Biomedical subjects

R T Gazzinelli

Publications and source records attributed to R T Gazzinelli.

At least 73 records · Page 4Linked to original sources

PubMed1995

HIV infection suppresses type 1 lymphokine and IL-12 responses to Toxoplasma gondii but fails to inhibit the synthesis of other parasite-induced monokines.

Individuals infected with Toxoplasma gondii normally develop resistance to the parasite, resulting in an asymptomatic chronic infection. In AIDS patients, this resistance is lost leading to reactivation of infection and development of encephalitis. To characterize the cytokine response of T. gondii-infected individuals, PBMC were cultured in vitro in the presence or absence of crude tachyzoite Ags (STAg). When stimulated with STAg, PBMC from T. gondii-infected donors, but not controls, produced high levels of Type 1 lymphokines (IL-2 and IFN-gamma) as well as the monokine IL-12, in the absence of detectable Type 2 lymphokines (IL-4 and IL-5). In contrast, cells of individuals from both groups produced high levels of IL-1, IL-6, and TNF-alpha when exposed to the same Ag preparation. By using highly purified elutriated cells, we demonstrated that monocytes are a major source of these monokines. The above findings were further expanded by analyzing the cytokine responses induced by STAg in PBMC from patients co-infected with T. gondii and HIV. Our results demonstrate that parasite-specific IL-2 and IFN-gamma responses are greatly impaired even before AIDS development, as is IL-12 synthesis by PBMC from HIV-infected individuals stimulated with STAg. In contrast, the release of IL-6 and TNF-alpha triggered by STAg is either not affected or augmented during HIV infection.

AIDS-Related Opportunistic Infections↗

PubMed1995

IL-12 prevents mortality in mice infected with Histoplasma capsulatum through induction of IFN-gamma.

Histoplasma capsulatum is a pathogenic fungus found in discrete geographic locations throughout the world. The fungus invades the reticuloendothelial organs such as the spleen and liver of immunocompetent hosts where it is usually controlled. However, in individuals with immune deficiency, histoplasmosis is a severe and potentially fatal disease. Resistance to this infection is due primarily to a cellular immune response mediated by T cells and macrophages. Moreover, IFN-gamma is critical in activating macrophages to kill the organism. Herein we study the regulation of cytokine induction in mice infected with H. capsulatum and the effects of IL-12 in the course of infection. Mice infected with H. capsulatum and treated with neutralizing Abs to IFN-gamma, TNF-alpha, or IL-12 experienced accelerated mortality, indicating that endogenous production of these cytokines plays an important role in response to infection. In contrast, mice treated with IL-12 or a neutralizing Ab to IL-4 at the initiation of infection had substantially diminished mortality. Moreover, mice infected and treated with IL-12 show a two- to threefold increase in the amount of IFN-gamma following in vitro stimulation with specific H. capsulatum Ag compared with the control infected mice. The protective effect of IL-12 could be abrogated if a neutralizing Ab to IFN-gamma was given at the same time, demonstrating that the role of IL-12 in protection was mediated by IFN-gamma. Additionally, infected mice treated with IL-12 had a severalfold decrease in the colony counts of H. capsulatum in spleen cells after 5 days of infection as compared with control animals. Lastly, spleen cells from infected animals treated with IL-12 showed a striking decrease in their proliferative response to mitogen or H. capsulatum Ag. Responses could be restored by adding inhibitors of IFN-gamma or of nitric oxide to the in vitro cultures. The above observations suggest that IL-12 may be useful in immunologic intervention against this opportunistic pathogen.

Animals↗

PubMed1995

Induction and regulation of host cell-mediated immunity by Toxoplasma gondii.

