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At least 973 records · Page 54Linked to original sources
PubMed1994

T cells of staphylococcal enterotoxin B-tolerized autoimmune MRL-lpr/lpr mice require co-stimulation through the B7-CD28/CTLA-4 pathway for activation and can be reanergized in vivo by stimulation of the T cell receptor in the absence of this co-stimulatory signal.

The CD28/CTLA-4 receptors on T cells interact with the B7 molecule on antigen-presenting cells (APC) to produce a co-stimulatory signal that determines the outcome of activation. The role of this co-stimulatory signal in T cell activation and loss of tolerance in autoimmune MRL-lpr/lpr mice has not been investigated previously. The present study examines the contribution of the CD28/CTLA-4 co-stimulatory pathway to the loss of T cell tolerance in V beta 8 transgenic MRL-lpr/lpr and (-)+/+ mice in which neonatal tolerance has been induced by the superantigen staphylococcal enterotoxin B (SEB). An artificial APC transfected with the murine B7 gene, and a CTLA-4-Ig fusion protein were used to analyze the significance of the CD28/CTLA-4 pathway in vitro. The CTLA-4-Ig fusion protein was also used to inhibit the pathway in vivo. Our results demonstrate that CD28 and CTLA-4 mRNA was overexpressed in the lymph nodes of lpr/lpr mice (MRL, C57BL/6, C3H and AKR), but not in +/+ mice of the same background strain. Lymph node T cells and thymocytes from SEB neonatally tolerized MRL-lpr/lpr mice that had undergone tolerance loss, proliferated when cultured with SEB and B7+ fibroblasts in vitro, but did not proliferate when the SEB was presented in the context of B7- fibroblasts. This in vitro tolerance loss could be prevented by blocking of B7 signaling by CTLA-4-Ig. This loss of tolerance did not occur in lymph node T cells from thymectomized MRL-lpr/lpr mice. SEB challenge of tolerized MRL-lpr/lpr mice in vivo led to weight loss, increased serum cytokine levels and depletion of V beta 8+ T cells. These effects were blocked by blocking of the co-stimulatory pathway by treatment with the CTLA-4-Ig fusion protein prior to and during challenge with SEB. T cells from thymus and lymph nodes of these mice did not proliferate later in response to stimulation in vitro with SEB even in the presence of B7+ APC. Nonresponsiveness was not due to deletion of V beta 8+ CD28+ T cells, as the number of these cells was increased after treatment with SEB and the CTLA-4-Ig fusion protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Abatacept↗
PubMed1994

Effect of CTLA-4 chimeric protein on rat autoimmune anti-glomerular basement membrane glomerulonephritis.

The interaction of the T cell receptor with the antigen/major histocompatibility class II complex is insufficient to induce optimal T cell activation. Co-stimulatory signals, including those provided by CD28/CTLA-4 on T cells and B7 molecules (B7-1, -2, and -3) on antigen-presenting cells, are also required. CD28-B7 interactions can be blocked by a soluble human CTLA-4 chimeric protein (CTLA4Ig). We tested the effect of administration of CTLA4Ig on experimental anti-glomerular basement membrane (GBM) autoimmune glomerulonephritis in Wistar-Kyoto rats induced by immunization with bovine GBM. The disease is characterized by development of antibody to the alpha 3 chain of type IV collagen (Goodpasture's antigen), deposition of rat IgG in GBM, infiltration of the kidney by T cells and macrophages, severe crescent formation and renal failure leading to death in 5-6 weeks. Animals injected with human CTLA4Ig from day 0 to day 14 or to day 35 had reduced disease severity. Beneficial effects were observed even when injections were begun after the onset of glomerulonephritis on day 14. However, the rats developed antibody to the human CTLA4Ig, associated with reduction in levels of circulating CTLA4Ig. The results provide evidence for CD28/CTLA-4 signaling in rat autoimmune glomerulonephritis, and suggest that more effective inhibition of B7-dependent T cell activation, such as might be achieved with homologous CTLA4Ig, could be useful in the treatment of autoimmune diseases.

Abatacept↗
PubMed1994

B7/BB-1 antigen expression on adult human microglia studied in vitro and in situ.

