials and Methods

We searched PubMed, Embase, Clinicaltrials.gov, and Cochrane Library to identify studies published from inception to July 2017 that assessed MICA/B in patients with cancer. The hazard ratio (HR) and 95% confidence interval (CI) of MICA/B were extracted for overall survival (OS) analysis.

Results

A total of 19 studies comprising 2,588 patients with 10 different types of cancer were included in the study. Low sMICA/B levels were found associated with significantly longer OS (HR = 1.65, 95% CI [1.42–1.92], P < 0.00001). Patients with cancers of digestive system that exhibited high MICA/B expression had significantly longer OS in (HR = 0.56, 95% CI [0.39–0.80], P = 0.002) compared with those with lower MICA/B expression (I² = 35%, P = 0.18).

Conclusions

Serum soluble MICA/B represents a potential prognostic marker in various human cancers. High cell-surface MICA/B expression in cancers of the digestive system was found associated with increased survival.

MICA Gene Deletion in 3411 DNA Samples from Five Distinct Populations in Mainland China and Lack of Association with Nasopharyngeal Carcinoma (NPC) in a Southern Chinese Han population

Deletion of major histocompatibility complex class I chain-related genes A (MICA*Del) was investigated in 3,411 DNA samples from two southern Chinese Han populations (Hunan Han, HNH; Guangdong Han, GDH), two northern Chinese populations (Inner Mongolia Han, IMH; Inner Mongolia Mongol, IMM) and one southeastern Chinese Han population (Fujian Han, FJH) using an in-house polymerase chain reaction-sequence specific priming (PCR-SSP) assay, which enables direct discrimination between heterozygote and homozygote for MICA*Del. MICA*Del showed a frequency ranging from 0.8% in FJH to 5.7% in IMM (P_corrected < 0.05), indicating northward increase in frequency of MICA*Del in Chinese populations. In contrast to the association reported recently in a Taiwan Chinese population and a Malaysian Chinese cohort, MICA*Del distribution did not differ between 1,120 patients with nasopharyngeal carcinoma (NPC) and 1,483 normal controls in the HNH population (1.03% in NPC cases vs 1.18% in the controls, OR (95% CI) = 0.87 (0.51-1.47), p = 0.69). Further gender-stratified analysis also failed to disclose any male-specific association reported in a Taiwan Chinese population. Multi-locus typing of the 94 samples carrying MICA*Del revealed two new haplotypes, HLA-A*11:01-B*13:01-MICA*Del-MICB*009N-DRB1*04:06 and HLA-B*35:01-MICA*Del-MICB*009N-DRB1*15:01, in addition to HLA-B*48-MICA*Del. Unexpectedly, two samples with MICA*Del in the HNH population were each consistently found to have two distinct MICA alleles, indicating the existence of two MICA gene copies on certain HLA haplotypes. Based on the results from a sizeable case-control study, our data suggest that there is no association between MICA*Del and NPC in the southern Chinese Han population.

Alternative Splice Transcripts for MHC Class I-like MICA Encode Novel NKG2D Ligands with Agonist or Antagonist Functions

MHC class I chain-related proteins A and B (MICA and MICB) and UL16-binding proteins are ligands of the activating NKG2D receptor involved in cancer and immune surveillance of infection. Structurally, MICA/B proteins contain an α3 domain, whereas UL16-binding proteins do not. We identified novel alternative splice transcripts for MICA encoding five novel MICA isoforms: MICA-A, -B1, -B2, -C, and -D. Alternative splicing associates with MICA*015 and *017 and results from a point deletion (G) in the 5' splice donor site of MICA intron 4 leading to exon 3 and exon 4 skipping and/or deletions. These changes delete the α3 domain in all isoforms, and the α2 domain in the majority of isoforms (A, B1, C, and D). Endothelial and hematopoietic cells contained endogenous alternative splice transcripts and isoforms. MICA-B1, -B2, and -D bound NKG2D by surface plasmon resonance and were expressed at the cell surface. Functionally, MICA-B2 contains two extracellular domains (α1 and α2) and is a novel potent agonist ligand for NKG2D. We found that MICA-D is a new truncated form of MICA with weak affinity for NKG2D despite lacking α2 and α3 domains. MICA-D may functionally impair NKG2D activation by competing with full-length MICA or MICA-B2 for NKG2D engagement. Our study established NKG2D binding for recombinant MICA-B1 but found no function for this isoform. New truncated MICA isoforms exhibit a range of functions that may drive unexpected immune mechanisms and provide new tools for immunotherapy.

