Regulation of Trypanosoma cruzi infections in vitro and in vivo by transforming growth factor beta (TGF-beta)

Experimental autoimmune encephalomyelitis can be prevented and cured by infection with Trypanosoma cruzi

Trypanosoma cruzi is an intracellular parasite that induces a strong Th1-type response and immunosuppression during the acute phase of infection. To study how the infection with T. cruzi would modulate the development of an autoimmune disease, we immunized C57BL/6 mice and IL-10 or iNOS knock-out mice of the same background with the encephalitogenic MOG 35-55 peptide and infected them with T. cruzi. Our results demonstrate that infection with T. cruzi completely prevents EAE development and furthermore induces complete and lasting remission in mice that were infected with this parasite after they had developed clinical EAE. Nitric oxide and IL-10 participate in triggering the mechanisms associated with EAE suppression by the infection. Decreased lymphoproliferation and increased frequencies of Annexin-positive cells and of T cells bearing CD95, CD95L or CTLA-4 were observed in the spleen from immunized/infected mice, as well as lower IL-2 and increased TGF-beta production in comparison with only immunized mice. Our results indicate that several effector and regulatory mechanisms of the immune response that arise during the acute phase of T. cruzi infection lastingly affect the expansion and/or effector functions of encephalitogenic cells, preventing the onset or inducing complete remission of EAE.

CTLA-4 Blockage Increases Resistance to Infection with the Intracellular ProtozoanTrypanosoma cruzi

Recent studies have revealed an important role for CTLA-4 as a negative regulator of T cell activation. In the present study, we evaluated the importance of CTLA-4 to the immune response against the intracellular protozoan, Trypanosoma cruzi, the causative agent of Chagas' disease. We observed that the expression of CTLA-4 in spleen cells from naive mice cultured in the presence of live trypomastigote forms of T. cruzi increases over time of exposure. Furthermore, spleen cells harvested from recently infected mice showed a significant increase in the expression of CTLA-4 when compared with spleen cells from noninfected mice. Blockage of CTLA-4 in vitro and/or in vivo did not restore the lymphoproliferative response decreased during the acute phase of infection, but it resulted in a significant increase of NO production in vivo and in vitro. Moreover, the production of IFN-gamma in response to parasite Ags was significantly increased in spleen cells from anti-CTLA-4-treated infected mice when compared with the production found in cells from IgG-treated infected mice. CTLA-4 blockade in vivo also resulted in increased resistance to infection with the Y and Colombian strains of T. cruzi. Taken together these results indicate that CTLA-4 engagement is implicated in the modulation of the immune response against T. cruzi by acting in the mechanisms that control IFN-gamma and NO production during the acute phase of the infection.

Interferon-gamma-induced nitric oxide causes intrinsic intestinal denervation in Trypanosoma cruzi-infected mice

In this study, the role of nitric oxide (NO) in neuronal destruction during acute-phase Trypanosoma cruzi infection was evaluated in male C57BL/6 (WT, wild-type) mice and knockout mice [inducible nitric oxide synthase (iNOS)(-/-) and interferon (IFN)(-/-)]. Selected animals were infected by intraperitoneal injection of 100 trypomastigote forms of the Y strain of T. cruzi. Others were injected intraperitoneally with an equal volume of saline solution and served as controls. Our findings support those of previous studies regarding myenteric denervation in acute-phase T. cruzi infection. In addition, we clearly demonstrate that, despite the fact that parasite nests and similar inflammatory infiltrate in the intestinal wall were more pronounced in infected iNOS(-/-) mice than in infected WT mice, the former presented no reduction in myenteric plexus neuron numbers. Neuronal nerve profile expression, as revealed by the general nerve marker PGP 9.5, was preserved in all knockout animals. Infected IFN(-/-) mice suffered no significant neuronal loss and there was no inflammatory infiltrate in the intestinal wall. On days 5 and 10 after infection, iNOS activity was greater in infected WT mice than in controls, whereas iNOS activity in infected knockout mice remained unchanged. These findings clearly demonstrate that neuronal damage does not occur in NO-impaired infected knockout mice, regardless of whether inflammatory infiltrate is present (iNOS(-/-)) or absent (IFN(-/-)). In conclusion, our observations strongly indicate that myenteric denervation in acute-phase T. cruzi infection is because of IFN-gamma-elicited NO production resulting from iNOS activation in the inflammatory foci along the intestinal wall.

Activation of transforming growth factor beta by malaria parasite-derived metalloproteinases and a thrombospondin-like molecule

Much of the pathology of malaria is mediated by inflammatory cytokines (such as interleukin 12, interferon γ, and tumor necrosis factor α), which are part of the immune response that kills the parasite. The antiinflammatory cytokine transforming growth factor (TGF)-β plays a crucial role in preventing the severe pathology of malaria in mice and TGF-β production is associated with reduced risk of clinical malaria in humans. Here we show that serum-free preparations of Plasmodium falciparum, Plasmodium yoelii 17XL, and Plasmodium berghei schizont-infected erythrocytes, but not equivalent preparations of uninfected erythrocytes, are directly able to activate latent TGF-β (LatTGF-β) in vitro. Antibodies to thrombospondin (TSP) and to a P. falciparum TSP-related adhesive protein (PfTRAP), and synthetic peptides from PfTRAP and P. berghei TRAP that represent homologues of TGF-β binding motifs of TSP, all inhibit malaria-mediated TGF-β activation. Importantly, TRAP-deficient P. berghei parasites are less able to activate LatTGF-β than wild-type parasites and their replication is attenuated in vitro. We show that activation of TGF-β by malaria parasites is a two step process involving TSP-like molecules and metalloproteinase activity. Activation of LatTGF-β represents a novel mechanism for direct modulation of the host response by malaria parasites.

