Palmitoylation of MICA, a ligand for NKG2D, mediates its recruitment to membrane microdomains and promotes its shedding

MICA and MICB (MHC-class-I-related chain A/B) are transmembrane proteins expressed in pathological conditions that are ligands for NKG2D, an activating receptor found on cytotoxic lymphocytes. The recognition on target cells of NKG2D ligands leads to the activation of lysis and cytokine secretion by NK cells and T cells. Besides being expressed at the cell surface, MICA/B can be released as soluble proteins. Soluble NKG2D ligands downmodulate expression of the NKG2D receptor on lymphocytes, leading to a diminished cytotoxic response. Prior studies suggested that recruitment of MICA/B molecules to cholesterol-enriched microdomains was an important factor regulating the proteolytic release of these molecules. We now show that recruitment of MICA to these microdomains depends on palmitoylation of two cysteine residues that allow MICA molecules to reside in the membrane in the same domains as caveolin-1. Compared with WT molecules, nonpalmitoylated mutant MICA molecules were shed to the supernatant with low efficiency; however, both WT and mutant MICA were able to trigger NK cell cytotoxicity. These data suggest that the presence of NKG2D ligands at the plasma membrane is sufficient to activate cytotoxicity and reflect the need of different ligands to exploit different cellular pathways to reach the cell surface upon different stress situations.     

A dual function of NKG2D ligands in NK-cell activation

NK-cell killing requires both the expression of activating receptor ligands and low MHC class I expression by target cells. Here we demonstrate that the expression of any of the murine ligands for the NK-cell activating receptor NKG2D results in a concomitant reduction in MHC class I expression. We show this both in tumor cell lines and in vivo. NK-cell lysis is enhanced by the decrease in MHC class I expression, suggesting the change is biologically relevant. These results demonstrate that NKG2D ligand expression on target cells not only allows for activating receptor recognition, but also actively reduces expression of the inhibitory ligand, MHC class I, leading to enhanced recognition and killing by NK cells.     

HTRA1基因单核苷酸多态性与类风湿性关节炎的关联性研究

目的 探讨HTRA1基因单核苷酸多态性(single nucleotide polymorphisms,SNPs)和类风湿性关节炎(rheumatoid arthritis,RA)及其患者血清类风湿因子(rheumatoid factor,RF)、C反应蛋白((C-reactive protein, CRP)之间的相关性.方法 采用Snapshot法测定344例RA患者和288名正常健康人HTRA1基因5个SNPs(rs2014307、rs2248799、rs2300433、rs714816、rs2268356)位点基因型,终点散射比浊法测定RA患者血清RF和CRP水平.结果 RA组HTRA1基因SNPs(rs2014307、rs2248799、rs2300433、rs714816、rs2268356)基因型与正常对照组间差异均无统计学意义(P>0.05),单倍型分析也显示H豫A1基因RA组与正常对照组间差异无统计学意义(P>0.05),RA患者HTRA1基闪SNPs位点(rs2014307、rs2248799、rs714816、rs2268356)不同基因型之间血清RF水平比较差异无统计学意义(P>0.05),而rs2300433位点基因型(AA+AG)组的RF水平明显高于GG组((P<0.05).结论 已分析的与HTRA1基因相关的5个SNPs与中国汉族人种RA遗传易感性不相关,HTRA1基因rs2300433位点不同基因型RA患者体内RF水平有差别,HTRA1基因表达的丝氨酸蛋白酶可能参与了RA患者RF的表达.     

Association of NRAMP1 promoter gene polymorphism with the susceptibility and radiological severity of rheumatoid arthritis

The natural resistant-associated macrophage protein 1 (NRAMP1) has been proposed as a candidate gene for the susceptibility to autoimmune diseases. In this study, the possible role of the functional polymorphism located at the promoter region of NRAMP1 gene in the susceptibility and clinical outcome of rheumatoid arthritis (RA) was investigated. A total of 141 Spanish RA patients and 194 controls previously typed for HLA-DRB1* were genotyped for the NRAMP1 polymorphism. No significant differences in the distribution of frequencies among RA patients and controls were observed. Nevertheless, when patients and controls were stratified according to their HLA shared epitope (SE) status, an increase of 2/2 genotype among SE-negative (SE-) patients with respect to SE- controls was observed (23% vs 7%, OR = 3.74, 95% CI 1.31-10.72). In addition, the possible role of this polymorphism in the clinical course of RA was investigated in a subgroup of 82 patients who were prospectively followed during a mean of 9 years. After follow-up, an increase of patients with the homozygous 2/2 genotype was detected among those with severe small joint radiological involvement: 73% of patients 2/2 had a severe form in contrast to 37% of patients with the genotype 2/3 and 30% of patients bearing 3/3 OR = 5.45, 95% CI 1.14-34.24). In conclusion, NRAMP1 gene promoter polymorphism could influence the radiological severity of rheumatoid arthritis and disease susceptibility, particularly in individuals lacking HLA-linked risk factors.     

