Antigen bias in T cell cross-priming

Activated CD8+ T cells detect virally infected cells and tumor cells by recognition of major histocompatibility complex class I-bound peptides derived from degraded, endogenously produced proteins. In contrast, CD8+ T cell activation often occurs through interaction with specialized antigen-presenting cells displaying peptides acquired from an exogenous cellular source, a process termed cross-priming. Here, we observed a marked inefficiency in exogenous presentation of epitopes derived from signal sequences in mouse models. These data indicate that certain virus- and tumor-associated antigens may not be detected by CD8+ T cells because of impaired cross-priming. Such differences in the ability to cross-present antigens should form important considerations in vaccine design.     

Recognition of a ubiquitous self antigen by prostate cancer-infiltrating CD8+ T lymphocytes

Substantial evidence exists that many tumors can be specifically recognized by CD8+ T lymphocytes. The definition of antigens targeted by these cells is paramount for the development of effective immunotherapeutic strategies for treating human cancers. In a screen for endogenous tumor-associated T cell responses in a primary mouse model of prostatic adenocarcinoma, we identified a naturally arising CD8+ T cell response that is reactive to a peptide derived from histone H4. Despite the ubiquitous nature of histones, T cell recognition of histone H4 peptide was specifically associated with the presence of prostate cancer in these mice. Thus, the repertoire of antigens recognized by tumor-infiltrating T cells is broader than previously thought and includes peptides derived from ubiquitous self antigens that are normally sequestered from immune detection.     

Glycolipid antigen processing for presentation by CD1d molecules

The requirement for processing glycolipid antigens in T cell recognition was examined with mouse CD1d-mediated responses to glycosphingolipids (GSLs). Although some disaccharide GSL antigens can be recognized without processing, the responses to three other antigens, including the disaccharide GSL Gal(alpha1-->2)GalCer (Gal, galactose; GalCer, galactosylceramide), required removal of the terminal sugars to permit interaction with the T cell receptor. A lysosomal enzyme, alpha-galactosidase A, was responsible for the processing of Gal(alpha1-->2)GalCer to generate the antigenic monosaccharide epitope. These data demonstrate a carbohydrate antigen processing system analogous to that used for peptides and an ability of T cells to recognize processed fragments of complex glycolipids.     

Endogenous MHC class II processing of a viral nuclear antigen after autophagy

CD4+ T cells classically recognize antigens that are endocytosed and processed in lysosomes for presentation on major histocompatibility complex (MHC) class II molecules. Here, endogenous Epstein-Barr virus nuclear antigen 1 (EBNA1) was found to gain access to this pathway by autophagy. On inhibition of lysosomal acidification, EBNA1, the dominant CD4+ T cell antigen of latent Epstein-Barr virus infection, slowly accumulated in cytosolic autophagosomes. In addition, inhibition of autophagy decreased recognition by EBNA1-specific CD4+ T cell clones. Thus, lysosomal processing after autophagy may contribute to MHC class II-restricted surveillance of long-lived endogenous antigens including nuclear proteins relevant to disease.     

CD8+ T cell cross-priming via transfer of proteasome substrates

"Cross-priming" describes the activation of na?ve CD8+ T cells by professional antigen-presenting cells that have acquired viral or tumor antigens from "donor" cells. Antigen transfer is believed to be mediated by donor cell-derived molecular chaperones bearing short peptide ligands generated by proteasome degradation of protein antigens. We show here that cross-priming is based on the transfer of proteasome substrates rather than peptides. These findings are potentially important for the rational design of vaccines that elicit CD8+ T cell responses.     

Normal development of mice deficient in beta 2M, MHC class I proteins, and CD8+ T cells

Major histocompatibility class I proteins display viral and self antigens to potentially responsive cells and are important for the maturation of T cells; beta 2-microglobulin (beta 2M) is required for their normal expression. Mouse chimeras derived from embryonic stem cells with a disrupted beta 2M gene transmitted the inactivated gene to their progeny. Animals homozygous for the mutated beta 2M gene were obtained at expected frequencies after further breeding. The homozygotes appeared normal, although no class I antigens could be detected on their cells and the animals are grossly deficient in CD4- CD8+ T cells, which normally mediate cytotoxic T cell function.     

