MHC Class I-related Chain A Research Articles

10: Incidence and Effect of Pre-Formed Antibodies to MICA in Cardiac Transplantation

Non-HLA antibodies may have a role in allograft rejection. Of interest is the development of antibodies (abs) to the MHC class-I related chain A (MICA) molecules, a polymorphic series of molecules with limited expression on endothelial and epithelial cells. The objectives of the study were to determine the frequency of pre-transplant MICA abs and their effect on graft survival.

Augmented serum level of major histocompatibility complex class I-related chain A (MICA) protein and reduced NKG2D expression on NK and T cells in patients with cervical cancer and precursor lesions

BackgroundCervical cancer is the second most common cancer in women worldwide. NK and cytotoxic T cells play an important role in the elimination of virus-infected and tumor cells through NKG2D activating receptors, which can promote the lysis of target cells by binding to the major histocompatibility complex class I-related chain A (MICA) proteins. Increased serum levels of MICA have been found in patients with epithelial tumors. The aim of this study was to compare the levels of soluble MICA (sMICA) and NKG2D-expressing NK and T cells in blood samples from patients with cervical cancer or precursor lesions with those from healthy donors.MethodsPeripheral blood with or without heparin was collected to obtain mononuclear cells or sera, respectively. Serum sMICA levels were measured by ELISA and NKG2D-expressing immune cells were analyzed by flow cytometry. Also, a correlation analysis was performed to associate sMICA levels with either NKG2D expression or with the stage of the lesion.ResultsSignificant amounts of sMICA were detected in sera from nearly all patients. We found a decrease in the number of NKG2D-expressing NK and T cells in both cervical cancer and lesion groups when compared to healthy donors. Pearson analysis showed a negative correlation between sMICA and NKG2D-expressing T cells; however, we did not find a significant correlation when the analysis was applied to sMICA and NKG2D expression on NK cells.ConclusionOur results show for the first time that high sMICA levels are found in sera from patients with both cervical cancer and precursor lesions when compared with healthy donors. We also observed a diminution in the number of NKG2D-expressing NK and T cells in the patient samples; however, a significant negative correlation between sMICA and NKG2D expression was only seen in T cells.

Anti–major histocompatibility complex class I-related chain A antibodies in organ transplantation

Candidate trigger antigens for alloreactive responses have been appearing continuously in the organ transplant scenario. Major histocompatibility complex class I-related chain A (MICA) is a polymorphic gene family, located near the HLA-B locus on chromosome 6, that encode a 62-kd cell surface glycoprotein. Endothelial cells, in addition to many cell lines, express MICA, whereas resting lymphocytes do not, making this polymorphic molecule a target for both cellular and humoral immune responses. Major histocompatibility complex class I-related chain A antigens are able to elicit the synthesis of alloantibodies in transplant recipients. These antibodies have been found in association with irreversible allograft rejection, an increased frequency of acute rejection episodes, and a significantly lower deceased donor graft survival, as well as in the eluates from rejected grafts. This review summarizes currently available information on MICA in the transplant setting. Undoubtedly, the questions that have surfaced surpass in excess the currently available answers.

MICA Polymorphism Identified by Whole Genome Array Constitutes a Disease Predisposition Factor in T-Cell Large Granular Lymphocyte Leukemia.

