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R T Gazzinelli

Publications and source records attributed to R T Gazzinelli.

At least 91 records · Page 5Linked to original sources
PubMed1992

IL-10 inhibits parasite killing and nitrogen oxide production by IFN-gamma-activated macrophages.

IL-10, a cytokine produced by CD4+ T lymphocytes belonging to the Th-2 subset, has previously been shown to inhibit the synthesis of IFN-gamma by both T cells and NK cells. We now demonstrate that IL-10 can also down-regulate IFN-gamma-dependent immunity by blocking the ability of that lymphokine to activate macrophages. Thus, IL-10, in a dose-dependent manner, inhibits the microbicidal activity of IFN-gamma-treated inflammatory macrophages against intracellular Toxoplasma gondii as well as the extracellular killing of schistosomula of Schistosoma mansoni. This suppression correlates with the inhibition by IL-10 of IFN-gamma-induced production of toxic nitrogen oxide metabolites, an effector mechanism previously implicated in the killing by macrophages of both parasite targets. IL-10 inhibition of nitric oxide production was shown to occur when the cytokine is given before or together with the IFN-gamma-activating stimulus, but not after its removal from the cultures and to require 12 h of contact for maximal suppressive effect on macrophage function. These results, taken together with previous findings on the down-regulation of Th1 lymphokine production by IL-10, indicate that the induction of IL-10 may be an important strategy by which parasites evade IFN-gamma-dependent, cell-mediated immune destruction.

Animals↗
PubMed1992

CD4+ subset regulation in viral infection. Preferential activation of Th2 cells during progression of retrovirus-induced immunodeficiency in mice.

Progressive lymphoproliferation and increasingly severe immunodeficiency are prominent features of a syndrome, designated mouse AIDS, which develops in susceptible strains of mice infected with the mixture of murine leukemia viruses, termed LP-BM5. Development of splenomegaly and lymphadenopathy, caused primarily by increases in B cell immunoblasts, requires the presence of CD4+ T cells and is assumed to be mediated by lymphokines produced by these cells inasmuch as progression of disease is markedly inhibited by treatment of infected mice with cyclosporin A. Studies of spleen cells from infected mice revealed spontaneous production of cytokines (IFN-gamma, IL-2, IL-4, IL-5, and IL-10) characteristic of Th0 (or a mixture of Th1 and Th2) T helper cells at 1 wk after infection. At later times, IFN-gamma and IL-2, characteristic products of Th1 helper clones, were expressed poorly, either spontaneously or after stimulation of cells with Con A. In contrast, IL-4, IL-5, IL-6, and IL-10, cytokines typically synthesized by Th2 cells, were produced in response to Con A or spontaneously through 18 wk post-infection. Increased serum IgE levels and enhanced IL-10 mRNA expression were consistent with expression of Th2 cytokines at biologically significant levels in vivo. Selective depletion of T cell subsets before stimulation with Con A showed that CD4+ T cells were the primary source of IL-2, IL-4, IL-10, and, to a lesser extent, IFN-gamma in spleens and lymph nodes of normal or infected mice. These results suggest that persistent activation of CD4+ T cells with the lymphokine profile of Th2 helper clones is responsible for chronic B cell stimulation, down-regulation of Th1 cytokines, and impaired CD8+ T cell function in mouse AIDS. This provides the first demonstration that, like many parasitic infections, viruses encoding potent antigenic stimuli can markedly affect the balance of Th subset expression.

Animals↗
PubMed1992

The microbicidal activity of interferon-gamma-treated macrophages against Trypanosoma cruzi involves an L-arginine-dependent, nitrogen oxide-mediated mechanism inhibitable by interleukin-10 and transforming growth factor-beta.