Association of NKG2D genetic polymorphism with susceptibility to chronic hepatitis B in a Han Chinese population

Natural killer (NK) cells are important antiviral effectors of innate immunity because of their contribution to virus elimination. NK cell‐mediated immunological reaction to hepatitis B virus (HBV) infection depends on a fine balance between inhibitory and activating receptors. The aim of the study was to investigate genetic polymorphisms in NK cell receptors (NKR)—KLRD1 (CD94), KLRK1 (NKG2D), KLRC4 (NKG2F), and KLRC1 (NKG2A)—to evaluate the association of NKR genetic polymorphisms with susceptibility to chronic hepatitis B in a Han Chinese population. Twelve single nucleotide polymorphisms (SNPs), including rs2302489 in CD94; rs2255336, rs2617160, rs7980470, rs 2734565, and rs17513986 in NKG2D; rs2617170, rs17549004, and rs3825295 in NKG2F; rs2734414, rs7301582, and rs2734440 in NKG2A, were selected in the present study. SNP genotyping was undertaken in 500 Han Chinese patients (285 patients with chronic hepatitis B and 215 patients who cleared HBV spontaneously) by a polymerase chain reaction‐restriction fragment length polymorphism (PCR‐RFLP) and by the TaqMan method. Single marker association analysis was conducted and the SNP rs2617160 with a TT genotype in NKG2D was associated significantly with an increased risk of chronic hepatitis B (P = 0.044; OR = 1.49; 95% CI = 1.01–2.19). Haplotype analysis with multiple loci indicated that there was no significant association between the haplotypes of the NKR genes and susceptibility to chronic hepatitis B. The SNP rs2617160 in NKG2D associated with susceptibility to chronic hepatitis B in a Han Chinese population. J. Med. Virol. 82:1501–1507, 2010. © 2010 Wiley‐Liss, Inc.     

Association of HLA-DQA1 (rs9272219) with susceptibility to rheumatoid arthritis in a Han Chinese population

HLA-DQA1 (rs9272219) has been previously reported that it is a susceptibility locus in rheumatoid arthritis (RA) of UK Caucasian population and North American; however, it has not reported in RA of Chinese population. Our study was to identify whether or not this relationship is reside between rs9272219 and RA in a Han Chinese population. 207 patients with RA and 199 control subjects were recruited. The single nucleotide polymorphism (SNP) of rs9272219 was tested in alleles and genotype frequencies and the data was analyzed by doing the statistic analysis of odds ratio (OR) and 95% confidence interval (CI) from multivariate unconditional logistic regression analyses after pairwise linkage disequilibrium (LD) was estimated. Finally, the Alleles and genotype frequencies distribution of rs9272219 locus among RA patients and control subjects were in accordance with Hardy-Weinberg equilibrium. We found significant association between rs9272219 and RA of Chinese population (OR 0.494, 95% confidence interval [95% CI] 0.354-0.688, P = 0 and OR 2.541, 95% CI 1.695-3.808, P = 0, respectively). In this study, we found that the SNP of rs9272219 in HLA-DQA1 is a potential susceptibility locus in RA of Han Chinese population; the results suggest that HLA-DQA1 may be related to the development of RA.     

骨保护素基因单核苷酸多态性与类风湿关节炎发病的相关性研究

 目的：探讨骨保护素（OPG）基因163A/G及245T/G单核苷酸多态性（SNPs）与我国汉族人群类风湿关节炎（RA）发病的相关性。方法：采用聚合酶链反应-限制性片段长度多态性（PCR-RFLP）技术检测我国南方汉族正常人群及RA患者的OPG 163A/G 和245T/G 2个SNP位点;进行Hardy-Weinberg平衡检验;计算基因型和等位基因频率,及这2个位点的连锁关系,并分析这2个SNP位点与RA的关系。结果：所研究基因分布符合Hardy-Weinberg平衡,163A/G 位点基因型AA、AG、GG分布频率在2组比较有显著差异（P<0.05）;等位基因A、G分布比较在2组有显著差异（P<0.05）,携带163GG基因型者发生RA的危险性是非携带者的1.219倍（OR=1219, 95％CI：1066~2.339, P<0.05)。但245T/G位点各基因型及等位基因频率在2组中均未见差异（P>005）。结论：OPG 基因 163A/G SNP可能与我国汉族人群RA发病相关,携带G等位基因可能是发病的危险因素。     