Pathology of Plasmodium chabaudi chabaudi infection and mortality in interleukin-10-deficient mice are ameliorated by anti-tumor necrosis factor alpha and exacerbated by anti-transforming growth factor beta antibodies

Interleukin-10 (IL-10)-deficient (IL-10(-/-)) mice infected with Plasmodium chabaudi (AS) suffer a more severe disease and exhibit a higher rate of mortality than control C57BL/6 mice. Here, we show that a drop in body temperature to below 28 degrees C and pronounced hypoglycemia of below 3 mM are reliable indicators of a lethal infection. Elevated inflammatory responses have been shown to accompany pathology in infected IL-10(-/-) mice. We show that neutralization of tumor necrosis factor alpha (TNF-alpha) in IL-10(-/-) mice abolishes mortality and ameliorates the hypothermia, weight loss, and anemia but does not affect the degree of hypoglycemia. These data suggest that TNF-alpha is involved in some of the pathology associated with a P. chabaudi infection in IL-10(-/-) mice but other factors play a role. IL-10(-/-) mice that survive a primary infection have been shown to control gamma interferon (IFN-gamma) and TNF-alpha production, indicating that other cytokines or mechanisms may be involved in their down-regulation. Significantly higher levels of transforming growth factor beta (TGF-beta), a cytokine with such properties, are present in the plasma of infected IL-10(-/-) mice at a time that coincides with the disappearance of IFN-gamma and TNF-alpha from the blood. Neutralization of TGF-beta in IL-10(-/-) mice resulted in higher circulating amounts of TNF-alpha and IFN-gamma, and all treated IL-10(-/-) mice died within 12 days with increased pathology but with no obvious increase in parasitemia. Our data suggest that a tight regulation of the balance between regulatory cytokines such as IL-10 and TGF-beta and inflammatory cytokines such as IFN-gamma and TNF-alpha is critical for survival in a mouse malaria infection.

Transforming growth factor-beta-Smad signaling pathway negatively regulates nontypeable Haemophilus influenzae-induced MUC5AC mucin transcription via mitogen-activated protein kinase (MAPK) phosphatase-1-dependent inhibition of p38 MAPK

In contrast to the extensive studies on the role of transforming growth factor-beta (TGF-beta) in regulating cell proliferation, differentiation, and apoptosis over the past decade, relatively little is known about the exact role of TGF-beta signaling in regulating host response in infectious diseases. Most of the recent studies have suggested that TGF-beta inhibits macrophage activation during infections with pathogens such as Trypanosoma cruzi and Leishmania, thereby favoring virulence. In certain situations, however, there is also evidence that TGF-beta has been correlated with enhanced resistance to microbes such as Candida albicans, thus benefiting the host. Despite these distinct observations that mainly focused on macrophages, little is known about how TGF-beta regulates host primary innate defensive responses, such as up-regulation of mucin, in the airway epithelial cells. Moreover, how the TGF-beta-Smad signaling pathway negatively regulates p38 mitogen-activated protein kinase (MAPK), a key pathway mediating host response to bacteria, still remains largely unknown. Here we show that nontypeable Haemophilus influenzae, a major human bacterial pathogen of otitis media and chronic obstructive pulmonary diseases, strongly induces up-regulation of MUC5AC mucin via activation of the Toll-like receptor 2-MyD88-dependent p38 path-way. Activation of TGF-beta-Smad signaling, however, leads to down-regulation of p38 by inducing MAPK phophatase-1, thereby acting as a negative regulator for MUC5AC induction. These studies may bring new insights into the novel role of TGF-beta signaling in attenuating host primary innate defensive responses and enhance our understanding of the signaling mechanism underlying the cross-talk between TGF-beta-Smad signaling pathway and the p38 MAPK pathway.

Murine susceptibility to Chagas' disease maps to chromosomes 5 and 17

Chagas' disease is caused by the protozoan parasite Trypanosoma cruzi and commonly modelled in inbred mice. Susceptibility of mouse strains to experimental infection varies considerably. We quantified parasite tissue burdens in resistant and susceptible strains by real time PCR and applied a backcross strategy to map the genomic loci linked to susceptibility in inbred mice. Resistant B6D2F1 mice were backcrossed with susceptible C57BL/6 mice, and 46 of a total 192 offspring died after infection. Their genomes were scanned with microsatellite markers. One region on chromosome 17 was significantly linked to susceptibility, while another on chromosome 5 was suggestive of linkage.

Cissampelos sympodialis Eichl (Menispermaceae) leaf extract induces interleukin-10-dependent inhibition of Trypanosoma cruzi killing by macrophages

The aqueous fraction of the ethanolic extract (AFL) of Cissampelos sympodialis Eichl (Menispermaceae), popularly known as milona, has been shown to have both immunosuppressive and anti-inflammatory effects. In the present study we investigated the modulation of macrophage antimicrobicidal activity by in vitro treatment with the extract from C. sympodialis. Normal and thioglycolate-elicited mouse peritoneal macrophages were infected in vitro with the protozoan Trypanosoma cruzi DM28c clone. We observed that the AFL (used at doses ranging from 13 to 100 microg/ml) increased T. cruzi growth and induced a 75% reduction in nitric oxide production. This inhibition could be mediated by the stimulation of macrophage interleukin-10 (IL-10) secretion since the in vitro treatment with the AFL stimulated IL-10 production by T. cruzi-infected macrophages. These results suggest that the anti-inflammatory effect of the AFL from C. sympodialis could be, at least in part, mediated by the inhibition of macrophage functions and that the inhibition of macrophage microbicidal activity induced by the C. sympodialis extract may be mediated by the decrease in macrophage function mediated by interleukin-10 production.

Leukotriene B(4) induces nitric oxide synthesis in Trypanosoma cruzi-infected murine macrophages and mediates resistance to infection

