Antigen-specific human T cell factors. II. T cell suppressor factor: biologic properties

The in vitro induction of an ovalbumin-specific human T cell suppressor factor is described (TsF120-OA). The antigen-specific suppressive component can be purified by affinity chromatography from supernatants derived from Marbrook-Diener type cultures of peripheral blood T cells stimulated with a high dose of ovalbumin. TsF120-OA suppresses the antigen-induced PFC formation of human blood B cells in vitro in an antigen-specific way. The target of TsF120-OA activity is shown to be the T helper cell. No genetic restriction in the action of the factor is observed.     

Murine interstitial nephritis. IX. Induction of the nephritogenic effector T cell repertoire with an antigen-specific T cell cytokine

The experiments presented in this report describe the biochemical and functional characteristics of a soluble Th cell factor (ThF) which can induce a nephritogenic effector T cell repertoire producing autoimmune interstitial nephritis. The ThF is Ag-specific, I-A-restricted, and comprises two chains noncovalently linked as a heterodimer. One chain at approximately 78,000 Mr is related to the TCR/Id and expresses a framework determinant (14-30) common to Ag-binding factors, and the other chain at approximately 82,000 Mr is I-A+. Together these chains can replace their parent cell by providing cognate help to precursor effector T lymphocytes in the presence of accessory cells, tubular Ag, and IL-2.     

Functional analysis of human T cell subsets defined by monoclonal antibodies. III. Regulation of helper factor production by T cell subsets

In the present report we extended our previous studies demonstrating that obligatory T-T interactions are important in regulating human immune responses in vitro. Functionally distinct human T cell subsets were isolated by complement-mediated lysis using the monoclonal antibodies OKT4 and OKT8. Evidence was obtained that during allogeneic interactions, OKT4+, but not OKT8+, responder T cells are required to generate helper factor(s) capable of polyclonally activating human B cells independent of additional T cell help. Importantly, the alloantigen-induced helper factor(s) production and/or release was found to be suppressed by addition of graded numbers of radiosensitive OKT8+ cells. On the other hand, no evidence was obtained that supernatant derived from alloactivated OKT8+ cells could counterbalance the helper activity generated in the presence of supernatant from alloactivated OKT4+ cells. Furthermore, OKT8+ cells, known to suppress PWM-driven B cell differentiation in the presence of OKT4+ cells, do not suppress B cell differentiation induced by preformed helper factor even in the presence of OKT4+ cells. These data further underscore the importance of functional T-T interactions in immunoregulation in vitro and support the idea that the target of suppression of B cell differentiation, induced either by alloantigen-triggered helper factor or PWM, are OKT4+ cells and not B cells themselves.     

The role of macrophages in the generation of T helper cells. V. Evidence for differential activation of short-lived T1 and long-lived T2 lymphocytes by the macrophage factors GRF and NMF.

The generation of T helper cells in vitro requires macrophages or macrophage-derived factors such as genetically related macrophage factor (GRF) or nonspecific macrophage factor (NMF). However, there is a basic difference of T helper cell induction when using particulate antigens. The present study demonstrates that this difference is based on the activation of two different T cell subsets. GRF activates short-lived 'T1' cells which amplify the induction of T2 cells, which are the helper cell precursors. Thus, the genetic restriction of T helper cell induction seen with soluble antigen or GRF lies on the level of macrophage or GRF interaction with T1 cells. NMF (or macrophages) and particulate antigens directly activate the helper cell precursor (T2) indicating no requirement for T1-T2 cooperation. The direct activation of the helper cell precursor with particulate antigens does not require histocompatible macrophages or NMF from histocompatible macrophages. The present results may explain some of the discrepancies reported in the literature concerning the genetic requirements and specificity of T cell activation.     

