Augmentation of the CD8+ T cell response by IFN-gamma in IL-12-deficient mice during Toxoplasma gondii infection.
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The importance of IFN-gamma in regulating the host CD8+ T cell response during microbial infection has not been delineated. Mice deficient for the p40 chain of the IL-12 heterodimer have impaired IFN-gamma production and are susceptible to infection with the intracellular parasite Toxoplasma gondii. The administration of exogenous IFN-gamma to parasite-infected p40-/- mice increases survival and up-regulates the depressed CD8+ T cell response following infection. CD8+ T cells isolated from cytokine-treated p40-/- mice exhibit an increase in both precursor CTL frequency and IFN-gamma production compared with untreated controls. The enhancement of the CD8+ T cell response is independent of CD4+ T cell help. These CD8+ T cells induce protective immunity against a lethal challenge when adoptively transferred into naive p40-/- and IFN-gamma-/- mice. These observations indicate that IFN-gamma can regulate the CD8+ T cell response during T. gondii infection. (+info)
Impaired T cell proliferation in acute dengue infection.
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Decreased proliferative responses to mitogens and recall Ags have been observed in PBMC obtained during several acute human viral infections. To determine whether cell-mediated responses are altered during acute dengue infection, we examined the proliferative responses of PBMC from children enrolled in a prospective study of dengue infections in Thailand. All responses of PBMC during acute illness were compared with the same patients' PBMC obtained at least 6 mo after their infection. Proliferative responses to PHA, anti-CD3, tetanus toxoid, and dengue Ags were decreased significantly in PBMC obtained during the acute infection. The proliferative responses to PHA were restored by the addition of gamma-irradiated autologous convalescent or allogeneic PBMC. Cell contact with the irradiated PBMC was necessary to restore proliferation. Non-T cells from the acute PBMC of dengue patients did not support proliferation of T cells from control donors in response to PHA, but T cells from the PBMC of patients with acute dengue proliferated if accessory cells from a control donor were present. Addition of anti-CD28 Abs restored anti-CD3-induced proliferation of the PBMC of some patients. The percentage of monocytes was reduced in the acute sample of PBMC of the dengue patients. Addition of IL-2 or IL-7, but not IL-4 or IL-12, also restored proliferation of acute PBMC stimulated with anti-CD3. The results demonstrate that both quantitative and qualitative defects in the accessory cell population during acute dengue illness result in a depression of in vitro T cell proliferation. (+info)
Serum levels of IL-7 in bone marrow transplant recipients: relationship to clinical characteristics and lymphocyte count.
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IL-7 is produced by stromal cells and is the major lympho- and thymopoietic cytokine. IL-7 induces proliferation and differentiation of immature thymocytes, and protects thymocytes from apoptosis by induction of bcl-2 expression. The regulation of IL-7 production is poorly characterized, although down-regulation by transforming growth factor-beta (TGF-beta) has been described. We measured the serum levels of IL-7 before and after bone marrow transplant (BMT) in 32 children undergoing BMT for genetic diseases (severe combined immune deficiency (SCID) and thalassemia), aplastic anemia, and acute lymphoblastic and non-lymphoblastic leukemia (ALL and ANLL). Prior to BMT, the highest IL-7 levels were observed in patients with SCID and ALL, i.e. those patients with genetic or acquired lymphopenia. Patients with thalassemia and ANLL had normal levels of IL-7. Over the 8 weeks following BMT, the IL-7 levels of patients with SCID and ALL fell as the absolute lymphocyte count (ALC) increased. No detectable change in IL-7 levels was observed in the patients with thalassemia and ANLL. Levels of IL-7 were highest in the young infants with SCID compared to the age-matched controls. Together, the data demonstrate that serum levels of IL-7 in lymphopenic patients are inversely related to patient age and the absolute lymphocyte count (ALC). The inverse relationship to ALC suggests that there is either direct regulation of stromal production or more likely, binding of secreted IL-7 to lymphocytes expressing IL-7 receptors. (+info)
Effect of CD8+ T-cell depletion on bronchial hyper-responsiveness and inflammation in sensitized and allergen-exposed Brown-Norway rats.