In this study, we have examined the expression and function of B7/BB-1 on individual glial cells, by utilizing surgically resected adult human central nervous system (CNS) tissues, tissues derived from fetal human CNS, and pathology material from cases of multiple sclerosis (MS). Immunofluorescence analysis using enriched adult human derived cultures of microglia and oligodendrocytes, and mixed microglia/astrocyte cultures, demonstrated that B7/BB-1 was expressed on microglia. Adult human-derived oligodendrocytes and astrocytes, and human fetal astrocytes were B7/BB-1 negative under all culture conditions. Flow cytometry studies demonstrated a low basal level of B7/BB-1 expression on microglia that was up-regulated following incubation with interferon-gamma (IFN-gamma). Co-culture of purified fresh allogeneic CD4+ T cells with microglia for 24 h resulted in clustering of T cells around microglia and microglial B7/BB-1 expression. Preincubation of microglia with an anti BB-1 monoclonal antibody (mAb) prior to microglia: CD4+ T cell co-cultures resulted in partial inhibition of the ability of microglia both to present recall antigen to autologous CD4+ T cells and to present antigen to allogeneic CD4+ T cells in primary mixed lymphocyte reaction (1 degree MLR). The CTLA-4 Ig fusion protein inhibited the ability of microglia to present antigen in both antigen presentation assays to an even greater extent than did the anti BB-1 mAb. The BB-1 antibody also inhibited the ability of microglia to stimulate previously activated T cells in a secondary 2 degrees MLR. In sections of multiple sclerosis brain, B7/BB-1 expression was observed on activated microglia in select parenchymal lesions, and on perivascular cells and infiltrating monocytes. B7/BB-1 immunoreactivity was not found in normal appearing white matter from MS brain or from non-inflammatory brain specimens. Our results indicate that the B7/BB-1 molecule plays a functional role in the capacity of microglia to serve as CNS antigen-presenting cells that can both initiate and perpetuate CD4+ T cell activation.

Abatacept↗
PubMed1995

CD28 functions as an adhesion molecule and is involved in the regulation of human IgE synthesis.

Activated T cells induce IgE switching in B cells via a combination of lymphokines and direct T:B cell contact. As CD28-deficient mice have reduced basal levels of IgG1 and IgG2a and diminished Ig class switching, we investigated whether the CD28/B7.1 (CD80) ligand pairing might also be involved in human IgE regulation. Co-incubation of an allergen-specific, human T cell clone with tonsillar B cells caused a marked up-regulation of CD28 expression, whereas, in contrast, CD45 RB expression was unaffected. To test whether blocking the CD28: B7.1 interaction affected IgE synthesis, a dialyzed anti-CD28 monoclonal antibody (mAb) was added to cultures containing tonsillar B cells, pre-activated T cell clones and interleukin-4. Anti-CD28 treatment caused a reproducible, dose-dependent inhibition of IgE, but not IgG synthesis that was accompanied by a visible decrease in cell aggregate formation. Conversely, an anti-B7.1 mAb had no effect in this system. The effect of blocking CD28-ligand interactions on lymphocyte adhesion was formally assessed on human T cell clones and B cell lines using dual intracellular staining and flow cytometry. Co-incubation with an anti-CD28 mAb, but not control IgG or anti-B7.1 mAb, resulted in a marked impairment of conjugate formation that correlated well with T cell surface expression of CD28. Using this system we found that an anti-CTLA-4 mAb but not an anti-B7.2 mAb inhibited T:B cell conjugate formation. Lastly, in addition to a direct effect of anti-CD28 mAb on conjugate formation, 14-day culture of T and B cells in the presence of anti-CD28 caused a marked decrease of ICAM-1 (CD54) expression on aggregated lymphocytes. In contrast, LFA-1 (CD18) expression was unaffected. We, therefore, conclude that the T cell co-stimulatory molecule CD28 is involved in the regulation of IgE synthesis in vitro. CD28 may act to a limited extent as an adhesion molecule, though apparently not by pairing with B7.1 or B7.2. It is more likely that ligation of CD28 under certain conditions modulates the expression of other T and B cell surface molecules.

Abatacept↗
PubMed1995

Studies on the interdependence of gp39 and B7 expression and function during antigen-specific immune responses.