Large granular lymphocyte leukemia (LGL) is a disease of semiautonomous proliferation of cytotoxic T-cells (CTL) often accompanied by immune cytopenias, particularly neutropenia. LGL related cytopenias have been attributed to LGL cellular cytotoxicity or proapoptotic cytokines rather than intrinsic properties of the neutrophils. The association of LGL with autoimmunity suggests that genetic predisposition may contribute to disease pathogenesis. We studied 69 patients with LGL leukemia using a case-control approach; control populations included ethnically matched healthy individuals (N=82) and disease controls of aplastic anemia (N=48) and kidney transplant recipients (N=48). Initially, we applied the Illumina 12K non-synonymous SNP array to a subcohort of 36 LGL patients and 54 healthy controls (training set). Results were subjected to independent hypothesis-generating biostatistical algorithms. First, Exemplar automated analysis determined disease prediction based on independent χ2 analysis for each SNP. As expected, no SNP in this underpowered study reached Bonferroni corrected statistical significance, but our analysis allowed for ranking based on p-value. Second, Random Forests, a nonparametric tree method was applied, whereby all SNP information was calculated multivariately to predict disease. In a non-Mendelian inherited disease, this method more closely reflects the biology of complex polygenic traits; remarkably, those SNP identified by Random Forest were among the highest ranking SNP by Exemplar. Our initial hypothesis-generating set identified 1 SNP in unknown gene C8orf31 and 4 SNP within the MHC class I related-chain A (MICA) gene. We focused on MICA, a non-peptide presenting, tightly regulated stress response HLA molecule that could play a role in pathogenesis of neutropenia in LGL. To further substantiate our finding, the initial training set results were subjected to technical validation; fidelity was rechecked by PCR genotyping with 93% concordance. Biological validation was determined by confirmation in an independent test set consisting of 33 LGL patients and additional 28 controls. As only limited numbers of SNP were tested, there was no need for α-error adjustment. MICA SNP rs1063635 was found to have the most predictive value in both the training set (PPV=56%, NPV=89%) and test set (PPV=64%, NPV=86%). Overall, the control frequency of this SNP in homozygous form was 12% vs 60% in LGL (p<.01, OR=9.1). MICA alleles have been implicated in autoimmune diseases and malignancies. Although this SNP may not define a particular MICA genotype, it is possible that it is in linkage disequilibrium with genotype-defining polymorphisms. To study the functional consequences of our findings, flow cytometric analysis using anti-MICA antibodies was performed, which identified higher expression of MICA in neutrophils from patients as compared to controls (p=.04). MICA overexpression decreased after immunosuppressive therapy (p<.01). While the mechanism of MICA induction is unknown, we stipulate that the presence of MICA alleles leads to a persistent stimulatory signal in LGL predisposing to clonal outgrowth. In sum, our findings suggest that MICA polymorphisms may represent a predisposition factor in LGL and/or LGL-associated neutropenia.

Autologous Human Cord Blood CD4+CD25+ T Cells Stimulate CD8+ T Cell Killing Activity, and Their Expression of NKG2D and Granzyme B.

CD8+ T cells are crucial for host defense against viruses and tumor cells. Upon antigen recognition, CD8+ T cells proliferate and acquire effector functions. From mouse studies mainly, CD4+CD25+ T cells have been recognized to have suppressive immunomodulatory activity. Because of a concern that human CD4+CD25+ T cells contain both activated and regulatory T cells we chose to study this population from human cord blood (CB) which contains naïve cells, which are not activated. Human CB cells were isolated using magnetic cell separation of CD4+cells and subsequent purification by magnetic beads of these cells that co-expressed CD25. We assessed whether CD4+CD25+ T cells from cord blood influenced function of autologous effector CD8+ T cells. Upon co-culturing CB CD8+ T cells with autologous CD4+CD25+ cells, we found that CD4+CD25+ T cells positively promoted CD8+ T cell function. This included induction of Granzyme B (GrB), a protease crucial for killing target cells and a hallmark of CD8+ T cell effector function. GrB expression was detected by intracytoplasmic flow cytometry. We also assessed effects on NKG2D, a costimulatory receptor known to promote CD8+ T cell effector responses to viruses and tumor cells. It is believed that down-modulation of NKG2D expression is a major obstacle for CD8+ T cell-mediated tumor rejection often observed in cells from cancer patients. Ligation-induced down-regulation of NKG2D expression was observed after culturing CD8+ T cells on anti-NKG2D-coated plates; effects that were dose-dependent. We examined whether the CD4+CD25+ cells could enhance restoration of expression of NKG2D on CD8+ T cells by stimulating CD8+ T cells with anti-CD3 and IL-15 in the presence or absence of CD4+CD25+ T cells. Consistent with the previous noted positive effect of CD4+CD25+ T cells on GrB expression, they also enhanced NKG2D expression during anti-CD3 stimulation. We then determined if CD4+CD25+ T cells had effects on CD8+ T cell cytotoxicity against the C1R B lymphoblast cell line, that expresses major histocompatibility complex (MHC) class I related chain A (MICA), a ligand for NKG2D. Consistent with the positive effects of CD4+CD25+ T cells on expression of GrB and NKG2D, CD4+CD25+ T cells enhanced the cytotoxic activity of CD8+ T cells to MICA-expressing target cells. In summary, CD4+CD25+ T cells isolated from CB enhanced induction of GrB and NKG2D expression in autologous CD8+ T cells during anti-CD3 and IL-15 stimulation, which helps to explain the stimulatory effect of CD4+CD25+ T cells on autologous CD8+ T cell cytotoxicity. Our results with human CB CD4+CD25+ T cells may reflect actions of subpopulations of these cells. Further characterization of subsets of CD4+CD25+ T cells are necessary to better define the specific population with the stimulatory actions on autologous CD8+ T cells that we observed. More defined characterization of CD4+CD25+ T cells are warranted before such cells are used for clinical intervention in human disorders.