New insights into CD4+ T cell abnormalities in systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune connective tissue disease that is characterized by vasculopathy and excessive deposition of extracellular matrix, which causes fibrosis of the skin and internal organs and eventually leads to multiorgan dysfunction. Studies have shown that CD4⁺ T cell activation is a key factor in the pathogenesis of scleroderma because activated T cells can release various cytokines, resulting in inflammation, microvascular damage and fibrosis. T helper cell 17 (Th17) and regulatory T (Treg) cell activities are a hallmark SSc, as Th17-type cytokines can induce both inflammation and fibrosis. More recently, several studies have reported new T cell subsets, including Th9 and Th22 cells, along with their respective cytokines in the peripheral blood, serum and skin lesions of individuals with SSc. Herein, we review recent data on various CD4⁺ T helper cell subsets in SSc, and discuss potential roles of these cells in promoting inflammation and fibrosis.     

Analysis of two distinct B cell activation pathways mediated by a monoclonal T helper cell. II. T helper cell secretion of interleukin 4 selectively inhibits antigen-specific B cell activation by cognate, but not noncognate, interactions with T cells

A single monoclonal T helper (Th) clone can activate B cells in two distinct pathways; a cognate pathway requiring a major histocompatibility complex (MHC)-restricted T-B cell interaction, and a noncognate pathway not requiring an MHC-restricted T-B cell interaction. The present study was undertaken to investigate whether Th cells mediating a given immune response provide further regulatory function to B cells other than helper function. It was demonstrated that conditions of high antigen concentration which activate a noncognate B cell activation pathway simultaneously inhibit IgG responses. The inhibition is shown to be mediated by the T cell factor interleukin 4, produced by activated cloned Th cells. The inhibitory effect of this factor is directed to B cells and is MHC-unrestricted, antigen-nonspecific, and IgG class-specific. In addition to being susceptible to the effects of augmenting cells and suppressor cells, cloned Th cell populations can therefore themselves function as regulatory cells to inhibit IgG responses when stimulated with high dose of specific antigen. These results indicate that Th cells function to regulate B cells both positively and negatively, depending upon the activation conditions.     

Antigen-induced T suppressor cells regulate the autoreactive T helper-B cell interaction

The T suppressor (Ts) cell population that functions to regulate antigen-specific MHC-restricted T helper (Th)-B cell interactions also regulates the activation of B cells by cloned autoreactive Th cells. Activated Ts cells were generated by in vivo priming and restimulation in vitro with high concentrations of the specific priming antigen. Once generated, this Ts population inhibits the Th-dependent activation of primed B cells by both antigen-specific and autoreactive T cells in an antigen-nonspecific manner. This suppression requires the participation of both Lyt-1+2- and Lyt-1-2+ T cells. It was also demonstrated that accessory cells were required for the induction of Ts cells. Moreover, the generation of suppression was MHC-restricted and required the recognition by T cells of Ia antigens on accessory cells. These studies demonstrate that the same or a very similar Ts cell population can function to inhibit the activation of B cells by antigen-specific as well as autoreactive T cells.     

Mouse splenic macrophage cell lines with different antigen-presenting activities for CD4+ helper T cell subsets and allogeneic CD8+ T cells.

A panel of seven mouse splenic macrophage cell lines, derived from cloned progenitors, was compared for their ability to present antigen to Th1 or Th2 helper T cell lines and hybridomas, as well as to naive T cells, and to provide accessory cell function for the synthesis of antibody from primed B cells. One of the cell lines expressed MHC class II molecules and was the only line with constitutive antigen-presenting activity for Th1 cells. It may represent a subset of splenic macrophages responsible for the activation of naive Th1 helper cells in situ. The remaining six cell lines responded to INF-gamma by up-regulating their class II expression and acquiring Th1 antigen-presenting activity. They may represent cells which, in situ, lack constitutive antigen-presenting activity but are promoted to presenting status by Th1-derived INF-gamma. Five of the cell lines provided accessory cell function to Th2 cells, as indicated by antibody synthesis in suspensions of spleen cells from primed mice depleted of their antigen-presenting cells. One of the cell lines lacking accessory cell activity had constitutive antigen-presenting activity for Th1 cells. This reciprocal expression of antigen-presenting activity supports the idea that Th1 and Th2 helper cells are activated by different antigen-presenting cells. Finally, the cell lines differed in their ability to constitutively induce an allogeneic response; a response that was limited to CD8+ T cells occurred in a CD4+ helper cell-independent manner and was unaffected by the addition of INF-gamma. The alloantigen-presenting macrophage cell lines also possessed the most efficient accessory cell activity for antibody synthesis. These cell lines, which represent a spectrum of antigen-presenting activities in the spleen afford models for defining the roles of macrophages in the induction of immune responses and for resolving issues concerning their development.     

