Precursor and effector phenotypes of activated human T lymphocytes

In mice, thymus-derived lymphocytes are differentiated into functional subclasses by their cell surface antigens. The Ly 1 determinants are present on T cells with a helper function, whereas Ly 2 and Ly 3 antigens are expressed on the surface of lymphocytes with suppressor or cytotoxic functions. In man also, T-cell subsets have been identified using allo- and heteroimmune sera and, more recently, using monoclonal antibodies, which seem to identify helper and suppressor or cytotoxic subpopulations. The major histocompatibility system (MHS)-encoded Ia antigens belong to several polymorphic families of membrane associated glycoproteins originally found on B lymphocytes; however, they have also been shown to be markers for suppressor T cells in mice. Recent studies have shown that in both mouse and man, T cells activated by a mixed lymphocyte reaction or by mitogens become Ia+. Furthermore, some human T lymphoid cells, either freshly isolated from peripheral blood or after in vitro activation by lectins or alloantigens, possess suppressor properties. We report here the phenotype of a T suppressor-cell subpopulation which was induced in long-term culture of lymphoid cells after activation with phytohaemagglutinin (PHA). Our results suggest that a subset of T cells was progressively expanded over a period of 8 days in culture and that, with the expression on the surface of these cells of 'Ia-like' antigens, they acquired the capacity to suppress the proliferative response of syngeneic or allogeneic lymphocytes to alloantigens or mitogens.     

Responses to the H-2Kba mutant involve recognition of syngeneic Ia molecules

Conventional antigens appear to be recognized by T lymphocytes only when associated with major histocompatibility complex (MHC) antigens. Using antigen-specific proliferation as a model for helper T lymphocytes, it has been demonstrated that Ly1+T cells recognize antigen presented in association with syngeneic Ia molecules. In contrast to responses to conventional antigens, however, a large number of studies have suggested that the stimulation of alloreactive Ly1+T cells, and helper T cells specific for allogeneic cytotoxic T lymphocyte (CTL) responses, involve the direct recognition of Ia alloantigens. For the generation of optimal allogeneic CTL activity it has been proposed that Ly1+T cells recognize allo-Ia antigens directly and provide help to pre-CTLs that respond to allo-H-2K and/or D determinants. Thus, the B6.C.H-2bm1 mutant (bm1, formerly referred to as Hz1), which is believed to consist of a substitution of two amino acids in the H-2Kb antigen, has presented a paradox, for it can stimulate strong mixed lymphocyte culture (MLC), graft versus host and CTL responses by T cells of H-2b haplotype mice in the apparent absence of any alloantigenic differences in the I region. We now present evidence that the stimulation of proliferative and helper T cells by the mutant B6.C.H-2bm1 results from the H-2Kba antigen being recognized in the context of syngeneic Ia determinants. Thus responses to both conventional antigens and allogeneic MHC gene products may proceed via the recognition of antigen in the context of self Ia molecules.     

口服耐受增效剂对抗原诱导性葡萄膜视网膜炎的作用

目的：观察口服牛视网膜S抗原与脂多糖(LPS)对Wistar大鼠抗原诱导性葡萄膜视网膜炎(AIU)的影响。方法：用纯化牛视网膜S抗原和福氏完全佐剂的混合乳剂致敏大鼠，14d后接种S抗原于致敏鼠眼玻璃体腔复制AIU模型。观察致敏前口服S抗原及LPS、单独口服S抗原或牛血清白蛋白(BSA)对AIU眼部表现和迟发型超敏反应(DTH)的影响。结果：与口服BSA组比较，口服S抗原及LPS组在AIU第1、3、5d的临床分级参数显降低，炎症持续时间显缩短，DTH显降低。与单独口服S抗原组比较，口服S抗原及LPS组在AIU的炎症持续时间显缩短，DTH显降低。结论：口服S抗原及LPS明显抑制AIU的炎性反应和DTH，口服LPS可加强S抗原对AIU的免疫抑制作用。     

Inhibition of pathogenic effect of effector T cells by specific suppressor T cells during influenza virus infection in mice

