Special Reports and Review ONCOGENES AND CELL IMMUNOGENITY：v－H－ras SUPPRESSING MHC CLASS I EXPRESSION IN MOUSE FIBROBLAST

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Allelic Polymorphism,Gene Duplication and Balancing Selection of MHC Class ⅡB Genes in the Omei Treefrog(Rhacophorus omeimontis)

The worldwide declines in amphibian populations have largely been caused by infectious fungi and bacteria. Given that vertebrate immunity against these extracellular pathogens is primarily functioned by the major histocompatibility complex（MHC） class Ⅱ molecules, the characterization and the evolution of amphibian MHC class Ⅱ genes have attracted increasing attention. The polymorphism of MHC class Ⅱ genes was found to be correlated with susceptibility to fungal pathogens in many amphibian species, suggesting the importance of studies on MHC class Ⅱ genes for amphibians. However, such studies on MHC class Ⅱ gene evolution have rarely been conducted on amphibians in China. In this study, we chose Omei treefrog（Rhacophorus omeimontis）, which lived moist environments easy for breeding bacteria, to study the polymorphism of its MHC class Ⅱ genes and the underlying evolutionary mechanisms. We amplified the entire MHC class ⅡB exon 2 sequence in the R. omeimontis using newly designed primers. We detected 102 putative alleles in 146 individuals. The number of alleles per individual ranged from one to seven, indicating that there are at least four loci containing MHC class ⅡB genes in R. omeimontis. The allelic polymorphism estimated from the 102 alleles in R. omeimontis was not high compared to that estimated in other anuran species. No significant gene recombination was detected in the 102 MHC class ⅡB exon 2 sequences. In contrast, both gene duplication and balancing selection greatly contributed to the variability in MHC class ⅡB exon 2 sequences of R. omeimontis. This study lays the groundwork for the future researches to comprehensively analyze the evolution of amphibian MHC genes and to assess the role of MHC gene polymorphisms in resistance against extracellular pathogens for amphibians in China.

MHC Class I Exon 4 in the Multiocellated Racerunners(Eremias multiocellata): Polymorphism, Duplication and Selection

The major histocompatibility complex （MHC） is a dynamic genetic region with an essential role in the adaptive immunity of jawed vertebrates. The MHC polymorphism is affected by many processes such as birth-and- death evolution, gene conversion, and concerted evolution. Studies investigating the evolution of MHC class I genes have been biased toward a few particular taxa and model species. However, the investigation of this region in nonavian reptiles is still in its infancy. We present the first characterization of MHC class I genes in a species from the family Lacertidae. We assessed genetic diversity and a role of selection in shaping the diversity of MHC class I exon 4 among 37 individuals of Eremias multiocellata from a population in Lanzhou, China. We generated 67 distinct DNA sequences using cloning and sequencing methods, and identified 36 putative functional variants as well as two putative pseudogene-variants. We found the number of variants within an individual varying between two and seven, indicating that there are at least four MHC class I loci in this species. Gene duplication plays a role in increasing copy numbers of MHC genes and allelic diversity in this species. The class I exon 4 sequences are characteristic of low nucleotide diversity. No signal of recombination is detected, but purifying selection is detected in β2-microglobulin interaction sites and some other silent sites outside of the function-constraint regions. Certain identical alleles are shared by Eremias multiocellata and E. przewalskii and E. brenchleyi, suggesting trans-species polymorphism. The data are compatible with a birth-and-death model of evolution.

RFLP OF HLA CLASS I GENES IN CHINESE POPULATION AND ITS CORRELATION WITH SEROLOGICALLY DEFINED ANTIGEN SPECIFICITIES

The restriction fragnent length polymorphisms （RFLPs） of HLA class I genes in 104 unrelated healthy Chinese individuals were analyzed with Southern blot assay. The DNAs from peripheral blood leucocytes were digested with EcoRI, EcoRV and XbaI respectively, and hybridized with 32P-labeled HLA class I probe （ 1.4Kb, B7 cDNA ）. The results showed that 3 EcoRI fragments （13.7, 8.1 and 5.2 Kb ）, 3 EcoR V fragments （11.3, 7.8 and 4.1 Kb） and 7 Xbal fragmnents （21.9, 19.2, 16.3, 6.0, 3.8, 1.8 and 1.5 Kb） were polymorphic. Ten of the fragments were found to be correlated significantly with the serologically de fined antigen specificities. The significance of this kind of correlation is discussed.