Effect of major histocompatibility complex haplotype matching by C4 and MICA genotyping on acute graft versus host disease in unrelated hematopoietic stem cell transplantation

We explored whether matching of human leukocyte antigen (HLA) haplotypes between the recipient and donor of hematopoietic stem cell transplantation (HSCT) predicted by C4 and MICA typing is associated with the incidence of acute graft versus host disease (aGVHD). DNA preparations collected from a total of 81 recipient and donor pairs were used for PCR-based C4 subtyping and/or MICA sequence-based typing. Incidences of aGVHD were compared according to C4 and MICA matching. The six most common MICA alleles were MICA*008:01, *010:01, *002:01, *004, *009:01/049, and *012:01. Among the 59 unrelated pairs, HLA alleles were matched in 34 (57.6%). C4 subtypes were identical between the recipient and donor in 28 (82.4%) HLA-matched unrelated pairs, while MICA genotypes were matched in all HLA-matched unrelated pairs. In the 22 HLA-matched related pairs, all recipients showed identical C4 subtypes with their respective donors. In multivariate analysis, C4 mismatch was a significant risk factor associated with the development of aGVHD in unrelated HSCT (hazard ratio=3.24, P=0.006). PCR-based C4 subtyping is a simple method for assessing the genetic identity of the HLA region between a recipient and unrelated donor. This test would be also useful for prediction of aGVHD in HSCT.

Microarrays for high-throughput genotyping of MICA alleles using allele-specific primer extension

The role of major histocompatibility complex (MHC) class I chain-related gene A (MICA), a ligand of NKG2D, has been defined in human diseases by its allele associations with various autoimmune diseases, hematopoietic stem cell transplantation (HSCT) and cancer. This study describes a practical system to develop MICA genotyping by allele-specific primer extension (ASPE) on microarrays. From the results of 20 control primers, strict and reliable cut-off values of more than 30,000 mean fluorescence intensity (MFI) as positive and less than 3000 MFI as negative, were applied to select high-quality specific extension primers. Among 55 allele-specific primers, 44 primers could be initially selected as optimal primer. Through adjusting the length, six primers were improved. The other failed five primers were corrected by refractory modification. MICA genotypes by ASPE on microarrays showed the same results as those by nucleotide sequencing. On the basis of these results, ASPE on microarrays may provide high-throughput genotyping for MICA alleles for population studies, disease-gene associations and HSCT.

MIC gene polymorphism and haplotype diversity in Zhuang nationality of Southern China

Zhuang ethnic minority is the largest minority group in China. Here, we report for the first time the polymorphisms of MICA and MICB in a healthy Zhuang population of 209 unrelated individuals. Using polymerase chain reaction-sequence specific priming (PCR-SSP) and sequencing-based typing (PCR-SBT), 13 MICA-sequence alleles and 5 MICA-STR alleles, as well as 11 MICB alleles were detected, among which MICA(∗)010, MICA(∗)A5 and MICB(∗)005:02 were the most frequent alleles. Linkage disequilibria was investigated and the most common two-locus haplotypes were MICB(∗)005:02-MICA(∗)010 and MICB(∗)014-MICA(∗)045. These results suggest informative genetic markers for investigating origins and evolution of MHC class I region haplotypes in Zhuang population.

Expression of major histocompatibility complex class I-related chain A/B (MICA/B) in pancreatic carcinoma