Assistance of microbial glycolipid antigen processing by CD1e

Complexes between CD1 molecules and self or microbial glycolipids represent important immunogenic ligands for specific subsets of T cells. However, the function of one of the CD1 family members, CD1e, has yet to be determined. Here, we show that the mycobacterial antigens hexamannosylated phosphatidyl-myo-inositols (PIM6) stimulate CD1b-restricted T cells only after partial digestion of the oligomannose moiety by lysosomal alpha-mannosidase and that soluble CD1e is required for this processing. Furthermore, recombinant CD1e was able to bind glycolipids and assist in the digestion of PIM6. We propose that, through this form of glycolipid editing, CD1e helps expand the repertoire of glycolipidic T cell antigens to optimize antimicrobial immune responses.     

结核分枝杆菌RD1区T细胞表位分布情况预测及分析

[目的]对结核分枝杆菌RD1区T细胞表位分布情况进行预测和分析。[方法]利用NetMHC server生物信息学软件,以和HLA-Ⅱ和HLA-Ⅰ类分子结合能力为指标,分别对结核分枝杆菌RD1区9个编码蛋白进行T细胞抗原表位预测。[结果]通过预测,共获得和HLA-Ⅱ类分子结合的抗原表位1580个和HLA-Ⅰ类分子结合的抗原表位336个。[结论]预测获得的T细胞抗原表位将对结核病特异性检测及新的结核疫苗研发起到借鉴作用。     

结核分枝杆菌RD1区T细胞表位分布情况预测及分析

[目的]对结核分枝杆菌RD1区T细胞表位分布情况进行预测和分析。[方法]利用NetMHC server生物信息学软件,以和HLA-Ⅱ和HLAⅠ-类分子结合能力为指标,分别对结核分枝杆菌RD1区9个编码蛋白进行T细胞抗原表位预测。[结果]通过预测,共获得和HLA-Ⅱ类分子结合的抗原表位1 580个和HLA-Ⅰ类分子结合的抗原表位336个。[结论]预测获得的T细胞抗原表位将对结核病特异性检测及新的结核疫苗研发起到借鉴作用。     

The role of B cells for in vivo T cell responses to a Friend virus-induced leukemia

B cells can function as antigen-presenting cells and accessory cells for T cell responses. This study evaluated the role of B cells in the induction of protective T cell immunity to a Friend murine leukemia virus (F-MuLV)-induced leukemia (FBL). B cell-deficient mice exhibited significantly reduced tumor-specific CD4+ helper and CD8+ cytotoxic T cell responses after priming with FBL or a recombinant vaccinia virus containing F-MuLV antigens. Moreover, these mice had diminished T cell responses to the vaccinia viral antigens. Tumor-primed T cells transferred into B cell-deficient mice effectively eradicated disseminated FBL. Thus, B cells appear necessary for efficient priming but not expression of tumor and viral T cell immunity.     

Editing of CD1d-bound lipid antigens by endosomal lipid transfer proteins

It is now established that CD1 molecules present lipid antigens to T cells, although it is not clear how the exchange of lipids between membrane compartments and the CD1 binding groove is assisted. We report that mice deficient in prosaposin, the precursor to a family of endosomal lipid transfer proteins (LTP), exhibit specific defects in CD1d-mediated antigen presentation and lack Valpha14 NKT cells. In vitro, saposins extracted monomeric lipids from membranes and from CD1, thereby promoting the loading as well as the editing of lipids on CD1. Transient complexes between CD1, lipid, and LTP suggested a "tug-of-war" model in which lipid exchange between CD1 and LTP is on the basis of their respective affinities for lipids. LTPs constitute a previously unknown link between lipid metabolism and immunity and are likely to exert a profound influence on the repertoire of self, tumor, and microbial lipid antigens.     

Extrafollicular activation of lymph node B cells by antigen-bearing dendritic cells

In contrast to na?ve T cells that recognize short antigen-derived peptides displayed by specialized antigen-presenting cells, immunoglobulin receptors of B lymphocytes primarily recognize intact proteins. How and where within a lymph node such unprocessed antigens become available for na?ve B cell recognition is not clear. We used two-photon intravital imaging to show that, after exiting high-endothelial venules and before entry into lymph node follicles, B cells survey locally concentrated dendritic cells. Engagement of the B cell receptor by the dendritic cell (DC)-associated antigen leads to lymphocyte calcium signaling, migration arrest, antigen acquisition, and extrafollicular accumulation. These findings suggest a possible role for antigen-specific B-DC interactions in promoting T cell-dependent antibody responses in vivo.     