Prevalence of class 1 integron and its gene cassettes carrying antibiotic resistance genes in drinking water treatment and distribution systems

Class 1 integrons are vital mobile genetic elements involved in the environmental transmission of antibiotic resistance genes(ARGs).However,knowledge about the diversity and abundance of class 1 integrons and gene cassettes during drinking water treatment and distribution is still limited.In this study,we aimed to uncover the prevalence of class 1 integrons in the drinking water treatment and distribution systems with the combination of culture-dependent and culture-independent methods.Further,we applied the nanopore sequencing method to characterize the diversity and arrangement of ARGs carried by class 1 integron-associated gene cassettes.A total of 42 isolates were inti-positive among the 208 strains isolated from drinking water,which tended to confer multi-drug resistance compared with intll-negative isolates.The absolute abundance of the intl1 average i.15×10^(9) copies/L in the source water and underwent the most significant reduction of over 99.9%after liquid chiorine disinfection.Furthermore,nanopore sequencing revealed that the class 1 integron-associated gene cassettes carried 51 subtypes of ARGs in drinking water,mainly conferring resistance to aminoglycosides and trimethoprim.The treatment processes,especially liquid chlorine disinfection,reduced most of the ARGs carried by gene cassettes,though some of the ARG subtypes persisted along the treatment and distribution ike aac(6)-Il,aadA,and dfrB2.The antibiotic resistance gene cassette array laac(6')-Ⅱ arr was most frequently detected,especially in the chlorinated water.This study underlined that drinking water was potential reservoir for integron-mediated ARGs transfer,indicating that the health risks of resistance gene cassettes in class 1 integrons deserved urgent attention.

Neutrophils in Atlantic salmon(Salmo salar L.)are MHC class II^(+)and secret IL-12p40 upon bacterial exposure

Antigen-presentation via major histocompatibility complex(MHC)to T cells is the key event to initiate adaptive immune responses.In teleosts,as in mammals,the main types of professional antigen-presenting cells(APCs)are dendritic cells(DCs),monocytes/macrophages,and B cells.In the current study,flow cytometry,immunostaining and qPCR have been used to show that neutrophils in the teleost fish Atlantic salmon(Salmo salar L.)have antigen-presenting properties.The neutrophils were positive for MHC class II,CD83 and CD80/86,and upon in vitro bacterial exposure,gene expression analysis of purified neutrophils showed that IL-12p40,which is essential for proliferation of naïve T cells,was highly upregulated at both 6 and 24 h post bacterial exposure.Based on presence of MHC class II and upregulation of molecules involved in antigen presentation and T cell activation,we suggest that neutrophils in Atlantic salmon have potential to function as professional APCs.This work makes an important basis for further exploring the potential of using neutrophils to develop new,targeted immunoprophylactic measures.

Isolation and characterization of class Ⅰ MHC genes in the giant panda(Ailuropoda melanoleuca)

Artificial breeding is an important project to protect,recover and reintroduce endangered species.Knowledge of the population's genetic diversity at functional loci is important for the establishment of effective captive breeding programs.The major histocompatibility complex(MHC) genes are ideal candidate genetic markers to inform planned breeding,due to their high levels of polymorphism and importance in the main immune coding region of the vertebrate genome.In this study,we constructed BAC-based contigs and isolated six functional MHC class Ⅰ genes from the giant panda(Ailuropoda melanoleuca),which we designated Aime-C,Aime-F,Aime-I,Aime-K,Aime-L and Aime-1906.Analyses of the tissue expression patterns and full-length cDNA sequences of these class I genes revealed that Aime-C,-F,-I and-L could be considered classical class Ⅰ loci,due to their extensive expression patterns and normal exonic structures.In contrast,Aime-K and-1906 appeared to be nonclassical genes based on their tissue-specific expression patterns and the presence of an abnormal exon 7 in both genes.We established techniques for genotyping exons 2 and 3 of the classical loci using locus-specific single strand conformation polymorphism(SSCP) and sequence analysis.In the Chengdu captive population,we identified one monomorphic locus(Aime-F) and three polymorphic loci with different numbers of alleles(4/4/4 exon 2 alleles at Aime-C/I/L and 6/5/5 exon 3 alleles at Aime-C/I/L).The distributions of the Aime-C,-I and-L alleles among members of different families were in good agreement with the known pedigree relationships,suggesting that the genotyping results are reliable.Therefore,the MHC-I genotyping techniques established in this study may provide a powerful tool for the future design of scientific breeding or release/reintroduction programs.