Major histocompatibility complex class I-related chain A and B (MICA/B) are two stress-inducible ligands that bind to the immunoreceptor NKG2D and play an important role in mediating cytotoxicity of NK and T cells. Release of MIC molecules from the cell surface is thought to constitute an immune escape mechanism of tumor cells and thus could be associated with more aggressive course of tumor growth. In this study, we investigated the expression of MICA/B in ductal pancreatic carcinoma and serum in relation to tumor stage, differentiation and survival. MICA/B expression in tumor tissues and sera from patients with pancreatic cancer were analyzed by immunohistochemical staining (IHC), western blotting and ELISA, respectively. MICA/B expression was present in 17 of 22 (77%) of the tumors but not in normal pancreatic ductal epithelial cells. Poorly differentiated tumors showed more pronounced MICA/B expression compared to differentiated tumors, but did not correlate significantly to other tumor characteristics. MICA/B-negative tumors displayed significantly lower incidence of lymph node metastases (p<0.01), and less mortality within 3 years following resection (p<0.02). In conclusion, tissue levels of MICA/B expression were elevated in pancreatic cancer cells without elevated levels in serum, despite well-recognized acute phase reactants in serum. Poorly differentiated tumors showed high MICA/B expression, which was related to extended tumor lymph node metastases and less frequent long-term survival.

Major histocompatibility complex class I-related chain A allele mismatching, antibodies, and rejection in renal transplantation

Even when kidney allografts are well matched for human leukocyte antigen (HLA) and anti-HLA antibodies are not detected, graft rejection can still occur. There is evidence that some patients who lose their graft have antibodies specific for major histocompatibility complex (MHC) class I-related chain A (MICA) antigens. We investigated whether mismatching MICA alleles associates with MICA antibody production and graft rejection or dysfunction. MICA and HLA antibody screening in 442 recipients was performed, and specificities were confirmed in a subgroup of 227 recipients using single-antigen multiplex technology. For assignment of MICA antibody specificity, we used three independent assays. In addition, MICA alleles of 227 recipients and donors were determined by DNA sequencing. In all, 17 patients (7.5%) had MICA antibodies, and 13 patients (6%) developed MICA donor-specific antibodies (DSA). Multivariate analysis revealed MICA mismatching, as an independent significant factor associated with the presence of MICA antibodies (p = 0.009), and 14 mismatched MICA residues significantly correlated with MICA antibody production. MICA and HLA antibodies significantly associated with acute rejection (AR) and MICA DSA and HLA DSA correlated with decreased graft function by univariate and multivariate analysis. We conclude that mismatching for MICA epitopes in renal transplantation is a mechanism leading to production of MICA antibodies that associate with AR and graft dysfunction.

The role of major histocompatibility complex class I chain-related gene A antibodies in organ transplantation

PURPOSE OF REVIEW

Major histocompatibility complex class I chain-related gene A (MICA) antigens are expressed on the endothelium, they are polymorphic and have been shown to be recognized by antibodies produced by transplant recipients. Methods for detection of these antibodies have become available. In the 15th International Histocompatibility Workshop, a study for MICA antibody testing and of MICA genotyping was organized.

RECENT FINDINGS

Antibodies against MICA antigens have been determined either using cells transfected with MICA alleles or recombinant MICA antigens. MICA epitopes were characterized by empirical study of human sera and by correlation with MICA polymorphic amino acids. Sera were absorbed with cells transfected with MICA alleles and site-directed mutagenesis was employed to analyze complex sera. A number of clinical studies have shown associations of antibodies against MICA with decreased survival of kidney transplants and in one investigation with acute rejection in recipients of heart allografts.

SUMMARY

In addition to the HLA antigens, which elicit a strong immune response against allografted organs, the MICA antigens may be recognized as foreign and induce the production of MICA-specific antibodies. Antibodies against MICA have been associated with a decrease in the survival of organ allografts. The results suggest the MICA antigens are transplantation antigens that can induce an immune response associated with graft failure.

Sustained CTL activation by murine pulmonary epithelial cells promotes the development of COPD-like disease

Chronic obstructive pulmonary disease (COPD) is a lethal progressive lung disease culminating in permanent airway obstruction and alveolar enlargement. Previous studies suggest CTL involvement in COPD progression; however, their precise role remains unknown. Here, we investigated whether the CTL activation receptor NK cell group 2D (NKG2D) contributes to the development of COPD. Using primary murine lung epithelium isolated from mice chronically exposed to cigarette smoke and cultured epithelial cells exposed to cigarette smoke extract in vitro, we demonstrated induced expression of the NKG2D ligand retinoic acid early transcript 1 (RAET1) as well as NKG2D-mediated cytotoxicity. Furthermore, a genetic model of inducible RAET1 expression on mouse pulmonary epithelial cells yielded a severe emphysematous phenotype characterized by epithelial apoptosis and increased CTL activation, which was reversed by blocking NKG2D activation. We also assessed whether NKG2D ligand expression corresponded with pulmonary disease in human patients by staining airway and peripheral lung tissues from never smokers, smokers with normal lung function, and current and former smokers with COPD. NKG2D ligand expression was independent of NKG2D receptor expression in COPD patients, demonstrating that ligand expression is the limiting factor in CTL activation. These results demonstrate that aberrant, persistent NKG2D ligand expression in the pulmonary epithelium contributes to the development of COPD pathologies.