Toxoplasma gondii is a highly infectious intracellular parasite which, if left unchecked by the immune system, rapidly overwhelms its intermediate hosts, as illustrated by the pathogenesis of toxoplasmic encephalitis in patients with AIDS. In order to insure both its host's and consequently its own survival simultaneously, T. gondii induces a potent gamma-interferon (IFN-gamma)-dependent cell-mediated immunity early in infection that controls the replication of the protozoan and facilitates transformation into the dormant cyst stage. The protective IFN-gamma is derived from three sources: natural killer cells; and CD4+ and CD8+ T lymphocytes, which can partially compensate for each other in knockout mice lacking the appropriate major histocompatibility complex-restricting elements. At least two properties of the parasite appear to be responsible for the early induction of these effector cells. The first is a hydrophobic molecule (or group of related molecules) that triggers interleukin 12 (IL-12), tumour necrosis factor alpha and IL-1beta synthesis in macrophages. This response can also promote HIV replication in the same cells. The second is a superantigen activity that drives IFN-gamma-producing Vbeta5+ CD8+ T cells. These potentially lethal responses are later regulated through the triggering of IL-10 and by the induction of anergy in the superantigen-stimulated Vbeta5+ T cell population.

Animals↗

PubMed1995

Effects of IL-12 on immune responses to microbial infections: a key mediator in regulating disease outcome.

Recent studies have documented that the immunoregulatory functions of IL-12 may play a role in promoting endogenous protective responses during infections and/or contribute to pathology resulting from unregulated cytokine expression. Pathogen induction of IL-12 elicits interferon-gamma production by natural killer cells, which contributes to early defense during certain bacterial, parasitic, and viral infections. IL-12 also facilitates the development of T helper type 1 (Th1) lymphocytes required for late protection against bacteria, parasites, and fungi. During viral infections, however, there appear to be mechanisms independent of IL-12 for inducing protective T-cell responses. In contrast, negative regulation of IL-12 during acute infections can be a key event in the establishment of chronic infection and protection against harmful excessive cellular immune response. Under appropriate conditions, IL-12 has therapeutic efficacy for promoting defense against a variety of pathogens, and for use as a vaccine adjuvant to enhance beneficial Th1 over detrimental Th2 lymphocyte responses. This information extends knowledge about the regulation of immune responses to infectious agents, and provides new insights for the development of treatment and adjuvant strategies to potentiate beneficial or inhibit detrimental endogenous immune responses.

Animals↗

PubMed1994

In vivo treatment with interleukin 12 protects mice from immune abnormalities observed during murine acquired immunodeficiency syndrome (MAIDS).

Lymphoproliferation, chronic B cell activation resulting in hypergammaglobulinemia, and profound immunodeficiency are prominent features of a retrovirus-induced syndrome designated murine acquired immunodeficiency syndrome (MAIDS). In vivo treatment of infected mice with recombinant interleukin 12 (IL-12) beginning at the time of infection or up to 9 wk after virus inoculation markedly inhibited the development of splenomegaly and lymphadenopathy, as well as B cell activation and Ig secretion. Treatment with IL-12 also had major effects in preventing induction of several immune defects including impaired production of interferon gamma (IFN-gamma) and IL-2 and depressed proliferative responses to various stimuli. The therapeutic effects of IL-12 on the immune system of mice with MAIDS were also associated with reduced expression of the retrovirus that causes this disease (BM5def), with lesser effects on expression of ecotropic MuLV. IL-12 treatment was not effective in IFN-gamma knockout mice or in infected mice treated simultaneously with IL-12 and anti-IFN-gamma. These results demonstrate that induction and progression of MAIDS are antagonized by IL-12 through high-level expression of IFN-gamma and may provide an experimental basis for developing treatments of retrovirus-induced immune disorders with similar immunopathogenic mechanisms.

Animals↗

PubMed1994

Parasite-induced IL-12 stimulates early IFN-gamma synthesis and resistance during acute infection with Toxoplasma gondii.