The present study was carried out to determine the effector mechanism of anti-Trypanosoma cruzi activity by interferon (IFN)-gamma plus lipopolysaccharide (LPS)-treated macrophages. A macrophage cell line (IC-21) that failed to mount an appreciable oxidative burst was nevertheless found able to control T. cruzi growth after exposure to IFN-gamma alone or IFN-gamma plus LPS. Moreover, microbicidal functions of both inflammatory macrophages and IC-21 against T. cruzi was found to be inhibited in the presence of NG-monomethyl-L-arginine (NGMMA), a competitive inhibitor of L-arginine. Addition of supplemental L-arginine to the culture overcame the capacity of NGMMA to block activated macrophage anti-T. cruzi functions. The ability of NGMMA to reverse both parasite growth inhibition and killing by IFN-gamma plus LPS-activated macrophages was found to correlate with the suppression of nitrite accumulation in the culture supernatants. Together, these results implicate the L-arginine-dependent production of nitric oxide in T. cruzi killing by activated macrophages. We also tested the ability of interleukin(IL)-10 and transforming growth factor (TGF)-beta, to block regulation of T. cruzi growth in this system. Both IL-10 and TGF-beta inhibited anti-parasite function by IFN-gamma-activated macrophages, with an optimal dose of 100 units/ml and 0.5 ng/ml, respectively. Moreover, when used in combination, suboptimal doses of IL-10 and TGF-beta were found to produce a synergistic inhibitory effect in the regulation of T. cruzi growth. The ability of IL-10 and TGF-beta to suppress microbicidal function was also positively correlated with inhibition of nitrite generation in macrophage culture supernatants. These results predict an in vivo role for IL-10 and TGF-beta in promoting parasite survival in the face of the host cell-mediated immune response.

Animals↗
PubMed1992

Role of T-cell derived cytokines in the downregulation of immune responses in parasitic and retroviral infection.

Parasitic infection is frequently accompanied by a downregulation in host cell-mediated immunity. Recent studies suggest that this modulation of helper T cells and effector cell function can at least in part be attributed to the action of a set of inhibitory cytokines produced by T lymphocytes as well as by a number of other cell types. The best characterized of these inhibitory lymphokines are IL-4, IL-10 and TGF-beta. Interestingly, both IL-4 and IL-10 are produced by the Th2 but not the Th1 subset of CD4+ helper cells. The former subset dominates in many situations of chronic or exacerbated parasitic infection and is thought to suppress Th1 function as a consequence of the cross-regulatory activity of these two cytokines. The latter hypothesis is supported by recent experiments demonstrating that mAb-mediated neutralization of IL-10 reverses suppressed IFN-gamma responses and/or disease susceptibility in mice with parasitic infections. In vivo neutralization of TGF-beta has also been reported to increase host resistance to parasite challenge. In addition to suppressing T-cell differentiation, function or proliferation, IL-4, IL-10 and TGF-beta each inhibit the ability of IFN-gamma to activate macrophages for killing of both intracellular and extracellular parasites. Moreover, the three cytokines are able to synergize with each other in downregulating these parasiticidal effects. Interestingly, each of the cytokines inhibits the production of reactive nitrogen oxides, an effector mechanism previously demonstrated to play a major role in parasite killing by activated macrophages. In the case of IL-10, this suppression of nitrogen oxide production appears to result from an inhibition of TNF-alpha synthesis leading to defective macrophage stimulation. While distant from parasites in their biology and phylogeny, some retroviruses also appear to induce an over-production in downregulatory cytokines which is closely associated with the onset of immunodeficiency. Thus, in an animal model involving infection of mice with LP-BM5 MuLV and in human HIV infection, Th2 (IL-10 and/or IL-4) cytokine synthesis is increased while Th1 (IFN-gamma and/or IL-2) cytokine production is suppressed. These observations suggest that cytokine-mediated cross-regulation may play a role in the pathogenesis of acquired immune deficiency disease, contributing both to the progression of retroviral infection and the increase in susceptibility to opportunistic infections and malignancy. Observations of similar cytokine cross-regulatory activities in organisms as diverse as helminths, protozoa and retroviruses predict that comparable mechanisms may operate in a wide variety of infectious diseases.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Opportunistic infections and retrovirus-induced immunodeficiency: studies of acute and chronic infections with Toxoplasma gondii in mice infected with LP-BM5 murine leukemia viruses.