Evidence for no relevance of anti-major histocompatibility complex class I-related chain a antibodies in liver transplantation

The polymorphic major histocompatibility complex class I-related chain A (MICA) antigen is being increasingly recognized as a potential target molecule for immune cells during allograft rejection. Here we studied whether MICA is a target antigen for antibodies in liver transplant patients. Eighty-four patients were investigated for the presence of MICA antibodies before and after liver transplantation with MICA-transfected cells and flow cytometry. MICA typing was performed by polymerase chain reaction. Expression of MICA in liver cells was determined by reverse-transcription polymerase chain reaction, Western blotting, and flow cytometry. Liver biopsy specimens from liver transplant patients were examined for MICA expression. A total of 22 of 84 (26%) patients had MICA antibodies either pre-transplant (8/84, 9.5%) or post-transplant (14/84, 17%). No correlation between rejection frequencies (14/22, 63%) or other clinical parameters was observed in patients with MICA antibody versus those without MICA antibody (29/62, 47% P = not significant). We found weak messenger RNA expression for MICA in liver cells but no protein or cell surface expression. In addition, no MICA expression in liver biopsy sections from liver transplant patients was observed at any time point, including rejections. Thus, our preliminary results demonstrate no causal relationship between the presence of MICA antibodies and liver allograft rejections. Therefore, it is likely that MICA may not be an important target antigen during liver allograft rejections.

Associations of MICB with cervical cancer in north-eastern Thais: identification of major histocompatibility complex class I chain-related gene B motifs influencing natural killer cell activation

The expression of MICB, a member of the major histocompatibility complex class I chain-related gene B family, is induced in response to cellular stress. It is one of the ligands to the NKG2D receptor. MICB is polymorphic, but the distribution of MICB polymorphism in north-eastern Thais and their potential associations with cancer have not yet been elucidated. In this study, polymerase chain reaction-sequence-specific primers were developed to identify 15 MICB alleles and one group of alleles. We performed MICB typing in 100 healthy north-eastern Thai females (NETF) and 99 cervical cancer patients to evaluate the association of MICB polymorphisms and the risk of developing cervical cancer. Eight and nine alleles were detected in the NETF and cervical cancer respectively. MICB*00502 was associated negatively with a corrected P-value of 0.0009, suggesting the existence of a protective allele in cervical cancer. Amino acid substitutions carried by this allele were investigated for their potential involvement in natural killer (NK) cell activation. Although lysine at amino acid position 80 (Lys80) and aspartic acid at position 136 (Asp136) were associated negatively with cervical cancer, only MICB carrying Asp136 could induce NK cell killing more efficiently than MICB-Lys80 when the NK cells were blocked by anti-NKG2D. This result suggested that aspartic acid at position 136 may affect NKG2D binding, leading to different degrees of immune cell activation.

HLA and MICA associations with head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a very aggressive tumour arising from the epithelial lining of the upper aerodigestive tract. The precise mechanisms involved in the pathogenesis of HNSCC have not been elucidated. Previous studies observed aberrant HLA expression patterns on HNSCC tumour cells and this study focused on the allelic polymorphism of HLA genes and the MHC class I chain related gene A (MICA) and HNSCC. We investigated whether associations with HLA and/or MIC alleles or haplotypes are involved in the pathogenesis of HNSCC and could explain the observed HLA expression patterns. Patients and controls were typed for HLA-A, HLA-B, HLA-C, HLA-DRB1 and HLA-DQB1 with sequence specific priming (SSP), supplemented with sequencing based typing (SBT). MICA allelic polymorphism was included and MICA allele assignment was based upon the combination of high resolution SBT of exons 2-4 in combination with repeat analysis and nucleotide polymorphism of exon 5. HLA-B *35 (p=0.014, OR=0.31) and HLA-B *40 (p=0.013, OR=2.9) were significantly associated in respectively the metastasized patients and the oral cavity patients. In addition, the HLA-B *40-DRB1 *13 haplotype (p=0.016, OR=4.1) was more often observed in the oral cavity patient group. The biological significance of the prevalence of specific HLA haplotypes in patients with oral cavity HNSCC and metastasizing HNSCC requires further investigation.

