双阴性调节性T细胞在免疫抑制中的作用及其机制

αβTCR+CD3+CD4-CD8-双阴性调节性T细胞(DN Treg细胞）被证实具有通过对效应性T细胞的直接杀伤作用从而抑制免疫应答的能力。DN Treg细胞与特异性抗原接触后增加其调节活性,该过程部分通过其对抗原呈递细胞表面MHC抗原肽复合物的识别作用介导。DN Treg细胞与靶细胞接触后可通过Fas和Fas配体之间的交互作用介导其杀伤效应。对DN Treg细胞功能特性、分子表达方式及其激活机制的深入研究将有助于探索临床新的治疗手段。     

Antigen specificity of immune suppression by myeloid-derived suppressor cells

Among the mechanisms set in motion by the tumor to escape the control of the immune system, MDSCs play a central role in inducing tolerance to a variety of anti-tumor effectors, including T lymphocytes. It has been demonstrated that MDSCs expand in tumor-bearing mice and in cancer patients, leading to an impairment of T cell reactivity against the tumor. However, as the presence of MDSCs is not correlated with a general immune suppression, it was advanced that a mechanism regulating the specificity of MDSC inhibition must be present. In this article, we review the literature showing that MDSCs exert their immune-suppressive function on Ag-specific T cell responses but at times, also on mitogen-activated T lymphocytes, therefore bypassing the Ag dependency. We propose that the features of MDSC-mediated immune suppression might be influenced not only by the specific microenvironment in which MDSCs expand and by the tumor characteristics but also by the levels of activation of the target lymphocytes.     

The role of suppressor T cells in regulation of immune responses

Suppressor T cells play important roles in the regulation of immune responses and the mediation of dominant immunologic tolerance. Studies of suppressor T-cell function have been hampered until their recent identification as a minor fraction (approximately 10%) of CD4 ( +) T cells that coexpress CD25. CD4(+)CD25(+ ) T cells have been shown to play a critical role in the prevention of organ- specific autoimmunity and allograft rejection. Because tumor antigens are self- antigens, it is not surprising that CD4(+)CD25(+) T cells also inhibit the induction of tumor immunity. The spectrum of activity of CD4(+ ) CD25(+) cells extends to non-self-antigens, including infectious agents. Indeed, T cell-mediated suppression might be responsible for the low level of chronic infection seen with many pathogens. Interestingly, however, this persistent level of infection might be beneficial to the host and needed for maintenance of immunologic memory. Although CD4(+ ) CD25(+) T cells are capable of inhibiting T(H)2 responses, their role in the suppression of allergic responses has not been firmly established. Depending on the desired immune response, enhancement or restraint of suppressor T-cell function might be required. Therefore immunologic or pharmacologic manipulation of regulatory T-cell populations represents an important future approach to immunotherapy of a wide range of immune responses.     

Anergic T cells effect linked suppression

Although the phenomenon of T cell-mediated suppression is well established, particularly in experimental models of transplantation, the mechanisms involved in this form of immunoregulation remain controversial. We have recently demonstrated, using an in vitro system, that anergic T cells can act as suppressor cells by competing for the membrane of the antigen-presenting cell (APC) and for locally produced interleukin-2. In the experiments described here we have explored the ability of anergic T cells to effect linked suppression in antigen-specific and allospecific responses. We observed that anergic antigen-specific CD4⁺ T cells can inhibit T cells restricted by a different major histocompatibility complex (MHC) class II molecule provided that both restriction elements are expressed by the same APC. In addition, anergic allospecific clones could also effect linked suppression since they could regulate not only T cells specific for the same alloantigen but also responder T cells with direct allospecificity for a second allogeneic MHC molecule or with indirect, self MHC-restricted allospecificity for a processed MHC class I alloantigen. Furthermore, the regulatory effect of the anergic T cells was dependent on cell contact, was not dependent upon irradiation, and was maintained during in vitro culture. These data demonstrate that linked suppression can be effected by anergic T cells in vitro. In the clinical context this raises the possibility that induction of tolerance to a single alloantigen could serve to regulate the immune response to an allograft carrying several MHC and minor antigen differences.     