Functional heterogeneity among human inducer T cell clones

Analysis of mouse CD4+ inducer T cells at the clonal level has established that a dichotomy among CD4+ T cell clones exists with regard to types of lymphokines secreted. Mouse T cell clones designated Th1 have been shown to secrete IL-2 and IFN-gamma, whereas T cell clones designated Th2 have been shown to produce IL-4 but not IL-2 or IFN-gamma. To determine if such a dichotomy in the helper inducer T cell subset occurred in man, we examined a panel of human CD4+ helper/inducer T cell clones for patterns of lymphokine secretion and for functional activity. We identified human T cell clones which secrete IL-4 but not IL-2 or IFN-gamma, and which appeared to correspond to murine Th2 clones. In marked contrast to murine IL-2 secreting Th1 clones which do not produce IL-4 or IFN-gamma, we observed that some human T cell clones secrete IL-2, and IFN-gamma as well as IL-4. Southern blot analysis indicated that these multi-lymphokine-secreting clones represented the progeny of a single T cell. IL-4 secretion did not always correlated with enhanced ability to induce Ig synthesis. Although one T cell clone which secreted IL-2, IL-4, and IFN-gamma could efficiently induce Ig synthesis, another expressed potent cytolytic and growth inhibitory activity for B cells, and was ineffective or inhibitory in inducing Ig synthesis. These results indicate that although the equivalent of murine Th2 type cells appears to be present in man, the simple division of T cells into a Th1 and Th2 dichotomy may not hold true for human T cells.     

General characterization of human cytomegalovirus-specific proliferative CD4+ T cell clones

Over 80 human T helper cell (Th) clones reactive with human cytomegalovirus (HCMV) were generated using purified whole Towne strain HCMV as the in vitro antigen. These cloned T cells are CD3+, CD4+, CD8- and proliferate specifically to HCMV. All of the clones tested produce interleukin 2 and gamma-interferon and failed to show HCMV-specific cytotoxicity or natural killer (NK) activity. Most of the Th clones recognize multiple laboratory-adapted and wild-type strains of HCMV. The Th clones were also tested for their reactivity to a major envelope glycoprotein complex (gcI) and a 64,000 dalton internal matrix protein. Our results show that both proteins as well as other unidentified protein(s) are involved in Th responses to HCMV.     

Helper T cell interactions.

Studies of the relationship between carrier-primed helper T cell dose and the antibody response to a hapten on that carrier reveal evidence for two synergistic T helper cells. One of these two T cells is absent in agammaglobulinemic mice. This finding is not due to suppression; instead, T helper cells from these mice interact synergistically with T helper cells from normal mice, as would be predicted if two populations of cells are present in normal mice, while only one is present in the agammaglobulinemic mice. These findings, taken together with studies in similar systems, suggest that one of the two T helper cells recognizes immunoglobulin on B cells, while the other is specific for carrier. It remains to be determined whether both cells show the phenomenon of major histocompatibility complex restriction, or whether this a property of one of the cells only. It is also not clear whether the Ig-recognizing T cell is also carrier specific, or whether its apparent carrier specificity in this system reflects an ability of the carrier to bring together Ig and an I region gene product into a unique configuration on the B cell surface.     

T helper cell activation and human retroviral pathogenesis.

T helper (Th) cells are of central importance in regulating many critical immune effector mechanisms. The profile of cytokines produced by Th cells correlates with the type of effector cells induced during the immune response to foreign antigen. Th1 cells induce the cell-mediated immune response, while Th2 cells drive antibody production. Th cells are the preferential targets of human retroviruses. Infections with human T-cell leukemia virus (HTLV) or human immunodeficiency virus (HIV) result in the expansion of Th cells by the action of HTLV (adult T-cell leukemia) or the progressive loss of T cells by the action of HIV (AIDS). Both retrovirus infections impart a high-level activation state in the host immune cells as well as systemically. However, diverging responses to this activation state have contrasting effects on the Th-cell population. In HIV infection, Th-cell loss has been attributed to several mechanisms, including a selective elimination of cells by apoptosis. The induction of apoptosis in HIV infection is complex, with many different pathways able to induce cell death. In contrast, infection of Th cells with HTLV-1 affords the cell a protective advantage against apoptosis. This advantage may allow the cell to escape immune surveillance, providing the opportunity for the development of Th-cell cancer. In this review, we will discuss the impact of Th-cell activation and general immune activation on human retrovirus expression with a focus upon Th-cell function and the progression to disease.     