Antibodies against MICA Antigens and Kidney-Transplant Rejection

Good HLA-A, HLA-B, and HLA-DR matches do not guarantee rejection-free renal transplantation. Some kidney transplants fail despite such matches, suggesting that other antigens might be targets for rejection. Major-histocompatibility-complex (MHC) class I-related chain A (MICA) antigens are polymorphic and can elicit antibody production. We sought to determine whether an immune response to MICA antigens might play a role in the failure of kidney allografts. Pretransplantation serum samples from 1910 recipients of kidney transplants from deceased donors were tested for anti-MICA antibodies with an assay in which single MICA antigens were attached to polystyrene microspheres. Antibodies against MICA alleles were detected in 217 of the 1910 patients (11.4%). The presence of MICA antibodies was associated with renal-allograft rejection. The mean (+/-SE) 1-year graft-survival rate was 88.3+/-2.2% among recipients with anti-MICA antibodies as compared with 93.0+/-0.6% among recipients without anti-MICA antibodies (P=0.01). Among recipients of first kidney transplants, the survival rate was even lower among MICA antibody-positive patients (87.8+/-2.4%) than among MICA antibody-negative recipients (93.5+/-0.6%, P=0.005). In addition, the association of MICA sensitization with reduced graft survival was more evident in kidney-transplant recipients with good HLA matching: among 326 recipients who received well-matched kidneys (0 or 1 HLA-A plus HLA-B plus HLA-DR mismatch), sensitization against MICA was associated with poorer allograft survival (83.2+/-5.8% among those with anti-MICA antibodies vs. 95.1+/-1.3% among those without such antibodies, P=0.002). Presensitization of kidney-transplant recipients against MICA antigens is associated with an increased frequency of graft loss and might contribute to allograft loss among recipients who are well matched for HLA.

Engagement of TLR3, TLR7, and NKG2D Regulate IFN-γ Secretion but Not NKG2D-Mediated Cytotoxicity by Human NK Cells Stimulated with Suboptimal Doses of IL-12

NK cells express different TLRs, such as TLR3, TLR7, and TLR9, but little is known about their role in NK cell stimulation. In this study, we used specific agonists (poly(I:C), loxoribine, and synthetic oligonucleotides containing unmethylated CpG sequences to stimulate human NK cells without or with suboptimal doses of IL-12, IL-15, or IFN-alpha, and investigated the secretion of IFN-gamma, cytotoxicity, and expression of the activating receptor NKG2D. Poly(I:C) and loxoribine, in conjunction with IL-12, but not IL-15, triggered secretion of IFN-gamma. Inhibition of IFN-gamma secretion by chloroquine suggested that internalization of the TLR agonists was necessary. Also, secretion of IFN-gamma was dependent on MEK1/ERK, p38 MAPK, p70(S6) kinase, and NF-kappaB, but not on calcineurin. IFN-alpha induced a similar effect, but promoted lesser IFN-gamma secretion. However, cytotoxicity (51Cr release assays) against MHC class I-chain related A (MICA)- and MICA+ tumor targets remained unchanged, as well as the expression of the NKG2D receptor. Excitingly, IFN-gamma secretion was significantly increased when NK cells were stimulated with poly(I:C) or loxoribine and IL-12, and NKG2D engagement was induced by coculture with MICA+ tumor cells in a PI3K-dependent manner. We conclude that resting NK cells secrete high levels of IFN-gamma in response to agonists of TLR3 or TLR7 and IL-12, and this effect can be further enhanced by costimulation through NKG2D. Hence, integration of the signaling cascades that involve TLR3, TLR7, IL-12, and NKG2D emerges as a critical step to promote IFN-gamma-dependent NK cell-mediated effector functions, which could be a strategy to promote Th1-biased immune responses in pathological situations such as cancer.