Mice infected with an aerosol of influenza type A virus, or immunized with purified UV-inactivated whole virus or with viral subunits, develop a transient delayed-type hypersensitivity (DTH) which peaks 5-7 days after immunization. The intensity of DTH is greatly enhanced and sustained when mice are pretreated with cyclophosphamide. The reaction is maximal 24 h after elicitation, has classical tuberculin-type histology and is transferable by immune H-21 region restricted Lyt-1+2- T cells (Td) but not by immune serum. These Td cells not only fail to protect mice against influenza virus infection, but increase the mortality rate due to influenzal pneumonia following challenge with homologous lethal virus. On the other hand, antigen-specific suppressor T (Ts) cells which inhibit DTH are readily generated during influenza virus infection, and are detectable for at least 40 days thereafter. The ease with which they are induced and maintained during the infection may be of evolutionary advantage. In support of this, we now report that these Ts cells can reverse the pathogenic effect of Td cells thereby demonstrating a beneficial influence of Ts cells in a viral disease.     

Immunization to a syngeneic sarcoma by a monoclonal auto-anti-idiotypic antibody

Idiotypic networks regulate the immune response to a variety of antigens. Antibodies generated against other antibodies, called anti-idiotypic antibodies, can themselves mimic antigen and elicit a specific immune response. They have been shown to induce delayed-type hypersensitivity (DTH) to model antigens in the mouse. As anti-idiotypic antibodies are thought to be involved in the response to tumour-associated antigens we tested whether injection of monoclonal antibodies derived from mice hyperimmunized to a syngeneic, chemically induced sarcoma could mimic antigen and induce DTH to the sarcoma in naive mice. One of the monoclonal antibodies, 4.72, primed BALB/c mice for DTH to the sarcoma but not for DTH to another sarcoma or to sheep erythrocytes. Antibody 4.72 did not induce DTH in mice of immunoglobulin allotype congeneic strains nor did it bind to the sarcoma cells. As antibodies specific for this sarcoma have not been detected, we do not know whether idiotype on immunoglobulin molecules is recognized by antibody 4.72. However, as the response induced by antibody 4.72 was both antigen-specific and allotype-restricted, analogous to those induced by anti-idiotypic antibodies in other systems, we propose that antibody 4.72 is an anti-idiotypic antibody.     

The circumsporozoite protein is an immunodominant protective antigen in irradiated sporozoites

Malaria infection starts when mosquitoes inject sporozoites into the skin. The parasites enter the blood stream and make their way to the liver where they develop into the exo-erythrocytic forms (EEFs). Immunization with irradiated sporozoites (IrSp) leads to robust protection against malaria infection in rodents, monkeys and humans by eliciting antibodies to circumsporozoite protein (CS) that inhibit sporozoite infectivity, and T cells that destroy the EEFs. To study the role of non-CS antigens in protection, we produced CS transgenic mice that were tolerant to CS T-cell epitopes. Here we show that in the absence of T-cell-dependent immune responses to CS, protection induced by immunization with two doses of IrSp was greatly reduced. Thus, although hundreds of other Plasmodium genes are expressed in sporozoites and EEFs, CS is a dominant protective antigen. Nevertheless, sterile immunity could be obtained by immunization of CS transgenics with three doses of IrSp.     

Minor but not major histocompatibility antigens of thymus epithelium tolerize precursors of cytolytic T cells

Treatment of fetal thymuses with 2-deoxyguanosine depletes these organs of many haematopoietic cells, and if such thymuses are transplanted into allogeneic athymic nude mice, intrathymic development of cytolytic T-lymphocyte precursors (CTL-P) occurs, including those which are specific for class I major histocompatibility complex (MHC) antigens expressed by the thymus epithelium. Thus, T cells from BALB/c (H-2d) nude mice transplanted with allogeneic C57BL/6 (H-2b) thymic epithelium can be stimulated in vitro to produce CTL specific for H-2b class I MHC antigens. We report here that thymocytes and lymph node T cells from such mice are responsive in mixed leukocyte reaction in the absence of exogenous growth factors, indicating that lack of tolerance is manifest at the level of CTL-P and proliferating T cells. We also show that T cells from such mice are tolerant to minor histocompatibility antigens of the thymus donor in the context of MHC antigens of the recipient. The results indicate that haematopoietic rather than epithelial cells tolerize CTL-P and that donor-type minor but not major histocompatability antigens can be presented in tolerogenic form by haematopoietic cells expressing recipient-type MHC antigens.     

