Leishmania amazonensis sabotages host cell SUMOylation for intracellular survival

Leishmania parasites use elaborate virulence mechanisms to invade and thrive in macrophages. These virulence mechanisms inhibit host cell defense responses and generate a specialized replicative niche, the parasitophorous vacuole. In this work, we performed a genome-wide RNAi screen in Drosophila macrophage-like cells to identify the host factors necessary for Leishmania amazonensis infection. This screen identified 52 conserved genes required specifically for parasite entry, including several components of the SUMOylation machinery. Further studies in mammalian macrophages found that L. amazonensis infection inhibited SUMOylation within infected macrophages and this inhibition enhanced parasitophorous vacuole growth and parasite proliferation through modulation of multiple genes especially ATP6V0D2, which in turn affects CD36 expression and cholesterol levels. Together, these data suggest that parasites actively sabotage host SUMOylation and alter host transcription to improve their intracellular niche and enhance their replication.

Automatic detection of the parasite Trypanosoma cruzi in blood smears using a machine learning approach applied to mobile phone images

Chagas disease is a life-threatening illness caused by the parasite Trypanosoma cruzi. The diagnosis of the acute form of the disease is performed by trained microscopists who detect parasites in blood smear samples. Since this method requires a dedicated high-resolution camera system attached to the microscope, the diagnostic method is more expensive and often prohibitive for low-income settings. Here, we present a machine learning approach based on a random forest (RF) algorithm for the detection and counting of T. cruzi trypomastigotes in mobile phone images. We analyzed micrographs of blood smear samples that were acquired using a mobile device camera capable of capturing images in a resolution of 12 megapixels. We extracted a set of features that describe morphometric parameters (geometry and curvature), as well as color, and texture measurements of 1,314 parasites. The features were divided into train and test sets (4:1) and classified using the RF algorithm. The values of precision, sensitivity, and area under the receiver operating characteristic (ROC) curve of the proposed method were 87.6%, 90.5%, and 0.942, respectively. Automating image analysis acquired with a mobile device is a viable alternative for reducing costs and gaining efficiency in the use of the optical microscope.

α-Gal immunization positively impacts Trypanosoma cruzi colonization of heart tissue in a mouse model

Chagas disease, caused by the parasite Trypanosoma cruzi, is considered endemic in more than 20 countries but lacks both an approved vaccine and limited treatment for its chronic stage. Chronic infection is most harmful to human health because of long-term parasitic infection of the heart. Here we show that immunization with a virus-like particle vaccine displaying a high density of the immunogenic α-Gal trisaccharide (Qβ-αGal) induced several beneficial effects concerning acute and chronic T. cruzi infection in α1,3-galactosyltransferase knockout mice. Approximately 60% of these animals were protected from initial infection with high parasite loads. Vaccinated animals also produced high anti-αGal IgG antibody titers, improved IFN-γ and IL-12 cytokine production, and controlled parasitemia in the acute phase at 8 days post-infection (dpi) for the Y strain and 22 dpi for the Colombian strain. In the chronic stage of infection (36 and 190 dpi, respectively), all of the vaccinated group survived, showing significantly decreased heart inflammation and clearance of amastigote nests from the heart tissue.

C57BL/6 α-1,3-Galactosyltransferase Knockout Mouse as an Animal Model for Experimental Chagas Disease

The leading animal model of experimental Chagas disease, the mouse, plays a significant role in studies for vaccine development, diagnosis, and human therapies. Humans, along with Old World primates, alone among mammals, cannot make the terminal carbohydrate linkage of the α-Gal trisaccharide. It has been established that the anti-α-Gal immune response is likely to be a critical factor for protection against Trypanosoma cruzi (T. cruzi) infection in humans. However, the mice customarily employed for the study of T. cruzi infection naturally express the α-Gal epitope and therefore do not produce anti-α-Gal antibodies. Here, we used the C57BL/6 α-1,3-galactosyltransferase knockout (α-GalT-KO) mouse, which does not express the α-Gal epitope as a model for experimental Chagas disease. We found the anti-α-Gal IgG antibody response to an increase in α-GalT-KO mice infected with Arequipa and Colombiana strains of T. cruzi, leading to fewer parasite nests, lower parasitemia, and an increase of INF-γ, TNF-α, and IL-12 cytokines in the heart of α-GalT-KO mice compared with α-GalT-WT mice on days 60 and 120 postinfection. We therefore agree that the C57BL/6 α-GalT-KO mouse represents a useful model for initial testing of therapeutic and immunological approaches against different strains of T. cruzi.