MICA-STR, HLA-B haplotypic diversity and linkage disequilibrium in the Hunan Han population of southern China

Major histocompatibility complex (MHC) class I chain-related gene A (MICA) is located 46 kb centromeric to HLA-B and encodes a stress-inducible protein. MICA allelic variation is thought to be associated with disease susceptibility and immune response to transplants. This study was aimed to investigate the haplotypic diversity and linkage disequilibrium between human leukocyte antigen (HLA)-B and (GCT)(n) short tandem repeat in exon 5 of MICA gene (MICA-STR) in a southern Chinese Han population. Fifty-eight randomly selected nuclear families with 183 members including 85 unrelated parental samples were collected in Hunan province, southern China. HLA-B generic typing was performed by polymerase chain reaction-sequence-specific priming (PCR-SSP), and samples showing novel HLA-B-MICA-STR linkage were further typed for HLA-B allelic variation by high-resolution PCR-SSP. MICA-STR allelic variation and MICA gene deletion (MICA*Del) were detected by fluorescent PCR-size sequencing and PCR-SSP. Haplotype was determined through family segregation analysis. Statistical analysis was applied to the data of the 85 unrelated parental samples. Nineteen HLA-B specificities and seven MICA-STR allelic variants were observed in 85 unrelated parental samples, the most predominant of which were HLA-B*46, -B60, -B*13, and -B*15, and MICA*A5, MICA*A5.1 and MICA*A4, respectively. Genotype distributions of HLA-B, MICA-STR loci were consistent with Hardy-Weinberg proportions. The HLA-B-MICA-STR haplotypic phases of all 85 unrelated parental samples were unambiguously assigned, which contained 30 kinds of HLA-B, MICA-STR haplotypic combinations, nine of them have not been reported in the literature. Significant positive linkage disequilibria between certain HLA-B and MICA-STR alleles, including HLA-B*13 and MICA*A4, HLA-B*38 and MICA*A9, HLA-B*58 and MICA*A9, HLA-B*46 and MICA*A5, HLA-B*51 and MICA*A6, HLA-B*52 and MICA*A6, and HLA-B60 and MICA*A5.1, were observed. HLA-B*48 was linked to MICA*A5, MICA*A5.1 and MICA*Del. HLA-B*5801-MICA*A10 linkage was found in a family. Our data indicated a high degree of haplotypic diversity and strong linkage disequilibrium between MICA-STR and HLA-B in a southern Chinese Han population, the data will inform future studies on anthropology, donor-recipient HLA matching in clinical transplantation and HLA-linked disease association.

A typing system for the major histocompatibility complex class I chain related genes A and B using polymerase chain reaction with sequence-specific primers