In vitro and in vivo studies were performed to assess the involvement of IL-12 in resistance to acute and chronic infection with an avirulent strain of Toxoplasma gondii. Our previous findings implicated macrophages as a major source of parasite-induced IL-12. This finding was confirmed by showing that peritoneal macrophages exposed to either live parasites or soluble tachyzoite Ags produce IL-12 protein. In mice, increased expression of IL-12 (p40) mRNA in both spleen and peritoneal cells was detected as early as 2 days postinfection. Treatment with neutralizing mAbs against IL-12 increased the susceptibility of C57BL/6, BALB/c, and severe combined immunodeficient (SCID) mice to acute infection, which resulted in 100% mortality within the first 15 days after parasite inoculation. In contrast, neutralization of endogenously produced IL-12 had no effect when given during chronic infection. In agreement with the survival data, treatment with anti-IL-12 resulted in decreased IFN-gamma and enhanced Th2 (IL-4 and IL-10) cytokine synthesis by splenocytes when given during acute, but not chronic, toxoplasmosis. Sorting experiments on spleen cells from acutely infected mice indicated that both CD4+ lymphocytes and NK1.1+/CD3- cells contribute to the early IFN-gamma response. In contrast, CD4+ cells were found to be the major source of the cytokine during chronic disease. Together, these results suggest that the stimulation of macrophage-derived IL-12 plays a major role in both the induction of resistance and Th1 cell subset selection in acute T. gondii infection, but may not be required to maintain established immunity.

Animals↗

PubMed1994

Toxoplasma gondii: acquired ocular toxoplasmosis in the murine model, protective role of TNF-alpha and IFN-gamma.

DNA and mRNA amplification by the polymerase chain reaction (PCR), immunohistochemical, and histopathology were performed in the eyes and brains from C57BL/6 mice infected with an avirulent strain of Toxoplasma gondii (ME49). Focal ocular inflammation and retinal pigment epithelial involvement were commonly observed after 15 days of infection. Four weeks after infection a stable number of cysts was observed in the brain but rarely in the eye, and they did not elicit an inflammatory response. In most of the ocular lesions the presence of the parasite could not be demonstrated even with the PCR technique. B1 DNA fragments of T. gondii were detected in only 4 of 11 eyes tested by PCR and Southern blot hybridization. Treatment of mice with mAbs against T cells (CD4 plus CD8) or cytokines (IFN-gamma or TNF-alpha) resulted in a marked increase of ocular lesions, more often associated with the presence of the parasite and the severity of inflammatory response. This model and the techniques utilized here can improve our understanding of the respective roles of parasite proliferation and immune mechanisms involved in the pathogenesis of acquired ocular toxoplasmosis.

Animals↗

PubMed1993

Emergence of NK1.1+ cells as effectors of IFN-gamma dependent immunity to Toxoplasma gondii in MHC class I-deficient mice.

CD8+ T lymphocytes have been reported to play a major role in the protective immune response against acute infection with Toxoplasma gondii. In order to further assess the role of CD8+ cells in resistance against this protozoan we examined the ability of beta 2m-deficient mice, which fail to express MHC class I molecules and peripheral CD8+ lymphocytes, to survive tachyzoite challenge following vaccination with an attenuated parasite mutant. Surprisingly, vaccination of beta 2m-deficient mice induced strong resistance to lethal challenge, with > 50% surviving beyond 3 months. Vaccinated beta 2m-deficient mice, but not control heterozygotes, showed a five- to six-fold expansion in spleen cell number and approximately 40% of the splenocytes were found to express the NK markers NK1.1 and asialo GM1. Spleen cells from the vaccinated beta 2m-deficient animals failed to kill either infected host cells or the NK target YAC-1. However, high levels of IFN-gamma were secreted when the cells were cultured in vitro with soluble T. gondii lysate, and this response was abolished by NK1.1+ but not CD4+ and CD8+ lymphocyte depletion, implicating the NK1.1+ population as the major source of IFN-gamma. More importantly, vaccine-induced immunity in beta 2m-deficient mice was completely abrogated by in vivo administration of antibody to NK1.1, asialo GM1, or IFN-gamma. Together, the data suggest that in class I-deficient mice vaccinated against T. gondii, the absence of CD8+ effector cells is compensated for by the emergence of a population of NK1.1+ and asialo GM1+ cells which lack cytolytic activity, and that the protective action of these cells against the parasite is attributable to IFN-gamma production. The induction of this novel NK population may provide an approach for controlling opportunistic infections in immunocompromised hosts.