Characterization of MHC class Ⅱ A genes in Hainan Eld's deer(Cervus eldi hainanus)

The major histocompatibility complex(MHC) genes play pivotal roles in the immune system of vertebrates against antigens.They are also significant indicators of genetic structure,and are vital to species-level population viability analyses and disease risk assessments.In this study,two DRA and two DQA sequences were isolated from Hainan Eld's deer(Cervus eldi hainanus) using rapid amplification of cDNA ends(RACE) and single-strand conformation polymorphism-heteroduplex(SSCP-HD) analysis.Nucleotide sequence analysis revealed large differences between the two DQA sequences,especially in their exon 2 regions,but only minimal differences between the variants of the DRA gene.Comparison of the predicted amino acid sequences of the Ceel-MHC class Ⅱ A variants with those from six other species revealed that these molecules share high homology among ruminants.A phylogenetic tree of four class Ⅱ A sequences from Hainan Eld's deer and the other species placed the newly identified DQA and DRA genes on two distinct branches(100%-supportively),and further divided the two DQA sequences into 98%-supportive DQA1 and 99%-supportive DQA2 clusters,respectively.Therefore,this study identified monomorphic Ceel-DQA1 and Ceel-DQA2 genes,and one dimorphic Ceel-DRA gene from Hainan Eld's deer.

H pylori receptor MHC classⅡcontributes to the dynamic gastric epithelial apoptotic response

AIM： To investigate the role of MHC class Ⅱ in the modulation of gastric epithelial cell apoptosis induced by H pylori infection. METHODS： After stimulating a human gastric epithelial cell line with bacteria or agonist antibodies specific for MHC class Ⅱ and CD95, the quantitation of apoptotic and anti-apoptotic events, including caspase activation, BCL-2 activation, and FADD recruitment, was performed with a fluorometric assay, a cytometric bead array, and confocal microscopy, respectively. RESULTS： Pretreatment of N87 cells with the anti-MHC class ⅡIgM antibody RFD1 resulted in a reduction in global caspase activation at 24 h of H pylori infection. When caspase 3 activation was specifically measured, crosslinking of MHC class Ⅱ resulted in markedly reduced caspase activation, while simple ligation of MHC class Ⅱ did not. Crosslinking of MHC class Ⅱ also resulted in an increased activation of the anti-apoptosis molecule BCL-2 compared to simple ligation. Confocal microscope analysis demonstrated that the pretreatment of gastric epithelial cells with a crosslinking anti-MHC class Ⅱ IgM blocked the recruitment of FADD to the cell surface. CONCLUSION： The ability of MHC class Ⅱ to modulate gastric epithelial apoptosis is at least partially dependent on its crosslinking. The crosslinking of this molecule has anti-apoptotic effects during the earlier time points of Hpylori infection. This effect is possibly mediated by the ability of MHC class Ⅱ to modulate the activation of the pro-apoptotic receptor Fas by blocking the recruitment of the accessory molecule FADD, and this delay in apoptosis induction could allow for prolonged cytokine secretion by Hpylori-infected gastric epithelial cells.

H pylori receptor MHC class Ⅱ contributes to the dynamic gastric epithelial apoptotic response