T cell suppressor factor from human glioblastoma cells is a 12.5-kd protein closely related to transforming growth factor-beta.

T cell suppressor factor produced by human glioblastoma cells inhibits T cell proliferation in vitro and more specifically interferes with interleukin-2 (IL-2)-dependent T cell growth. Here we report the purification of this factor from conditioned medium of the human glioblastoma cell line 308. Amino-terminal sequence analysis of the 12.5-kd protein demonstrates that eight out of the first 20 amino acids are identical to human transforming growth factor-beta. Purified glioblastoma-derived T cell suppressor factor and transforming growth factor-beta from porcine platelets inhibit both IL-2-induced proliferation of ovalbumin-specific T helper cells and lectin-induced thymocyte proliferation with similar specific activities. If released by glioblastoma cells in vivo, the factor may contribute to impaired immunosurveillance and to the cellular immunodeficiency state detected in the patients.     

Enhancing effect of IFN-gamma on helper T cell activity and IL 2 production

A single injection of young murine immune interferon (IFN-gamma) in young (3 mo) or old (14 to 24 mo) mice 3 days before carrier-priming significantly enhances helper T cell activity of their spleen cells. Maximal enhancement is attained when IFN-gamma is injected once immediately before priming or for 4 consecutive days from the time of priming. Helper activity for anti-TNP antibody response was titrated in vitro by adding graded numbers of spleen cells from HRBC-primed mice of a given age to cultures containing a constant number of spleen cells from 3-mo-old normal mice and TNP-HRBC. When T cell-enriched spleen cells from HRBC-primed young or old mice, uninjected or injected with IFN-gamma, were separated by nylon wool filtration into passed (Thi) and adherent (Th2) cells, the helper activity of both T cell subpopulations was found to be enhanced by IFN-gamma injection. Helper activity of purified Th1 and Th2 cells was also increased by their in vitro preincubation with IFN-gamma. Furthermore, interleukin 2 (IL 2) production by mitogen-activated spleen cells from young and old mice is enhanced by addition of IFN-gamma to cultures. These data altogether indicate that IFN-gamma plays an important role in immunoregulation of helper T cell activity.     

Cytokine-modulated regulation of helper T cell populations

Helper T (Th) cells are a crucial component of the adaptive immune system and are of fundamental importance in orchestrating the appropriate response to pathogenic challenge. They fall into two broad categories defined by the cytokines each produces. Th1 cells produce interferon- gamma and are required for effective immunity to intracellular bacteria, viruses and protozoa whereas Th2 produce IL-4 and are required for optimal antibody production to T-dependent antigens. A great deal of experimental data on the regulation of Th1 and Th2 differentiation have been obtained but many essential features of this complex system are still not understood. Here we present a mathematical model of Th1/Th2 differentiation and cross regulation. We model Fas-mediated activation-induced cell death (AICD) as this process has been identified as an important mechanism for limiting clonal expansion and resolving T cell responses. We conclude that Th2 susceptibility to AICD is important for stabilizing the two polarized arms of the T helper response, and that cell-cell killing, not suicide, is the dominant mechanism for Fas-mediated death of Th1 effectors. We find that the combination of the anti-proliferative effect of the cytokine TGF- beta and the inhibiting influence of IL-10 on T cell activation are crucial controls for Th2 populations. We see that the strengths of the activation signals for each T helper cell subset, which are dependent on the antigen dose, co-stimulatory signals and the cytokine environment, critically determine the dominant helper subset. Switches from Th1- to Th2-dominance may be important in chronic infection and we show that this phenomenon can arise from differential AICD susceptibility of T helper subsets, and asymmetries in the nature of the cross-suppressive cytokine interactions. Our model suggests that in some senses a predominantly type 2 reaction may well be the "default" pathway for an antigen-specific immune response, due to these asymmetries.     