Brefeldin A specifically inhibits presentation of protein antigens to cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTLs) recognize foreign antigens, including viral proteins, in association with major histocompatibility complex (MHC) class I molecules. Brefeldin A, a specific inhibitor of exocytosis, completely and reversibly inhibited the presentation of viral proteins, but not exogenous peptides, to MHC class I-restricted CTLs directed against influenza virus antigens. The effect of brefeldin A on antigen presentation correlated with its inhibition of intracellular transport of newly synthesized class I molecules. Brefeldin A is thus a specific inhibitor of antigen processing for class I-restricted T cell recognition. Its effect on antigen presentation supports the idea that exogenous peptide antigens associate with cell surface class I molecules, whereas protein antigens processed via the cytosolic route associate with nascent class I molecules before they leave the trans-Golgi complex.     

A virus-encoded "superantigen" in a retrovirus-induced immunodeficiency syndrome of mice.

The development of an immunodeficiency syndrome of mice caused by a replication-defective murine leukemia virus (MuLV) is paradoxically associated with a rapid activation and proliferation of CD4+ T cells that are dependent on the presence of B cells. The responses of normal spleen cells to B cell lines that express the defective virus indicated that these lines express a cell surface determinant that shares "superantigenic" properties with some microbial antigens and Mls-like self antigens. This antigen elicited a potent proliferative response that was dependent on the presence of CD4+ T cells and was associated with selective expansion of cells bearing V beta 5. This response was markedly inhibited by a monoclonal antibody specific for the MuLV gag-encoded p30 antigen.     

Self-nonself discrimination by T cells

The alpha beta T cell receptor (TCR) recognizes antigens that are presented by major histocompatibility complex (MHC)-encoded cell surface molecules by binding to both the antigen and the MHC molecules. Discrimination of self from nonself antigens and MHC molecules is achieved by negative and positive selection of T cells in the thymus: potentially harmful T cells with receptors that bind to self antigens plus self MHC molecules are deleted before they can mount immune responses. In contrast, the maturation of useful T cells with receptors that bind foreign antigens plus self MHC molecules requires the binding of their receptor to MHC molecules on thymic epithelium in the absence of foreign antigen. The binding of the TCR to either class I or class II MHC molecules directs differentiation of the selected cells into either CD4-8+ (killer) or CD4+8- (helper) T cells, respectively.     

Defective presentation of endogenous antigen by a cell line expressing class I molecules

Cytotoxic T lymphocytes (CTLs) recognize class I major histocompatibility complex (MHC) molecules associated with antigenic peptides derived from endogenously synthesized proteins. Binding to such peptides is a requirement for class I assembly in the endoplasmic reticulum (ER). A mutant human cell line, T2, assembles and transports to its surface some, but not all, class I MHC molecules. The class I molecules expressed on the surface of T2 do not present peptides derived from cytosolic antigens, although they can present exogenously added peptides to CTL. The transported class I molecules may interact weakly with an unknown retaining factor in the ER such that they can assemble despite the relative shortage of peptides.     

Recognition of HLA-A2 by cytotoxic T lymphocytes after DNA transfer into human and murine cells

A gene coding for the major histocompatibility antigen HLA-A2 was transferred into human HLA-A2 negative M1 cells and murine L cells. Following transfection, these cells expressed molecules at the cell surface that are biochemically indistinguishable from HLA-A2 antigens on the human cell line JY from which the HLA-A2 gene was isolated. The M1A2 cells were recognized and lysed by a cytolytic T-cell clone specific for HLA-A2. The transfected L cells which express HLA-A2 in association with human beta 2-microglobulin were not lysed by this T-cell clone. The specific cytolysis of M1A2 cells could be inhibited by monoclonal antibodies to HLA-A2, and monoclonal antibodies to T3, T8, and LFA-1 on cytotoxic T lymphocytes. These results suggest that killing by allospecific T cells requires HLA-A2 antigens as well as other species-specific structures on the target cell surface.     