The Major Histocompatibility Complex (MHC) class I chain related (MIC) A and B genes are important additional loci within the MHC. We have developed a MICA and MICB typing system using the polymerase chain reaction with sequence-specific primers (PCR-SSP), which operates under the same conditions as our routine HLA-A, -B, and -C typing method. We designed 95 primers in 84 SSP mixtures for MICA and 39 primers in 29 mixtures for MICB. This detected and differentiated all 55 MICA and 19 MICB alleles (except MICA*00701 from MICA*026, MICA*00201 from MICA*020, and three MICB alleles, which are intronic variations). A computer program confirmed the MICA amplification reactivity of each SSP mixture and evaluated the typing set for MICA allele combination ambiguities. Seventy-six "reference" DNA samples were used for validation: 50 from International Histocompatibility Workshop B lymphoblastoid cell lines (IHW BCLs) and 26 MICA-typed samples from two laboratories. The reference material identified 28 out of the 55 MICA alleles and 13 of the 19 MICB alleles, and directly validated 62 of the 84 MICA and 20 of the 29 MICB SSP mixtures. Our genotyping agreed with 283 out of the 286 (98.95%) MICA and MICB reference laboratories' allele assignments or the consensus assignments. Two of the discrepancies remain unresolved, whereas one was probably due to a reference laboratory's failure to differentiate alleles differing in exon 5 of the MICA gene. A comparison of the MICA and MICB allele assignments between laboratories identified a "disagreement rate" of 19.4% for MICA alleles and 13.1% for MICB alleles. Accordingly, we have compiled "consensus" MICA and MICB genotypes for the 50 IHW BCLs tested, which have been confirmed by our typing. We also typed 166 random blood donors. Their MICA and MICB carriage and allele frequencies and HLA-B, MICA, MICB linkage disequilibrium parameters and haplotype frequencies largely concurred with other published data on United Kingdom subjects, further supporting the validity of our typing system. This PCR-SSP system is a simple, reliable and rapid technique for typing MICA and MICB alleles. It is easily updated as new alleles are identified but clearly requires a continuing validation review until all known MICA and MICB alleles have been identified.

Gender-specific associations between MICA-STR and nasopharyngeal carcinoma in a southern Chinese Han population

Previous studies have identified several HLA-B specificities that are associated with nasopharyngeal carcinoma (NPC) in populations of Chinese descent, in particular HLA-B35, -B38, -B46, and -B58. Perhaps except for HLA-B46, other associations cannot be simply accounted for by the linkage disequilibrium between HLA-A and B loci. The human major histocompatibility complex (MHC) class I chain-related gene A (MICA) maps 46 kb centromeric to HLA-B and is highly polymorphic; it encodes a stress-inducible protein which functions as a ligand for the NKG2D/DAP10 complex to activate natural killer (NK) cells, gammadelta T cells, and CD8(+) T cells. We postulated MICA gene as a susceptibility factor for nasopharyngeal carcinoma, an Epstein-Barr virus-associated malignancy. In this study, 218 unrelated patients newly diagnosed with NPC and 196 randomly selected healthy controls from southern China mainland were analyzed for the short tandem repeat polymorphism of exon 5 of MICA gene (MICA-STR) and MICA gene deletion, using fluorescent polymerase chain reaction-gene scanning (PCR/size-sequencing) and polymerase chain reaction-sequence-specific priming (PCR/SSP) technology. MICA*A9 was present at significantly increased frequency in the patient group (P (C)=0.0001002, OR=2.528, 95% CI=1.636-3.907), whereas the frequency of MICA*A5.1 was significantly decreased (P (C)=0.006, OR=0.594, 95% CI=0.437-0.806). Gender-based stratification revealed a significant increase of MICA*A9 frequency (P (C)=0.000072, OR=3.255, 95% CI=1.855-5.709) and a significant decrease of MICA*A5.1 frequency (P (C)=0.000737, OR=0.486, 95% CI=0.337-0.702) in male patients with NPC (N=166), compared with male normal controls (N=120). A significant interaction between MICA*A9 and gender was observed ([see text]=41.58, P=0.0001). Statistics also revealed heterogeneity of effects among MICA*A5.1/MICA*A9-bearing phenotypes and a dose-dependent effect of MICA*A5.1 and MICA*A9 on NPC risk in male subgroup. This constitutes the first demonstration of a gender-specific association between MICA-STR polymorphism and NPC, which could largely be attributable to the underlying gender-related mechanisms that modulate MICA gene expression. The results provide strong supporting evidence suggesting that MICA*A9 may be a genetic risk factor for NPC in male individuals in this population. The potential interaction between MICA and other non-HLA host factors and environmental exposures remains to be further studied.

