Adjuvant regulation of T cell function.

The effect of complete Freund's adjuvant (CFA) on distinct T cell functions was investigated. Adjuvant was found to suppress the generation of cytolytic T cells in vivo when mixed with allogeneic P815 cells before immunization of C57BL/6 mice. Inoculation of the mice with either adjuvant or adjuvant emulsified with allogeneic cells resulted in whole splenic populations or immunoabsorbent-purified T cells that did not generate cytolytic activity in vitro against allogeneic cells. Mixing T cells from normal and adjuvant-treated mice before in vitro sensitization resulted in suppression of lytic activity. However, memory T cells were not subject to the same suppressive regulation as were precytotoxic T cells since adjuvant had no effect on subsequent boosting of memory.     

miRNA对T细胞分化与功能的调节作用

miRNA是一类长度为19~24 nt的内源性非编码小分子RNA,主要通过抑制mRNA的翻译或使其降解对靶基因实现转录后水平的调控。miRNA与T细胞的分化及功能密切相关,参与自身免疫性疾病、感染性疾病、肿瘤等多种病理过程的免疫调控。本文综述了近年来发现的miRNA在T细胞分化与功能调节中的作用,特别是其在抗感染与抗肿瘤免疫中的作用。     

Novel function of IFN-gamma: negative regulation of dendritic cell migration and T cell priming

IFN-gamma is considered to be a Th1 cytokine with immunomodulatory effects on a variety of immune cells. In this study, we determined whether dendritic cell (DC) function was aberrant in IFN-gamma knockout (GKO) mice. The results demonstrated that IFN-gamma deficiency did not interfere with bone marrow-derived DC development and maturation in vitro. However, functional analysis showed that bone marrow-derived DC from GKO mice had altered cytokine secretion, allostimulatory and Ag presentation capacity, chemokine receptor expression, and in vitro chemotaxis. LPS induced the recruitment of DC from different organs into the spleen; epicutaneously sensitized DC with hapten (FITC) accumulated in the draining lymph nodes and CD11c(+) DC levels in the draining lymph nodes from autoantigen (interphotoreceptor retinoid-binding protein) immunized mice were enhanced in GKO mice as compared with wild-type mice. After treatment of GKO mice with i.p. IFN-gamma injection restored IFN-gamma levels in vivo, DC migration decreased in response to LPS or FITC. IFN-gamma altered the adaptive immune responses in vivo, since T cell priming and IL-2 production were increased in interphotoreceptor retinoid-binding protein-immunized GKO mice. Furthermore, in IFN-gamma-treated GKO mice, experimental autoimmune uveitis score enhancement and T cell activation were eliminated. Taken together, IFN-gamma appears to play a negative regulatory role on in vivo DC function, resulting in suppression of Ag-specific T cell priming.     

Costimulatory Effect of Fas in Mouse T Lymphocytes

To induce proper immune responses, T lymphocytes require two types of stimuli, antigen-specific and costimulatory signals. Among costimulatory molecules, CD28-engagement promotes the survival and proliferation of both naive and memory T cells. In addition, it is now believed that Fas may play a role in T cell activation in the human system. It is, however, controversial whether Fas can act as a costimulatory signal in the murine system. Thus, we investigated fundamental differences in the capacity to induce proliferation of T cells between Fas and CD28 in mice. Fas-mediated T cell proliferation was observed only with a full mitogenic dose of anti-CD3 antibodies, whereas CD28 engagement was able to enhance T cell proliferation in the presence of a suboptimal level of anti-CD3 antibody. Furthermore, Fas-engaged T cells showed faster response in the upregulation of CD25 and CD69 expression than CD28-engaged ones. Here, we report that Fas might play a role in mature T cell activation in the mouse system through a different mechanism from that in CD28 costimulation.     

Costimulatory Effect of Fas in Mouse T Lymphocytes

To induce proper immune responses, T lymphocytes require two types of stimuli, antigen-specific and costimulatory signals. Among costimulatory molecules, CD28-engagement promotes the survival and proliferation of both naive and memory T cells. In addition, it is now believed that Fas may play a role in T cell activation in the human system. It is, however, controversial whether Fas can act as a costimulatory signal in the murine system. Thus, we investigated fundamental differences in the capacity to induce proliferation of T cells between Fas and CD28 in mice. Fas-mediated T cell proliferation was observed only with a full mitogenic dose of anti-CD3 antibodies, whereas CD28 engagement was able to enhance T cell proliferation in the presence of a suboptimal level of anti-CD3 antibody. Furthermore, Fas-engaged T cells showed faster response in the upregulation of CD25 and CD69 expression than CD28-engaged ones. Here, we report that Fas might play a role in mature T cell activation in the mouse system through a different mechanism from that in CD28 costimulation.     