Mice infected with LP-BM5 murine leukemia viruses develop a syndrome, termed mouse AIDS (MAIDS), characterized by increasingly severe immunodeficiency and progressive lymphoproliferation. Virus-infected mice were examined for the ability to resist acute infection and to control chronic infection with the protozoan Toxoplasma gondii, a major opportunistic pathogen of individuals infected with human immunodeficiency virus. Mice infected with the retroviruses for 2 or 4 weeks responded normally to challenge with the parasite, but mice inoculated with the protozoan 8 or 12 weeks after viral infection died with acute disease due to T. gondii. Increased sensitivity to acute infection was associated with a reduced ability to produce gamma interferon (IFN-gamma) and with established changes in CD4+ T-cell function. Mice latently infected with T. gondii and then inoculated with the retrovirus mixture were found to reactivate the parasite infection, with 30 to 40% of dually infected animals dying between 5 and 16 weeks after viral infection. Reactivation was associated with reduced proliferation and impaired production of IFN-gamma in response to stimulation with soluble T. gondii antigens or to concanavalin A. Continuing resistance to lethal reactivation in the remaining mice was shown to require CD8+ T cells and expression of IFN-gamma. In addition, it was found that chronic infection with T. gondii altered the course of MAIDS by inhibiting the progression of splenomegaly and immunodeficiency and reducing the expression of both the helper and etiologic defective viruses. These results support previous studies which indicate that infection with T. gondii is controlled by synergistic interactions between CD4+ and CD8+ T cells, the functions of which are progressively impaired during the course of MAIDS.

Acute Disease↗
PubMed1991

CD8+ T cells from mice vaccinated against Toxoplasma gondii are cytotoxic for parasite-infected or antigen-pulsed host cells.

Mice vaccinated with a live temperature sensitive mutant (TS-4) of Toxoplasma gondii develop complete resistance to subsequent challenge with a highly virulent Toxoplasma strain (RH). Because CD8+ T cells have been demonstrated to be critical to this protective immunity in vivo, the involvement of cytotoxic T lymphocytes in the killing of infected cells in vaccinated mice was investigated. After restimulation in vitro, splenic T cells from vaccinated mice of either the BALB/c or C57BL/6 strains were found to kill syngeneic bone marrow-derived macrophages infected with TS-4 tachyzoites or preincubated with soluble T. gondii Ag. Unimmunized control mice or mice vaccinated with heat-killed TS-4 tachyzoites failed to generate significant CTL activity in vitro. Moreover, the observed lytic reaction was found to be target specific, not killing uninfected or unpulsed macrophages even when included as bystanders in the assay. Target lysis did not depend on the production by the effector cells of either a cytotoxic supernatant factor or IFN-gamma. Depletion of CD8+ cells from the splenic effector cell population, however, abrogated the cytotoxic activity, whereas depletion of CD4+ cells had little effect. The MHC restriction of the Toxoplasma-specific cytolytic reaction was confirmed in studies using effector cells from BALB/c mice and targets from congenic or mutant haplotype strains. These experiments indicated that target killing is primarily restricted by genes mapping within the H-2D/Ld loci. Together, these results establish MHC-restricted cytolysis as a major parameter of CD8+ effector function against T. gondii and indicate that, in the case of this protozoan, Ag presentation to CD8+ lymphocytes can occur as a result of either processing within infected cells or exogenous uptake of parasite Ag.

Animals↗
PubMed1991

Synergistic role of CD4+ and CD8+ T lymphocytes in IFN-gamma production and protective immunity induced by an attenuated Toxoplasma gondii vaccine.