Tumor-induced tolerance and immune suppression by myeloid derived suppressor cells

Summary: Emerging evidence indicates that the Achilles' heel of cancer immunotherapies is often the complex interplay of tumor-derived factors and deviant host properties, which involve a wide range of immune elements in the lymphoid and myeloid compartments. Regulatory lymphocytes, tumor-conditioned myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages, and dysfunctional and immature dendritic cells take part in a complex immunoregulatory network. Despite the fact that some mechanisms governing tumor-induced immune tolerance and suppression are starting to be better understood and their complexity dissected, little is known about the diachronic picture of immune tolerance. Based on observations of MDSCs, we present a time-structured and topologically consistent idea of tumor-dependent tolerance progression in tumor-bearing hosts.     

天花粉蛋白合成肽通过激活抑制性CD8~+ T细胞诱导免疫抑制

为了探讨天花粉蛋白合成肽(M-Tk)诱导免疫抑制的机制,应用小鼠针对可溶性抗原OVA的增殖系统,检测M-Tk处理后对淋巴细胞增殖的抑制作用和细胞因子格局的变化,以及M-Tk激活的T淋巴细胞亚群的表型及功能。结果表明,M-Tk可诱导一群CD8+ T抑制性细胞,其表型为CD8+CD28-CTLA4+,采用双层非接触共培养系统发现,该群抑制性细胞主要依赖于细胞因子IL-10、IL-4和细胞间接触发挥免疫抑制作用。     

Monocyte suppressor function in burns: T cell-monocyte interaction in mediating suppression

Reduced in vitro T cell mitogen-induced transformation, low proportion of T cells and increased proportion of non-T cells were found in blood mononuclear cells of patients with severe burns 3-12 days after the injury. High spontaneous proliferation of non-T cells was observed and could be related mainly to the B cell fraction. Monocytes mediated suppression of mitogen-stimulated T cell proliferation. We further studied the role of monocytes in the enhanced suppressor activity of Con A-activated T cells and found that in this assay system, the patient's T cells mediated suppression in collaboration with monocytes. In vitro, increased suppressor function was probably the result of in vivo stimulation of inhibitory activity ascribed to both monocytes and T cells of patients. Addition of indomethacin to cell cultures markedly reduced suppression of lymphocyte proliferation. Less significant reduction was noted when the patient's T cells were activated in vitro by Con A. Adjuvant treatment of burn patients with indomethacin may play a role in alleviating suppression of immune response in these patients.     

Control of primary IgM antibody responses to H-2 alloantigens by antigen-bearing live B lymphocytes

Alloantigen-bearing (H-2d+) peripheral red blood cells, but not red cell-depleted H-2d+ spleen cells, induce primary IgM anti-H-2d plaque-forming cell responses. In this study it is reported that the primary antibody responses to H-2d+ peripheral red blood cells can be markedly suppressed by a subpopulation of H-2d+ spleen cells when they are injected simultaneously or a few days before injection of red blood cells. This suppression was antigen (H-2d)-specific, did not depend on T cells of either the donor or the recipient, and strictly required live donor cells. An energy-dependent action of the donor cell cortex and some proliferation of donor cells in the recipient seemed to be involved in the mechanism of suppression. The donor-suppressor cell type was largely present in the spleen but not in the bone marrow and thymus, and was present in the spleen of athymic nude mice. The suppressor cells displayed the properties of B lymphocytes: they adhered to the nylon wool but not to glass, were of relatively low density (rho less than 1.09), and were surface Ig+, Ia+, Fc receptor-positive but Thy-1-. H-2d+ suppressor-donor B lymphocytes might directly signal to antigen-specific recipient B cells competing with the signal provided by H-2d+ red blood cells for the B cell activation.     