Animals↗

PubMed1993

Acute cerebral toxoplasmosis is induced by in vivo neutralization of TNF-alpha and correlates with the down-regulated expression of inducible nitric oxide synthase and other markers of macrophage activation.

C57BL/6 mice infected with the ME-49 strain of Toxoplasma gondii develop a progressive encephalitis culminating in 100% mortality between 12 and 15 wk after intraperitoneal inoculation of the parasite. Moreover, when injected at 4 wk after infection with anti-IFN-gamma mAb, progression of toxoplasmic encephalitis is markedly accelerated, resulting in death of the animals by 9 to 12 days posttreatment. In this study, we investigated the expression of mRNAs encoding cytokines as well as lymphocyte and macrophage markers during the development of toxoplasmic encephalitis. High levels of lymphocyte CD4 and CD8 surface Ag transcript were detected in the brains of mice throughout the infection. In addition from 2 to 4 wk we found elevations of Th1 (IFN-gamma and IL-2) but not of Th2 (IL-4 and IL-5) cytokine mRNAs. The elevation in Th1 cytokines was accompanied by increases in the expression of monokine (IL-1, IL-6, IL-10, granulocyte macrophage-colony stimulating factor [GM-CSF], and TNF-alpha) mRNAs, as well as markers expressed by activated macrophages (major histocompatibility class II [Ia], inducible nitric oxide synthase [iNOS] and macrophage activation gene 1 [Mag-1]). Interestingly, after 8 wk of infection with T. gondii we observed a dramatic decrease of Th1 cytokine and most monokine (IL-1, IL-6, GM-CSF, and TNF-alpha) as well as Mag-1 and iNOS mRNA levels. This down-regulation was associated with enhanced necrosis and neutrophilic infiltrates in the brain accompanied by increased expression of genes expressed specifically by the tachyzoite stage of T. gondii (T. gondii surface antigen 1 [SAG-1] and T. gondii surface antigen 2 [SAG-2]). Similarly, in mice chronically infected with T. gondii and treated with anti-IFN-gamma mAb the resulting pathology was associated with decreased expression of TNF-alpha and iNOS and increased expression of SAG-1 and SAG-2. Moreover, treatment with anti-TNF-alpha mAb also resulted in enhanced pathology, which correlated with low levels of iNOS mRNA and high levels of tachyzoite-specific mRNAs. Together these results suggest that reactivation of T. gondii results from a down-regulation of IFN-gamma and TNF-alpha expression leading to decreased macrophage or microglial cell activation, release of parasite growth, and subsequent tissue damage.

Acute Disease↗

PubMed1993

Interleukin 12 is required for the T-lymphocyte-independent induction of interferon gamma by an intracellular parasite and induces resistance in T-cell-deficient hosts.

Immunity against the intracellular protozoan Toxoplasma gondii is highly dependent on interferon gamma (IFN-gamma). We have previously shown that, in addition to T lymphocytes, natural killer (NK) cells can be stimulated by the parasite to produce this cytokine by a reaction requiring adherent accessory cells and tumor necrosis factor alpha. We now demonstrate that a recently characterized cytokine, interleukin 12 (IL-12), is also necessary for parasite-induced IFN-gamma synthesis by NK cells. Anti-IL-12 antibodies completely inhibited T. gondii or bacterial endotoxin-stimulated IFN-gamma production by NK-enriched spleen cells from severe combined immunodeficient mice. Moreover, potent NK cytokine responses were induced by the combination of IL-12 and tumor necrosis factor alpha. In addition, adherent spleen cells from scid/scid mice or thyoglycollate-elicited macrophages from BALB/c animals produced high levels of both IL-12 (p40) and tumor necrosis factor alpha mRNAs when exposed to either live tachyzoites, parasite extracts, or endotoxin, confirming that these cytokines are produced by accessory cells. Finally, in vivo studies showed that treatment with recombinant IL-12 results in prolonged survival of scid mice after infection with T. gondii by means of a response dependent on both IFN-gamma and NK cells. Together the data argue that IL-12 is required for the T-cell-independent triggering of NK cells by intracellular parasites and that the cytokine may be useful for inducing this protective pathway in immunodeficient hosts.