Cryoelectron Tomographic Analysis of an HIV-neutralizing Protein and Its Complex with Native Viral gp120

Identifying structural determinants of human immunodeficiency virus (HIV) neutralization is an important component of rational drug and vaccine design. We used cryoelectron tomography and atomic force microscopy to characterize the structure of an extremely potent HIV-neutralizing protein, D1D2-Ig alpha tp (abbreviated as D1D2-IgP), a polyvalent antibody construct that presents dodecameric CD4 in place of the Fab regions. We show that D1D2-IgP has a novel structure, displaying greater flexibility of its antibody arms than the closely related IgM. Using simian immunodeficiency virus in complex with D1D2-IgP, we present unequivocal evidence that D1D2-IgP can cross-link surface spikes on the same virus and on neighboring viruses. The observed binding to the viral envelope spikes is the result of specific CD4-gp120 interaction, because binding was not observed with MICA-IgP, a construct that is identical to D1D2-IgP except that major histocompatibility complex Class I-related Chain A (MICA) replaces the CD4 moiety. CD4-mediated binding was also associated with a significantly elevated proportion of ruptured viruses. The ratio of inactivated to CD4-liganded gp120-gp41 spikes can be much greater than 1:1, because all gp120-gp41 spikes on the closely apposed surfaces of cross-linked viruses should be incapable of accessing the target cell surface and mediating entry, as a result of inter-virus spike cross-linking. These results implicate flexibility rather than steric bulk or polyvalence per se as a structural explanation for the extreme potency of D1D2-IgP and thus suggest polyvalence presented on a flexible scaffold as a key design criterion for small molecule HIV entry inhibitors.

MICA Gene Polymorphism in the Pathogenesis of Type 1 Diabetes

Type 1 diabetes mellitus (T1DM) is a typical autoimmune disease and results from the destruction of insulin-producing beta cells of the pancreas. It develops in the presence of genetic susceptibility, even though more than 85% of patients with T1DM do not have a close relative with the disorder. The etiology of T1DM is complex, and both genetic and environmental factors play important roles. A permissive genetic background is required for the development of the islet autoimmune process. The strongest genetic association idengified is that with HLA class II genes located on the short arm of chromosome 6. It is well known that both HLA DRB1*04-DQA1*0301-DQB1*0302 (DR4-DQ8) and DRB1*03-DQA1*0501-DQB1*0201 (DR3-DQ2) are positively, and DRB1*15-DQA1*0102-DQB1*0602 is negatively, associated with T1DM. However, only a minority of the subjects carrying the high-risk haplotypes/genotypes develops the disease, which suggests that additional genes play a crucial role in conferring either protection or susceptibility to T1DM. Major histocompatibility complex (MHC) class I chain-related A (MICA) is located in a candidate susceptibility region and activates natural killer (NK) cells, T cells and gammadelta CD8 T cells by its receptor NKG2D. The polymorphism of the MICA gene is associated with T1DM in different populations as demonstrated in several papers published in the last 7 years.

Enhancement of natural killer (NK) cell cytotoxicity by fever-range thermal stress is dependent on NKG2D function and is associated with plasma membrane NKG2D clustering and increased expression of MICA on target cells

Circulating NK cells normally experience temperature gradients as they move about the body, but the onset of inflammation can expose them and their targets to febrile temperatures for several hours. We found that exposure of human peripheral blood NK cells and target cells to fever-range temperatures significantly enhances lysis of Colo205 target cells. A similar effect was not observed when NK cell lines or IL-2-activated peripheral blood NK cells were used as effectors, indicating that thermal sensitivity of effectors is maturation or activation state-dependent. Use of blocking antibodies revealed that this effect is also dependent on the function of the activating receptor NKG2D and its ligand MHC class I-related chain A (MICA). On NK cells, it was observed that thermal exposure does not affect the total level of NKG2D surface expression, but does result in its distinct clustering, identical to that which occurs following IL-2-induced activation. On tumor target cells, a similar, mild temperature elevation results in transcriptional up-regulation of MICA in a manner that correlates with increased sensitivity to cytolysis. Overall, these data reveal that NK cells possess thermally responsive regulatory elements, which facilitate their ability to capitalize on reciprocal, stress-induced changes simultaneously occurring on target cells during inflammation and fever.