CCL3/Macrophage Inflammatory Protein-1α Is Dually Involved in Parasite Persistence and Induction of a TNF- and IFNγ-Enriched Inflammatory Milieu in Trypanosoma cruzi-Induced Chronic Cardiomyopathy

CCL3, a member of the CC-chemokine family, has been associated with macrophage recruitment to heart tissue and parasite control in the acute infection of mouse with Trypanosoma cruzi, the causative agent of Chagas disease. Here, we approached the participation of CCL3 in chronic chagasic cardiomyopathy (CCC), the main clinical form of Chagas disease. We induced CCC in C57BL/6 (ccl3^+/+) and CCL3-deficient (ccl3^−/−) mice by infection with the Colombian Type I strain. In ccl3^+/+ mice, high levels of CCL3 mRNA and protein were detected in the heart tissue during the acute and chronic infection. Survival was not affected by CCL3 deficiency. In comparison with ccl3^+/+, chronically infected ccl3^−/− mice presented reduced cardiac parasitism and inflammation due to CD8⁺ cells and macrophages. Leukocytosis was decreased in infected ccl3^−/− mice, paralleling the accumulation of CD8⁺ T cells devoid of activated CCR5⁺ LFA-1⁺ cells in the spleen. Further, T. cruzi-infected ccl3^−/−mice presented reduced frequency of interferon-gamma (IFNγ)⁺ cells and numbers of parasite-specific IFNγ-producing cells, while the T. cruzi antigen-specific cytotoxic activity was increased. Stimulation of CCL3-deficient macrophages with IFNγ improved parasite control, in a milieu with reduced nitric oxide (NO_x) and tumor necrosis factor (TNF), but similar interleukin-10 (IL-10), concentrations. In comparison with chronically T. cruzi-infected ccl3^+/+ counterparts, ccl3^−/− mice did not show enlarged heart, loss of left ventricular ejection fraction, QTc prolongation and elevated CK-MB activity. Compared with ccl3^+/+, infected ccl3^−/− mice showed reduced concentrations of TNF, while IL-10 levels were not affected, in the heart milieu. In spleen of ccl3^+/+ NI controls, most of the CD8⁺ T-cells expressing the CCL3 receptors CCR1 or CCR5 were IL-10⁺, while in infected mice these cells were mainly TNF⁺. Lastly, selective blockage of CCR1/CCR5 (Met-RANTES therapy) in chronically infected ccl3^+/+ mice reversed pivotal electrical abnormalities (bradycardia, prolonged PR, and QTc interval), in correlation with reduced TNF and, mainly, CCL3 levels in the heart tissue. Therefore, in the chronic T. cruzi infection CCL3 takes part in parasite persistence and contributes to form a CD8⁺ T-cell and macrophage-enriched cardiac inflammation. Further, increased levels of CCL3 create a scenario with abundant IFNγ and TNF, associated with cardiomyocyte injury, heart dysfunction and QTc prolongation, biomarkers of severity of Chagas' heart disease.