BALB/c mice vaccinated with a temperature-sensitive mutant (TS-4) of Toxoplasma gondii develop complete resistance to lethal challenge with a highly virulent toxoplasma strain (RH). This immunity is known to be dependent on IFN-gamma synthesis. In vitro and in vivo T cell depletions were performed in order to identify the subsets responsible for both protective immunity and IFN-gamma production. When stimulated with crude tachyzoite Ag in vitro, CD4+ cells from vaccinated mice produced high levels of TH1 cytokines (IL-2 and IFN-gamma) but not TH2 cytokines (IL-4 and IL-5). CD8+ cells, in contrast, produced less IFN-gamma and no detectable IL-2. Nevertheless, they could be induced to synthesize IFN-gamma when exposed in culture to exogenous IL-2. In vivo treatment with anti-CD4 plus anti-CD8 or anti-IFN-gamma antibodies during challenge infection completely abrogated resistance to T. gondii. In contrast, treatment with anti-CD4 alone failed to reduce immunity, whereas anti-CD8 treatment partially decreased vaccine-induced resistance. These results suggest that although IFN-gamma and IL-2-producing CD4+ lymphocytes are induced by vaccination, IFN-gamma-producing CD8+ T cells are the major effectors of immunity in vivo. Nevertheless, CD4+ lymphocytes appear to play a synergistic role in vaccine-induced immunity, probably through the augmentation of IFN-gamma synthesis by the CD8+ effector cells. This hypothesis is supported by the observation that when giving during vaccination, as opposed to after challenge, anti-CD4 antibodies are capable of blocking protective immunity.

Animals↗
PubMed1991

Direct lysis of Trypanosoma cruzi: a novel effector mechanism of protection mediated by human anti-gal antibodies.

Anti-gal antibodies directed against a carbohydrate epitope present in mouse laminin (galactosyl alpha 1-3 galactose) and detected in high levels in sera from patients in the acute phase of Chagas disease are responsible for the direct lysis (DL) of Trypanosoma cruzi blood forms independent of either the classic or alternative complement pathways. Furthermore, the lectins Euonymus europaeus (EE) specific for the carbohydrates gal alpha 1-3 gal present a similar lytic activity against T. cruzi at the same concentrations of purified anti-gal antibodies. The DL activity was tested with several other lectins but Concanavalin A (Con A) specific for alpha-D-mannose and alpha-D-glucose was the only one also presenting lytic activity. The lectins and anti-gal antibodies lytic activity can be inhibited by specific carbohydrates suggesting that this phenomenon is related to the capability of these lectins or anti-gal antibodies to bind to a crucial surface component of T. cruzi. Moreover, the infectivity of T. cruzi blood forms to mice was clearly inactivated by incubation with acute chagasic sera (ACS) but not by ACS absorbed by immunoaffinity chromatography with mouse laminin, a strong evidence that high levels of anti-gal antibodies participate in the decline of the parasitaemia from the acute to the chronic phase in Chagas disease.

Animals↗
PubMed1991

Effect of high sucrose diets on carcass composition in conventional and germ-free mice.

1. The effect of dietary sucrose on carcass composition was determined in conventional (CV) and germ-free (GF) mice fed on a control diet and on diets containing 20 and 40% sucrose. 2. Germ-free mice fed the control diet were heavier than their conventional counterparts. CV mice fed on sucrose diets were, however, heavier than their GF counterparts. 3. GF mice fed on high-sucrose diets showed a lower lipid content on carcass than the GF controls and their CV counterparts. 4. CV mice fed the high-sucrose diets were heavier than the conventional animals fed on the control diet. 5. The water content in the carcass of GF mice fed on high sucrose diets was higher than that of controls, as well as their CV counterparts. 6. The present results suggest different lipidogenic effect of dietary sucrose in germ-free and conventional mice.

Animal Feed↗
PubMed1990

Identification of Toxoplasma gondii in paraffin-embedded sections by the polymerase chain reaction.

We used the polymerase chain reaction to amplify DNA fragments specific to Toxoplasma gondii. The sensitivity of the technique allowed for the detection of as few as ten cultured T. gondii tachyzoites. We applied the same amplification technique to deparaffinized ocular sections from two cases of ocular toxoplasmosis. Although toxoplasmic cysts could only be seen in one eye by optical microscopy, polymerase chain reaction allowed the identification of the parasite in both cases. Our study indicates the feasibility of a sensitive DNA-based assay to complement pathologic studies of an ocular parasitic disease.

Adult↗
PubMed1990

Two modes of idiotypic stimulation of T lymphocytes from patients with Chagas' disease: correlations with clinical forms of infection.