Control of immune responses by immunoregulatory T cells

Immunoregulatory T cells play a key role in modifying the immune responses to self antigens, tumor antigens, and pathogenic organisms. This review summarizes recent data on naturally occurring CD4⁺ regulatory T cells that constitutively express CD25 (CD25⁺T_reg). We examine the markers that can be used to differentiate these cells from effector T cells, what is known about their mode of action in controlling the activity of effector T cells, the antigenic specificity of CD25⁺T_reg, and their ability to survive and to be selected in vivo. We also summarize specific information on the role of CD25⁺T_reg in controlling anti-tumor responses, an area were manipulation of this subset holds particular clinical promise.     

髓样抑制细胞免疫抑制机理的研究

目的:研究荷瘤小鼠来源的髓样抑制细胞(Myeloid derived suppressor cell,MDSC)在肿瘤免疫抑制中的作用机理。方法:用Percoll分离法从荷瘤小鼠的脾脏和骨髓中分离Gr-1+CD11b+MDSC;用流式细胞术检测MDSC对T细胞增殖的抑制作用;分别用生化法和ELISA技术检测MDSC体外培养上清中抑制性因子NO、ROS和IL-10、TGF-β的含量。结果:MDSC在荷瘤小鼠的脾脏和骨髓中聚集增多,且其在骨髓中所占的比例显著高于脾脏;MDSC可以明显抑制脾脏细胞的增殖,体外培养6小时的MDSC可以分泌大量NO、ROS和IL-10、TGF-β。结论:本实验进一步证实MDSC可以通过分泌大量NO、ROS和IL-10、TGF-β抑制T细胞增殖。     

Biochemical purification of detergent-solubilized H-2 alloantigens

A multistep Chromatographic fractionation scheme is described for purifying the H-2K^b and H-2D^b major histocompatibility antigens as isolated from the murine lymphoblastoid cell line EL4 (H-2^b haplotype). The membrane-integrated antigen molecules were solubilized with the non-ionic detergent NP-40 and were purified by gel filtration chromatography, ion exchange chromatography and affinity chromatography with lentil lectin conjugated to Sepharose. During the latter procedure, use of a linear gradient monosaccharide elution effected partial separation of the H-2K^b and H-2D^b antigens. At this stage the H-2 glycoproteins were highly purified based on several criteria. Upon polyacrylamide gel electrophoresis in SDS the major band migrates with a mol. wt of approximately 45,000 daltons corresponding to the mol. wt of antigens obtained by immunoprecipitation. Moreover, near identity of the profiles of the arginine-containing tryptic peptides from chromatographically-purified and immunoprecipitated H-2K^b preparations suggests that a high degree of homogeneity has been achieved in the Chromatographic purification. As is demonstrated, mg quantities of the H-2K^b and the H-2D^b antigens can be isolated and partially separated from each other by this purification scheme thereby opening the way for structural studies of the H-2K and H-2D molecules by a variety of biochemical methods.     

Regulation of immune responses by natural killer T cells

Natural killer T (NKT) cells, which comprise a minor population of T cells in primary and secondary lymphoid organs, possess phenotypic characteristics of both NK and T cells. NKT cells respond to various external stimuli by an early burst of cytokines, including IL-4 and IFN-gamma. Thus, a key immunoregulatory role has been attributed to them. Autoimmune diseases, especially type I diabetes (TID), may be caused by dysregulation of the immune system, which leads to hyporesponsiveness of regulatory T helper 2 (Th2) cells and promotion of autoimmune Th1 cells. Furthermore, several lines of evidence exist to support the notion that an NKT cell deficiency in individuals at risk of TID may be causal to TID. As a result, targeting NKT cells using immunotherapeutic agents may prove beneficial in the prevention or recurrence of TID. Indeed, our data demonstrate that stimulation of NKT cells with a specific ligand prevents the onset and recurrence of TID in nonobese diabetic (NOD) mice.     