Interactions between T and B cells are dynamic and regulated by interacting receptor: co-receptors. Interactions between CD40 and its ligand, gp39, and the CD28/CTLA-4 and B7 family members play a decisive role in regulating the progression of cognate interactions. The interdependence of gp39-CD40 and CD28/CTLA-B7 expression and function was studied in vitro during an antigen-induced immune response using T cells from mice expressing a transgenic T cell receptor (TCR). gp39 was induced on pigeon cytochrome c (PCC)-transgenic T cells in the presence of antigen and antigen-presenting cells. The antigen-induced expression of gp39 on transgenic T cells was inhibited by antibodies to class II major histocompatibility complex, CD4 and LFA-1, but not by CTLA-4 Ig, anti-B7-1 or anti-B7-2. These data established that the antigen-induced expression of gp39 was not dependent on co-stimulation via CD28/CTLA-4. The addition of PCC also resulted in the modest expression of B7-1 and a more robust expression of B7-2 on the cognate B cells. The addition of anti-gp39 blocked the up-regulated expression of B7-1 and partially blocked the up-regulated expression of B7-2. The addition of anti-gp39 and anti-interleukin-4 inhibited antigen-induced expression of B7-2 on B cells to near background levels. Studies on the up-regulation of B7-1 and B7-2 on resting B cells showed that soluble gp39 up-regulated B7-1 and B7-2 expression on B cells. In addition, interleukin-4 and interferon-gamma up-regulated B7-2 expression on B cells. Taken together, these data demonstrate that the antigen-induced expression of gp39 is dependent on TCR-derived signals, yet independent of CD28/CTLA-4 co-stimulatory signals. Cognate interactions also resulted in the modest enhancement of B7-1 expression and a more profound expression of B7-2 which were completely or partially dependent on gp39-CD40 interactions.

Abatacept↗
PubMed1995

Activation of human peripheral blood dendritic cells induces the CD86 co-stimulatory molecule.

Maximal T lymphocyte responses require presentation of antigen by major histocompatibility complex molecules and delivery of one or more co-stimulatory signals. Interaction of the CD28 molecule on T lymphocytes with its ligands on antigen-presenting cells (APC) initiates a critical co-stimulatory pathway inducing T lymphocyte proliferation and cytokine secretion. Dendritic cells (DC) are potent APC for a primary T lymphocyte response and potential CD28/CTLA-4 ligands on DC are, therefore, of particular functional relevance. In these experiments, the expression and function of the CD28/CTLA-4 ligands B7.1 (CD80) and B7.2 (CD86) were examined on human blood DC. Resting DC populations directly isolated by immunodepletion of lineage marker-positive cells lacked cell membrane expression of CD80 and expressed little or no CD86, although CD86, but not CD80 mRNA was detected by reverse transcription-polymerase chain reaction analysis. In contrast, low-density DC isolated after culture in vitro strongly expressed CD86 surface protein, but expressed limited or no CD80, although mRNA for both molecules were detected. Short-term culture of directly isolated DC up-regulated both CD80 and CD86 expression. Analysis of the kinetics of CD28/CTLA-4 ligand induction showed that surface CD86 was present within 8 h, whereas CD80 antigen was first detected after 24 h of culture. The functional importance of CD28/CTLA-4 ligand up-regulation on DC during T lymphocyte interactions was demonstrated by the ability of both CTLA-4Ig and CD86 monoclonal antibodies (mAb), but not CD80 mAb, to block an allogeneic mixed lymphocyte reaction stimulated by DC populations initially negative for CD80 and CD86. These results demonstrate that CD86 is both the earliest and functionally the predominant co-stimulatory CD28/CTLA-4 ligand on DC.

Abatacept↗
PubMed1995

Localization in situ of the co-stimulatory molecules B7.1, B7.2, CD40 and their ligands in normal human lymphoid tissue.

Functional interactions between B and T lymphocytes are known to depend on the expression of co-stimulatory molecules B7.1/CD80, B7.2/CD86 and their counter-receptors CD28 and CTLA4, as well as CD40 and its ligand CD40L. To study the role of these molecules in situ, an immunohistochemical analysis was carried out on normal human lymphoid tissue. In the germinal centers (GC), B7.1 and B7.2 were differentially expressed. In the dark zone, centroblasts were predominantly B7.1+, while centrocytes in the light zone were B7-2+, resulting in reversed gradients of both markers in GC. Follicle mantle cells were negative for B7.1 and B7.2. Macrophages and interdigitating dendritic cells (IDC) in T cell zones both expressed B7.1 and B7.2. Moreover, clusters of B7.2+ T cells were demonstrated in interfollicular areas. Intrafollicular CD4+ T cells in GC, predominantly in the apical light zone, expressed CD28 and CTLA4, as did the majority of interfollicular T cells. CTLA4 showed a striking excentric cytoplasmic staining, which was also seen on T cells activated in vitro. CD40 was expressed on all B cells and more strongly on macrophages and IDC. Moreover, small clusters of T cells in a rim outside the GC showed CD40 expression. CD40L was expressed both on intrafollicular CD4+ T cells as well as on T cells in T cell zones. The differential distribution of co-stimulatory molecules in different compartments of normal human lymphoid tissue in situ indicates that these interactions play a distinctive role in different stages of B cell differentiation and in the immune response.