14th International HLA and Immunogenetics Workshop: Report on the Prospective Chronic Rejection Project

An international collaborative study of 45 transplant centers was undertaken at the 14th International HLA (human leukocyte antigen) and Immunogenetics Workshop to see if HLA antibodies detected posttransplant are predictive of chronic graft failure. With the newly developed assay, MICA (major histocompatibility complex class I-related chain A) antibodies were also measured and their effect analyzed. Total of 5219 sera from patients who were more than 6 months posttransplant with functioning graft were tested for HLA antibodies by enzyme-linked immunosorbent assay, flow cytometry, or Luminex. HLA antibodies were found in 27.2% of kidney patients, 23.6% in the liver, 52.7% in the heart, and 21.7% in the lung. The method of antibody testing did not have a marked influence on the frequency of antibodies detected. MICA antibodies were detected in 15% of kidney patients, 30% of heart patients, and 31% of liver patients. Among 948 kidney patients who had HLA antibodies, 7.3% had rejected their graft within 1 year of testing, compared with 1.7% in 2615 patients without HLA antibodies (P= 0.8 x 10(-17)). Death occurred in 1.4% of total kidney patients and did not correlate to the presence of antibodies. We conclude that patients with posttransplant HLA antibodies indeed have a higher rate of chronic graft failure and that posttransplant antibodies are predictive of chronic rejection.

MICA marks additional risk factors for Type 1 diabetes on extended HLA haplotypes: An association and meta-analysis

The association of the HLA complex on chromosome 6 does not explain total linkage of the HLA region to Type 1 Diabetes (T1D), leading to the hypothesis that there may be additional causal genes in the HLA region for immune-related disorders. Reports on the MHC Class I chain-related A ( MICA) gene as candidate for association with T1D are contradicting. We investigated whether variation in MICA is associated to T1D in a cohort of 350 unrelated individuals with juvenile-onset T1D and 540 control subjects, followed by a meta-analysis of 14 studies. We also investigated an HLA-independent association for MICA with T1D. In our case-control study, we found that the MICA*A5 variant was significantly associated with an increased risk for T1D, while MICA*A6 was significantly associated with a decreased risk that was confirmed by our meta-analysis. However, the meta-analysis did not show an association of MICA*A5 T1D. Analysis of MICA alleles conditional on T1D-associated high-risk MHC class II haplotypes revealed that MICA*A6 was associated with an increased risk for T1D when this marker co-occurred with HLA DQ2DR17 T1D-risk-haplotypes. In contrast, MICA*A6 reduced the risk from the HLA DQ8DR4 T1D-risk haplotype. Moreover, MICA*A9 showed a significant association to increased risk for T1D on DQ8DR4 haplotypes. Co-inheritance of MICA*A6 with the HLA DQ2DR17 haplotype in T1D indicates this haplotype may carry the additional genetic factors for T1D, but our study does not support an independent association between MICA variants and T1D.

The Activating NKG2D Ligand MHC Class I-Related Chain A Transfers from Target Cells to NK Cells in a Manner That Allows Functional Consequences

Recently, it has become apparent that surface proteins commonly transfer between immune cells in contact. Inhibitory receptors and ligands exchange between cells during NK cell surveillance and we report here that NK cells also acquire activating ligands from target cells. Specifically, the stress-inducible activating ligand for NKG2D, MHC class I-related chain A (MICA), transferred to NK cells upon conjugation with MICA-expressing target cells. Acquisition of MICA from target cells was dependent on cell contact and occurred after accumulation of MICA at the immunological synapse. Moreover, transfer of MICA was facilitated by specific molecular recognition via NKG2D and augmented by Src kinase signaling. Importantly, MICA associated with its new host NK cell membrane in an orientation that allowed engagement with NKG2D in trans and indeed could down-regulate NKG2D in subsequent homotypic interactions with other NK cells. MICA captured from target cells could subsequently transfer between NK cells and, more importantly, NK cell degranulation was triggered in such NK cell-NK cell interactions. Thus, NK cells can influence other NK cells with proteins acquired from target cells and our data specifically suggest that NK cells could lyse other NK cells upon recognition of activating ligands acquired from target cells. This mechanism could constitute an important function for immunoregulation of NK cell activity.