Release of hemopoietic factors by normal human T cell lines with either suppressor or helper activity

We analyzed the release of activities capable of stimulating the in vitro growth of human hemopoietic progenitor cells by long-term cultured T cell growth factor (TCGF)-dependent human T lymphocytes. Seven cell lines tested produced colony-stimulating activity (CSA) as well as burst-promoting activity (BPA). The CSA stimulated primarily the growth of the cells forming colonies after 14 days of incubation. In addition the supernatants from these seven T-cell lines showed the ability to induce the in vitro growth of mixed granulocyte, erythroid, megakaryocyte, macrophage colonies (CFU-GEMM). The release of hemopoietic factors did not depend on the presence of accessory cells or phytohemagglutinin or serum during the incubation for factor production. In six of the T cell lines the majority of the cells were reactive to the OKT 8 monoclonal antibody (MoAb), whereas one cell line contained mostly OKT 4+ cells. Suppressor activity was detected in three tested OKT 8+ cell lines, while the one OKT 4+ displayed helper activity. All cell lines produced hemopoietic factors with equal efficiency. These results indicate that factors affecting human hematopoiesis are produced by normal T lymphocytes in long-term culture and this property is not related to the helper or suppressor activity of the cultured cells.     

Filarial parasite-specific T cell lines: induction of IgE synthesis

The development of T lymphocyte lines and clones of defined specificity has provided an important method for investigating T cell recognition of foreign antigens as well as T cell influence on B cell activity. We described previously a parasite-specific T cell line (TCL) derived from a patient with a naturally acquired filarial infection and elevated levels of serum IgE. The TCL is composed of Leu-3+ helper cells and is maintained independent of exogenous growth factors. In the present study, we used these T cells to investigate their immunoregulatory function on the in vitro IgE response. These parasite-specific T cells can provide isotype-specific help for antigen-induced IgE production by B cells in vitro. Autologous T cells profoundly suppress IgE production in a concentration-dependent manner. Furthermore, soluble factors generated from these filarial-specific TCL after antigen stimulation are able to induce the production of IgE in normal human cells not already synthesizing measurable amounts of IgE in vitro. Partial physicochemical characterization of this factor has shown that it is heat labile, has an m.w. between 10,000 and 30,000 M(r), and is a mannose-rich glycoprotein.     

Transforming growth factor-beta enhances the in vivo effector function and memory phenotype of antigen-specific T helper cells in experimental autoimmune encephalomyelitis.

Transforming growth factor-beta (TGF-beta) had a profound effect on the in vitro phenotypic development of Ag-activated Th cells and enhanced the in vivo effector function of these cells upon adoptive transfer. Previous studies have shown that there are two types of Th cell populations found in unimmunized animals, naive helper cells, which are short-lived and express low levels of CD44 and high levels of CD45R and Mel-14, and memory helper cells, which have a long life span and express high levels of CD44 and low levels of CD45R and Mel-14. Culturing of Ag-specific murine Th cell lines and clones in the presence of TGF-beta greatly enhanced both the memory phenotype of the cultured cells and the effector function upon adoptive transfer in experimental autoimmune encephalomyelitis. Histologic evaluation of spinal cords from recipients receiving passively transferred murine T cell lines cultured with TGF-beta revealed large demyelinated plaques (multiple sclerosis-like) that were not present in animals receiving cells cultured with Ag alone. TGF-beta also enhanced the capability of myelin basic protein-specific Lewis rat T cell lines to transfer experimental autoimmune encephalomyelitis and potentiated a purified protein derivative-specific rat helper cell line to transfer delayed type hypersensitivity. Thus, the effects of TGF-beta did not appear to be limited by species specificity, Ag specificity, or in vivo T cell function. This is the first study showing that TGF-beta can potentiate the development and maintenance of the Th cell memory phenotype in vitro and enhance their in vivo effector function in an animal disease model.