T cells against a bacterial heat shock protein recognize stressed macrophages

Heat shock proteins are evolutionarily highly conserved polypeptides that are produced under a variety of stress conditions to preserve cellular functions. A major antigen of tubercle bacilli of 65 kilodaltons is a heat shock protein that has significant sequence similarity and cross-reactivity with antigens of various other microbes. Monoclonal antibodies against this common bacterial heat shock protein were used to identify a molecule of similar size in murine macrophages. Macrophages subjected to various stress stimuli including interferon-gamma activation and viral infection were recognized by class I-restricted CD8 T cells raised against the bacterial heat shock protein. These data suggest that heat shock proteins are processed in stressed host cells and that epitopes shared by heat shock proteins of bacterial and host origin are presented in the context of class I molecules.     

猪CD127流式单克隆抗体的研制

[目的]研制出猪CD127(调节因子IL-7受体α链)流式单克隆抗体,为研究分析猪淋巴细胞亚群,尤其是猪Treg细胞亚群提供流式细胞分析抗体,也为进一步探究猪抗病性状与免疫机制间的关系打下基础.[方法]克隆猪CD127基因片段,通过原核载体诱导表达出相应的融合蛋白,以纯化后的融合蛋白免疫Balb/c小鼠,然后取其脾细胞与SP2/0骨髓瘤细胞融合,综合ELISA和流式细胞仪检测筛选出亚克隆抗体,并采用Western blotting验证所得亚克隆抗体能否与猪淋巴细胞上的CD127特异性结合.[结果]猪CD127基因cDNA全长1999 bp,第49~1428 bp为开放阅读框(ORF),编码459个氨基酸,其中前21位氨基酸为信号肽,成熟肽N端第1~219位氨基酸为胞外蛋白,第220~242位氨基酸为跨膜蛋白,第243~459位氨基酸为胞内蛋白.以pET28a和pET32a原核载体诱导表达CD127胞外片段可获得大小介于34~43 kD的融合蛋白,经Ni亲和层析柱纯化后用于免疫Balb/c小鼠,6只免疫小鼠血清中的多克隆抗体均能对猪淋巴细胞中的CD3阳性细胞(CD3+)进行共标记,其中以M2和M4两只免疫小鼠抗血清对CD3+的共标记效果较优,分群清晰;但流式细胞仪检测发现,仅2.3%的CD3+能与M2混合池培养基上清液中的分泌抗体共标记,而67.0%的CD3+能与M4混合池培养基上清液中的分泌抗体共标记,且分群清晰.从M4混合池中筛选出6株效价稳定的亚克隆细胞株(1E2、1D8、2F3、2F8、3C6和4E1),且以1D8、2F3、2F8和3C6亚克隆抗体标记的CD3+较多,其培养基上清液中的分泌抗体在猪胸腺和肌肉样品中均能检测出大小约50 kD的单一目的条带.[结论]制备获得的猪CD127流式单克隆抗体可与T淋巴细胞表面的IL-7受体特异性结合,同时在流式细胞仪检测过程中可用于猪Treg细胞亚群检测.     

Thymocyte expression of RAG-1 and RAG-2: termination by T cell receptor cross-linking.

The expression of the V(D)J [variable (diversity) joining elements] recombination activating genes, RAG-1 and RAG-2, has been examined during T cell development in the thymus. In situ hybridization to intact thymus and RNA blot analysis of isolated thymic subpopulations separated on the basis of T cell receptor (TCR) expression demonstrated that both TCR- and TCR+ cortical thymocytes express RAG-1 and RAG-2 messenger RNA's. Within the TCR+ population, RAG expression was observed in immature CD4+CD8+ (double positive) cells, but not in the more mature CD4+CD8- or CD4-CD8+ (single positive) subpopulations. Thus, although cortical thymocytes that bear TCR on their surface continue to express RAG-1 and RAG-2, it appears that the expression of both genes is normally terminated during subsequent thymic maturation. Since thymocyte maturation in vivo is thought to be regulated through the interaction of the TCR complex with self major histocompatibility complex (MHC) antigens, these data suggest that signals transduced by the TCR complex might result in the termination of RAG expression. Consistent with this hypothesis, thymocyte TCR cross-linking in vitro led to rapid termination of RAG-1 and RAG-2 expression, whereas cross-linking of other T cell surface antigens such as CD4, CD8, or HLA class I had no effect.