Patients with chronic Trypanosoma cruzi infections have peripheral auto-anti-idiotype (Id) T cells that proliferate on exposure to immunoaffinity-purified antibodies against T. cruzi epimastigote antigens (EPI). The responses of some patients' (group 1) peripheral blood mononuclear cells (PBMC) to anti-EPI antibodies from sera of patients with the cardiac form of Chagas' disease (Id-C) were inhibited by chloroquine, but responses of other patients' (group 2) PBMC to Id-C were not inhibited. PBMC responses of both group-1 and -2 patients to anti-EPI antibodies from asymptomatic (indeterminate) patients (Id-I) were inhibited by chloroquine, as were their responses to the antigens in EPI. Most patients (69%) in group 1 had indeterminate Chagas' disease, and 100% of the patients in group 2 had severe, cardiac or digestive Chagas' disease. Both the direct (chloroquine-insensitive) and indirect (processed) modes of stimulation by anti-EPI antibodies required adherent cells. In group 2 (direct stimulation), this requirement was met by exogenous IL-1, and neither anti-HLA-DR,DP(DQ) monoclonal antibody (mAb) nor sodium azide inhibited T-cell proliferation. Indirect Id stimulation of group-1 cells by Id-I or Id-C, and group-2 cells by Id-I or EPI, was inhibited by anti-HLA-DR,DP(DQ) mAb or sodium azide, and exogenous IL-1 alone did not support this processed, MHC-mediated T-cell stimulation, but live adherent cells did. The mode of activation of auto-anti-Id T cells from patients with Chagas' disease depends on the clinical form of infection of both the cell donor and the donor of the stimulating anti-EPI antibodies.

Adult↗
PubMed1990

Identification and partial characterization of Trypanosoma cruzi antigens recognized by T cells and immune sera from patients with Chagas' disease.

Trypanosoma cruzi antigenic specificities involved in human T-cell and antibody responses were compared in chronic chagasic patients affected with cardiomyopathy (C) or with the indeterminate form (I), the asymptomatic form of chronic Chagas' disease. T-cell Western blotting (immunoblotting) was performed to identify the most active antigens in epimastigote extracts (EPI-Ag). The patterns of peripheral blood mononuclear cell (PBMC) and T-cell proliferative responses induced by fractions blotted to nitrocellulose were heterogeneous, but the computation of their frequency distribution disclosed some important antigen specificities. Molecules ranging from 100 to 150 kilodaltons (kDa) were frequently stimulatory to PBMC from I patients (5 of 8 cases) and were less so when confronted with C patient (1 of 7 cases) lymphocytes. In contrast, both groups of patients actively responded to fractions ranging from 48 to 57 and 28 to 32 kilodaltons (kDa). The Western immunoblotting patterns of antibody reactivity displayed by 17 C and 15 I patients were also similar, yielding outstanding staining in the molecular mass ranges of 70 to 80 and 43 to 57 kDa. The latter antigen complex was recognized by 100% of the 32 chronic Chagas' disease serum specimens tested and closely corresponded to the migratory position recognized by T cells of most patients tested. The identification of the active molecules contained in the 43- to 57-kDa region was sought, with a focus on GP57/51, an antigen with well-established serodiagnostic properties. Immunoblotting analysis of EPI-Ag with a monoclonal antibody to GP57/51 confirmed its presence within the predicted molecular weight region. Highly purified GP51 was then used to demonstrate directly its capacity to promote specific PBMC proliferative responses in vitro. Data computed from a survey with 12 patients have shown a linear correlation (r = 0.93) between PBMC responses to EPI-Ag and to purified GP51, suggesting that the immune response to this particular glycoprotein may be an important component of human immune responses against T. cruzi.

Animals↗
PubMed1988

Idiotype stimulation of T lymphocytes from Trypanosoma cruzi-infected patients.