AIM： TO investigate the role of MHC class Ⅱ in the modulation of gastric epithelial cell apoptosis induced by H pylori infection. METHODS： After stimulating a human gastric epithelial cell line with bacteria or agonist antibodies specific for MHC class Ⅱ and CD95, the quantitation of apoptotic and anti-apoptotic events, including caspase activation, BCL-2 activation, and FADD recruitment, was performed with a fluorometric assay, a cytometric bead array, and confocal microscopy, respectively. RESULTS： Pretreatment of N87 cells with the anti-MHC class Ⅱ IgM antibody RFD1 resulted in a reduction in global caspase activation at 24 h of H pylori infection. When caspase 3 activation was specifically measured, crosslinking of MHC class Ⅱ resulted in a marked reduced caspase activation, while simple ligation of HHC class Ⅱ did not. Crosslinking of HHC class Ⅱ also resulted in an increased activation of the anti-apoptosis molecule BCL-2 compared to simple ligation. Confocal microscope analysis demonstrated that the pretreatment of gastric epithelial cells with a crosslinking anti-HHC class Ⅱ IgH blocked the recruitment of FADD to the cell surface. CONCLUSION： The results presented here demonstrate that the ability of MHC class Ⅱ to modulate gastric epithelial apoptosis is at least partially dependent on its crosslinking. Furthermore, while previous research has demonstrated that MHC class Ⅱ signaling can be proapoptotic during extended ligation, we have shown that the crosslinking of this molecule has anti-apoptotic ef-fects during the earlier time points of Hpylori infection. This effect is possibly mediated by the ability of MHC class Ⅱ to modulate the activation of the pro-apoptotic receptor Fas by blocking the recruitment of the accessory molecule FADD, and this delay in apoptosis induction could allow for prolonged cytokine secretion by Hpyloriinfected gastric epithelial cells.

Differential recognition of MHC class I molecules of xeno-/allo-endothelial cells by human NK cells

Using human umbilical vein endothelial cells (HUVEC) and porcine aortic endothelial cells (PAEC) as target cells, human peripheral blood NK cells (PBNK) and NK92 cells as effector cells, the differential cytotoxicities of NK cells to allo- and xeno-endothelial cells were studied. The influence of MHC class I molecules on the cytotoxicity of human NK cells was assayed using acid treatment, and blockades of MHC class I antigens, CD94 and KIR (NKB1). The results indicated that the killing of PAEC by the two kinds of NK cells is higher than that of HUVEC. After acid-treatment, the cytotoxicity of the two kinds of NK cells to PAEC and HUVEC is significantly enhanced, but the magnitude of the enhancement is different. The enhancement of NK killing to acid treated HUVEC is much greater than that to PAEC. Blockade of CD94 mAb did not alter the NK cytotoxicity, while blockade of NKB1 mAb enhanced the cytotoxicity of PBNK to HUVEC and PAEC by 95% and 29% respectively. The results above suggested that the differential recognition of MHC I molecules of xeno-endothelial cells by human NK cells could be the major reason for higher NK cytotoxicity to PAEC. KIR might be the primary molecule that transduced inhibitory signals when endothelial cells were injured by NK cells.

Immunohistochemical Studies of Macrophages and MHC Class Ⅱ -positive Cells in the Iris and Ciliary Body of Lewis Rats

Purpose:To investigate the density, distribution and morphology of macrophages and MHC class II -positive dendritic cells in the iris and ciliary body of lewis rats. Methods:Immunohistochemistry was performed using monoclonal antibodies specific to monocytes and macrophages (ED1,ED2) and MHC class II -positive cells (OX6) on wholemounts of the iris-ciliary body complex isolated form normal lewis rats.Results:A well developed network of macrophages was present in the iris and ciliary body of normal lewis rats. These cells, morphologically displaying dendriti-form or pleiomorphic appearance, were more densely arranged in mid-iris (950 + 189 cells/mm2) than in iris base (482 ± 78 cells/mm2) and pupil margin (595 ± 92 cells/mm2). A similar network of MHC class II -positive cells with a cell density 452 ± 78 cells/mm2 was almost uniformly distributed in the iris of normal lewis rats.Conclusions : A network of macrophages and MHC class II -positive cells was established in the iris and ciliary body of

Assessment of 188Re marked anti MHC class II antibody by peripheral blood mononuclear cells stimulated by donor alloantigen

Background Previous studies showed that anti MHC-II monoclone antibody （MAb） only had partial inhibiting effect of alloreactive mixed lymphocyte reaction （MLR） in vitro and it was unsteady and non-persistent. The aim of this research was to determine whether radioactive isotope 188Re marked MHC-II antibody could benefit the allograft acceptance in transplantation as compared to normal MHC-II antibody. Methods 188Re was incorporated to 2E9/13F（ab＇）2 which is against swine MHC class II antigen （MAb-~88Re）. Porcine peripheral blood mononuclear （PBMC） cells were examined for proliferation and cytokine mRNA expression after stimulation with MHC-II MAb or MAb-188Re. Results The proliferative response of recipient PBMCs in mixed lymphocyte reaction （MLR） to donor alloantigen showed that the stimulation index of MAb-188Re group was significantly lower than the MHC-II MAb group and control （P 〈0.05）. mRNA expression of interleukin 2, interferon y and tumor necrosis factor a （type 1 cytokines） was lower in MAb-188Re group than the MHC-II MAb group, while interleukin 10 （type 2 cytokines） was higher in MAb-~aSRe group in the first 24 hours. Conclusion MAb-188Re could help the graft acceptance by inhibiting T cell proliferation, lowering the expression of type 1 cytokines and elevating the type 2 cytokines produced by PBMC.