The production of nitric oxide (NO) by gamma interferon (IFN-gamma)-activated macrophages is a major effector mechanism during experimental Trypanosoma cruzi infection. In addition to IFN-gamma, chemoattractant molecules, such as platelet-activating factor (PAF) and CC chemokines, may also activate macrophages to induce NO and mediate the killing of T. cruzi in an NO-dependent manner. Here we investigated the ability of leukotriene B(4) (LTB(4)) to induce the production of NO by macrophages infected with T. cruzi in vitro and whether NO mediated LTB(4)-induced parasite killing. The activation of T. cruzi-infected but not naive murine peritoneal macrophages with LTB(4) induced the time- and concentration-dependent production of NO. In addition, low concentrations of LTB(4) acted in synergy with IFN-gamma to induce NO production. The NO produced mediated LTB(4)-induced microbicidal activity in macrophages, as demonstrated by the inhibitory effects of an inducible NO synthase inhibitor. LTB(4)-induced NO production and parasite killing were LTB(4) receptor dependent and were partially blocked by a PAF receptor antagonist. LTB(4) also induced significant tumor necrosis factor alpha (TNF-alpha) production, and blockade of TNF-alpha suppressed LTB(4)-induced NO release and parasite killing. A blockade of LTB(4) or PAF receptors partially inhibited IFN-gamma-induced NO and TNF-alpha production but not parasite killing. Finally, daily treatment of infected mice with CP-105,696 was accompanied by a significantly higher level of blood parasitemia, but not lethality, than that seen in vehicle-treated animals. In conclusion, our results suggest a role for LTB(4) during experimental T. cruzi infection. Chemoattractant molecules such as LTB(4) not only may play a major role in leukocyte migration into sites of inflammation in vivo but also, in the event of an infection, may play a relevant role in the activation of recruited leukocytes to kill the invading microorganism in an NO-dependent manner.

[Immunopathology of leprosy: the complexity of the mechanisms of host immune response to Mycobacterium leprae]

Leprosy, whose etiologic agent Mycobacterium leprae, is an illness of ample clinical and immunopathological spectrum. Its clinical manifestations are correlated with distinct immunologic forms, varying from a vigorous immune response mediated by cells to M. leprae, with Th1 standard in the tuberculoid polar region, to an absence of specific cellular response to antigens of M. leprae in the lepromatous polar region, with predominance of Th2 response and exacerbation of humoral response. It is probable that different polymorphic genes determine susceptibility to M. leprae. Additional studies are necessary to clarify the complex interactions between cytokines and the role of the phenotypic diversity of cells network that contribute to the host defense. The comprehension of such mechanisms will provide new insights for the identification of agonists and/or antagonists for pro- or anti-inflammatory effects, and also will indicate possible situations for its appropriate use in immunologic and/or immunotherapeutic interventions.

BAD1, an essential virulence factor of Blastomyces dermatitidis, suppresses host TNF-alpha production through TGF-beta-dependent and -independent mechanisms

We investigated how BAD1, an adhesin and virulence factor of Blastomyces dermatitidis, suppresses phagocyte proinflammatory responses. Wild-type yeast cocultured with murine neutrophils or macrophages prompted release of a soluble factor into conditioned supernatant that abolished TNF-alpha production in response to the fungus; isogenic, attenuated BAD1 knockout yeast did not have this effect. Phagocytes released 4- to 5-fold more TGF-beta in vitro in response to wild-type yeast vs BAD1 knockout yeast. Treatment of inhibitory, conditioned supernatant with anti-TGF-beta mAb neutralized detectable TGF-beta and restored phagocyte TNF-alpha production. Similarly, addition of anti-TGF-beta mAb into cultures of phagocytes and wild-type yeast reversed BAD1 inhibition of TNF-alpha production. Conversely, TGF-beta treatment of phagocytes cultured with knockout yeast suppressed TNF-alpha production. Hence, TGF-beta mediates BAD1 suppression of TNF-alpha by wild-type B. dermatitidis cultured in vitro with phagocytes. In contrast to these findings, neutralization of elevated TGF-beta levels during experimental pulmonary blastomycosis did not restore BAD1-suppressed TNF-alpha levels in the lung or ameliorate disease. Soluble BAD1 was found to accumulate in the alveoli of infected mice at levels that suppressed TNF-alpha production by phagocytes. However, in contrast to yeast cell surface BAD1, which induced TGF-beta, soluble BAD1 failed to do so and TNF-alpha suppression mediated by soluble BAD1 was unaffected by neutralization of TGF-beta. Thus, BAD1 of B. dermatitidis induces suppression of TNF-alpha and progressive infection by both TGF-beta-dependent and -independent mechanisms.

Transforming growth factor-beta expression in human retinal pigment epithelial cells is enhanced by Toxoplasma gondii: a possible role in the immunopathogenesis of retinochoroiditis

Retinochoroiditis caused by Toxoplasma gondii infection results in inflammation and necrosis of the retina. We have used human retinal pigment epithelial cultures (HRPE) as an in vitro model to investigate the role of TGF-beta in T. gondii-induced retinochoroiditis. RT-PCR analyses showed enhanced steady state levels of TGF-beta1 and TGF-beta2 mRNA in T. gondii-infected HRPE. Uninfected HRPE secrete TGF-beta1 in a latent form while 10-30% of the secreted TGF-beta2 was in the active form. T. gondii infection induced a significant increase (P < 0.01) in total TGF-beta1 and TGF-beta2 secretion by HRPE. In addition, soluble extracts of T. gondii (ST) stimulated secretion of both TGF-beta1 and TGF-beta2 significantly (P < 0.01). Interestingly, T. gondii infection as well as ST of the parasites completely inhibited secretion of the active form of TGF-beta2. Studies evaluating the effect of TGF-beta on T. gondii replication in HRPE revealed that TGF-beta enhanced parasite replication. The interactions between host retinal cells and T. gondii may play an active role in the pathogenesis of retinochoroiditis.

Transforming growth factor beta concentrations and interferon gamma responses in cerebrospinal fluid of horses with equine protozoal myeloencephalitis