Evidence from in vitro studies that tolerance to self antigens is MHC-restricted

Mature T cells respond to foreign antigens in the context of self major histocompatibility complex (MHC)-encoded products: T helper cells recognize antigen in the context of class II molecules, while cytotoxic T cells (CTL) recognize antigen plus class I molecules. Recent evidence suggests that the MHC-restricted T cell is unable to recognize either the foreign antigen or the self-MHC product alone, but only a complex of the two. Unresponsiveness to self antigens--self tolerance--implies the deletion or suppression of clones of T cells having reactivity to self antigens. Here we demonstrate the presence in normal mice of T cells which recognize self antigens together with allogeneic MHC products. This finding suggests the MHC restriction of T-cell recognition during the entire process of T-cell ontogeny, that is, MHC restriction of self tolerance.     

Genetically restricted suppressor T-cell clones derived from lepromatous leprosy lesions

Leprosy is a spectral disease in which immune responses to Mycobacterium leprae correlate with the clinical, bacteriological and histopathological manifestations of disease, so study of its pathology provides insights into immunoregulatory mechanisms in man. At the tuberculoid pole, patients have few lesions in the skin which contain rare organisms and are able to mount strong cell-mediated immune responses to M. leprae antigens. In contrast, at the lepromatous pole, patients have disseminated skin lesions containing large numbers of acid-fast bacilli and are selectively unresponsive to antigens of M. leprae. M. leprae-induced suppressor cells derived from peripheral blood have been reported to be active in vitro, yet their in vivo significance has remained unclear. Because the focal point of the immune response to M. leprae is the skin lesion consisting of lymphocytes and macrophages, we have recently developed methods for isolating lymphocytes from skin biopsies of leprosy patients. We report here that two T8 clones derived from lepromatous leprosy skin biopsies, in the presence of lepromin, suppress concanavalin A (Con-A) responses both of peripheral blood mononuclear cells and of T4 clones in an HLA-D (HLA, histocompatibility locus antigen)-restricted manner. Moreover, these T8 clones suppressed responses of HLA-D-matched, but not HLA-D-mismatched antigen-responsive T4 clones to M. leprae antigens, indicating that T-cell suppression is major histocompatibility complex (MHC)-restricted at some level in man.     

Neonatal T-cell tolerance to minimal immunogenic peptides is caused by clonal inactivation

The mechanisms underlying T-lymphocyte tolerance induced in neonatal mice are still unknown. It is unclear whether the tolerant state is the result of inactivation of T cells on exposure to antigen during development or of active suppression by other T cells specific for the same antigen. To distinguish between these two hypotheses, we have analysed the specificity of tolerance to three cytochrome peptides which differ by only a single amino-acid substitution in the epitope recognized by proliferative T cells. The peptides stimulate proliferative responses which are highly specific with minimal cross-reactivity. As antigen-induced clonal inactivation would address the same cells normally activated by that antigen, the specificity of tolerance should exactly match that of the proliferative response to the antigen, and each cytochrome peptide should induce tolerance to itself alone. Conversely, as T-suppressor (Ts) and T-proliferative (Tp) cells almost invariably seem to recognize distinct, non-overlapping determinants on protein antigens, suppressor-mediated tolerance should not be affected by substitutions in the proliferative T-cell epitope. Tolerance would depend solely on the existence of a shared suppressor determinant, so each cytochrome peptide should induce cross-tolerance to the others. We found that the specificity of tolerance matched that of the proliferative response: each peptide induced tolerance for itself but the response to the variants was unaltered. This result strongly supports the hypothesis of clonal inactivation as an important mechanism in induction of neonatal tolerance.     