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We examined the role of CD8+ T cells in a Brown-Norway rat model of asthma, using a monoclonal antibody to deplete CD8+ T cells. Ovalbumin (OA)-sensitized animals were given anti-CD8 antibody (0.5 mg/rat) intravenously 1 week prior to exposure to 1% OA aerosol and were studied 18-24 hr after aerosol exposure. Following administration of anti-CD8 antibody, CD8+ cells were reduced to <1% of total lymphocytes in whole blood and in spleen. In sensitized animals, OA exposure induced bronchial hyper-responsiveness (BHR), accumulation of eosinophils, lymphocytes and neutrophils in bronchoalveolar lavage (BAL) fluid, and also an increase in tissue eosinophils and CD2+, CD4+ and CD8+ T cells in airways. Anti-CD8 antibody caused a further increase in allergen-induced BHR (P<0.03, compared with sham-treated animals), together with a significant increase in eosinophil number in BAL fluid (P<0.05). While CD2+ and CD4+ T cells in airways were not affected by anti-CD8 treatment, the level of CD8+ T cells was significantly reduced in sensitized, saline-exposed animals (P<0.04, compared with sham-treated rats), and sensitized and OA-challenged rats (P<0.002, compared with sham-treated rats). Using reverse transcription-polymerase chain reaction, an increase of T helper (Th)2 cytokine [interleukin (IL)-4 and IL-5], and also of Th1 cytokine [interferon-gamma (IFN-gamma) and IL-2], mRNA in the lung of sensitized and OA-exposed animals was found; after CD8+ T-cell depletion, Th1 cytokine expression was significantly reduced (P<0.02), while Th2 cytokine expression was unchanged. CD8+ T cells have a protective role in allergen-induced BHR and eosinophilic inflammation, probably through activation of the Th1 cytokine response. (+info)
Inactivation of misselected CD8 T cells by CD8 gene methylation and cell death.
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Misselected CD8 cells that express T cell receptors (TCRs) that do not recognize class I major histocompatibility complex (MHC) protein can emerge from thymic selection. A postthymic quality control mechanism that purges these cells from the repertoire is defined here. The failure of mature CD8 cells to simultaneously engage their TCR and CD8 coreceptor triggers an activation process that begins with inhibition of CD8 gene expression through remethylation and concludes with up-regulation of surface Fas and Fas ligand and cellular apoptosis. Thus, inhibition of a death signal through continued TCR-CD8 coengagement of MHC molecules is a key checkpoint for the continued survival of correctly selected T cells. Molecular defects that prevent delivery of the death signal to mistakenly selected T cells underlie the expansion of double-negative T cells, which is the cellular signature of a subset of systemic autoimmune diseases. (+info)
Characterization of the interleukin-1beta-converting enzyme/ced-3-family protease, caspase-3/CPP32, in Hodgkin's disease: lack of caspase-3 expression in nodular lymphocyte predominance Hodgkin's disease.