Particular genetic variants of ligands for natural killer cell receptors may contribute to the HLA associated risk of primary sclerosing cholangitis

Combinations of killer immunoglobulin-like receptors (KIRs) and HLA class I ligands that reduce natural killer (NK) cell inhibition have been shown to increase risk for autoimmune diseases. We aimed to clarify to what extent such combinations influence susceptibility to primary sclerosing cholangitis (PSC). Three hundred and sixty-five Scandinavian PSC patients and 368 healthy controls were genotyped for the presence or absence of genes encoding all KIRs using a PCR-SSP approach. KIR binding site variation of HLA-A, -B and -C was also determined. The KIR gene frequencies were similar among patients and controls. However, the frequency of HLA-Bw4 and -C2, which are ligands for the inhibitory KIRs 3DL1 and 2DL1, respectively, was significantly reduced in PSC patients as compared with controls (38.2% vs. 54.7%, P(corrected)[P(c)]=0.0006 and 42.7% vs. 56.9%, P(c)=0.009, respectively). Two HLA risk haplotypes in PSC (carrying DRB1*0301 or DRB1*1501, respectively) were devoid of both of these alleles, and carried the 5.1 variant of the major histocompatibility complex class I chain-related A (MICA) gene previously reported to influence PSC susceptibility. Particular variants of ligands for NK cell receptors encoded at three neighbouring genes in the HLA complex may contribute to PSC associations observed in this genetic region.

Soluble MICA as an independent prognostic factor for the overall survival and progression-free survival of multiple myeloma patients

Major histocompatibility complex class I-related chain A (MICA) molecules are frequently expressed in lymphoproliferative malignancies including multiple myeloma (MM). MICA activates NK cells and co-stimulates T cells by interaction with its immunoreceptor NKG2D. In contrast, soluble MICA (sMICA) molecules impair the functions of NKG2D + T and NK cells, which may facilitate tumor cell escape from immunosurveillance. Here, we analyzed the clinical relevance of sMICA in 97 MM patients. sMICA (mean ± SEM pg/ml) was significantly increased ( p < 0.0001) in patients (429 ± 20) compared to controls (230 ± 20; N = 43). Serial determination showed a strong correlation between increments of sMICA and paraprotein levels ( r = 0.543, p < 0.0001, N = 49). sMICA levels > 305 pg/ml are associated with a poor overall ( p = 0.004) and progression-free survival ( p = 0.002). Multivariate analysis revealed sMICA as an independent predictive factor for overall ( p = 0.007) and progression-free survival ( p = 0.002). Thus, our results suggest sMICA as a potent prognostic marker in MM, which may be useful to identify risk patients.

167-P: High resolution MHC class-I related chain a (MICA) genotyping and analysis of HLA-B – MICA haplotypes in a Turkish population sample

167-P: High resolution MHC class-I related chain a (MICA) genotyping and analysis of HLA-B – MICA haplotypes in a Turkish population sample

Microsatellite polymorphisms of the MICA gene among Japanese patients with Behçet’s disease

Background: Behçet's disease (BD) is a multisystemic inflammatory disease of unknown origin. Because some researchers have recently suggested a primary association of BD with the A6 allele of the human major histocompatibility complex class I chain-related A ( MICA) gene, we investigated microsatellite polymorphisms of the MICA gene in subjects with and without BD. Methods: This was a case-control study of 23 Japanese patients with BD and 23 Japanese volunteers without BD who were compared for MICA microsatellite polymorphisms using the polymerase chain reaction (PCR). We also analysed associations between 5 MICA alleles and the clinical features of patients. Results: There was no significant difference between case patients and control subjects in phenotype frequencies. The MICA-A6 allele showed the strongest positive correlation with the human leukocyte antigen allele HLA-B5I. Allele A5 showed a strong positive correlation with age at onset and a strong negative correlation with iridocyclitis and HLA-B5I. A4 showed a strong negative correlation with ocular lesions and HLA-B5I. Patients with the MICA-A6 allele had significantly higher HLA positivity than patients without the allele. Interpretation: While the MICA-A6 allele had no significant association with BD, it showed a strong association with HLA-B5I. This finding suggests that an association between MICA-A6 and BD may be a secondary phenomenon related to HLA-B5I. As several associations with MICA alleles and clinical features have been found, further investigation is expected to elucidate the biological mechanism of action of the MICA protein relative to disease onset .

