Role of CD40 ligand and CD28 in induction and maintenance of antiviral CD8+ effector T cell responses.
(25/7255)
The primary aim of this report was to evaluate the immune responses of CD40 ligand-deficient (CD40L-/-) mice infected with two viruses known to differ markedly in their capacity to replicate in the host. Lymphocytic choriomeningitis virus (LCMV) is a natural mouse pathogen that replicates widely and extensively, whereas vesicular stomatitis virus (VSV) spreads poorly. We found that the primary response of CD40L-/- mice toward VSV is significantly impaired; proliferation of both CD4+ and CD8+ cells is reduced 2- to 3-fold, few CD8+ cells acquire an activated phenotype, and little functional activity is induced. Very similar results were obtained in VSV-infected, CD28-deficient mice. In contrast, neither CD40L nor CD28 was required for induction of a primary CD8+ response toward LCMV. Surprisingly, lack of CD4+ T cells had no impact on the primary immune response toward any of the viruses, even though the CD40 ligand dependence demonstrated for VSV would be expected to be associated with CD4 dependence. Upon coinfection of VSV-infected mice with LCMV, the requirement for CD40 ligand (but not CD28) could be partially bypassed, as evidenced by a 3-fold increase in the frequency of VSV-specific CD8+ T cells on day 6 postinfection. Finally, despite the fact that the primary LCMV-specific CD8+ response is virtually unimpaired in CD40L-/- mice, their capacity to maintain CD8+ effector activity and to permanently control the infection is significantly reduced. Thus, our results demonstrate that the importance of CD40/CD40L interaction for activation of CD8+ T cells varies between viruses and over time. (+info)
Differentiating between memory and effector CD8 T cells by altered expression of cell surface O-glycans.
(26/7255)
Currently there are few reliable cell surface markers that can clearly discriminate effector from memory T cells. To determine if there are changes in O-glycosylation between these two cell types, we analyzed virus-specific CD8 T cells at various time points after lymphocytic choriomeningitis virus infection of mice. Antigen-specific CD8 T cells were identified using major histocompatibility complex class I tetramers, and glycosylation changes were monitored with a monoclonal antibody (1B11) that recognizes O-glycans on mucin-type glycoproteins. We observed a striking upregulation of a specific cell surface O-glycan epitope on virus-specific CD8 T cells during the effector phase of the primary cytotoxic T lymphocyte (CTL) response. This upregulation showed a strong correlation with the acquisition of effector function and was downregulated on memory CD8 T cells. Upon reinfection, there was again increased expression of this specific O-glycan epitope on secondary CTL effectors, followed once more by decreased expression on memory cells. Thus, this study identifies a new cell surface marker to distinguish between effector and memory CD8 T cells. This marker can be used to isolate pure populations of effector CTLs and also to determine the proportion of memory CD8 T cells that are recruited into the secondary response upon reencounter with antigen. This latter information will be of value in optimizing immunization strategies for boosting CD8 T cell responses. (+info)
Augmentation of LTC(4) synthesis in human eosinophils caused by CD3-stimulated Th2-like cells in vitro.
(27/7255)
We assessed the effect of anti-CD3-stimulated secretion of cultured human Th1- and Th2-like cells on leukotriene C(4) (LTC(4)) secretion in isolated human eosinophils. T helper (Th) cell subsets were generated from human naive CD4(+) T cells cocultured with irradiated human transformed B cells and either recombinant human interleukin (rhIL)-1beta plus rhIL-6 plus rhIL-12 for Th1-like cells or rhIL-1beta plus rhIL-6 plus rhIL-4 for Th2-like cells. Coincubation of eosinophils with 1:5 dilution of Th2-supernatant (Sup) caused an increase in LTC(4) secretion caused by 0.1 microM formyl-Met-Leu-Phe and 5 microg/ml cytochalasin B from 921 +/- 238 to 3,067 +/- 1,462 pg/10(6) eosinophils (P < 0.01). Th1-Sup at the same dilution had no augmenting effect on stimulated secretion of LTC(4) in eosinophils despite substantial concentrations of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the supernatant. Dilution of Th1-Sup caused increased LTC(4) that returned to baseline after immunoabsorption of GM-CSF, suggesting the presence of a possible inhibitory factor. We demonstrate that pretreatment of eosinophils with 1:5 dilution of Th2-Sup but not of Th1-Sup causes substantial augmentation of LTC(4) secretion in vitro and establishes that human Th2 cells cause direct augmentation of LTC(4) secretion within 15-30 min of exposure. (+info)
Effect of zidovudine on the primary cytolytic T-lymphocyte response and T-cell effector function.