Anti-Trypanosoma cruzi epimastigote antibodies (anti-epi) from pooled and individual sera from patients with chronic Chagas' disease were purified on immunoaffinity columns of epimastigotes antigens (epi) coupled to activated Sepharose 4B. SDS-PAGE analysis of purified anti-epi preparations showed only the presence of human IgG H and L chains. These antibodies preparations showed similar Western blotting profiles as the sera pools from which they originated. The main polypeptides recognized by anti-epi had apparent molecular masses 31, 46, 51, 75 and 85 kDa. No difference in these patterns were detected between anti-epi from pooled sera of cardiac (anti-epiC) and indeterminate (anti-epiI) clinical forms. Anti-epi preparations (20 to 60 micrograms/ml) of pooled and individual sera stimulated proliferation of homologous and autologous PBMN or T-lymphocyte-enriched population. The stimulatory ability was dependent upon the PBMN-anti-epi combinations. There is no direct correlation between the level of PBMN response to epi and anti-epi stimuli. Comparison of the stimulatory activities of anti-epiC vs anti-epiI on PBMN of either cardiac or indeterminate group of patients indicate that anti-epiC is significantly more active than anti-epiI (p less than 0.025). These data demonstrate the presence of auto-anti-idiotypic-T cells in chagasic patients and lead to the possibility that idiotype/anti-idiotype interactions may play a role in determining the pathogenesis of chagasic cardiopathy.

Animals↗
PubMed1988

Anti-Trypanosoma cruzi and anti-laminin antibodies in chagasic patients after specific treatment.

The antibody response to Trypanosoma cruzi epimastigote and trypomastigote stages, as well as to laminin, was studied in several groups of chagasic patients. In six patients who were cured of the parasite, the serum antibody titers as revealed by indirect immunofluorescence and hemagglutination tests against epimastigotes (conventional serology) and a complement-mediated lysis test with living trypomastigotes did not differ from those of normal individuals. In seven presumably cured patients, although the complement-mediated lysis test turned negative, conventional serology remained positive. Sera from this group of so-called "dissociated" patients presented significant lower mean antibody titers against epimastigote but not trypomastigote stages than did sera from 14 untreated patients (P less than 0.01). Most of the antibodies against trypomastigotes, including the residual levels found in cured patients, were absorbed by mouse laminin. In fact, significantly higher titers of anti-laminin antibodies were observed in sera from untreated chagasic patients (1.131 +/- 0.458) and cured patients (1.103 +/- 0.572) than in sera from eight normal individuals (0.459 +/- 0.402) (P less than 0.01). The anti-laminin titers were higher in sera of patients of blood group A or O than in those of patients of group B or AB. In Western blotting (immunoblotting) analysis against trypomastigotes, sera from chronic untreated patients recognized many polypeptide bands ranging from 26 to 160 kilodaltons, whereas no protein bands were observed with sera from cured patients. Only faint bands of parasite proteins were observed with sera of dissociated patients. In conjunction, the above data suggest that the anti-trypomastigote antibodies which persist after parasitological cure of patients with Chagas' disease are due mainly to cross-reactive epitopes from mouse laminin.

Animals↗
PubMed1988

Idiotypic/anti-idiotypic interactions in schistosomiasis and Chagas' disease.

Immunoaffinity-purified antibodies against soluble Schistosoma mansoni egg antigens (SEA) were isolated from the sera of patients with schistosomiasis mansoni. Similarly, antibodies against Trypanosoma cruzi epimastigote antigens were obtained from sera of patients with Chagas' disease. These antibody preparations were used in culture to demonstrate the presence of anti-idiotypic T lymphocytes in peripheral blood mononuclear cell preparations from patients with either schistosomiasis mansoni or Chagas' disease, or with both of these infections. Only cells from patients with schistosomiasis or both infections proliferated upon exposure to the anti-SEA antibodies. Conversely, only cells from patients with Chagas' disease or both infections responded to anti-epimastigote antibodies. Western blot analysis of SEA and epimastigote antigens, developed by patients' sera or by immunoaffinity-purified antibody preparations, substantiated that anti-SEA immunoaffinity-purified antibodies only reacted with components of SEA, and anti-epimastigote immunoaffinity-purified antibodies only reacted with components of epimastigote antigenic preparation. These studies demonstrate the presence of anti-idiotypic T lymphocytes in the peripheral blood of patients with schistosomiasis or Chagas' disease which are specific for idiotypes generated during these infections.

Animals↗