五龙鹅MHC ClassⅠ基因克隆及同源建模研究

主要组织相容性复合体（MHC）与动物机体对外源性抗原的免疫应答之间存在关联。从GenBank/DDBJ/EMBL基因库中读取鸡、其他鸟类、爬行类和哺乳类的MHC ClassⅠ基因进行序列分析设计引物，使用LA—PCR法从五龙鹅的基因组中克隆了MHC ClassⅠ基因序列（DNA序列和mRNA序列GenBank登录号分别为：AM114925和AM114924），并分析其基因组结构。运用生物信息学技术对测序结果进行分析显示：基因组DNA由8个外显子和7个内含子组成，与鸡基因序列同源率为60．8％～64．1％，与人的同源率为42．9％。分子进化树进一步揭示了五龙鹅与鸡、其他鸟类、爬行类、哺乳类以及人类的进化关系，同源建模分析发现该基因由氨基末端结构域和羧基末端结构域构成。

赤点石斑鱼(Epinephelus akaara)MHC IIB基因的克隆与表达多态性分析

主要组织相容性复合体（Major histocompatibility complex，MHC）是脊椎动物体内重要的非特异性免疫基因之一。为了研究赤点石斑鱼的MHC基因的结构与表达特性，本研究运用RACE，Realtime PCR及SSCP等技术，首次成功克隆获得赤点石斑鱼（Epinephelus akaara）非特异性免疫因子MHC IIB基因的4个cDNA全序列，序列全长为1195～1355bp，含有3’UTR、启动子、多肽结合区（β1）、IGC区（β2）、跨膜区、胞质区和5’UTR区，编码区大小为750bp。氨基酸序列分析发现赤点石斑鱼MHC IIB分子具有经典MHC蛋白分子的空间结构，在多肽结合区存在极其丰富的变异，β1区由1个α螺旋与4个反向平行的β折叠构成多肽结合区，β2区由多个β折叠构成2个反向平行的三明治结构。利用SSCP技术研究了赤点石斑鱼MHC IIB的表达多态性，发现其在头肾、心、肝等12个组织器官中均能有效表达，表达多态性也异常丰富。此外，根据MHC IIB分子中相对保守的IGC区氨基酸序列构建了脊椎动物的系统进化树，也表明了该分子的IGC区氨基酸序列可以作为研究鱼类物种间进化关系的良好标记。

草鱼MHC class Ⅰ等位基因克隆及其多态性分析

为了阐明草鱼MHC class I等位基因的结构与多态性,进一步研究其与疾病的关系,从草鱼cDNA文库中克隆了MHC class I基因(Ctid-MHC I);并通过对12个个体Ctid-MHC I的克隆,分析了其等位基因的多态性与三级结构.结果显示Ctid-MHC I等位基因在α1与α2区域变异幅度大,可分为6类(Ctid-MHC I-UA-UF),9型(A-I);但是其三级结构和抗原多肽结合的关键性氨基酸十分保守.结果阐明了草鱼MHC class I分子在8个区域(A-H)置换率高,存在插入或缺失以及长度变异,使等位基因呈现高度多态性.动物MHC class I分子系统树也提示了我国大陆架上鱼类、两栖类、鸟类、哺乳动物和人的遗传距离与分枝年代.