Abatacept↗
PubMed1995

CD28:B7 interactions promote T cell adhesion.

CD28 activation by antibody-mediated ligation has been shown to provide an important co-stimulatory signal for T cell adhesion to purified protein ligands. However, the effect of CD28 ligation by one of its natural ligands, B7.1, on T cell adhesion to other cells has not been studied. Therefore, in the present manuscript, we characterized the adhesive interactions between human T cells and B7.1-transfected major histocompatibility complex class II+ and class II- melanoma cells. In our studies, human T cells and T cell clones adhered to B7.1-transfected melanoma cells, but not to untransfected parental cells. The adhesive reaction in this model was rapid, occurring within 15 min, and was inhibited by anti-B7.1 antibody and soluble CTLA-4 immunoglobulin. Antibody inhibition studies demonstrated that adhesion between T cells and B7.1-transfected melanoma cells was mediated by interactions between LFA-1:ICAM-1 and CD2:LFA-3. Inhibition by pharmacological agents demonstrated that the CD28-induced adhesion required specific intracellular signaling events. A protein kinase C inhibitor, staurosporin, significantly inhibited T cell binding to transfected melanoma cells, while cyclosporin A and wortmannin, an inhibitor of phosphatidylinositol-3-kinase, did not. These results suggest that the presence of B7 on various cell populations may activate lymphocytes to adhere better, thus promoting activation, cytolysis, and migration.

Abatacept↗
PubMed1995

Transdermal immunization with large proteins by means of ultradeformable drug carriers.

By means of novel, ultradeformable and self-optimizing agent carriers called transfersomes, large molecules can be brought into the body through intact permeability barriers. This permits non-invasive immunization through normal skin and gives rise to a similar or even slightly higher antibody titer than subcutaneous injections of the same immunogen formulation. The former type of immunization also results in a higher IgA/IgG ratio in the blood than the repeated immunogen injections, as shown here for a soluble protein, human serum albumin, as well as for an integral membrane protein, gap junction protein, in mice.

Administration, Cutaneous↗
PubMed1996

Evidence that induction of tolerance in vivo involves active signaling via a B7 ligand-dependent mechanism: CTLA4-Ig protects V beta 8+ T cells from tolerance induction by the superantigen staphylococcal enterotoxin B.

Co-stimulation through CD28 is thought to be necessary for the activation of unprimed CD4+ T cells, which are otherwise rendered tolerant. However, we previously found that CD4+ T cell priming was normal or augmented in mice which overexpressed a soluble form of CTLA4 where co-stimulation through CD28 was abrogated. To investigate this CD4+ T cell response, we exploited the capacity of the superantigen staphylococcal enterotoxin B to stimulate T lymphocytes bearing V beta 8+, which represent approximately 30% of all CD4+ T cells. In litter-mate controls of CTLA4-Ig transgenic mice, immunization with staphylococcal enterotoxin B leads to expansion, followed by deletion of V beta 8+ T cells, and the remaining cells are tolerant when stimulated in vitro. Comparable expansion and deletion of V beta 8 T cells occurs in CTLA4-Ig transgenic mice. However, in contrast to normal mice, the remaining V beta 8+ T cells from CTLA4-Ig transgenic mice are not anergic and remain responsive to superantigen in vitro.

Abatacept↗
PubMed1996

Human dendritic cells activate T lymphocytes via a CD40: CD40 ligand-dependent pathway.