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Azidothymidine (AZT) and other nucleoside analogues, used to treat AIDS, can cause severe clinical side effects and are suspected of suppressing immune cell proliferation and effector immune cell function. The purpose of the present study was to quantitatively measure the effects of AZT on cytotoxic T-lymphocyte (CTL) priming and to determine if the major histocompatibility complex-restricted CTL killing was affected by AZT exposure. For this purpose, we employed a murine alloantigen model and limiting-dilution analysis (LDA) to estimate cytotoxic effector cell frequencies of alloreactive splenocytes treated with drug during antigen sensitization. This noninfectious model was chosen to avoid analysis of a virus-compromised immune system. Exposure of splenocytes to therapeutic concentrations of AZT (2 to 10 microM) caused a two- to threefold dose-dependent reduction in CLT precursor frequency. This reduction was caused by decreased proliferation of alloantigen-specific CTLs rather than loss of function, because full cytolytic function could be restored by adjusting the AZT-treated effector/target cell ratios to that of untreated cells. In addition, when AZT was added to the assay system at various times during antigen sensitization there was a time-related loss of the suppressive effect on the generation of cytolytic effector function, suggesting that functional CTLs are not affected by even high doses of AZT. Taken together, the data indicate that the reduction of CTL function associated with AZT treatment is due to a quantitative decrease of effector cell precursor frequency rather than to direct drug cytotoxicity or interference with mediation of cytolysis. Furthermore, antigen-naive immune cells were most sensitive to this effect during the first few days following antigen encounter. (+info)
Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibit T cell-mediated cytotoxicity by inhibiting Fas ligand expression.
(29/7255)
We reported recently that the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) protect CD4+ T cells against Ag-induced apoptosis by down-regulating the expression of Fas ligand (FasL). Because the cytotoxic activity of CD8+ CTLs is mediated through two mechanisms, which involve the perforin/granzyme and the FasL/Fas pathways, in this study we investigated the effects of VIP/PACAP on the generation and activity of allogeneic CTLs, of CD8+ T1 and T2 effector cells and of alloreactive peritoneal exudate cytotoxic T cells (PEL) generated in vivo. VIP/PACAP did not affect perforin/granzyme-mediated cytotoxicity, perforin gene expression, or granzyme B enzymatic activity, but drastically inhibited FasL/Fas-mediated cytotoxicity against allogeneic or syngeneic Fas-bearing targets. VIP/PACAP inhibit CTL generation, but not the activity of competent CTLs. The inhibition is associated with a profound down-regulation of FasL expression, and these effects are mediated through both VPAC1 and VPAC2 receptors. VIP/PACAP inhibit the FasL/Fas-mediated cytotoxicity of T1 effectors and do not affect T2 cytotoxicity, which is entirely perforin/granzyme mediated. Similar effects were observed in vivo. Both the FasL/Fas-mediated cytotoxicity and FasL expression of cytotoxic allogeneic PELs generated in vivo in the presence of VIP or PACAP were significantly reduced. We conclude that, similar to their effect on CD4+ T cells, the two structurally related neuropeptides inhibit FasL expression in CD8+ cytotoxic T cells and the subsequent lysis of Fas-bearing target cells. (+info)
Mycobacterium tuberculosis-reactive CD8+ T lymphocytes: the relative contribution of classical versus nonclassical HLA restriction.