Suppression of the cytotoxic T cell response to minor alloantigens in vivo. Linked recognition by suppressor T cells

This report describes the activity of transferable suppressor T cells (Ts) generated in vivo in response to minor alloantigens. These Ts cells are antigen specific in both primary and secondary in vivo cytotoxic T lymphocyte responses to minor alloantigens and are the result of a host response rather than of a graft-vs.-host reaction. The Ts cells are produced soon after immunization and their activity is transient. They act via "linked recognition", since they can suppress the cytotoxic T lymphocyte response to noncross-reactive minor antigens, but only if these are presented on the same antigenic cell. A model for dominant low responsiveness in (high X low responder)F1 animals is proposed, whereby Ts cells, activated via the low responder allele, work by linked recognition to suppress helper cells activated via the high responder allele.     

TGF-beta: the perpetrator of immune suppression by regulatory T cells and suicidal T cells

Innate and adaptive immunity function to eliminate foreign invaders and respond to injury while enabling coexistence with commensal microbes and tolerance against self and innocuous agents. Although most often effective in accomplishing these objectives, immunologic processes are not fail-safe and may underserve or be excessive in protecting the host. Checks and balances to maintain control of the immune system are in place and are becoming increasingly appreciated as targets for manipulating immunopathologic responses. One of the most recognized mediators of immune regulation is the cytokine transforming growth factor-beta (TGF-beta), a product of immune and nonimmune cells. Emerging data have unveiled a pivotal role for TGF-beta as a perpetrator of suppression by CD4(+)CD25(+) regulatory T (Treg) cells and in apoptotic sequelae. Through its immunosuppressive prowess, TGF-beta effectively orchestrates resolution of inflammation and control of autoaggressive immune reactions by managing T cell anergy, defining unique populations of Treg cells, regulating T cell death, and influencing the host response to infections.     

Feedback regulation of immune suppression by a suppressor factor

Mouse hybridomas generated by fusion between a lactate dehydrogenase-B (LDH-B)-specific B10.A(2R) T suppressor (Ts) cell line and the BW5147 thymoma secrete two suppressor factors, TsF-A and TsF-E. The factors carry the same antigen-binding chains but different major histocompatibility complex (MHC) chains (A_β-like and E_β-like, respectively). The TsF-A suppresses the proliferation of A-restricted, LDH-B-specific T helper (Th) cells. In this report we demonstrate that the addition of the TsF-E (isolated on immunosorbent columns with E^k- or J^k-specific antibodies) to the culture of LDH-B-primed B10.A(2R) lymph node cells turns the nonrespnder (suppressed) cultures into proliferating ones, and that this change is antigen specific. This enhancing effect occurs in the early phase of the cell culture; the factor has no effect when added 2 days after the initiation of the culture. Because pretreatment of the Ly-2⁺ but not of the Ly-1⁺2^? cells with TsF-E induces responsiveness, it is very likely that the targets of the factor are the Ts cells or their precursors that belong to the Ly-2⁺ subset. An incubation period of about 4 h is necessary for the TsF-E to expert its action. The enhancing effect of the TsF-E is abrogated by monoclonal antibodies specific for E^k and J^k antigenic determinants. However, only some of the antibodies that retain the TsF-E on the immunosorbent column neutralize the factor in a functional test. Antibody blocking studies also indicate that the MHC determinants involved in the interaction between the antigen-presenting and the Ts cell during Ts cell activaton, and in the TsF-E Ts cell interaction are either very similar or identical. We interpret the data as indicating that the Ts cells or their precursors recognize the TsF-E with the same receptors as they use for the recognition of LDH-B together with the E^k on the antigen-presentign cells. The recognition of the TsF-E inactivates the Ts cell so that proliferation of Th cells then occurs unhindered. Thus, the production of the TsF-E may provide a feedback mechanism that regulates the activation of the Ts cells and, consequently, the degree of suppression in the response to LDH-B.