Molecular regulation of satellite cell function

Quiescent satellite cells are responsible for the repair of post-natal skeletal muscle. These cells are easily identified by their unique morphology within skeletal muscle as well as by several recently elucidated molecular markers. Careful examination of the function of these markers has provided insight into the early events surrounding satellite cell specification and activation. However, the origin of these cells, as well as the mechanisms by which this population is maintained within the adult remain elusive. Furthermore, the ability of non-muscle derived stem cells and the potential multipotency of satellite cells have altered the traditional views of skeletal muscle regeneration.     

Autologous regulation of naive T cell homeostasis within the T cell compartment

Naive T cells undergo spontaneous slow proliferation on adoptive transfer into syngeneic T cell (T)-deficient hosts. Recent work has shown that such "homeostatic" T cell proliferation is driven by MHC molecules loaded with self-peptides rather than foreign peptides. Because naive T cells in normal T-sufficient hosts remain in interphase despite continuous contact with self-MHC/peptide ligands, T cells apparently inhibit homeostatic proliferation of neighboring T cells. To address this, we have investigated the requirements necessary for "bystander" T cells to inhibit homeostatic proliferation of other T cells. Three key findings are reported. First, homeostatic proliferation of T cells only occurs in specific microenvironments, namely the T cell compartment of the secondary lymphoid tissues. Second, direct entry into T cell compartments is also required for bystander inhibition of homeostatic proliferation. Third, bystander inhibition is mediated largely by naive rather than activated/memory T cells and does not require proliferation or TCR ligation. These findings suggest that homeostasis of naive T cells is unlikely to be regulated through competition for systemic soluble factors or for specific stimulatory self-MHC/peptide ligands. Rather, the data favor mechanisms that involve competition for local non-MHC stimulatory factors or direct cell-to-cell interactions between the T cells themselves within the T cell compartment.     

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.     

Comparing antigen-independent mechanisms of T cell regulation

Key features of the kinetics of T lymphocyte proliferative responses are remarkably insensitive to the nature of the antigenic stimulus. This consistency suggests the presence of an antigen-independent mechanism regulating T cell clonal expansion. Knowledge of such a mechanism could allow us to modulate T helper cell (CD4+) and cytotoxic T cell (CD8+) responses more effectively. Using a simple mathematical model of T cell proliferation and death, we investigate a variety of plausible mechanisms and compare the model predictions to experimental data from the literature. We find that irrespective of the details of the mechanism, rates of apoptosis must progressively increase to control a T cell response. If apoptosis is mediated by cell-cell contact this alone is sufficient to regulate both (CD4+) and (CD8+) T cell responses. Proliferation of both T cell subsets can also be regulated by an internal programme, by cytokine signalling, or by an APC-mediated route. To regulate (CD8+) T cells these mechanisms must change both apoptosis and division rates, and this change must occur with time not division number.     

The function of GPI-anchored proteins in T cell development, activation and regulation of homeostasis

Many glycosylphosphatidyl-inositol-anchored proteins (GPI-AP) are expressed on T lymphocytes. Ligand or mAb-mediated aggregation of all GPI-AP tested to date results in the initiation of signal transduction pathways via the activation of src family protein tyrosine kinases. Src family kinases co-localise with GPI-AP in specialised sub-domains of the plasma membrane, referred to as detergent insoluble membrane microdomains (DIGS), which are thought to function as signalling platforms. GPI-AP may play a role in the regulation of T cell clonal expansion and effector functions at multiple levels, including the initiation of T cell activation through the antigen receptor complex, the regulation of ongoing responses supported by persisting antigen, as well as proliferative responses to the major T cell growth factor, IL-2. Evidence supporting the role of GPI-AP in the regulation of T cell development, activation and homeostasis is discussed, as well as insights provided by studies in humans and mice lacking GPI-AP.     