The CD40:CD40 ligand (CD40L) interaction provides T lymphocyte-mediated help for B lymphocyte and monocyte function but has also been shown to serve as a co-stimulus for T lymphocyte activation. In this report, we studied the regulation of CD40 expression and its functional relevance for the human dendritic cell (DC) stimulation of T lymphocytes. Only a small subpopulation of directly isolated blood DC expressed CD40. However, CD40 was rapidly up-regulated by culture, and its expression was further enhanced by interleukin (IL)-1 alpha, IL-1 beta, IL-3, tumor necrosis factor-alpha and granulocyte/macrophage-colony-stimulating factor. Expression of CD40L on DC was not detected. The proliferation of T lymphocytes in an allogeneic mixed leukocyte reaction, stimulated by blood DC or epidermal Langerhans cells, was significantly reduced in the presence of the CD40 immunoglobulin (CD40Ig) fusion protein or CD40L monoclonal antibodies. Cross-linking of CD40 on directly isolated DC with mouse CD40L trimer (mCD40LT) markedly augmented CD80 and CD86 up-regulation. Nevertheless, the same cross-linking mCD40LT inhibited DC stimulated T lymphocyte proliferation. When CD40Ig was added simultaneously with CTLA-4Ig, only minimal and variable additional inhibition of DC-stimulated allogeneic T lymphocyte proliferation and IL-2 secretion was observed, compared to each fusion protein alone. These results suggest that both CD80/CD86-dependent and -independent components of DC-T lymphocyte CD40:CD40L co-stimulation exist and further emphasize that the majority of blood DC have to differentiate or be activated to express co-stimulatory molecules.

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PubMed1996

Interleukin-12 and B7.1 co-stimulation cooperate in the induction of effective antitumor immunity and therapy of established tumors.

Interleukin-12 (IL-12) promotes specific and long-lasting anti-tumor immunity mediated by T cells in a variety of murine tumor models. IL-12 also synergizes with B7.1 (CD80) co-stimulation to induce proliferation and cytokine production by both human and murine T cells in vitro. We evaluated the combined anti-tumor efficacy of IL-12 and B7.1 gene delivery in two apparently poorly immunogenic tumor models (TS/A and MCA207). In both of these models, expression of B7.1 and production of IL-12 in the inoculum led to improved anti-tumor immunity, with up to 80% long-term tumor-free animals (vs 0-20% of mice remaining tumor free when inoculated with either B7.1- or IL-12-transfected tumors alone). Tumor-free mice were capable of rejecting a subsequent rechallenge with the wild-type tumor in 66% of the cases. Cooperativity was dependent upon the level of IL-12 secreted by engineered cells. IL-12 delivery required B7 expression of therapeutic effects to be observed in these models. Vaccines provided at a site distal to a control, non-transfected tumor slowed (TS/A) or abrogated (MCA207) the progression of wild-type tumors. The synergistic anti-tumor effects associated with combined application of B7.1- and IL-12-transfected tumors were partially negated by systemic administration of the CD28-B7.1/B7.2 antagonist CTLA4-Ig or by inoculation with neutralizing antibodies directed against murine interferon-gamma or tumor necrosis factor-alpha, two cytokines elicited in response to IL-12 stimulation. These data support the potential clinical utility of combined gene therapy using IL-12- and B7.1-engineered autologous cells (tumor or fibroblasts) as a vaccine to elicit specific anti-tumor immunity.

Abatacept↗
PubMed1996

CD28/CTLA4-B7 interaction is dispensable for T cell stimulation by mouse mammary tumor virus superantigen but not for B cell differentiation and virus dissemination.

B cells are the primary targets of infection for mouse mammary tumor virus (MMTV). However, for productive retroviral infection, T cell stimulation through the virally-encoded superantigen (SAG) is necessary. It activates B cells and leads to cell division and differentiation. To characterize the role of B cell differentiation for the MMTV life cycle, we studied the course of infection in transgenic mice deficient for CD28/CTLA4-B7 interactions (mCTLA4-H gamma 1 transgenic mice). B cell infection occurred in CTLA4-H gamma 1 transgenic mice as integrated proviral DNA could be detected in draining lymph node cells early after infection by polymerase chain reaction analysis. In mice expressing I-E, B cells were able to present the viral SAG efficiently to V beta 6+ T cells. These cells expanded specifically and were triggered to express the activation marker CD69. Further stages of progression of infection appeared to be defective. Kinetics experiments indicated that T and B cell stimulation stopped more rapidly than in control mice. B cells acquired an activated CD69+ phenotype, were induced to produce IgM but only partially switched to IgG secretion. Finally, the dissemination of infected cells to other lymph nodes and spleen was reduced and the peripheral deletion of V beta 6+ T cells was minimal. In contrast, in mice lacking I-E, T cell stimulation was also impaired and B cell activation undetectable. These data implicate B7-dependent cellular interactions for superantigenic T cell stimulation by low-affinity TCR ligands and suggest a role of B cell differentiation in viral dissemination and peripheral T cell deletion.