The following experiment was performed to test the hypothesis that transforming growth factor beta (TGF-beta) concentration varies in the cerebrospinal fluid and serum of horses with EPM and to determine if cerebrospinal fluid (CSF) alters the interferon-gamma (IFN-gamma) rersponse of equine peripheral blood mononuclear cells (PBMCs). The concentration of transforming growth factor-beta (TGF-beta2) was investigated in the serum and cerebrospinal fluid (CSF) of 18 horses (9 normal, 9 affected with equine protozoal myeloencephalitis [EPM]). The TGF-beta2 assay was validated in a group of 6 normal horses. Intra-assay variability was 4.7%, and interassay variability was 10.7%. The slope of the curve of the unknown samples of various volumes demonstrated parallelism with a curve developed using equal volumes of assay kit standard. Assay of normal and EPM-affected horses found that TGF-beta2 was present in both the serum and CSF of all animals. However, the concentration of TGF-beta2 in the CSF was less (P = 0.03) in EPM-affected horses (144 pg/ml) than in normal horses (256 pg/ml). In addition, the effect of CSF from normal and EPM-affected horses on the production of interferon-gamma (IFN-gamma) by PHA-P stimulated PBMCs from normal horses was investigated using a bioassay. It was found that CSF from normal and EPM-affected horses enhanced IFN-gamma activity from PHA-P stimulated peripheral blood mononuclear cells (P < or = 0.05); however, the response to CSF from EPM-affected horses was no different than the response to CSF from normal horses. Treatment of cells with anti-TGF-beta2 monoclonal antibodies slightly increased the response when co-incubated with CSF from normal horses, and slightly decreased it when co-incubated with CSF from EPM-affected horses. These differences, however, did not achieve statistical significance (P > 0.05). Results of this study indicated that production of TGF-beta2 is altered in horses with EPM, and that CSF appears to contain substances which alter the inflammatory reaction to plant lectins. These findings confirm the immunomodulatory properties of CSF and suggest new techniques for future research regarding the pathophysiology of EPM.

IL-12-independent IFN-gamma production by T cells in experimental Chagas' disease is mediated by IL-18

IL-12p35-deficient (IL-12p35(-/-)) mice were highly susceptible to Trypanosoma cruzi infection and succumbed during acute infection, demonstrating the crucial importance of endogenous IL-12 in resistance to experimental Chagas' disease. Delayed immune responses were observed in mutant mice, although comparable IFN-gamma and TNF-alpha blood levels as in wild-type mice were detected 2 wk postinfection. In vivo and in vitro analysis demonstrated that T cells, but not NK cells, were recruited to infected organs. Analysis of mice double deficient in the recombinase-activating gene 2 (RAG2) and IL-12p35, as well as studies involving T cell depletion, identified CD4(+) T cells as the cellular source for IL-12-independent IFN-gamma production. IL-18 was induced in IL-12p35(-/-) mice and was responsible for IFN-gamma production, as demonstrated by in vivo IL-18 neutralization studies. In conclusion, evidence is presented for an IL-12-independent IFN-gamma production in experimental Chagas' disease that is T cell and IL-18 dependent.

Invasive candidiasis stimulates hepatocyte and monocyte production of active transforming growth factor beta

Candida albicans is an opportunistic fungal pathogen and a major cause of morbidity and mortality in patients with compromised immune function. The cytokine response to tissue invasion by C. albicans can influence the differentiation and function of lymphocytes and other mononuclear cells that are critical components of the host response. While the production of transforming growth factor beta (TGF-beta) has been documented in mice infected with C. albicans and is known to suppress phagocyte function, the cellular source and role of this cytokine in the pathogenesis of systemic candidiasis are not well understood. We have investigated the source of production of TGF-beta by immunohistochemical studies in tissue samples from patients with an uncommon complication of lymphoreticular malignancy, chronic disseminated candidiasis (CDC), and from a neutropenic-rabbit model of CDC. Liver biopsy specimens from patients with documented CDC demonstrated intense staining for extracellular matrix-associated TGF-beta1 within inflammatory granulomas, as well as staining for TGF-beta1 and TGF-beta3 within adjacent hepatocytes. These results correlate with the immunolocalization of TGF-beta observed in livers of infected neutropenic rabbits, using a neutralizing antibody that recognizes the mature TGF-beta protein. Human peripheral blood monocytes incubated with C. albicans in vitro release large amounts of biologically active TGF-beta1. The data demonstrate that local production of active TGF-betas by hepatocytes and by infected mononuclear cells is a component of the response to C. albicans infection that most probably contributes to disease progression in the immunocompromised host.

Tumour necrosis factor alpha receptors: role in the physiopathology of protozoan parasite infections

Tumour necrosis factor alpha (TNF alpha) is an important cytokine in immune regulation and resistance to various micro-organisms. It provides signals to the target cells through two different receptors: TNFR1 and TNFR2. The present report reviews the role of TNF receptors (TNFRs) in the immune response against protozoan parasite infections of medical interest (Toxoplasma gondii, Leishmania major, Trypanosoma cruzi, Plasmodium spp.). TNF alpha has been regarded as a modulator cytokine in host defence against protozoans infections and recent findings on experimental gene-deficient mice have showed that TNF alpha/TNFRs pathway may be beneficial for host protection during these infections.

Differential expression of mRNA coding for the alpha-2-macroglobulin family and the LRP receptor system in C57BL/6J and C3H/HeJ male mice

Expression of mouse A2M (MAM), murinoglobulin (MUG), the A2M receptor or LDL-Receptor related protein (A2MR/LRP) and the Receptor Associated Protein (RAP) were measured by northern blotting of mRNA isolated from liver, heart and peritoneal macrophages from C3H/HeJ and C57BL/6J (B6) mice. Marked differences between males of the two mouse strains were observed for MAM and MUG mRNA levels in liver, which were reflected in plasma levels of both proteinase inhibitors, as confirmed by immune-electrophoresis. C3H/HeJ mice had higher levels of the MAM and MUG mRNA and their corresponding plasma proteins than B6 mice. B6 mice expressed higher levels of LRP mRNA relative to C3H/HeJ mice but had lower levels of RAP mRNA. LRP receptor activity, assayed by fluoresceinated-A2M binding, was higher in B6 cells. The present data contribute to the knowledge of genetic background characteristics among male mouse of these two strains, which can take part in many biological events such as lipid metabolism, inflammation and immune response to different infectious agents.