T cell regulation of collagen-induced arthritis in mice. I. Isolation of Type II collagen-reactive T cell hybridomas with specific cytotoxic function

After immunization with native type II collagen (CII), susceptible strains of mice (H-2q) develop a polyarthritis that mimics rheumatoid arthritis. Although the underlying mechanisms are still undefined, T cells and particularly CD4+ lymphocytes seem to play a crucial role in the initiation of collagen-induced arthritis. To investigate whether CD8+ cells may participate in the pathogenesis of the disease, we have generated lines and clones of cytotoxic T cell hybridomas reactive to CII by fusion of lymph node and spleen cells from bovine native CII-primed C3H.Q (H-2q) mice and the AKR-derived thymoma cell line BW 5147. Clones were selected for their ability to lyse syngeneic macrophages pulsed with bovine native CII in an Ag-dependent manner. The two hybrid clones that were characterized, exhibited cell surface phenotypes of cytotoxic cells and reacted with CII purified from various species. However, each of them recognized different determinants on the CII molecule. P3G8 clone was specific for an epitope shared by CII and type XI collagen, whereas P2D9 clone reacted with CII and type IX collagen. Both hybridomas recognized CII-pulsed targets in association with H-2Kq molecules. These data indicate that the two CII-specific cytotoxic clones recognize different epitopes that are shared by other articular collagens and will allow us to test their influence on the development of arthritis in vivo.     

T-cell regulation of B-lymphoblastoid cell line function

Seventeen B-lymphoblastoid cell lines (B-LCLs) have been studied for their ability to intereact with normal T cells and produce IgG and IgM in culture. All B-LCLs were HLA homozygous, having been derived from consanguineous donors by in vitro transformation with Epstein-Barr virus, 1 × 10⁴ B-LCLs were cultured with 0, 5, 10, or 20 times as many normal peripheral blood T cells in a 0.2-ml culture. Culture supernatants were removed after 3 and 6 days and assayed for IgG and IgM by a radioimmunoassay. Thirteen of the cell lines were able to secrete immunoglobulin (50–6000 ng/ml), primarily IgG, when cultured without T cells. Addition of T cells (sheep erythrocyte rosette-forming cells) modulated immunoglobulin production, causing either marked enhancement or suppression depending upon the B-cell line. T cells cultured without the B-LCLs did not secrete immunoglobulin above the background level of the immunoassays (6.25 ng/ml). Cell lines which did not secrete IgM when cultured alone could frequently be induced to do so when T cells from select donors were added. Under these conditions, IgM was generally found only in the supernatant fluid removed after 6 days. Taken together, these results suggest that B-LCLs contain cells of at least two stages, those that secrete IgG and resting cells capable of secreting IgM. Furthermore, cells at both stages can be regulated by normal T cells.     

Cytokine regulation of endothelial cell function.

Endothelial cells have long been viewed as a passive lining of blood vessels endowed essentially with negative properties such as that of being nonreactive to blood components. It is now evident that upon exposure to environmental signals, cytokines in particular, vascular cells undergo profound changes in gene expression and function that allow these cells to participate actively in inflammatory reactions, immunity, and thrombosis. Different mediators (e.g., interleukin-1 [IL-1] and interferon-gamma) activate relatively distinct sets of functions. These functional programs expressed in activated endothelial cells include the production by the same cells of cytokines (e.g., IL-1, IL-6, chemotactic cytokines, and colony-stimulating factors), which regulate hematopoiesis, the differentiation and proliferation of T and B lymphocytes, and the extravasation of leukocytes. The identification of cytokine circuits through which vascular cells participate to thrombotic, inflammatory, and immune reactions provides novel targets for therapeutic intervention.     

Anti-idiotypic regulation of an insulin-reactive T cell clone

A series of MHC-restricted, bovine-insulin-(BI) reactive T cell clones were generated. The specificity of one group was shown to be for an insulin A-chain loop determinant; the other group apparently demonstrated specificity of a B-chain determinant and/or amino acid residue A4. Guinea pig anti-idiotypic antisera were prepared against two idiotypically related BI monoclonal antibodies of similar A-chain loop specificity. These reagents were able to modulate the antigen-specific proliferation of an insulin-reactive, A-chain loop-specific T cell clone. Because the monoclonal antibodies and the T cell clone recognize a similar molecular domain of the insulin molecule, these data suggest that the anti-idiotypic sera mimic an insulin-like determinant, perhaps by bearing an "internal image" of the antigen and thereby interfering with T cell antigen recognition. Further, these results suggest that such reagents may be useful in characterization of T cell antigen receptor specificity and lend further credence to the concept of idiotypic-anti-idiotypic regulation of the immune response.     

CXCR3 in T cell function

CXCR3 is a chemokine receptor that is highly expressed on effector T cells and plays an important role in T cell trafficking and function. CXCR3 is rapidly induced on naïve cells following activation and preferentially remains highly expressed on Th1-type CD4⁺ T cells and effector CD8⁺ T cells. CXCR3 is activated by three interferon-inducible ligands CXCL9 (MIG), CXCL10 (IP-10) and CXCL11 (I-TAC). Early studies demonstrated a role for CXCR3 in the trafficking of Th1 and CD8 T cells to peripheral sites of Th1-type inflammation and the establishment of a Th1 amplification loop mediated by IFNγ and the IFNγ-inducible CXCR3 ligands. More recent studies have also suggested that CXCR3 plays a role in the migration of T cells in the microenvironment of the peripheral tissue and lymphoid compartment, facilitating the interaction of T cells with antigen presenting cells leading to the generation of effector and memory cells.     