Balance between activating NKG2D,DNAM‐1, NKp44 and NKp46 and inhibitory CD94/NKG2A receptors determine natural killer degranulation towards rheumatoid arthritis synovial fibroblasts

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation and synovial hyperplasia leading to progressive joint destruction. Fibroblast‐like synoviocytes (FLS) are central components of the aggressive, tumour‐like synovial structure termed pannus, which invades the joint space and cartilage. A distinct natural killer (NK) cell subset expressing the inhibitory CD94/NKG2A receptor is present in RA synovial fluid. Little is known about possible cellular interactions between RA‐FLS and NK cells. We used cultured RA‐FLS and the human NK cell line Nishi, of which the latter expresses an NK receptor repertoire similar to that of NK cells in RA synovial fluid, as an in vitro model system of RA‐FLS/NK cell cross‐talk. We show that RA‐FLS express numerous ligands for both activating and inhibitory NK cell receptors, and stimulate degranulation of Nishi cells. We found that NKG2D, DNAM‐1, NKp46 and NKp44 are the key activating receptors involved in Nishi cell degranulation towards RA‐FLS. Moreover, blockade of the interaction between CD94/NKG2A and its ligand HLA‐E expressed on RA‐FLS further enhanced Nishi cell degranulation in co‐culture with RA‐FLS. Using cultured RA‐FLS and the human NK cell line Nishi as an in vitro model system of RA‐FLS/NK cell cross‐talk, our results suggest that cell‐mediated cytotoxicity of RA‐FLS may be one mechanism by which NK cells influence local joint inflammation in RA.     

Association of vitamin D receptor gene polymorphisms with susceptibility to asthma in Tunisian children: A case control study

Background

Vitamin D and its nuclear receptor (VDR) are linked to asthma in a genetic and immunologic basis. Polymorphisms in the VDR gene may alter the actions of vitamin D and then influence the development and the severity of asthma.

Aims

We aimed at elucidating the genetic association of VDR gene polymorphisms with susceptibility to asthma in Tunisian children and with serum vitamin D levels.

Methods

The study included 155 patients recruited from Abderrahmen MAMI hospital in Tunisia and two hundred twenty five healthy individuals matched with patients in age and sex for comparison. VDR genotypes were determined by PCR-RFLP method using endonuclease FokI, BsmI, TaqI and ApaI and vitamin D was assessed with a radioimmunoassay kit.

Results

The distribution of genotype frequencies differed significantly between asthmatics and controls (FokI: P = 0.04; BsmI: P = 0.006; TaqI: P = 0.006). Haplotype analyses revealed a significant association between bAt and bat haplotypes and asthma (P = 0.00076, P = 0.016). When patients were stratified according to atopic status and stage of severity, no significant association was detected with VDR variants. No association was found between VDR SNPs and serum 25-hydroxyvitamin D levels.

Conclusion

Our study shows a relation between VDR gene polymorphisms and susceptibility to asthma in children.     

Association of allograft inflammatory factor-1 gene polymorphism with rheumatoid arthritis

Human allograft inflammatory factor-1 (AIF-1) is a cytoplasmic protein primarily identified in human and rat allografts, and data from several studies suggest an important role for AIF-1 in inflammatory processes. The aim of this study was to examine the association between AIF1 rs2269475:C>T polymorphism and rheumatoid arthritis (RA). AIF1 genotype was determined by means of the polymerase chain reaction-restriction fragment length polymorphism method in 276 White patients with RA and 236 healthy subjects. The frequency of the AIF1 rs2269475 TT genotype was significantly higher in the patients with RA than in the controls (OR=5.59, 95% CI: 1.22-25.55). The frequency of T allele carriers in the patient group with RA was 31.9% vs 19.1% among controls (P=0.0003). Moreover, the frequency of individuals positive for anti-cyclic citrullinated peptide (anti-CCP) antibodies was significantly elevated in the T allele carriers (OR=8.82, 95% CI: 2.06-37.7). It is noteworthy that no significant linkage disequilibria between the AIF1 C/T and DRB1 alleles associated with RA development and anti-CCP antibody production [including the most frequent, i.e. *04 (32.7%) and *01 (23.5%)] (P>0.1) were found. Our results show that the AIF1 rs2269475 T allele is associated with increased risk of RA development. Moreover, the frequency of individuals positive for anti-CCP antibodies is significantly increased among T allele carriers.     