IRF3 inhibits IFNγ-mediated restriction of intracellular pathogens in macrophages independently of type I interferons

Macrophages use an array of innate immune sensors to detect intracellular pathogens and to tailor effective antimicrobial responses. In addition, extrinsic activation with the cytokine interferon gamma (IFNγ) is often required as well to tip the scales of the host-pathogen balance toward pathogen restriction. However, little is known about how host pathogen sensing impacts the anti-microbial IFNγ-activated state. We observed that in the absence of IRF3, a key downstream component of pathogen sensing pathways, IFNγ-primed macrophages more efficiently restricted the intracellular bacterium Legionella pneumophila and the intracellular protozoan parasite Trypanosoma cruzi. This effect was not mediated by Type I interferons, the key cytokines known to be induced by IRF3, or by the sensing adaptors MyD88/TRIF, MAVS, and STING. However, IRF3-deficient macrophages displayed a significantly altered IFNγ-induced gene expression program, with upregulation of microbial restriction factors such as Nos2. Furthermore, Nos2 activity was required for the enhanced IFNγ-mediated restriction of T. cruzi observed in IRF3-deficient macrophages. Finally, we found that IFNγ-primed but not resting macrophages largely excluded the activated form of IRF3 from the nucleus. These data are consistent with a relationship of mutual inhibition between IRF3 and IFNγ-activated programs, possibly as a component of a partially reversible mechanism for modulating the activity of potent innate immune effectors such as Nos2 in the context of intracellular infection.

RIPK1 and PGAM5 Control Leishmania Replication through Distinct Mechanisms

Leishmaniasis is an important parasitic disease found in the tropics and subtropics. Cutaneous and visceral leishmaniasis affect an estimated 1.5 million people worldwide. Despite its human health relevance, relatively little is known about the cell death pathways that control Leishmania replication in the host. Necroptosis is a recently identified form of cell death with potent antiviral effects. Receptor interacting protein kinase 1 (RIPK1) is a critical kinase that mediates necroptosis downstream of death receptors and TLRs. Heme, a product of hemoglobin catabolism during certain intracellular pathogen infections, is also a potent inducer of macrophage necroptosis. We found that human visceral leishmaniasis patients exhibit elevated serum levels of heme. Therefore, we examined the impact of heme and necroptosis on Leishmania replication. Indeed, heme potently inhibited Leishmania replication in bone marrow-derived macrophages. Moreover, we found that inhibition of RIPK1 kinase activity also enhanced parasite replication in the absence of heme. We further found that the mitochondrial phosphatase phosphoglycerate mutase family member 5 (PGAM5), a putative downstream effector of RIPK1, was also required for inhibition of Leishmania replication. In mouse infection, both PGAM5 and RIPK1 kinase activity are required for IL-1β expression in response to Leishmania However, PGAM5, but not RIPK1 kinase activity, was directly responsible for Leishmania-induced IL-1β secretion and NO production in bone marrow-derived macrophages. Collectively, these results revealed that RIPK1 and PGAM5 function independently to exert optimal control of Leishmania replication in the host.

CD14+CD16+ monocytes play distinct role in Plasmodium vivax malaria (MPF3P.817)

During malaria, the Plasmodium triggers high levels of cytokines, which both help the immune response controlling the parasite and contribute to the symptoms observed during the diseases. Our data show that monocytes are the main source of cytokines upon P. vivax infection, suggesting their important role during disease. While it is recognized that monocytes are heterogeneous, the physiological relevance of this is not yet completely understood. The different monocyte subsets seem to reflect developmental stages with distinct roles. Our goal is to define the role of monocyte during P. vivax infection. Our data show that higher levels of cytokines, accompanied by increased frequencies of monocytes in P. vivax-infected patients. The infection triggers the expression of activation markers, adhesion molecules and chemokine receptors on monocytes. Moreover, these cells can be distinguished into three monocyte subsets based on the expression of CD14 and CD16. Each of these subsets display an distinct profile, suggesting that they distinctly act during P. vivax infection to induce inflammation, control the infection and modulate immune response. Importantly, CD14+CD16+ monocytes displayed higher phagocytic activity and killing potential than their other counterparts. Identification of mechanisms that regulate monocyte responses during malaria will provide important information on the development of therapeutic strategies that are targeted to modify their particular cell subsets

CASPASE-1 SIGNALING IS REQUIRED FOR CONTROL OF TRYPANOSOMA CRUZI INFECTION IN VIVO. (117.27)