Animals↗

PubMed1993

Toxoplasma gondii induces a T-independent IFN-gamma response in natural killer cells that requires both adherent accessory cells and tumor necrosis factor-alpha.

Spleen cells from scid mice produce high levels of IFN-gamma when exposed to either live tachyzoites of Toxoplasma gondii or a soluble parasite extract. Small numbers of parasites are sufficient to stimulate this response, which is also induced by cell-free supernatants of cultured tachyzoites. The parasite molecules responsible for triggering IFN-gamma production are heat-labile but resistant to freezing and thawing. Depletion of NK cells or adherent cells from the splenocyte population abolishes the response. Moreover, cultured bone marrow-derived NK cells are stimulated by Toxoplasma to produce IFN-gamma, but only when supplemented with adherent peritoneal washout or thioglycollate-induced exudate cells. Supernatants of macrophages preincubated with T. gondii extract also induce IFN-gamma synthesis by cultured NK cells. Addition of neutralizing mAb against TNF-alpha abolishes the IFN-gamma response of scid spleen cells exposed to the parasite or of NK cells incubated with supernatants of adherent cells stimulated with T. gondii extract. Moreover, splenic adherent cells produce low levels of TNF-alpha in response to the parasite. Nevertheless, TNF-alpha alone is not sufficient to trigger IFN-gamma production from purified NK cell populations. These findings provide the first example of the stimulation of T-independent IFN-gamma production by a protozoan. The ability of T. gondii to trigger this pathway may underlie its induction of strong IFN-gamma-dependent nonspecific and specific cell-mediated immunity.

Animals↗

PubMed1993

Antibodies to Trypanosoma cruzi express idiotypic patterns that can differentiate between patients with asymptomatic or severe Chagas' disease.

Immunization of rabbits with pools of immunoaffinity-purified anti-Trypanosoma cruzi epimastigote antibodies derived from patients with different clinical forms of Chagas' disease induces antiidiotypic sera that can distinguish between anti-epimastigote antibodies from patients with asymptomatic (indeterminate (IND)) or severe (cardiac (CARD)) Chagas' disease. These idiotypically different anti-EPI antibodies from patients with the different clinical forms do not differ in their anti-epimastigote activities or isotypes. Analysis of immunoaffinity purified antibodies from individual chagasic patients by specific competitive ELISA generally confirms that Id-specific rabbit antisera can differentiate the clinical forms of the source of the antibodies. Based on these data, immunoaffinity-purified antibodies from patients share many Id with those from IND patients, although antibodies from IND patients express much lower levels of the distinctive Id characteristic of CARD patients. Reduction and alkylation of antibodies from IND patients reduces somewhat, but does not abolish, the ability of their Id to be recognized idiotypically, and to effectively inhibit in competitive ELISA. In contrast, reduction and alkylation of antibodies from CARD patients almost completely eliminates the ability of their predominant Id to be either recognized by, or inhibit, the appropriate systems. These data imply that the expression of the major Id that define CARD patients by these serologic anti-Id systems is largely dependent on the tertiary conformation of the Ig molecule. This agrees with our earlier studies on the respective differential abilities of CARD vs IND Id to stimulate anti-Id T cells by direct stimulation vs processing and presentation mechanisms.

Animals↗

PubMed1993

Bone marrow macrophages process exogenous Toxoplasma gondii polypeptides for recognition by parasite-specific cytolytic T lymphocytes.