MICA, MICB, and MHC Beta Block Matching in Bone Marrow Transplantation: Relevance to Transplantation Outcome

Genetic testing of the MHC is required for selection of donors for bone marrow transplantation. The outcome of related bone marrow transplantation is usually superior to that of unrelated bone marrow transplantation. This may be the result of inaccurate or incomplete genetic testing employed for selection of donor for transplantation. Based on MHC haplotype matching, MHC block matching has been developed for selection of potential unrelated donor. Block matching has been shown previously to improve outcome when added to the conventional method of human leukocyte antigen (HLA) typing for selection of donors. In this study, we have retrospectively analyzed 44 donor recipient pairs from the Australian Bone Marrow Donor Registry Repository with respect to matching of HLA-B and HLA-Cw by sequence-based typing and MICA and MICB by polymerase chain reaction-sequence specific primer and MHC beta block matching and correlated these results with survival. Beta block matching was correlated with MIC matching (p < 0.005) and with HLA-B and HLA-Cw matching. Patients who were HLA-B and -Cw matched had significantly improved survival when they were additionally matched for MHC beta block (p(c) = 0.04) or MIC (p(c) = 0.05).

Associations of major histocompatibility complex class I chain-related molecule polymorphisms with Behcet's disease in Caucasian patients

HLA-B*51 is known to be associated with Behcet's disease (BD) in many ethnic groups. The pathogenic gene, however, may lie close to the HLA-B locus and therefore be in linkage disequilibrium with HLA-B*51. On the basis of the proximity of MIC genes to HLA-B, their expression pattern and their affinity for the activating NKG2D receptor on natural killer (NK) cells and gammadelta T cells, these molecules have been postulated as susceptibility factors in BD. DNA from 56 western European Caucasians with BD and 90 Caucasian controls were analysed by polymerase chain reaction using allele-specific primers for MICA and MICB alleles. An increased allele frequency of MICA*009 was found in the BD patient group (25.0%) when compared with the controls (7.2%). This was associated with a corresponding decrease in MICA*008 in the BD patients (36.6%) compared with the controls (46.7%), which was not significant. MICA*009 was strongly associated with the presence of HLA-B*51 in patients and controls. No significant difference in frequency of MICB alleles was found between patients and controls. Both HLA-B*51 and MICA*009 are strongly associated with BD in a pure Caucasian BD patient group, and the two alleles are in linkage disequilibrium. No MICB allele was found to associate significantly with the disease, an unexpected finding considering the close proximity of the MICA and MICB loci. Our results suggest that while MICB does not influence the development of BD, polymorphisms in MICA may be pathogenic, perhaps through the interaction with NK and gammadelta T cells.

Molecular typing of human leukocyte antigen and related polymorphisms following whole genome amplification

Reliable, high-resolution genotyping of human leukocyte antigen (HLA) polymorphisms is often compromised by DNA samples of suboptimal quality or limited quantity. We tested the feasibility of molecular typing for variants at HLA and neighboring loci using whole genome amplification (WGA) strategy facilitated by the Phi29 DNA polymerase. With little (5-100 ng) starting genomic DNA of varying quality and source materials, WGA was deemed successful in 167 of 169 DNA from 47 cell lines, 100 European Americans, and 22 native Africans. The Phi29-processed DNA provided adequate templates for polymerase chain reaction (PCR)-based analyses of several HLA (A, B, C, DRB1, and DQB1) and related loci (HFE, MICA, and 10 microsatellites) in the 6p24.3-6p21.3 region, with PCR amplicons ranging from 92 to 2200 bp. Five different genotyping techniques resolved and confirmed 364 genotypes when both original and Phi29-processed DNA worked in PCRs. General population genetic analyses provided additional evidence that WGA may represent a reliable and simple approach to securing ample genomic DNA for typing HLA, MICA, and related variants.

Loss of nonclassical MHC molecules MIC-A/B expression during progression of uveal melanoma

Uveal melanoma differs from cutaneous melanoma with respect to aetiology, metastatic behaviour and immune biology. The notion that loss of classical MHC class I molecules in uveal melanoma lesions is associated with an improved prognosis suggests that NK cells act as the predominant cells responsible for immune surveillance of this tumour. Consequently, immune escape mechanisms of uveal melanoma should impair the innate immunity. To this end, expression of the ligand for the NK receptor NKG2D, that is, MIC-A/B was expressed by 50% of primary tumours, but none of the metastatic lesions. MIC⁺ tumours were characterised by a NKG2D⁺ infiltrate, which was absent in MIC⁻ lesions subsequent to chemoimmune therapy. Strikingly, MIC-A/B expression in metastatic lesions was observed subsequent to chemotherapy with fotemustine in one case. In summary, MIC/NKG2D interactions seem to be involved in the immune surveillance of primary uveal melanomas, whereas for metastatic tumours this ligand/receptor system seems not to be relevant, thus, suggesting an immune selection of MIC negative tumour cells.