PTEN function in mammalian cell size regulation

The PTEN tumor suppressor gene is a lipid phosphatase that negatively regulates cell survival mediated by the phosphatidyl inositol 3' kinase-protein kinase B/Akt signaling pathway. Recent in vivo studies have revealed a novel role for PTEN in the size control of neurons. Dysregulation of cell growth control by PTEN is associated with the neurological disorder Lhermitte-Duclos disease. PTEN may regulate cell size through effects on protein translation.     

The plasticity of regulatory T cell function

Regulatory T cells (T(regs)) can suppress a wide variety of cell types, in diverse organ sites and inflammatory conditions. Whereas T(regs) possess multiple suppressive mechanisms, the number required for maximal function is unclear. Furthermore, whether any interrelationship or cross-regulatory mechanisms exist to orchestrate and control their utilization is unknown. In this study, we assessed the functional capacity of T(regs) lacking the ability to secrete both IL-10 and IL-35, which individually are required for maximal T(reg) activity. Surprisingly, IL-10/IL-35 double-deficient T(regs) were fully functional in vitro and in vivo. Loss of IL-10 and IL-35 was compensated for by a concurrent increase in cathepsin E (Ctse) expression, enhanced TRAIL (Tnfsf10) expression, and soluble TRAIL release, rendering IL-10/IL-35 double-deficient T(regs) functionally dependent on TRAIL in vitro and in vivo. Lastly, whereas C57BL/6 T(regs) are normally IL-10/IL-35 dependent, BALB/c T(regs), which express high levels of cathepsin E and enhanced TRAIL expression, are partially TRAIL dependent by default. These data reveal that cross-regulatory pathways exist that control the utilization of suppressive mechanisms, thereby providing T(reg) functional plasticity.     

Lipid regulation of cell membrane structure and function

Recent studies of structure-function relationships in biological membranes have revealed fundamental concepts concerning the regulation of cellular membrane function by membrane lipids. Considerable progress has been made in understanding the roles played by two membrane lipids: cholesterol and phosphatidyl-ethanolamine. Cholesterol has been shown to regulate ion pumps, which in some cases show an absolute dependence on cholesterol for activity. These studies suggest that an essential role that cholesterol plays in mammalian cell biology is to enable crucial membrane enzymes to provide function necessary for cell survival. Studies of phosphatidylethanolamine regulation of membrane protein activity and regulation of membrane morphology led to hypotheses concerning the roles for this particular lipid in biological membranes. New information on lipid-protein interactions and on the nature of the lipid head groups has permitted the development of mechanistic hypotheses for the regulation of membrane protein activity by phosphatidyl-ethanolamine. In addition, intermediates in the lamellar-nonlamellar phase transitions of membrane systems containing phosphatidylethanolamine, or other lipids with similar properties, have recently been implicated in facilitating membrane fusion. Finally, studies of transmembrane movement of lipids have provided new insight into the regulation of membrane lipid asymmetry and the biogenesis of cell membranes. These kinds of studies are harbingers of a new generation of progress in the field of cell membranes.     

T cell regulation of polyclonal B cell responsiveness. II. Evidence for a deficit in T cell function in mice with an X-linked B lymphocyte defect.

In addition to the x-linked B cell maturation deficit previously reported in CBA/N mice, a functional T cell defect has now been observed. T lymphocyte regulation of the polyclonal PFC response was studied within the context of this x-linked immunodeficiency model. The ability of 1) B cells from (CBA X CBA/CaJ)F1, male mice to respond to nonspecific T cell helper signals and 2) T cells from NCF1 male mice to provide such signals was investigated under in vitro conditions by using bacterial lipopolysaccharide (LPS) as the polyclonal activator. B lymphocytes from both male and female NCF1 mice were receptive to T cell help rendered by NCF1 female T cells. Male T cells. however, were unable to augment polyclonal B cell responses of either NCF1 male or female B cells to LPS. Treatment with ATS + C reduced the polyclonal response of female but not male spleen cells to LPS. This deficit could not be overcome by the use of greater numbers of NCF1 male T cells. The observation that this deficiency in T cell regulation is not due to active suppression suggests that the results may be attributable to an intrinsic T cell defect.