Modulation of chemokine production and inflammatory responses in interferon-gamma- and tumor necrosis factor-R1-deficient mice during Trypanosoma cruzi infection

Infection with Trypanosoma cruzi causes a strong inflammatory reaction at the inoculation site and, later, in the myocardium. The present study investigates the role of cytokines as modulators of T. cruzi-induced chemokine expression in vivo and in vitro. In macrophage cultures, although the stimulation with interferon (IFN)-gamma increases the expression of IP-10, it blocks KC expression. Tumor necrosis factor (TNF)-alpha, on the other hand, potentiates KC, IP-10, macrophage inflammatory protein-1alpha, and JE/monocyte chemotatic protein-1 expression. Interleukin-10 and transforming growth factor-beta inhibited almost all chemokines tested. The role of IFN-gamma and TNF-alpha in chemokine modulation during infection was investigated in T. cruzi-infected IFN-gamma-deficient (GKO) or TNF-R1/p55-deficient (p55-/-) mice. The expression of chemokines detected in the inoculation site correlated with the infiltrating cell type observed. Although GKO mice had a delayed and intense neutrophilic infiltrate correlating with the expression of KC and macrophage inflammatory protein-2, none of the above was observed in p55-/- mice. The detection of infiltrating T cells, Mig, and IP-10 in the myocardium was observed in wild-type and p55-/-, but not in GKO mice. Together, these results suggest that the regulatory roles of IFN-gamma and TNF-alpha on chemokine expression may play a crucial role in the modulation of the inflammatory response during T. cruzi infection and mediate resistance to infection.

Transforming growth factor-beta suppresses interferon-gamma-induced toxoplasmastatic activity in murine macrophages by inhibition of tumour necrosis factor-alpha production

Activation of macrophages plays an important role in the host resistance against intracellular pathogens. Various mechanisms are employed to control the activation processes and limit tissue damage by factors produced by activated macrophages. One of these mechanisms is the production of macrophage-deactivating cytokines, such as tumour growth factor (TGF)-beta. The present study concerns the effects of TGF-beta on interferon (IFN)-gamma-induced activation of murine macrophages with respect to induction of toxoplasmastatic activity, and production of tumour necrosis factor (TNF)-alpha, prostaglandin E2 (PGE2) and reactive nitrogen intermediates (RNI). IFN-gamma activation of macrophages resulted in inhibition of T. gondii proliferation [mean fold increase (FI) = 1.8, control mean FI = 7.0]; polymyxin B had no effect on this activation. The IFN-gamma-induced toxoplasmastatic activity of macrophages was inhibited by TGF-beta (mean FI = 6.3), which was also found for the IFN-gamma-induced production of TNF-alpha, RNI and PGE2 by macrophages. We found that PGE2, which has macrophage deactivating properties, was not involved in the inhibition of macrophage activation by TGF-beta. The deactivating activities of TGF-beta on the IFN-gamma-induced toxoplasmastatic activity and production of RNI are mediated by inhibition of production of TNF-alpha. Addition of exogenous TNF-alpha during the incubation of macrophages with IFN-gamma and TGF-beta abrogated the deactivating activity of TGF-beta. In sum, the results demonstrate that inhibition of TNF-alpha production is a key factor in the TGF-beta-induced suppression of macrophage activation with respect to toxoplasmastatic activity and RNI production.

IL-4 and IL-13 regulate the induction of indoleamine 2,3-dioxygenase activity and the control of Toxoplasma gondii replication in human fibroblasts activated with IFN-gamma

The ability of up-regulatory [recombinant (r) IFN-gamma, rIFN-beta and rTNF-alpha] and down-regulatory (rIL-4, rIL-10 and rIL-13) cytokines to control the expression of indoleamine 2,3-dioxygenase (INDO) and anti-Toxoplasma activity in the human fibrosarcoma cell line 2C4 was evaluated. Activation of fibroblasts with rIFN-gamma, rIFN-beta and rTNF-alpha resulted in augmentation of INDO expression and activity leading to 40.0, 25.0 and 27.0 % inhibition of tachyzoite growth, respectively. An additive effect was observed when host cells were incubated with rIFN-gamma plus rTNF-alpha. With regard to the down-regulatory cytokines we observed that IL-4 as well as IL-13, but not IL-10, induced significant inhibition of IFN-gamma-induced control of parasite replication, INDO mRNA expression and tryptophan catabolism. Similarly, IL-4 but not IL-10 inhibited the cell surface expression of HLA-DR and CD2 induced by IFN-gamma. Consistent with these findings we were able to detect by reverse transcription-PCR the expression of mRNA for different chains of IL-4 and IL-13 receptors (IL-4Ralpha, IL-13Ralpha1 and IL-13Ralpha2) but not for IL-10 receptor in the 2C4 and other human lung fibroblast cell lines (LL24 and MRC5). Together our results indicate that IL-4 and IL-13, but not IL-10, are implicated in the negative regulation of IFN-gamma-induced anti-Toxoplasma activity in human cells from fibroblast lineage.

Production of transforming growth factor-beta 1 (TGF-beta1) by blood monocytes from patients with different clinical forms of leprosy

In the present study, the concentration of TGF-beta1 secreted by adherent cells isolated from human peripheral blood mononuclear cells (PBMC) and either stimulated with PGL-1 or lipopolysaccharide (LPS) or left unstimulated was determined by ELISA. The cells were isolated from untreated patients with different clinical forms of leprosy and healthy individuals. The adherent cells exhibited spontaneous release of TGF-beta1 in all clinical forms of leprosy and in healthy individuals; however, lepromatous leprosy/borderline leprosy (LL/BL) patients presenting erythema nodosum leprosum (ENL) displayed significantly higher concentrations of TGF-beta1 than either the other patients studied or the controls. These high TGF-beta1 levels were consistently observed when LL/BL ENL cells were stimulated with phenolic glycolipid (PGL-1) or LPS, and even in the absence of a stimulus (P < 0.01). The most significant differences in TGF-beta1 levels were observed when comparing the results in the presence of PGL-1 from ENL with, in order of significance: tuberculoid leprosy (TT) patients (P < 0.001), LL/BL patients without ENL (P < 0.01), healthy individuals (P < 0.01) and borderline-borderline/borderline-tuberculoid (BB/BT) patients with reversal reaction (RR) (P < 0.01). The BB/BT patients produced equivalent levels of TGF-beta1 compared with LL/BL patients without ENL, for all types of stimuli (P > 0.05). In contrast, TT patients produced the lowest levels of TGF-beta1 among all the subjects studied (both patients and healthy controls), especially following PGL-1 stimulation (P < 0.001, and P < 0.05, respectively). In conjunction with our previous data regarding TGF-beta1 expression in dermal lesions, it appears that TGF-beta1 probably plays different roles in leprosy: (i) to mediate a suppressive action locally, associated with the presence of PGL-1, and (ii) to induce proinflammatory effects when secreted systemically by monocytes, thereby acting as a modulatory cytokine in the acute inflammatory reactions of ENL and associated with the Th2 immune response in multibacillary forms of leprosy.