Anti-idiotypic T cells suppress rejection of renal allografts in rats

Kidney allografts between inbred rats differing at the major histocompatibility complex (MHC) are normally rejected, usually within 10 to 12 days. In many strain combinations, however, permanent graft acceptance can be induced by either immunological enhancement or a short course of immunosuppressive chemotherapy. In both cases, prolonged graft survival is accompanied by the appearance in the spleen of a population of suppressor cells. When transferred to a syngeneic host, these cells abrogate or strikingly diminish the rejection response elicited by a renal allograft of the same genotype as the original kidney donor. We have now examined the properties of these suppressor cells and have detected a subpopulation that proliferates in vitro when stimulated by irradiated syngeneic T blasts reactive to MHC alloantigens of the kidney donor strain. Comparable proliferation, however, is not induced either by syngeneic blasts reactive to a third strain or by polyclonal syngeneic blasts. These results support the hypothesis that this subpopulation is anti-idiotypic, with specificity for the idiotypes carried by syngeneic T cells stimulated by the kidney allograft. Such anti-idiotypic cells could function as suppressors.     

Cytotoxic T lymphocytes against a soluble protein

Thymus-derived (T) lymphocytes recognize antigen in conjunction with surface glycoproteins encoded by major histocompatibility complex (MHC) genes. Whereas fragments of soluble antigens are presented to T helper lymphocytes (TH), which carry the CD4 antigen, in association with class II MHC molecules, CD8-bearing cytotoxic T lymphocytes (CTL) usually see cellular antigens (for instance virally-encoded proteins) in conjunction with MHC class I molecules. The different modes of antigen presentation may result from separate intracellular transport: vesicles containing class II molecules are thought to fuse with those carrying endocytosed soluble proteins. Class I molecules, in contrast, can only pick up degradation products of intracellular proteins (see refs 7 and 8). This makes biological sense; during an attack of a virus, class I-restricted CTL destroy infected cells and class II-restricted TH guide the humoural response to neutralize virus particles and toxins. But here we provide evidence that CTL specific for ovalbumin fragments can be induced with soluble protein, and that intracellular protein degradation provides epitopes recognized by these CTL. These findings suggest the existence of an antigen presenting cell that takes up soluble material and induces CTL.     

Functional and molecular organisation of an antigen-specific suppressor factor from a T-cell hybridoma

Thymus-dependent (T) lymphocytes have been shown to have antigen specificity. The antigen receptor on T lymphocytes, in contrast to that on B lymphocytes, does not appear to be of the conventional immunoglobulin (Ig) type. Studies on the antigen-specific factors derived from helper and suppressor T cells (Ts) demonstrated that they possess determinants with antigen binding affinity and products of genes in the H-2 complex (MHC). Furthermore, antibodies against the variable region of Ig heavy chains or idiotypes have been shown to react with T-cell antigen receptors as well as antigen-specific helper and suppressor T-cell factors (TsF). It is, therefore, conceivable that at least two gene products are involved in the structural entity of these receptors: one each coded for by genes in either. To establish the molecular nature of the recognition component of T cells we have used homogeneous TsF from a T-cell hybridoma with a specific function. We report here that the antigen binding and I-J coded molecules on TsF are independently synthesised in the cytoplasm, and are secreted as an associated form of the two molecules; this association is required for antigen-specific suppression of antibody response.     

Specific immune responses induced by a multi-epitope antigen of hepatitis C virus in mice and rabbits

Five highly conserved and immunogenic epitopes of hepatitis C virus (HCV) have been chosen to form a multi-epitope antigen gene and fused with β-galactosidase gene to express a hybrid GZ-PCX antigen, which could be specifically recognized by human HCV sera. High level of anti-GZ-PCX IgG has been induced when mice or rabbits were immunized with GZ-PCX antigen emulsificated with complete Freund’s adjuvant or mixed with killed attenuatedSalmonella typhimurium SL3261. The specific anti-GZ-PCX IgG reached a high titer of 10^-6, which remained for several months. Specific cytotoxic T lymphocyte (CTL) effects, delayed type hypersensitivity reaction (DTH) and proliferation of peripheral lymphocytes have been induced by GZ-PCX antigen or synthetic peptides. High level of anti-GZ-PCX slgG has been detected in mice’s intestinal washing fluids, which indicates that the antigen induced mucosal immunity as well as systematic immunity. The studies show that the HCV multi-epitope antigen induces high level of specific immune responses without obvious toxicity, which might be able to provide protectivity to any HCV genotypes and isolates.     