Association of MICA polymorphism with rheumatoid arthritis patients in Koreans

To investigate whether genetic variations of MICA are associated with susceptibility to rheumatoid arthritis (RA), the (GCT)n microsatellite polymorphism of the transmembrane domain was analyzed in 144 Korean patients with RA and in 297 unrelated healthy controls. The allele frequency of MICA*A9 significantly decreased in RA patients compared with controls (9.0% vs. 15.3%, odds ratio [OR] = 0.55, p = 0.0098, p_c = 0.049), whereas the frequency of the MICA*A4 and MICA*A5.1 alleles tended to increase in RA patients (21.2% vs. 14.8%, OR = 1.55, p = 0.018, p_c > 0.05; 20.5% vs. 15.0%, OR = 1.46, p = 0.0403, p_c > 0.05). By subgroup analysis, the MICA*A4 allele significantly increased in seropositive RA patients versus controls (23.0% vs. 14.8%, OR = 1.69, p = 0.0082, p_c = 0.041). HLA-DRB1*0405 was strongly associated with RA (p_c = 0.0000008), and strong linkage disequilibrium was observed between HLA-DRB1*0405 and MICA*A4 alleles in controls (p_c = 0.000004) as well as in RA patients (p_c = 0.0012). In Korean patients, HLA-DRB1*0405 was primarily associated with RA and the weak association of RA with MICA*A4 was secondary to that with HLA-DRB1*0405. Additionally, MICA*A9 might have a weak protective effect on the susceptibility to RA in Koreans.     

HLA‐G regulatory variants and haplotypes with susceptibility to recurrent pregnancy loss

HLA‐G is a nonclassical Class I major histocompatibility complex (MHC) gene. This gene has a limited protein alteration that is produced by alternative splicing and can be important in the preservation of pregnancy. Recent findings suggest that alteration in HLA‐G gene expression can lead to pregnancy failure, such as recurrent pregnancy loss (RPL). As the promoter SNPs of the gene may impact the HLA‐G expression levels, the study of these SNPs is very important. In this study, for the promoter region of HLA‐G gene in the case group (100 women with a history of two or more repeated miscarriages) and the control group (100 women with at least two successful pregnancies), PCR reaction was performed. Thereafter, PCR products were sequenced and the results were compared between the two groups. The results showed that ?1573T>C and ?1746C>A SNPs in the promoter of the HLA‐G gene associated with RPL. The outcome of the haplotype analysis also showed that the association of two haplotypes, including H1 (ATCCAGGTACGCAA) and H2 (CTTCGAGAACGCAG) with RPL, is significant. The results showed that H1 is associated with a decreased and H2 is associated with an increased risk of RPL. These results indicate the importance of the HLA‐G promoter SNPs in the pregnancy outcome. But to reach a more definite conclusion, subsequent studies on 3′ UTR and other positions with polymorphism in the 5′ UTR regions larger samples are necessary.     

人NKG2D的基因克隆及其在CHO细胞中的表达

目的:构建重组人NKG2D真核表达载体并在CHO细胞表达重组人NKG2D。方法:用RT-PCR方法从NK-92细胞中调取NKG2D基因片段,克隆到pGEM-TEasy载体并对克隆的DNA片段进行序列分析。用限制内切酶EcoRI和BamHI消化pGEM-TEasy/NKG2D重组质粒,分离NKG2D片段,并插入真核表达质粒pEGFP-N1的相应限制酶位点,酶谱分析鉴定重组表达载体pEGFP-N1/NKG2D。然后经脂质体介导转染CHO细胞。应用荧光显微镜观测、Westernblot方法和免疫组化染色对转染细胞内pEGFP-N1/NKG2D的表达进行鉴定。结果:RT-PCR扩增获得650bp基因片段,经DNA序列分析证明所获得的DNA序列与文献报道的NKG2D序列一致。转染的CHO细胞在荧光显微镜下发出强绿色荧光,Westernblot分析显示重组蛋白能特异地与抗人NKG2D单克隆抗体结合;免疫组化检测显示,转染的CHO中有棕色颗粒,证明所构建的NKG2D真核表达载体可以在细胞中表达。结论:构建了人NKG2D的哺乳动物细胞表达载体,并成功地在CHO细胞中获得重组人NKG2D的表达。     