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Apoptosis (programmed cell death) serves an important role in the normal morphogenesis, immunoregulation, and homeostatic mechanisms in both normal and neoplastic cells. Caspase-3/CPP32, a member of the ICE/Ced-3-family of cysteine proteases, is an important downstream mediator of several complex proteolytic cascades that result in apoptosis in both hematopoietic and nonhematopoietic cells. Previous studies have demonstrated that caspase-3 is commonly expressed in classical Hodgkin's disease (CHD); however, the biological significance of its expression in Hodgkin's disease is unknown. In this report, the expression of caspase-3 in nodular lymphocyte predominance Hodgkin's disease (NLPHD) was evaluated by immunohistochemistry; in addition, we investigated the role of caspase-3 in CD95 (Fas)-mediated apoptosis in three CHD cell lines. Formalin-fixed, paraffin-embedded tissue sections from 11 cases of NLPHD were immunostained for caspase-3 using a polyclonal rabbit antibody that detects both the 32-kd zymogen and the 20-kd active subunit of the caspase-3 protease. Only 1/11 cases of NLPHD demonstrated caspase-3 immunopositivity in lymphocytic/histiocytic cells. Caspase-3 expression was also evaluated in three CHD cell lines, HS445, L428, and KMH2. Whereas caspase-3 expression was detected in HS445 and L428 cell lines, no expression was found in KMH2 cells by immunohistochemical staining. Treatment of HS445 and L428 cell lines for 72 hours with agonistic CD95 monoclonal antibody induced marked apoptosis that was significantly inhibited by pretreatment with the caspase-3 inhibitor, DEVD-FMK, as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay and flow cytometric analysis of 7-amino-actinomycin D staining. In addition, a significant increase in caspase-3 activity as determined by an enzyme colorimetric assay was detected in HS445 and L428 cells after 48 hours of CD95 stimulation. In marked contrast, treatment of caspase-3-deficient KMH2 cells with anti-CD95 mAb did not demonstrate an increase in caspase-3 activity or induce apoptosis. These data demonstrate caspase-3 is important for CD95-mediated apoptosis in CHD cell lines. In addition, the majority of NLPHD cases examined in this study failed to express detectable levels of caspase-3, suggesting these tumor cells may be resistant to apoptotic stimuli dependent on caspase-3 activity. Furthermore, these data suggest the differential expression of caspase-3 noted between NLPHD and CHD may provide additional evidence that each is a unique disease entity. (+info)
Transplantation of anergic histoincompatible bone marrow allografts.
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BACKGROUND: Successful allogeneic bone marrow transplantation relies on global immunosuppression or elimination of T cells. In contrast, the induction of anergy can inactivate specific sets of alloreactive T cells in the donor marrow. Previous work has shown that anergy can be induced by blocking the interaction of the B7 molecule on the surface of antigen-presenting cells with the CD28 molecule on the surface of T cells, thus preventing key signaling events essential for the activation of T cells. To investigate the feasibility of this approach with respect to transplantation of histoincompatible bone marrow, we undertook a clinical trial of ex vivo induction of anergy in T cells present in donor marrow to recipient alloantigens. METHODS: Outcomes in 12 transplant recipients were evaluated. The recipients' peripheral-blood lymphocytes were collected before myeloablation and served as alloantigen-presenting cells. To induce alloantigen-specific anergy, bone marrow from a donor mismatched with the recipient for one HLA haplotype was cocultured with irradiated cells from the recipient for 36 hours in the presence of CTLA-4-Ig, an agent that inhibits B7:CD28-mediated costimulation. After conventional myeloablation and immunoprophylaxis, the treated donor cells were transfused into the recipient. RESULTS: After the induction of anergy, the frequency of T cells capable of recognizing alloantigens of the recipient in donor marrow was sharply reduced (P<0.001), whereas the responsiveness to alloantigens from persons unrelated to the recipient or the donor was unaffected (P=0.51). In the 11 patients who could be evaluated, the haploidentical bone marrow cells engrafted. Of these 11 patients, 3 had acute graft-versus-host disease (GVHD) confined to the gastrointestinal tract. No deaths were attributable to GVHD. Five of the 12 patients were alive and in remission 4.5 to 29 months after transplantation. CONCLUSIONS: Donor bone marrow treated ex vivo to induce anergy to alloantigens from the recipient can reconstitute hematopoiesis in vivo with a relatively low risk of GVHD. (+info)
Cutting edge: apoptosis of superantigen-activated T cells occurs preferentially after a discrete number of cell divisions in vivo.
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Staphylococcal enterotoxins are bacterial products that display superantigen activity in vitro as well as in vivo. For instance, staphylococcal enterotoxin B (SEB) polyclonally activates T cells that bear the Vbeta8 gene segment of the TCR. SEB-activated T cells undergo a burst of proliferation that is followed by apoptosis. Using an in vivo adaptation of a fluorescent cell division monitoring technique, we show here that SEB-activated T cells divide asynchronously, and that apoptosis of superantigen-activated T cells is preferentially restricted to cells which have undergone a discrete number of cell divisions. Collectively, our data suggest that superantigen-activated T cells are programmed to undergo a fixed number of cell divisions before undergoing apoptosis. A delayed death program may provide a mechanistic compromise between effector functions and homeostasis of activated T cells. (+info)