The Toll-like receptors (TLRs), 2, 4 and 9 are important to immunity against Trypanosoma cruzi, etiologic agent of Chagas disease. A new family of pattern recognition receptors, Nod-like receptors (NLRs) is described, including NLRP3, which associates to ASC forming a complex that active caspase-1, called inflammasome. This complex is required for cleavage of the active forms of the IL-1β and IL-18. Here, we investigated the role of caspase-1 in the immune response against T. cruzi. First we verify if T. cruzi triggers caspase-1 activation in murine bone marrow-derived macrophages (BMMs). We found high caspase-1 activation in BMMs from WT mice, but not from ASC-/- mice. The blockage of potassium efflux, oxygen radicals reactive (ROS) and B catahepsin (activators of caspase-1 via ASC) resulted in inhibition of caspase-1 activation in BMMs from WT mice. To understand the role of caspase-1, WT, caspase-1-/- and ASC-/- mice were infected with Y strain of T.cruzi. Our results showed that ASC-/- and caspase-1-/- mice presented higher mortality, whereas WT are resistant to infection. In addition, caspase-1-/- mice presented higher myocarditis, increased cardiac damages and more parasites in this tissue on day 17 p.i. Together, these results suggest that caspase-1 dependent of ASC is crucial to infection against T. cruzi. These results reveal new mechanisms involved in the innate immunity against this parasite, which could contribute to new approaches in the control of this disease.

Unraveling the lethal synergism betweenTrypanosoma cruzi infection and LPS: A role for increased macrophage reactivity

Various infections sensitize to lethal shock by promoting hyperactivation of macrophages to LPS stimulation. Although macrophages are thought to be deactivated upon contact with apoptotic cells during Trypanosoma cruzi infection, T. cruzi infection also sensitizes mice to endotoxemia. Herein, we studied the mechanisms of sensitization to endotoxemia in T. cruzi-infected mice in order to solve the paradox. Live (but not fixed) trypomastigotes from various stocks sensitized mice to endotoxemia. Mice deficient in glycolipid recognition (TLR2(-/-) and CD1d(-/-)) were sensitized by infection to challenge with LPS. Infected mice hyperproduced TNF and IL-10 upon LPS challenge. Infected TNF-R1(-/-), macrophage migration inhibitory factor (MIF)(-/-) and IFN-gamma(-/-) mice were lethally sensitized, but infected TNF-R1(-/-) mice administered anti-MIF survived shock with LPS. Macrophages from infected mice hyperproduced TNF in response to LPS stimulation and displayed increased expression of TLR4 compared to non-infected controls. Treatment with the PGE(2) synthesis inhibitor acetylsalicylic acid (AAS) in vivo reduced parasitemia and enhanced LPS-stimulated production of TNF by macrophages, but the effect was less in infected mice than in normal mice. Nevertheless, AAS treatment did not increase the susceptibility of infected mice to sublethal shock with LPS. Our results point to independent MIF and TNF/TNF-R1 lethal pathways and suggest a role for hyperactivated macrophages in T. cruzi-sensitized LPS-induced shock.

Models of HIV type 1 proviral gene expression in wild-type HIV and MLV/HIV transgenic mice

Two proviral HIV transgenic mouse models, one bearing wild-type HIV proviral DNA and the other a modified provirus in which the viral LTRs contained the core enhancer of the Moloney murine leukemia virus (MLV), were compared. The MLV/HIV chimeric LTR, in which the MLV enhancer replaced the NF-kappa B-binding motifs, was transcriptionally active in human and murine cells in vitro and virus containing the chimeric LTR was replication competent in human cell cultures. Transgenic mice derived from microinjections of chimeric MLV/HIV proviral DNA transcribed HIV genes at a greater frequency and at higher levels than wild-type HIV proviral transgenic mice. MLV/HIV mice were also more apt to develop disease; wasting, periocular infections, and a degenerative myopathy characterized the most predominant phenotype. The tissue specificities of the wild-type and chimeric LTRs in transgenic mice were remarkably similar, but a significant difference was apparent in lymphoid cells. Basal level and LPS-inducible HIV gene expression occurred in peritoneal and bone marrow-derived macrophages from wild-type HIV transgenic mice. In contrast, HIV gene expression in macrophages from MLV/HIV mice was undetectable, even following LPS induction. However, cultured splenocytes from MLV/HIV mice supported HIV proviral gene transcription better than splenocytes from HIV mice, particularly after induction with LPS or anti-IgD antibody but not with concanavalin A. These data suggest that in transgenic mice, the HIV and MLV/HIV LTRs display a differential tropism for macrophages and B cells, respectively. HIV and MLV/HIV transgenic mice represent alternative models amenable to in vivo studies of HIV gene regulation in lymphoid cells, the induction of HIV-related disease and the evaluation of anti-HIV therapies.