Abrogation of oral tolerance by contrasuppressor T cells suggests the presence of regulatory T-cell networks in the mucosal immune system

Continuous ingestion of a thymus-dependent (TD) antigen differentially affects two compartments of the immune system. A secretory IgA antibody response is induced in mucosal tissues, concurrent with a state of antigen-specific systemic unresponsiveness to parenteral challenge, termed oral tolerance. The precise mechanisms whereby gut antigenic exposure induces oral tolerance are unknown, although T-suppressor cells, anti-idiotypic networks and immune complex formation have all been proposed. Here we show that the systemic unresponsiveness of mice made orally tolerant to the TD antigen sheep red blood cells (SRBC) is reversed by the adoptive transfer of Lyt-1+,2-, Vicia villosa lectin-adherent and I-J+ T cells derived from mice which are genetically resistant to the induction of oral tolerance to SRBC. This T-cell subpopulation has the characteristics of contrasuppressor effector T cells (Tcs). Small numbers of these Tcs cells reverse SRBC-specific tolerance both in vivo and in vitro. This finding offers new insight into the mechanisms of oral tolerance induction and maintenance, and suggests that a network of T cells are involved in the regulation of host responses to ingested antigens.     

Induction of cytotoxic T-cell responses in vivo in the absence of CD4 helper cells

Cytotoxic T lymphocytes (CTL) seem to provide the major line of defence against many viruses. CTL effector functions are mediated primarily by cells carrying the CD8 (Ly-2) antigen (CD8+ cells) and are triggered by interactions of the T-cell receptor with an antigenic complex, often termed 'self plus X', composed of viral determinants in association with class I molecules of the major histocompatibility complex (MHC). The mechanism(s) of induction of virus-specific CTL in vivo is poorly understood, but data from in vitro experiments suggest that their generation is strictly dependent on functions provided by CD4+ helper T cells (also referred to as L3T4+; or TH) that respond to antigens in the context of class II (Ia) MHC determinants. The prevailing opinion that induction of most functions of CD8+ cells requires help provided by CD4+ cells has recently been challenged by the observation that CD8+ cells alone can mediate a variety of responses to alloantigens in vitro and in vivo; however, the possibility that CTL to self plus X could be generated in vivo in the absence of TH cells has not been evaluated. We report here that C57BL/6J (B6) and AKR/J mice, when functionally depleted of CD4+ cells by in vivo treatment with the CD4+-specific rat monoclonal antibody GK1.5 (refs 8-14) responded to ectromelia virus infection by developing an optimal in vivo virus-specific CTL response, and subsequently recovered from the disease (mousepox) that was lethal for similarly infected nude mice (CD4-, CD8-).     

Essential requirement for major histocompatibility complex recognition in T-cell tolerance induction

The induction of T-cell responses involves the recognition of extrinsic antigen in association with antigens of the major histocompatibility complex (MHC), in mice and man, with different T cells recognizing antigen in association with either class I (H-2K/D, HLA-A, B, C) or class II (Ia, HLA-D/DR) MHC antigens. However, the requirement of MHC recognition in the induction of immunological tolerance remains ill defined. With human T helper clones recognizing synthetic peptides of influenza haemagglutinin (HA-1), we have investigated the nature of antigen-induced stimulation, and antigen-induced antigen-specific unresponsiveness, immunological tolerance. Tolerance is not due to cell death, as the cells remain responsive to interleukin-2 and is associated with the loss of T3 antigen from the cell surface. Using monoclonal antibodies to the non-polymorphic regions of human class II antigens to inhibit the induction of T-cell tolerance we report here that induction of tolerance requires the recognition of MHC antigens.     