Abatacept↗
PubMed1996

Prevention and amelioration of collagen-induced arthritis by blockade of the CD28 co-stimulatory pathway: requirement for both B7-1 and B7-2.

Collagen type II-induced arthritis (CIA) is an experimental model of arthritis that has been successfully used to dissect the pathogenesis of human rheumatoid arthritis and to identify potential therapeutic targets. We have used this model to evaluate the role of T cell co-stimulation in both disease development and progression. T cell co-stimulation is provided by ligation of CD28 with either B7-1 or B7-2 present on antigen-presenting cells and can be prevented by a soluble form of CTLA-4 (CTLA-4Ig) which binds with high affinity to both B7-1 and B7-2. We found that administration of CTLA-4Ig at the time of immunization prevented the development of CIA and was associated with lack of lymphocyte expansion within the draining lymph node and failure to produce anti-collagen IgG1 or IgG2a antibodies. To determine which CD28 ligand plays a more dominant role in CIA, we treated mice with monoclonal antibodies (mAb) against either B7-1 or B7-2. Neither anti-B7-1 nor anti-B7-2 had any effect on the course of CIA when given alone, but resulted in reduced incidence and clinical scores when given together. Interestingly, when treatment was delayed until after the onset of clinical disease, both CTLA-4Ig or anti-B7-1 plus anti-B7-2 mAb still ameliorated disease. Effective treatment was associated with a reduction in interferon-gamma production by lymph node cells following stimulation in vitro, suggesting that Th1 responses were diminished. This study points to a critical role of CD28 co-stimulation in the development and perpetuation of CIA in DBA/1 mice. Interestingly, it demonstrates an active role for T cells in the later stages of this disease and implicates both B7-1 and B7-2-mediated co-stimulation in the pathogenesis of CIA.

Abatacept↗
PubMed1996

CD28-deficient mice generate an impaired Th2 response to Schistosoma mansoni infection.

Engagement of CD28 on T cells provides a co-stimulatory signal necessary for T cell activation and differentiation. Recent findings suggest that priming of T helper (Th)2 cells is more dependent on CD28 activation that Th1 cells. The present study examines whether mice that lack expression of CD28 as a result of gene targeting are capable of generating a Th2 response characteristic during infection with the intravascular trematode parasite Schistosoma mansoni. Mutant and control mice were either inoculated in the footpad with S. mansoni eggs (a potent inducer of a Th2 response) or infected percutaneously with the parasite. Draining lymph nodes (after footpad injection) or spleen cells (after natural infection) were harvested at 12 days and 8 weeks, respectively, and examined for cytokine responses to egg antigens. CD28-deficient mice (-/-) generated diminished egg antigen-driven interleukin (IL)-4 and IL-5 production (by 5- to 17-fold, respectively) compared to CD28-expressing (+/+) littermates. In contrast, lymphocyte proliferation and interferon (IFN)-gamma production to egg antigens were equivalent for mutant and control mice. Infected CD28-/- mice also had reduced immunoglobulin secretion. Serum levels of parasite antigen-specific IgG1 and polyclonal IgE were significantly diminished in CD28-/- compared to CD28+/+ mice. Lack of CD28 expression had no effect on granuloma formation around eggs trapped in the liver, but increased susceptibility of mice to primary schistosomiasis infection. These studies indicate that CD28 activation contributes to T cell priming required for generation of a Th2 response to an intravascular dwelling helminth parasite.

Abatacept↗
PubMed1996

The role of tyrosine phosphorylation and PTP-1C in CTLA-4 signal transduction.