UBASH3A gene polymorphisms and expression profile in rheumatoid arthritis

Objectives: Recent evidence has demonstrated that UBASH3A play a pivotal role in multiple autoimmune diseases. In this study, we explored the association between UBASH3A gene single-nucleotide polymorphisms (SNPs) and rheumatoid arthritis (RA) in a Chinese Han population. We also comparatively evaluated the UBASH3A expression profile in peripheral blood mononuclear cells (PBMCs) from patients with RA and healthy controls.

Methods: Four UBASH3A polymorphisms (rs1893592, rs11203203, rs2277798, and rs3788013) were studied in 553 patients with RA and 587 controls in a Chinese population. Genotyping was performed using the Fluidigm 192.24 Dynamic Array Integrated Fluidic Circuit (IFC). For gene expression study, UBASH3A mRNA levels of 30 RA patients and 31 healthy individuals were assessed by real-time quantitative polymerase chain reaction (RT-qPCR). Data were analyzed by SPSS 19.0 software.

Results: A significant association between rs1893592 polymorphism and RA was found under all genetic models (all p<.05). We also discovered a significant association between rs3788013 polymorphism and RA in the allele and genotype distributions, as well as the recessive model (all p<.05). Moreover, we found the genotype distribution and allele frequency of rs1893592 were significantly associated with RF phenotype in the RA patients (χ²?=?6.786, p=.034; χ²?=?4.534, p=.033; respectively). We also found the genotype distribution and allele frequency of rs2277798 were significantly associated with anti-CCP phenotype in the RA patients (χ²?=?7.873, p=.020; χ²?=?4.473, p=.034; respectively). However, we did not detect any significant associations between rs11203203 and RA susceptibility and autoantibody profiles (all p>.05). The mRNA expression of UBASH3A was increased in PBMCs of patients with RA when compared to healthy controls (p=.001).

Conclusions: Our observations suggested that the dysregulation of UBASH3A might be associated with the pathogenesis of RA, and UBASH3A gene polymorphisms (rs1893592 and rs3788013) might contribute to RA susceptibility in Chinese Han population.     

D6S273 microsatellite polymorphism and susceptibility to rheumatoid arthritis

Abstract: Rheumatoid arthritis (RA) is a chronic articular inflammatory disease associated with HLA-DR genes that share a five amino acid sequence motif, QKRAA or QRRAA, from position 70 to 74 in the third hypervariable region of the DRB1 molecule. Since these associations between DRB1 genes and susceptibility to RA are incomplete, we examined the role of a CA repeat polymorphic microsatellite marker, D6S273, located between HSP70 and Bat2 genes in the class III region of MHC, in susceptibility to RA. Ninety-seven adult patients with seropositive RA and 100 normal healthy subjects were studied. Two D6S273 alleles (132 and 138) showed significant differences in their prevalence in RA patients as compared to normal controls; allele 132 was significantly higher in total patients and in DRB1 QKRAA/QRRAA epitope-positive patients, and allele 138 was significantly higher in QKRAA/QRRAA-negative patients. Analysis of data suggested that the association of D6S273 132 allele with RA was secondary to that of DRB1 genes. On the other hand, D6S273 138 allele showed primary association with RA susceptibility in QKRAA/QRRAA epitope-negative patients. The D6S273 138 allele thus provides an additional risk in RA susceptibility. The results in the present study therefore suggest that two regions in MHC, DRB1 and D6S273, contribute to susceptibility to RA.     