IL-12 inhibits endotoxin-induced inflammation in the eye

Interleukin-12 (IL-12) is a heterodimeric cytokine that induces interferon (IFN)-gamma production and an increased generation of Th1 cells. Both IL-12 and IL-12 antagonists are being studied for the treatment of allergic reactions, autoimmune disease and malignancy. The goal of the present experiments was to examine the importance of IL-12 in endotoxin-induced ocular inflammation. The number of inflammatory cells infiltrating eyes with endotoxin-induced uveitis (EIU) was significantly increased in animals treated with intraperitoneal anti-IL-12 antibody when compared to control animals, but there was no difference in infiltrating inflammatory cells in the eyes of animals treated with IL-12 when compared to controls. In contrast, intraocular injection of IL-12 significantly inhibited the development of endotoxin-induced intraocular inflammation. The infiltrating inflammatory cells were reduced in the eyes of animals receiving intraocular IL-12 when compared to controls. Cytokine analysis of the aqueous humor obtained from eyes with EIU showed increased levels of IFN-gamma and decreased levels of IL-6 in eyes receiving intraocular IL-12. These data show that IL-12 has an inhibitory effect on endotoxin-induced inflammation in the eye and suggest that IL-12 can have an immunoregulatory function in some forms of inflammatory disease.

Contribution of nitric oxide to the host parasite equilibrium in toxoplasmosis

We studied the effect of nitric oxide (NO) production on the evolution of toxoplasmosis in C57BL/6 mice. Infection was induced by i.p. injection of Toxoplasma gondii strain ME49. NO synthesis was inhibited by treatment with aminoguanidine, a structural analogue of L-arginine. The severity of infection was evaluated by histopathologic examination of the brain. In the infected mice treated for 2 wk with aminoguanidine, we observed an increase in the number of toxoplasma tachyzoites and intracellular cysts accompanied by an exacerbated inflammation of the brain tissue compared with that in controls. When spleen cells from infected mice were stimulated in culture with toxoplasma Ag, there was a marked cytotoxic effect on cells collected during the acute stage of infection and an inhibition of proliferation of the remaining viable lymphocytes. These effects were correlated with high levels of NO and PGE2 production. The suppression of NO synthesis prevented cell death and restored the lymphocyte proliferative response as well as lymphokine production. The neutralization of IFN-gamma or TNF-alpha had no effect on NO production in the cultures of infected mouse spleen cells. Cultures in which purified macrophages and lymphocytes from infected and naive mice were mixed indicated that the production of NO was dependent on lymphocyte activation. In the later stages of infection, when the production of NO was abating, preventing PGE2 secretion with indomethacin also increased the lymphocyte proliferative response. We conclude that the opposing effects of NO in toxoplasmosis, which protects against Toxoplasma gondii and at the same time limits the immune response, probably contribute to the establishment of the characteristic chronic state of host parasite equilibrium.