Recently, there has been increasing interest in the inhibitory regulators of lymphocyte activation, and in particular, the role of CD28 homologue CTLA-4 in the regulation of T cell responses. Interaction of CTLA-4 with B7 ligands inhibits T cell responses, including T cell proliferation and interleukin-2 (IL-2) secretion. The mechanism(s) responsible for CTLA-4 signal transduction are unknown, but it has been suggested that tyrosine phosphorylation is involved. Here we demonstrate that phorbol ester phorbol 12-myrislate 13-acetate (PMA), which increases tyrosine phosphorylation by stimulating protein kinase C and p21ras, can overcome the CTLA-4-mediated inhibition of T cell proliferation. This provides the first functional evidence that tyrosine phosphorylation is involved in CTLA-4 signal transduction. Most interestingly, CTLA-4-mediated inhibition of IL-2 secretion was not influenced by the presence of PMA. Further, we demonstrate that CTLA-4 cross-linking inhibits proliferation and IL-2 secretion of T cells from motheaten mice. These mice lack PTP-1C, a tyrosine phosphatase which mediates in a number of lymphocyte inhibitory responses, indicating that PTP-1C is not essential for CTLA-4 signaling. Collectively, these results demonstrate that regulation of tyrosine phosphorylation plays a pivotal role in CTLA-4 function, and that the inhibition of the transition from G0/G1 to the S phase of the cell cycle and the inhibition of IL-2 secretion require distinct signaling pathways. These experiments provide a useful model system which can be used to elucidate the signaling pathways involved in CTLA-4 function and to understand how CTLA-4, CD28 and Tcell receptor-mediated signals are integrated in T cell responses to antigen.

Abatacept↗
PubMed1997

Blockade of CD28/B7 co-stimulation by mCTLA4-Hgamma1 inhibits antigen-induced lung eosinophilia but not Th2 cell development or recruitment in the lung.

We have studied the role of the CD28/B7 co-stimulatory pathway in the development of a Th2-type lung immune response. Mice injected two or three times intraperitoneally with ovalbumin in alum adjuvant and then re-exposed to the same antigen by intranasal (i.n.) inoculation show infiltration of the lung tissue and appearance in the broncho-alveolar lavage (BAL) fluid of significant numbers of eosinophils and lymphocytes, in a pattern which is reminiscent of asthmatic inflammation. The accumulation of eosinophils in the airways is completely dependent on interleukin (IL)-5 secretion by CD4+ T cells. We have used mice transgenic for a soluble form of murine CTLA-4 (mCTLA4-Hgamma1) which binds to B7 molecules on antigen-presenting cells, thereby preventing their interaction with T cell-expressed CD28. mCTLA4-Hgamma1-transgenic mice immunized intraperitoneally and challenged i.n. with ovalbumin failed to generate any eosinophil infiltration, suggesting that little or no IL-5 was secreted in the lungs of these mice. In contrast with the complete lack of eosinophils, the numbers and phenotypes of infiltrating lymphocytes were comparable in the lungs of mCTLA4-Hgamma1-transgenic and normal mice. Also, lung lymphocytes from immunized mCTLA4-Hgamma1-transgenic and normal mice could be shown to secrete comparable amounts of IL-4 and IL-5 when stimulated in culture in the absence of mCTLA4-Hgamma1. We conclude that mCTLA4-Hgamma1 can efficiently block the production of IL-5 during in vivo responses and inhibit eosinophil recruitment, but that it does not block the development of CD4+ T cells into Th2 cells with the potential to secrete IL-5.

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PubMed1997

Immunomodulatory effects of a plasmid expressing B7-2 on human immunodeficiency virus-1-specific cell-mediated immunity induced by a plasmid encoding the viral antigen.

B7 co-stimulation is essential for activating resting T cells following antigen recognition by the T cell receptor. To determine whether B7 has adjuvant activities on human immunodeficiency virus type-1 (HIV-1)-specific immunity induced by inoculation of a plasmid encoding HIV-1 env and rev (DNA vaccine), B7-1 and B7-2 expression plasmids were co-inoculated with the DNA vaccine. The delayed-type hypersensitivity response and cytotoxic T lymphocyte (CTL) activity were significantly enhanced when B7-2 expression plasmid was co-inoculated with the DNA vaccine, but were unaffected when the B7-1 expression plasmid was used with the vaccine instead. The immunological response enhanced by B7-2 decreased below the level of mice immunized with the DNA vaccine in combination with CTLA4Ig, an inhibitor of the B7/CD28 co-stimulatory signal, suggesting that this signal is critical for the enhanced response induced by co-inoculation of the DNA vaccine and B7-2 expression plasmid. This enhancement appeared to occur via an interferon-gamma (IFN-gamma)-dependent mechanism, as combined administration of the B7-2 plasmid and neutralizing anti-IFN-gamma antibody abrogated the virus-specific cell-mediated immunity. These results suggest that this gene-based co-inoculation strategy using HIV-1 viral antigen and B7-2 co-stimulatory molecule could be a powerful means of combating HIV-1 infection.

AIDS Vaccines↗