Association between angiotensin I-converting enzyme gene polymorphism and susceptibility to cancer: a meta analysis

Background: Angiotensin I-converting enzyme (ACE) gene plays an important role in the pathogenesis of cancers. The association between ACE insertion/deletion (I/D) polymorphism and the risk of various cancers has been studied. However, the results of these studies remain conflicting. Therefore, we performed a meta-analysis to evaluate the association between ACE I/D polymorphism and the risk of cancers. Methods: PubMed, Embase, ScienceDirect, Springer, CNKI, Wanfang, Weipu, CBM databases and Google Scholar were searched for case-control studies on ACE I/D polymorphism and the risk of cancers, published up to Dec 31, 2013. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of the association between ACE I/D polymorphism and cancer risk. Results: Thirty-five published studies with 5007 cases and 8173 controls were included. Overall, there were no significant association between ACE I/D polymorphism and the risk of cancers (II vs. ID+DD OR = 1.05, 95% CI = 0.89-1.23, I vs. D OR = 1.00, 95% CI = 0.89-1.13). However, when stratified by ethnicity, we found a significant association between this polymorphism and cancer risk in Caucasians (II vs. ID+DD: OR = 1.43, 95% CI = 1.02-2.00, I vs. D: OR = 1.23, 95% CI 1.01-1.49). Conclusion: ACE I/D polymorphism is associated with the cancer risk in Caucasians.     

MHC class I chain-related gene A-A5.1 allele is associated with ulcerative colitis in Chinese population

The human MHC class I chain-related gene A (MICA) plays a role in regulating protective responses by intestinal epithelial Vdelta1 gamma delta T cells and the polymorphism of MICA were reported to be related to several autoimmune diseases. The present study aimed to investigate the association of the microsatellite polymorphisms of TM region of MICA gene with the susceptibility to ulcerative colitis (UC) in Chinese population. The microsatellite polymorphisms of the MICA were genotyped in unrelated 86 Chinese patients with UC and 172 ethnically matched healthy controls by a semiautomatic fluorenscently labelled PCR method. All the subjects were the Chinese with Han nationality. The frequency of MICA-A5.1 homozygous genotype and A5.1 allele were significantly increased in UC patients compared with healthy controls (22.1%versus 7%, P = 0.0009, Pc = 0.0126, OR = 3.781, 95%CI: 1.738-8.225 and 30.2%versus 17.4%, P = 0.0014, Pc = 0.007, OR = 2.051, 95%CI: 1.336-3.148, respectively). Adjusted the effects of gender and age at onset, MICA-A5.1 homozygous genotype and A5.1 allele were also increased in the UC patients. Moreover MICA-A5.1 allele was significantly increased in frequency in the female UC patients (38.2%versus 21.0%, P = 0.0095, Pc = 0.0475, OR = 2.326, 95%CI: 1.234-4.382). Logistic regression analysis also revealed that gender was independently associated with UC patients carried MICA-A5.1 allele (P = 0.046, OR (male) = 0.511, 95% CI: 0.264-0.987). Although the UC patients with extensive colitis (32.5%versus 17.4% in the healthy controls, P = 0.005, Pc = 0.025) and the UC patients with extraintestinal manifestations (36%versus 17.4% in the healthy controls, P = 0.0039, Pc = 0.0195) were more likely to carry the MICA-A5.1 allele, EIMs was associated with extent of disease (P < 0.0001, OR (with EIMs) = 3.511, 95% CI 1.747-7.056) and MICA-A5.1 allele was not associated with UC patients with extensive colitis or with EIMs in the logistic regression analysis. Therefore, the MICA-A5.1 homozygous genotype and A5.1 allele were closely associated with UC and the MICA-A5.1 allele was positively associated with the female UC patients in Chinese population.     

The inhibitory NK cell receptor CD94/NKG2A and the activating receptor CD94/NKG2C bind the top of HLA-E through mostly shared but partly distinct sets of HLA-E residues

The human non-classical MHC class I molecule HLA-E is a ligand for both an inhibitory NK cell receptor (CD94/NKG2A) and an activating receptor (CD94/NKG2C). To identify HLA-E surface recognized by both receptors, especially to determine if both receptors recognize the same epitope, we made a series of individually Ala-substituted HLA-E proteins and analyzed their binding to CD94/NKG2A orCD94/NKG2C. Eight HLA-E mutations that significantly impaired HLA-E binding to CD94/NKG2A are all found in the top of alpha1/alpha2 domain of HLA-E. These results suggest that CD94/NKG2A binds a HLA-E surface equivalent to a NKG2D binding site on MICA. Of the eight mutations that impaired HLA-E binding to CD94/NKG2A, six significantly impaired HLA-E binding to CD94/NKG2C suggesting that CD94/NKG2C also binds a similar surface of HLA-E. Unexpectedly, the two HLA-E mutations (D69A and H155A) selectively abrogated HLA-E binding to CD94/NKG2A, not largely affected CD94/NKG2C. These results indicate that a mostly shared, but partly distinct set of HLA-E residues is discriminated by the two receptors.