Contribution of nitric oxide to the host parasite equilibrium in toxoplasmosis

We studied the effect of nitric oxide (NO) production on the evolution of toxoplasmosis in C57BL/6 mice. Infection was induced by i.p. injection of Toxoplasma gondii strain ME49. NO synthesis was inhibited by treatment with aminoguanidine, a structural analogue of L-arginine. The severity of infection was evaluated by histopathologic examination of the brain. In the infected mice treated for 2 wk with aminoguanidine, we observed an increase in the number of toxoplasma tachyzoites and intracellular cysts accompanied by an exacerbated inflammation of the brain tissue compared with that in controls. When spleen cells from infected mice were stimulated in culture with toxoplasma Ag, there was a marked cytotoxic effect on cells collected during the acute stage of infection and an inhibition of proliferation of the remaining viable lymphocytes. These effects were correlated with high levels of NO and PGE2 production. The suppression of NO synthesis prevented cell death and restored the lymphocyte proliferative response as well as lymphokine production. The neutralization of IFN-gamma or TNF-alpha had no effect on NO production in the cultures of infected mouse spleen cells. Cultures in which purified macrophages and lymphocytes from infected and naive mice were mixed indicated that the production of NO was dependent on lymphocyte activation. In the later stages of infection, when the production of NO was abating, preventing PGE2 secretion with indomethacin also increased the lymphocyte proliferative response. We conclude that the opposing effects of NO in toxoplasmosis, which protects against Toxoplasma gondii and at the same time limits the immune response, probably contribute to the establishment of the characteristic chronic state of host parasite equilibrium.

Interleukin 12 acts directly on CD4+ T cells to enhance priming for interferon gamma production and diminishes interleukin 4 inhibition of such priming

Naive CD4+ T cells produce interleukin 2 (IL-2) but little IL-4 or interferon gamma (IFN-gamma). In vitro, they develop into IL-4 or IFN-gamma producers depending on the conditions of the priming culture. Using T-cell receptor transgenic CD4+ T cells, the role of IL-12 and IL-4 in antigen-specific priming was examined. IL-12 substantially enhanced the ability of naive CD4+ T cells to develop into cells that produced IFN-gamma upon restimulation. However, it was not essential since anti-IL-12 antibodies failed to block the priming for IFN-gamma observed in the absence of exogenous IL-12. When both IL-12 and IL-4 were present in the priming culture, IL-12 did not inhibit priming for IL-4 production. In contrast, IL-4 diminished but did not abolish priming for IFN-gamma production. In an accessory cell-independent priming system, IL-12 strikingly augmented priming for IFN-gamma production, indicating that it acts directly on T cells. IFN-gamma itself did not enhance priming for IFN-gamma production in either accessory cell-dependent or independent systems. In an accessory cell-dependent system, the IL-12-mediated enhancement was not blocked by adding neutralizing anti-IFN-gamma monoclonal antibody. However, in an accessory cell-independent system, anti-IFN-gamma antibody did inhibit priming for IFN-gamma production leaving open a role for IFN-gamma in the priming process. These data indicate that IL-12 has a major effect on the inductive phase of T-cell priming by enhancing commitment to IFN-gamma production and thus can profoundly influence the state of immunity that develops.

Simultaneous depletion of CD4+ and CD8+ T lymphocytes is required to reactivate chronic infection with Toxoplasma gondii

C57BL/6 mice chronically infected with an avirulent strain (ME-49) of Toxoplasma gondii were used to study the mechanisms by which T lymphocytes and IFN-gamma prevent reactivation of latent infection. Infected animals were treated with mAb, either anti-CD8, anti-CD4, anti-CD4 plus anti-CD8, anti-IFN-gamma, or anti-CD4 plus anti-IFN-gamma and the mice followed for survival, histopathology, cyst numbers, and spleen cell cytokine responses. In agreement with previously published findings, treatment with anti-IFN-gamma antibodies fully reactivated the asymptomatic infection, inducing massive necrotic areas in the brain with the appearance of free tachyzoites and death of all animals within 2 wk. Mice treated with the combination of anti-CD4 plus anti-CD8 antibodies showed augmented pathology and mortality nearly identical to the anti-IFN-gamma- treated animals. In contrast, treatment with anti-CD4 or anti-CD8 mAb alone failed to result in significantly enhanced brain pathology or mortality. In additional experiments, full reactivation of infection was observed in mice treated with anti-CD4 plus anti-IFN-gamma indicating that CD4+ lymphocytes are not required for the pathology resulting from IFN-gamma neutralization. Cytokine measurements on parasite Ag-stimulated spleen cells from mAb-treated mice indicated that both CD4+ and CD8+ cells produce IFN-gamma whereas only CD4+ cells contribute to parasite Ag-induced IL-2 synthesis. Together, these results suggest that CD4+ and CD8+ lymphocytes act additively or synergistically to prevent reactivation of chronic T. gondii infection probably through the production of IFN-gamma.