CD8+ T cells from mice vaccinated with an attenuated strain of Toxoplasma gondii have previously been shown to have cytolytic activity against bone marrow macrophages (BMM phi) preincubated with a soluble tachyzoite extract. In the present study, we show that class I-transfected L cells differ from BMM phi in that although both cell types are recognized CTL after infection, only BMM phi are killed after sensitization with soluble tachyzoite extract. Gel filtration studies indicated that the T. gondii Ag responsible for sensitization of BMM phi are macromolecules of M(r) > or = 12,000. In contrast, peptides derived by tryptic digestion of this material were found to sensitize both transfected L cells and BMM phi. Although exogenous beta 2-microglobulin markedly enhanced peptide sensitization of BMM phi, no such effect was observed using the macromolecular preparation. This result suggests a requirement for cellular internalization in the processing by BMM phi of soluble Ag for class I-restricted recognition. In related experiments, infected and Ag-sensitized BMM phi were found to express cross-reactive T. gondii epitopes, as determined by cold target inhibition studies. Supernatant derived by 100,000 x g centrifugation of tachyzoite extract had potent sensitizing activity, and after anion exchange chromatography most of the activity was associated with a single fraction. The p30 Ag was not detected by immunoblot analysis in the biologically active supernatant and chromatographic fractions. These findings establish the feasibility of identifying the parasite Ag recognized by CD8+ effectors by direct fractionation of T. gondii proteins coupled with sensitization of BMM phi targets.

Animals↗

PubMed1993

CD8+ T-cell interactions with Toxoplasma gondii: implications for processing of antigen for class-I-restricted recognition.

CD8+ T lymphocytes contribute to the control of acute and chronic T. gondii infection, and the activity of these cells is closely related to IFN gamma production. However, it is not clear whether CD8+ lymphocytes mediate protection solely by production of IFN gamma, or whether the lymphokine synergizes with CD8+ CTL activity. Interestingly, sensitization of bone marrow macrophages for CTL lysis can occur either as a result of infection or incubation with soluble T. gondii antigen. Thus, this system offers a powerful approach for analysing antigen processing pathways employed by intracellular protozoa, as well as for identifying the peptide epitopes which serve as targets for CD8(+)-dependent immunity.

Animals↗

PubMed1993

Differentiation of Toxoplasma gondii from closely related coccidia by riboprint analysis and a surface antigen gene polymerase chain reaction.

The tachyzoite of the human pathogen Toxoplasma gondii is morphologically indistinguishable from the proliferative stages of some other zoonotic coccidia, including Sarcocystis. To determine the identity of such coccidia obtained from human tissues and other sources, we compared riboprints (through restriction enzyme analysis of the polymerase chain reaction [PCR]-amplified small subunit rRNA gene) of the following protozoa: the RH and ts-4 strains of T. gondii, lines OH3 and S11, which are two recently isolated T. gondii-like parasites from Brazil, Neospora caninum, Sarcocystis species, and the malarial parasite Plasmodium berghei. In addition, the protozoan genomes were examined by PCR for homologs of surface antigen genes of T. gondii, and by Southern hybridization to the heterologous rRNA gene probe pSM 389. Strains OH3, S11, ts-4, and RH shared identical riboprints, and OH3, S11, and ts-4 have p22 and p30 surface antigen gene structures similar to RH. In contrast, riboprints for N. caninum and T. gondii differ with respect to Dde 1 sites, and moreover, their genomes vary significantly from one another at both the p22 and p30 gene loci. The riboprints of Sarcocystis and P. berghei differ markedly from T. gondii and N. caninum and from each other. Bam HI pSM 389 restriction fragment length polymorphisms differentiate ts-4 from RH, OH3, and S11. Our results confirm that OH3 and S11 are indeed T. gondii, but that N. caninum and T. gondii are likely to be separate species, thereby resolving previous uncertainties concerning the identity of these parasites. Together, the variation in riboprints and surface antigen gene structure reflects the phylogenetic diversity among these coccidia, and in addition, confirms the value of riboprinting in the identification of apicomplexan parasites such as T. gondii.