[Growth factors in the myocardium of patients with chronic chagasic cardiomyopathy]

In this work we quantified various growth factors in the myocardium of 19 patients with chronic chagasic cardiomyopathy and heart failure, through the immunoperoxidase technique. We looked for T. cruzi antigens, growth factors (GM-CSF, TGF-beta1, PDGF-A and PDGF-B) and inflammatory cells (CD4+, CD8+, CD20+ and CD68+). The mean ratio of CD4+/CD8+ T lymphocytes was 0.6 +/- 0.3. The mean number of positive interstitial cells was 5.9 +/- 3.1 for CD68+ (macrophages); 7.5 +/- 4.3 for PDGF-A+; 2.9 +/- 2.7 for PDGF-B+, 2.2 +/- 1.9 for TGF-beta1+ and 2.3 +/- 1.9 for GM-CSF+. The immunoreaction for PDGF-A was intense, occurring also in the endothelium, smooth muscle cells and the sarcolemma; there was no correlation between the number of positive interstitial cells and the semiquantitation of the same growth factors in the other cells. TGF-beta1 presented low expression in 100% of the cases. In conclusion, PDGF-A and B are probably the growth factors most related to the proliferative lesions and fibrosis present in chronic chagasic cardiomyopathy. GM-CSF and TGF-beta1 are present in low levels. There was no statistical correlation between growth factors and the quantity of the parasitic antigens.

Susceptible hosts: a resort for parasites right in the eye of the immune response

Trypanosomatid protozoan parasites express an aggressive strategy of parasitism by infecting host macrophages and inducing extensive T-lymphocyte activation. One goal of such strategy is to drive the immune response of genetically susceptible hosts to a state of unresponsiveness regarding parasite killing. Unresponsiveness is achieved through different mechanisms, depending on the parasite species. In this brief review, recent findings on the molecular and cellular bases of the parasites' exploitation of host immune responses are discussed.

Dual role for transforming growth factor beta-dependent signaling in Trypanosoma cruzi infection of mammalian cells

Expression of functional transforming growth factor beta (TGF-beta) receptors (TbetaR) is required for the invasion of mammalian cells by the protozoan parasite Trypanosoma cruzi. However, the precise role of this host cell signaling complex in T. cruzi infection is unknown. To investigate the role of the TGF-beta signaling pathway, infection levels were studied in the mink lung epithelial cell lines JD1, JM2, and JM3. These cells express inducible mutant TbetaR1 proteins that cannot induce growth arrest in response to TGF-beta but still transmit the signal for TGF-beta-dependent gene expression. In the absence of mutant receptor expression, trypomastigotes invaded the cells at a low level. Induction of the mutant receptors caused an increase in infection in all three cell lines, showing that the requirement for TGF-beta signaling at invasion can be divorced from TGF-beta-induced growth arrest. TGF-beta pretreatment of mink lung cells expressing wild-type TbetaR1 caused a marked enhancement of infection, but no enhancement was seen in JD1, JM2, and JM3 cells, showing that the ability of TGF-beta to stimulate infection is associated with growth arrest. Likewise, expression of SMAD7 or SMAD2SA, inhibitors of TGF-beta signaling, did not block infection by T. cruzi but did block the enhancement of infection by TGF-beta. Taken together, these results show that there is a dual role for TGF-beta signaling in T. cruzi infection. The initial invasion of the host cell is independent of both TGF-beta-dependent gene expression and growth arrest, but TGF-beta stimulation of infection requires a fully functional TGF-beta signaling pathway.

How are antibodies involved in the protective mechanism of susceptible mice infected with T. cruzi?

Host resistance to Trypanosoma cruzi is dependent on both natural and acquired immune responses. During the acute phase of the infection the presence of IFN-gamma, TNF-alpha, IL-12 and GM-CSF has been closely associated with resistance, whereas TGF-ss and IL-10 have been associated with susceptibility. Several investigators have demonstrated that antibodies are responsible for the survival of susceptible animals in the initial phase of infection and for the maintenance of low levels of parasitemia in the chronic phase. However, how this occurs is not yet understood. Our results and other data in the literature support the hypothesis that the protective role of antibodies in the acute phase of infection is dependent mostly on their ability to induce removal of bloodstream trypomastigotes from the circulation in addition to other concomitant cell-mediated events.

Intestinal immune responses to coccidiosis

Intestinal parasitism is a major stress factor leading to malnutrition and lowered performance and production efficiency of livestock and poultry. Coccidiosis is an intestinal infection caused by intracellular protozoan parasites belonging to several different species of Eimeria. Infection with coccidia parasites seriously impairs the growth and feed utilization of chickens and costs the US poultry industry more than $1.5 billion in annual losses. Although acquired immunity to Eimeria develops following natural infection, due to the complex life cycle and intricate host immune response to Eimeria, vaccine development has been difficult and a better understanding of the basic immunobiology of pertinent host-parasite interactions is necessary for developing effective immunological control strategies against coccidiosis. Chickens infected with Eimeria produce parasite specific antibodies in both the circulation and mucosal secretions but humoral immunity plays only a minor role in protection against this disease. Rather, recent evidence implicates cell-mediated immunity as the major factor conferring resistance to coccidiosis. This review will summarize current understanding of the avian intestinal immune system and its response to Eimeria as well as provide a conceptual overview of the complex molecular and cellular events involved in intestinal immunity to coccidiosis. It is anticipated that increased knowledge of the interaction between parasites and host immunity will stimulate the birth of novel immunological and molecular biological concepts in the control of intestinal parasitism.