Simultaneous depletion of CD4+ and CD8+ T lymphocytes is required to reactivate chronic infection with Toxoplasma gondii

C57BL/6 mice chronically infected with an avirulent strain (ME-49) of Toxoplasma gondii were used to study the mechanisms by which T lymphocytes and IFN-gamma prevent reactivation of latent infection. Infected animals were treated with mAb, either anti-CD8, anti-CD4, anti-CD4 plus anti-CD8, anti-IFN-gamma, or anti-CD4 plus anti-IFN-gamma and the mice followed for survival, histopathology, cyst numbers, and spleen cell cytokine responses. In agreement with previously published findings, treatment with anti-IFN-gamma antibodies fully reactivated the asymptomatic infection, inducing massive necrotic areas in the brain with the appearance of free tachyzoites and death of all animals within 2 wk. Mice treated with the combination of anti-CD4 plus anti-CD8 antibodies showed augmented pathology and mortality nearly identical to the anti-IFN-gamma- treated animals. In contrast, treatment with anti-CD4 or anti-CD8 mAb alone failed to result in significantly enhanced brain pathology or mortality. In additional experiments, full reactivation of infection was observed in mice treated with anti-CD4 plus anti-IFN-gamma indicating that CD4+ lymphocytes are not required for the pathology resulting from IFN-gamma neutralization. Cytokine measurements on parasite Ag-stimulated spleen cells from mAb-treated mice indicated that both CD4+ and CD8+ cells produce IFN-gamma whereas only CD4+ cells contribute to parasite Ag-induced IL-2 synthesis. Together, these results suggest that CD4+ and CD8+ lymphocytes act additively or synergistically to prevent reactivation of chronic T. gondii infection probably through the production of IFN-gamma.

Immunization against parasites: bridging the gap between attenuated and non-living vaccines

While great progress has been made in the last decade in defining parasite antigens which are targets of host protective responses, only limited success has been achieved in the use of these molecules as effective vaccines. A consistent problem is the failure of the candidate immunogens to induce levels of protection comparable to those obtained with attenuated vaccines against the same organisms. One explanation is that the purified or recombinant molecules employed have not been presented in a form or route which induces the correct T cell or cytokine response necessary for protection. As summarized in this overview, optimal immunization with attenuated vaccines is associated with characteristic patterns of T cell subset and cytokine induction and in at least several examples has been shown to be altered by exogenous cytokine. We hypothesize that cytokine manipulation may offer a useful strategy for improving the action of existing nonliving vaccines. The gap in efficacy between attenuated and dead vaccines could also be bridged by the use of live recombinant vaccine vectors. We have previously reported that paramyosin admixed with BCG can induce partial protection against Schistosoma mansoni in mice. Our preliminary results in the construction and testing of a recombinant BCG vector incorporating schistosome paramyosin are described.

Anti-laminin and specific antibodies in acute Chagas disease

A striking increase of anti-laminin antibodies contrasting with low levels of anti-Trypanosoma cruzi antibodies was detected by enzyme-linked immunosorbent assay in sera of 16 patients at the acute phase of Chagas disease. The mean absorbancies using an anti-human IgG conjugate were 6563 and 202 for laminin and T. cruzi antigens, respectively; with anti-IgM conjugate the titres were 3442 and 207, respectively. In addition, indirect immunofluorescence tests performed with trypomastigotes from blood or cell cultures have shown extremely high titres (up to 1:10 240), which declined when mouse laminin-absorbed sera were used instead, apparently confirming the presence of laminin in the surface membrane of the parasites. These results support the view that the high anti-laminin titres found in patients with Chagas disease are induced by the newly described galactosyl-alpha 1-3-galactose epitope present in T. cruzi trypomastigotes and shared by mouse laminin.