T cells can distinguish between allogeneic major histocompatibility complex products on different cell types

In the response of T cells to foreign antigens, the ligand for the T cell alpha/beta receptor is presented on a cell surface as a fragment of antigen complexed to one of the membrane molecules encoded in the major histocompatibility complex (MHC). The receptor apparently interacts via its variable elements (V beta, D beta, J beta, V alpha and J alpha) with residues within both the antigen and MHC portion of the ligand. The frequency of T cells responding to a conventional antigen plus self MHC is usually quite low, presumably reflecting the relative rarity of receptors with the particular combination of variable elements to match the antigen/MHC ligand. T cells also respond to allogeneic forms of MHC molecules in the absence of added antigen. In this case the frequency of responding T cells is very high. One hypothesis to explain this observation is that, in the absence of foreign antigen, MHC molecules are complexed to a large array of peptides derived from self-proteins. In this case the combination of the polymorphic MHC amino acid residues and many different self peptides presents so many possible ligands that the likelihood of recognition by a given T cell receptor is quite high. The recent crystallography experiments which revealed a dramatic binding cleft on the face of a human MHC molecule have given impetus to this view, but as yet there is no direct supporting evidence. We have recently described a close association between murine T cell receptors utilizing the V beta 17a element and reactivity to various allogeneic forms of the murine MHC molecule, I-E (ref. 8). In this paper, we show that this I-E ligand is detected on B cells, but not on I-E+ macrophages or fibroblasts expressing a transfected I-E gene. These results strongly suggest a B cell specific product combines with I-E to form the allogeneic ligand for V beta 17a+ receptors and thus support the concept of alloreactivity described above.     

Lymphocyte suppression in leprosy induced by unique M. leprae glycolipid

Leprosy remains a significant medical and social problem in many developing countries. The varied forms of the disease form a spectrum. At one pole, tuberculoid leprosy, patients develop high levels of cell-mediated immunity which results in the killing and clearing of bacilli in the tissues. At the lepromatous pole, patients exhibit a selective immunological unresponsiveness to antigens of Mycobacterium leprae so that the organisms inexorably multiply in the skin. We have suggested that in lepromatous leprosy one or a small number of unique antigenic determinants present on M. leprae might induce specific suppressor cells that inhibit the reactivity of helper T-cell clones capable of recognizing other specific or cross reactive determinants. Although unique epitopes have been identified by monoclonal antibodies on a small number of M. leprae proteins, the only unique species of antigen present in M. leprae, and not on any other species of mycobacteria so far examined, is a phenolic glycolipid (gly-I). We show here that this unique antigen of M. leprae is capable of inducing suppression of mitogenic responses of lepromatous patients' lymphocytes in vitro and provide evidence that the suppressor T cells recognize the specific terminal trisaccharide moiety.     

Killing of antigen-reactive B cells by class II-restricted, soluble antigen-specific CD8+ cytolytic T lymphocytes

Cytolytic T lymphocytes (CTLs) are generally thought to recognize cellular antigens presented by class I MHC molecules. A number of studies, however, have revealed responses of considerable magnitude involving both CD8+ and CD4+ CTLs with class II restriction, suggesting that class II-restricted CTLs recognizing exogeneous protein antigens may exist. As class II antigens are normally expressed on limited types of cells such as B cells and macrophages, such CTLs might be expected to exert a suppressive effect on antibody responses. Here we report that stimulation of mouse lymphocytes with a soluble antigen induced CD8+ and CD4+ CTLs specific for the antigen with class II restriction. The specific lysis was far more efficient when target B cells specifically recognized the antigen than when they did not, indicating that the primary targets for these CTLs are probably B cells expressing immunoglobulin receptors reactive for the same antigen molecule. These results suggest that the natural occurrence of such CTLs during immune responses may explain antigen-specific suppression on antibody responses by T cells.