IL-12 and IFN-gamma production, and NK cell activity, in acute and chronic experimental Trypanosoma cruzi infections

Resistance to acute Trypanosoma cruzi infection is mainly associated with a Th1 immune response, characterized by gamma-interferon (IFN-gamma) production and activation of macrophages. The outcome of the Th1 response in the spleen and serum of BALB/c and C3H mice infected with T. cruzi, Tulahuén strain was studied. The levels of interleukin-12 p40 (IL-12 p40) and IFN-gamma, as well as natural killer (NK) cell cytotoxicity were determined at different time-points during the acute phase, and the production of cytokines was also studied in the chronic infection. At 2 days post-infection (pi), spleen cells from C3H mice increased their NK cell activity and the ex vivo spontaneous release of both IL-12 p40 and IFN-gamma. On the other hand, BALB/c mice reached low levels of NK cell cytotoxicity and no IFN-gamma production was detected at this time pi, but the cytokine was released at high amounts in the second week of the infection. Seric IL-12 p40 concentrations showed a 3-fold increase in both mouse strains on the second day pi and remained high throughout the acute phase. However, seric IFN-gamma levels increased during the late acute infection and were higher in BALB/c than in C3H mice. In chronically infected mice IL-12 p40 was as high as in the acute phase in the serum of both strains, but only BALB/c mice still produced IFN-gamma. To the authors' knowledge this is the first report showing the protein levels of IL-12 p40 determined in vivo in acute and chronic T. cruzi infections. The results reveal differences between both mouse strains in the mechanisms controlling the onset and fate of the Th1 response triggered by the parasite and a long lasting pro-inflammatory stimuli.

Trypanosoma cruzi: the effect of nitric oxide synthesis inhibition on the CD4 T cell response to the trans-sialidase superfamily

During Trypanosoma cruzi infection the trans-sialidase superfamily stimulates the development of a large population of CD4 T lymphocytes that produces IFNgamma. These CD4 T cells fail to proliferate when stimulated in vitro. Why they fail to proliferate remains unclear. Nitric oxide is a critical component of the host immune response against T. cruzi, and to determine if NO inhibits trans-sialidase superfamily-specific proliferative responses, mice were fed either N(G)-nitro-L-arginine methylester (L-NAME), an inhibitor of inducible nitric oxide synthase (iNOS), or N(G)-nitro-D-arginine methyl ester (D-NAME), an inactive analog of L-NAME. The L-NAME-fed mice had increased parasitemia and mortality compared to the D-NAME-fed mice. Following stimulation with a T. cruzi trans-sialidase superfamily protein, splenocytes from both groups of mice failed to proliferate but continued to make similar amounts of IFNgamma, suggesting that the development of the trans-sialidase superfamily-specific CD4 response was not affected by iNOS inhibition. In addition, IL-2 receptor (IL-2R) expression was increased on T cells isolated from L-NAME-fed mice. These data suggest that during T. cruzi infection NO causes downregulation of IL-2R expression, but does not cause inhibition of trans-sialidase superfamily-specific CD4 T cell proliferation. Rather, the trans-sialidase superfamily proliferation may be inhibited by epitope variation.

Protective immunity induced by a Trypanosoma cruzi soluble extract antigen in experimental Chagas' disease. Role of interferon gamma

CBA/J mice can be protected against lethal infection with Trypanosoma cruzi by treatment using T. cruzi soluble extract antigen (TCSE). In vivo administration of TCSE (400 microg/mouse) into naive mice increased the cellular proliferative response to Con A and elevated the levels of IFN-gamma. The production of IFN-gamma was extremely important in controlling the replication of the parasite since the protective activity of TCSE was completely abrogated by in vivo treatment with an anti IFN-gamma neutralizing antibody. These results suggest that depending on the level, cytokine production results in the control of replication of the parasite in experimental Chagas' disease.

Uptake of apoptotic cells drives the growth of a pathogenic trypanosome in macrophages

After apoptosis, phagocytes prevent inflammation and tissue damage by the uptake and removal of dead cells. In addition, apoptotic cells evoke an anti-inflammatory response through macrophages. We have previously shown that there is intense lymphocyte apoptosis in an experimental model of Chagas' disease, a debilitating cardiac illness caused by the protozoan Trypanosoma cruzi. Here we show that the interaction of apoptotic, but not necrotic T lymphocytes with macrophages infected with T. cruzi fuels parasite growth in a manner dependent on prostaglandins, transforming growth factor-beta (TGF-beta) and polyamine biosynthesis. We show that the vitronectin receptor is critical, in both apoptotic-cell cytoadherence and the induction of prostaglandin E2/TGF-beta release and ornithine decarboxylase activity in macrophages. A single injection of apoptotic cells in infected mice increases parasitaemia, whereas treatment with cyclooxygenase inhibitors almost completely ablates it in vivo. These results suggest that continual lymphocyte apoptosis and phagocytosis of apoptotic cells by macrophages have a role in parasite persistence in the host, and that cyclooxygenase inhibitors have potential therapeutic application in the control of parasite replication and spread in Chagas' disease.

Maintaining the immunological balance in parasitic infections: a role for TGF-beta?

Transforming growth factor beta (TGF-beta) is an important regulator of inflammation, being proinflammatory at low concentrations and anti-inflammatory at high concentrations. As such, TGF-beta might be important in maintaining the balance between control and clearance of infectious organisms on the one hand and prevention of immune-mediated pathology on the other. In this article, Fakhereldin Omer, Jørgen Kurtzhals and Eleanor Riley review the immunoregulatory properties of TGF-beta in the context of parasitic infections. Data from murine malaria infections suggest that TGF-beta modifies the severity of the disease, and a number of potential protective mechanisms are discussed. Evidence is accumulating that TGF-beta is important for the regulation of other host-parasite interactions and that parasites might directly influence TGF-beta-dependent pathways via the synthesis of TGF-beta or TGF-beta-receptor homologues.

TGF-beta in infections and infectious diseases

Since it was first described as having the ability to inhibit macrophage activation, transforming growth factor-beta (TGF-beta) has been analyzed for its role in regulating immune responses to a variety of pathogens, including viruses, bacteria, yeast, and protozoa. Most of the studies have involved organisms that infect macrophages, and this discussion will attempt to highlight these findings. Perhaps the most work has been performed with protozoan pathogens, including Trypanosoma cruzi and a variety of Leishmania species, so the discussion will begin with these organisms. Other studies have focused on mycobacteria and viruses, including human immunodeficiency virus, so these areas will also be emphasized in the discussion. For the most part, investigators have reported that TGF-beta has, as expected, a negative influence on host responses and a beneficial effect on the survival and growth of intracellular pathogens. However, other studies have found that TGF-beta may have a positive or beneficial effect in some models of infection. This review will attempt to highlight studies and conclusions on the roles of TGF-beta in infection.