No primary association of MICA polymorphism with systemic lupus erythematosus

To replicate the described association between MHC class I chain-related A (MICA) gene polymorphism and susceptibility to systemic lupus erythematosus (SLE). MICA transmembrane microsatellite polymorphism was genotyped using a polymerase chain reaction (PCR)-based method. Genotyping of HLA-B* and DRB1* was performed using PCR and detection with a reverse sequence-specific oligonucleotide (SSO) probe system. Combined data for these three loci (HLA-B*, DRB1* and MICA) were obtained from a total of 333 patients and 361 healthy controls. Significant association with B*08 [P < 10(-7), odds ratio (OR) 3.17, 95% confidence interval (CI) 2.02-5.00], DRB1*0301 (P < 10(-7), OR 2.07, 95% CI 1.59-2.68) and MICA5.1 (P = 0.01, OR 1.23, 95% CI 1.04-1.46) was observed. The combinations DRB1*0301-MICA5.1-B8 and HLA-DRB1*0301-B*08-positive and MICA5-1-negative were more frequent among SLE patients (11.4 vs 3.3% in healthy controls, P = 3.9 x 10(-5), OR 3.76, 95% CI 1.85-7.73, and 6.9 vs 1.7%, P = 0.0007, OR 4.32, 95% CI 1.68-13.10, respectively). Additionally, individuals who were HLA-DRB1*0301-B*08-negative and MICA5-1-positive were less frequent among patients (22.2 vs 31.3% in healthy controls, P = 0.007, OR 0.63, 95% CI 0.44-0.89) and the magnitude of the OR was similar to that obtained in individuals negative for all the three factors (OR 0.69, 95% CI 050-0.94). Further analysis performed to detect independent association strongly suggested that the association between MICA5.1 and SLE is secondary to the linkage disequilibrium of this allele with B*08. Our results do not support an independent association of MICA gene polymorphism with susceptibility to SLE.

Soluble ULBP suppresses natural killer cell activity via down-regulating NKG2D expression

NKG2D is an activating receptor that is expressed on most natural killer (NK) cells and CD8 + T cells. MHC class I-related chain A(MICA) and UL16-binding protein (ULBP) 1, 2, and 3 are well-known ligands for NKG2D. Human gastric cancer cell lines, SNU216 and SNU638 cells which expressed UL16-binding protein (ULBP) were susceptible to NK cells in a NKG2D-dependent manner. However, SNU484 and SNU620 cells which had no ULBP on their surface were resistant to NK cells. ULBP 1, 2, and 3 are glycosylphosphatidylinositol (GPI)-anchored proteins which are sensitive to phosphatidylinositol-specific phospholipase C (PI-PLC). When SNU620 cells were treated with U73122, an inhibitor of PI-PLC, the surface expression of ULBP was elevated with increased NK susceptibility. Pre-incubating NK cells with culture supernatants of SNU620 or SNU638 cells, which contained soluble ULBP protein, reduced NK cell activity by decreasing surface expression of NKG2D in NK cells. Furthermore, recombinant ULBP-Fc induced the down-regulation of NKG2D expression in NK cells. Taken together, down-regulation of NKG2D by soluble ULBP provides a potential mechanism by which gastric cancer cells escape NKG2D-mediated attack by the immune cells.

Vδ1 T cell receptor binds specifically to MHC I chain related A: Molecular and biochemical evidences

Human MHC class I chain-related A (MICA) is a tumor-associated antigen that can be recognized by Vδ1 subset of tumor-infiltrating γδ T cells. We previously reported that immobilized recombinant MICA protein could induce the proliferation of tumor-infiltrating Vδ1 γδ T cells in vitro. But there has been no direct evidence showing the engagement of γδ T cell receptors (TCR) of the induced cells with MICA. In the current investigation, we show that MICA induces specific cytolytic activity of the expanded γδ T cells. We expressed the coupled V domains from the MICA-induced T cells as a single polypeptide chain VδVγ TCR (γδ scTCR). Such scTCR can specifically bind MICA of HeLa cells. Direct interaction of γδ scTCRs with in vitro expressed MICA was monitored using an IAsys biosensor. We found that the Vδ1 scTCR can specifically bind to immobilized MICA molecule and MICAα1α2 domains are responsible for the binding reaction.