(30/7255)
Previous studies in mice and humans models have suggested an important role for CD8+ T cells in host defense to Mycobacterium tuberculosis (Mtb). In humans, CD8+ Mtb-reactive T cells have been described that are HLA-A2-, B52-, as well as CD1-restricted. Recently, we have described Mtb-specific CD8+ T cells that are neither HLA-A-, B-, or C- nor group 1 CD1-restricted. At present, little is known about the relative contribution of each of these restriction specificities to the overall CD8+ response to Mtb. An IFN-gamma enzyme-linked immunospot assay was used to determine the frequency of Mtb-reactive CD8+ T cells directly from PBMC. The effector cell frequency among five healthy purified protein derivative-positive subjects was 1/7,600 +/- 4,300 compared with 1/16,000 +/- 7,000 in six purified protein derivative-negative controls. To determine the frequencies of classically, CD1-, and nonclassically restricted cells, a limiting dilution analysis was performed. In one purified protein derivative-positive subject, 192 clones were generated using Mtb-infected dendritic cells (DC). Clones were assessed for reactivity against control autologous DC, Mtb-infected autologous DC, and HLA-mismatched CD1+ targets (DC), as well as HLA-mismatched CD1- targets (macrophages). Of the 96 Mtb-reactive CD8+ T cell clones, four (4%) were classically restricted and 92 (96%) were nonclassically restricted. CD1-restricted cells were not detected. Of the classically restricted cells, two were HLA-B44 restricted and one was HLA-B14 restricted. These results suggest that while classically restricted CD8+ lymphocytes can be detected, they comprise a relatively small component of the overall CD8+ T cell response to Mtb. Further definition of the nonclassical response may aid development of an effective vaccine against tuberculosis. (+info)
Mechanisms of endotoxin tolerance in patients with alcoholic liver cirrhosis: role of interleukin 10, interleukin 1 receptor antagonist, and soluble tumour necrosis factor receptors as well as effector cell desensitisation.
(31/7255)
BACKGROUND: In patients with alcoholic liver cirrhosis, endotoxaemia is a frequent finding. Unknown mechanisms, however, prevent typical clinical symptoms of endotoxaemia in many patients. METHODS: We determined plasma levels of pro- and anti-inflammatory mediators, ex vivo cytokine secretion capacity, and expression of tumour necrosis factor (TNF) receptors on phagocytic blood cells in 49 patients with alcoholic cirrhosis and 41 age matched healthy controls. RESULTS: In addition to increased levels of proinflammatory cytokines in cirrhotic patients, we observed consistent upregulation of the anti-inflammatory mediators interleukin 10 (IL-10) (plasma 15.75 (1. 6) v 6.6 (1.3) pg/ml (p<0.001); ex-vivo 108.4 (22.0) v 40.1 (7.4) pg/ml (p<0.05)), interleukin 1 receptor antagonist (plasma 527.1 (83) v 331.4 (56) pg/ml (p<0.05); ex vivo 19.9 (3.4) v 10.2 (2.7) ng/ml (p<0.01)), and soluble TNF receptors (sTNF-R) in plasma (sTNF-RI 3157.2 (506.2) v 607.9 (300.3) pg/ml; sTNF-RII 3331.0 (506. 2) v 1066.4 (225.1) pg/ml (p<0.001 for both)). Desensitisation at the target cell level was indicated by reduced expression of TNF receptor I on granulocytes (64.8 (6.5) v 40.1 (7.3)% positive cells; p<0.05) and unaltered plasma levels of soluble E-selectin. CONCLUSION: In patients with alcoholic liver cirrhosis, upregulation of the pro- and anti-inflammatory cytokine system and simultaneous desensitisation of effector cells could explain the restricted systemic inflammatory response to chronic endotoxaemia. This alteration in immune status may lead to impairment of host defences against infections which are frequent complications of alcoholic cirrhosis. (+info)
Cytotoxic T lymphocyte-associated antigen 4 plays an essential role in the function of CD25(+)CD4(+) regulatory cells that control intestinal inflammation.
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It is now clear that functionally specialized regulatory T (Treg) cells exist as part of the normal immune repertoire, preventing the development of pathogenic responses to both self- and intestinal antigens. Here, we report that the Treg cells that control intestinal inflammation express the same phenotype (CD25(+)CD45RB(low)CD4(+)) as those that control autoimmunity. Previous studies have failed to identify how CD25(+) Treg cells function in vivo. Our studies reveal that the immune-suppressive function of these cells in vivo is dependent on signaling via the negative regulator of T cell activation cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), as well as secretion of the immune-suppressive cytokine transforming growth factor beta. Strikingly, constitutive expression of CTLA-4 among CD4(+) cells was restricted primarily to Treg cells, suggesting that CTLA-4 expression by these cells is involved in their immune-suppressive function. These findings raise the possibility that Treg cell function contributes to the immune suppression characteristic of CTLA-4 signaling. Identification of costimulatory molecules involved in the function of Treg cells may facilitate further characterization of these cells and development of new therapeutic strategies for the treatment of inflammatory diseases. (+info)