Human MHC class I chain related (MIC) genes: their biological function and relevance to disease and transplantation

Major histocompatibility complex (MHC) class I chain related (MIC) molecules show homology with classical human leukocyte antigen (HLA) molecules, but they do not combine with beta2 microglobulin, do not bind peptide and are not expressed on normal circulating lymphocytes. In response to stress, MIC proteins are expressed on the cell surface of freshly isolated gastric epithelium, endothelial cells and fibroblasts and engage the activating natural killer cell receptor NKG2D, which is found on many cells within the immune system. Despite the highly polymorphic nature of MIC genes, only one polymorphic position has been identified that appears to affect the binding of NKG2D. Alleles with a methionine at codon 129 have a 10-50-fold greater capacity to complex NKG2D than alleles with a valine at this position. Renal and pancreatic grafts with evidence of both acute and chronic rejection have been shown to express MIC proteins, and anti-MIC antibodies have been identified in the serum of these patients. Some MIC molecules which are expressed by tumours appear to shed and solubilize in plasma. This soluble form of MIC engages cells expressing NKG2D, rendering them inactive, and impairs tumour cytolysis. Similarly, a protein encoded by human cytomegalovirus (CMV) prevents MICB surface expression and subsequent NKG2D interaction. Whereas the benefit of solid organ transplantation may be hindered by the expression of MIC molecules on grafts, tumours and viruses may take advantage of the expression of MIC molecules on transformed and virus-infected cells in order to evade this recognition pathway.

MICA intron 1 sequences of conserved extended HLA haplotypes: implications for sequencing-based typing

The human major histocompatibility complex (MHC) class I chain-related gene A (MICA) has a high degree of genetic diversity. Several methods have been used in MICA typing. Recent studies reported different results for the same reference cell lines typed by different methods. By searching the GenBank, we found an indel polymorphism in MICA intron 1 corresponding to the area where one of the sequencing-based typing primers used by others is located. We investigated this polymorphism in 43 reference samples by primer cycle sequencing. This approach revealed three haplotype-specific patterns of polymorphisms in intron 1. This study provided evidence that one of the primers commonly used in MICA typing may fail to amplify both alleles in certain heterozygous combinations. Our data showed a correlation between the three patterns in MICA intron 1 and exon 5 short tandem repeat (STR) alleles. Being neutral ones, the intron 1 and STR polymorphisms appeared to mark the ancestral lineages better than the coding region polymorphisms.

MICB typing by PCR amplification with sequence specific primers

MICB is a member of the MIC (MHC class I chain-related gene) family. Sixteen MICB alleles have been described; however, the functional relevance and population distribution of MICB alleles or their potential association to disease has not yet been evaluated. In this study, we have developed a PCR system using sequence-specific primers (PCR-SSP) that allows unambiguous amplification of all MICB alleles. This approach has been applied to type 100 healthy unrelated individuals from the Spanish population. The extent of polymorphism in this population is lower than that initially expected, and only nine alleles were detected. The alleles MICB01021 (46%), MICB0103101 (13.5%), MICB0104 (13.5%) and MICB0106 (12.5%) were found to be the most frequent alleles. HLA-B and MICA transmembrane polymorphism typing were also performed in this population. Our data showed that MICB is in linkage disequilibrium with MICA and even with HLA-B. Thus, the linkage disequilibrium with MICA and HLA-B suggests that MICB is a potential candidate for those diseases classically associated with HLA class I alleles.

HLA-G and MIC expression in tumors and their role in anti-tumor immunity

Non-classical MHC class Ib molecules have attracted growing interest in recent years, especially because they interact with non-T-cell inhibitory or triggering receptors expressed on natural killer (NK) and T cells, suggesting that they have a role in immune recognition. Abnormalities in MHC class Ib expression are frequently found in human tumors of various histologies and might be associated with poor clinical outcome despite the local accumulation of immune competent cells. Available data suggest that the balance between activating and suppressing signals significantly influences the efficacy of the immune response and consequently of tumor progression.