Animals↗

PubMed1993

Use of Trypanosoma cruzi purified glycoprotein (GP57/51) or trypomastigote-shed antigens to assess cure for human Chagas' disease.

With the exception of assays for the detection of antibodies promoting complement-mediated lysis of Trypanosoma cruzi, serologic tests have generally failed to assess the effectiveness of chemotherapy for Chagas' disease. Conventional serology, although useful for the diagnosis of infection, is not capable of determining which patients have been cured. Here we demonstrate that a high proportion of antibodies detected by conventional serology (using fixed epimastigotes or trypomastigotes or crude extracts obtained therefrom) are directed against the carbohydrate residue galactosyl alpha 1- > 3 galactose (Gal alpha 1- > 3 Gal), a determinant also recognized by antibodies from noninfected healthy volunteers. In a study of 14 cured patients with long-term followup, we found that the persistently positive reactions detected using conventional serology were largely eliminated following immunoadsorption with melibiose. Because of their wide distribution among microorganisms of intestinal and pulmonary microflora, these carbohydrate determinants may keep stimulating lymphocytes previously primed by T. cruzi Gal alpha 1- > 3 Gal epitopes, thereby accounting for false-positive results in cured patients. Consistent with this proposition, enzyme-linked immunosorbent assays performed with two distinct T. cruzi antigen preparations that lack the Gal alpha 1- > 3 Gal epitope, namely purified GP57/51 and trypomastigote-shed antigens, were indeed capable of determining a cure after chemotherapy, albeit to a different degree. Collectively, the data indicate that conventional immunoassays prepared with highly specific T. cruzi antigens can be useful in the assessment of a cure after chemotherapy.

Acute Disease↗

PubMed1993

Host resistance to Toxoplasma gondii: model for studying the selective induction of cell-mediated immunity by intracellular parasites.

Cell-mediated immunity (CMI) provides a major host defense against infectious disease and malignancy. Nevertheless, the mechanisms underlying the induction of CMI remain poorly understood and this lack of knowledge remains an important impasse in the design of rationally based vaccines and immunotherapies. Toxoplasma gondii is an intracellular pathogen that, as part of its normal life cycle, induces a potent CMI response leading to host resistance. Studies on the interaction of this parasite with the immune system therefore provide a unique approach for identifying events that selectively lead to the triggering of host-protective CMI. In addition, this knowledge may provide new strategies for immunotherapy of opportunistic infections in immunodeficient hosts.

Animals↗

PubMed1992

IL-10 synergizes with IL-4 and transforming growth factor-beta to inhibit macrophage cytotoxic activity.

After activation with IFN-gamma, thioglycollate-elicited murine peritoneal macrophages kill schistosomula of Schistosoma mansoni in vitro by an L-arginine-dependent mechanism which involves the production of reactive nitrogen oxides (NO). In the present study we demonstrate that the regulatory cytokines IL-10, IL-4, and transforming growth factor-beta (TGF-beta) are potent inhibitors of this extracellular killing function of activated macrophages. Each cytokine was found to suppress killing of schistosomula in a dose-dependent fashion. The activity of IL-10 was not permanent, because subsequent treatment with additional IFN-gamma 2 to 6 h later reversed the inhibition of macrophage larval killing. More importantly, the combination of suboptimal levels of any two of these three cytokines was found to give a potent synergistic suppression of schistosomulum killing by IFN-gamma-treated macrophages. Similarly, IL-10, IL-4, or TGF-beta alone blocked the production of NO, and when used in combination these cytokines exhibited an enhanced inhibitory effect on nitrite production. Macrophage-mediated killing of schistosomula through the generation of NO has been shown previously to be a major effector mechanism of schistosome immunity. The results presented here suggest that the suppression of this mechanism by induction of the regulatory cytokines IL-10, IL-4, and TGF-beta, which are known to be produced during schistosome infection, may be an important strategy used by the parasite to evade macrophage-mediated immune destruction.

Animals↗