草鱼MHC class Ⅰ基因多态性及其与鱼体抗柱形病能力关系分析

用1对引物HMC6-S和MHC6-A分别从草鱼(Ctenopharyngodon idellus)40尾抗病个体和40尾易染个体的基因组DNA中扩增MHC基因片段,扩增产物长度为262bp。在262bp的核苷酸序列中,有50个(19%)多态位点。在其编码的87个氨基酸位点中,有16个多态位点(18.39%),其中有10个位点发生在多肽结合位点上(62.5%)。对核苷酸替代的类型和位点进行分析,发现多肽结合位点的非同义碱基替代率与同义碱基替代率均大于非多肽结合位点的非同义碱基替代率与同义碱基替代率,表明氨基酸替代替换集中出现在多肽结合位点(PBR)上。分析80个个体的测序结果,发现有17种不同的MHC classⅠ等位基因,编码17种不同的氨基酸序列。等位基因A、B、C、D是2个群体共有的,其中等位基因A出现的频率最高,占总样本数量的36.25%;等位基因E、F、G、H、I、P只出现在抗病个体中,等位基因J、K、L、M、N、O、Q只出现在易染个体中。

Occurrence and distribution of antibiotic resistance genes in the sediments of the East China Sea bays

The coastal area of the East China Sea has experienced rapid urbanization and industrialization in China since 1980 s, resulting in severe pollution of its environments.Antibiotic resistance genes(ARGs) are regarded as a kind of emerging pollutant with potential high risk. The sediment samples were collected from Hangzhou Bay(HB),Xiangshan Bay(XB), and Taizhou Bay(TB) to investigate the spatial occurrence and distribution of 27 ARGs and class I integron–integrase gene(intI1) in the coastal area of the East China Sea. The PCR results showed the frequent presence of 11 ARGs and intI1 in the sediments of the three bays. The qPCR results further showed that sulfonamide resistance was the most prevalent ARG type and antibiotic target replacement and protection were the most important resistance mechanisms in the sediments. Regarding the subtype of ARGs, sulI, tetW, and dfrA13 were the most abundant ARGs, in which sulI was higher in TB(based on both the absolute and relative abundances) and dfrA13 was higher in HB(based on the relative abundances). The network analysis revealed that intI1 had significant correlations with tetC, sulI, sulII, and blaPSE-1. Oil was the key connected factor, which had positive connections with sulI, sulII, and blaPSE-1. In addition, the joint effect of heavy metals and nutrients & organic pollutants might be crucial for the fate of ARGs in the coastal sediments.

赤点石斑鱼MHC IA基因的克隆与表达多态性分析

采用RACE技术,成功克隆获得赤点石斑鱼(Epinephelus akaara)非特异性免疫因子MHC IA基因的4个cDNA全序列,序列全长为1 680bp,含有3′UTR、启动子、多肽结合区(α1)、IGC区(α2)、跨膜区、胞质区和5′UTR区,编码区大小为1 074～1 080bp,共编码357～359个氨基酸,推测蛋白质分子质量约41.66ku.氨基酸序列分析发现赤点石斑鱼MHC IA分子具有经典MHC蛋白分子的空间结构,在多肽结合区则存在极其丰富的变异.利用Real time PCR和SSCP技术研究了赤点石斑鱼MHC IA的组织表达特异性和表达多态性,发现其在头肾、心、肝等12个组织器官中均能有效表达,在头肾,脾,胸腺等免疫组织表达量不仅高,表达多态性也异常丰富,而在与外界环境接触较多的鳃、肌肉、肠等组织表达较弱.此外,根据MHC IIB分子中相对保守的IGC区氨基酸序列构建了脊椎动物的系统进化树,也表明了该分子的IGC区氨基酸序列可以作为研究鱼类物种间进化关系的良好标记.

抗MHC I类单抗对NK细胞杀伤能力的影响

目的：探讨ＮＫ细胞杀伤与靶细胞表面ＭＨＣＩ类分子的关系。方法：用ＨＬＡＡＢＣ单抗培养上清或腹水封闭靶细胞Ｋ５６２表面的ＨＬＡＡＢＣ分子后，分别观察了外周血新鲜ＮＫ细胞、纯化ＮＫ细胞、ＬＡＫ细胞和ＣＤ３ＡＫ细胞对Ｋ５６２细胞杀伤能力的变化。结果：外周血新鲜ＮＫ细胞和纯化ＮＫ细胞对Ｋ５６２的杀伤率明显提高，ＣＤ３ＡＫ细胞的杀伤力明显降低，ＬＡＫ细胞的杀伤无明显变化。结论：ＮＫ细胞通过其表面受体识别靶细胞上的ＭＨＣＩ类分子而传递杀伤抑制性信号，抗ＨＬＡＡＢＣ单抗封闭了靶细胞上的ＨＬＡＡＢＣ等位基因而阻止了阴性信号的传导。