Local and systemic cytokine expression during experimental chronic Trypanosoma cruzi infection in a Cebus monkey model

Cebus apella is an acceptable model for chronic chagasic cardiomyopathy (CCC), since it is possible to experimentally induce cardiac lesions after 1 year of Trypanosoma cruzi infection. The T. cruzi Y strain, shown previously to produce CCC in C. apella monkeys, was used to experimentally infect 10 monkeys. Parasitological, serological and clinical parameters were monitored during a 19-month follow-up, and systemic cytokine responses were assessed sequentially in five monkeys selected according to the differential parasitemia pattern exhibited. Ten additional monkeys, infected with the same strain for 5, 10 and 12 years, were analysed cross-sectionally. Three monkeys/time point and one uninfected control animal were sacrificed for gross pathology, histology, presence of parasites, and local cytokine gene expression. Elevated expression of interleukin (IL)-4 was observed throughout the study in monkeys that had persistent, high parasitemias, whereas a high level of interferon (IFN)-gamma was seen in monkeys that controlled parasitemias soon after infection. Chronically infected monkeys expressed a nonpolarized, Th0-type response. Cardiac tissue collected from a monkey that succumbed to acute infection had elevated levels of proinflammatory cytokine [IL-1beta, IL-6, tumour necrosis factor-alpha] and interstitial cell adhesion molecule (ICAM)-1, platelet-derived growth factor (PDGF)-alpha, transforming growth factor (TGF)-beta and IL-10 transcripts. Cytokine production in cardiac tissue of chronically infected monkeys was also characterized by elevated expression of ICAM-1, PDGF-alpha and TGF-beta, which correlated with the detection of T. cruzi DNA by polymerase chain reaction.

The Surface Protein Superfamily of Trypanosoma cruzi Stimulates a Polarized Th1 Response That Becomes Anergic

Trypanosoma cruzi is an obligate intracellular parasite that chronically infects mammals. Extracellular mammalian stage trypomastigotes simultaneously express and release multiple members of the parasite’s surface protein superfamily; these extracellular proteins should stimulate MHC class II-restricted CD4 T cells. The surface protein superfamily, however, encodes variant epitopes that may inhibit this CD4 response. In this report the surface protein-specific CD4 response was investigated. CD4 cells isolated from acutely and chronically infected mice did not proliferate when stimulated with surface proteins. Adoptive transfer of surface protein-specific CD4 clones or immunization with a peptide encoding a surface protein T cell epitope protected mice during T. cruzi infection. These data strongly suggested that surface proteins were expressed and presented to CD4 cells during infection. Limiting dilution analysis identified an expanded population of surface protein-specific CD4 cells during the acute and chronic infection. These surface protein-specific CD4 cells did not produce IL-2 or IL-4, but did produce IFN-γ. Enzyme-linked immunospot analyses confirmed that many of the surface protein-specific CD4 cells produce IFN-γ. Together these results suggest that during T. cruzi infection a potentially protective CD4 response becomes anergic. It is possible that this anergy is induced by variant T cell epitopes encoded by the surface protein superfamily.

Transforming growth factor beta-induced failure of resistance to infection with blood-stage Plasmodium chabaudi in mice

The role of transforming growth factor beta (TGF-beta) in infection with Plasmodium chabaudi was investigated with resistant and susceptible mouse models. C57BL/10 mice produced gamma interferon (IFN-gamma) and nitric oxide (NO) shortly after infection and cleared the parasite spontaneously. In contrast, BALB/c mice showed a transient enhancement of TGF-beta production, followed by a relative lack of IFN-gamma and NO production, and succumbed to the infection. However, there was no correlation between levels of serum TGF-beta and splenic TGF-beta mRNA in both mouse strains before and after infection. Administration of recombinant TGF-beta (rTGF-beta) rendered resistant mice susceptible because of suppression of subsequent production of IFN-gamma and NO. Administration of anti-TGF-beta antibody to the infected BALB/c mice resulted in remarkable increases in serum IFN-gamma and NO, and the mice resisted the infection. Splenic CD4(+) T and CD11b+ cells of C57BL/10 mice were significantly activated after infection, but this was completely abrogated by administration of rTGF-beta. These results suggested that, in the P. chabaudi-susceptible but not resistant mice, production of TGF-beta was promoted, and subsequent failure of IFN-gamma- and NO-dependent resistance to the parasite was induced. This study is the first to indicate that TGF-beta production was the key event in failure of resistance to mouse malaria.

Successive tick infestations selectively promote a T-helper 2 cytokine profile in mice

Several studies have revealed that T lymphocytes and cytokines play a crucial role in determining the outcome of parasitic infections in terms of protective immunity. In this study we found that Rhipicephalus sanguineus tick saliva stimulates transforming growth factor-beta (TGF-beta), and reduces interleukin-12 (IL-12) secretion by cells from normal C3H/HeJ mice. Moreover, murine lymph node cells harvested 6 days after the fourth infestation with ticks presented an 82.4% decrease in their proliferative response to concanavalin A (Con A) compared with the response of control cells. In addition, lymph node cells cultured in the presence of Con A showed a T-helper 2-type (Th2-type) cytokine profile, represented by augmented IL-4 and IL-10 and TGF-beta. On the other hand, the IL-2, interferon-gamma (IFN-gamma) and IL-12 synthesis was significantly inhibited. These results indicate that ticks may modulate the host's immune response through saliva injection. Considering that C3H/HeJ mice develop no protective immunity to R. sanguineus infestation, our results suggest that tick-induced Th2-type cytokines and a decreased proliferative response probably lead the host to a susceptible state to both tick and tick-transmitted pathogens.

IL-4 and IL-10 Are Both Required for the Induction of Oral Tolerance

Protection from the development of experimental autoimmune uveitis (EAU) can be induced by feeding mice interphotoreceptor retinoid binding protein before uveitogenic challenge with the same protein. Two different regimens are equally effective in inducing protective tolerance, although they seem to do so through different mechanisms: one involving regulatory cytokines (IL-4, IL-10, and TGF-β), and the other with minimal involvement of cytokines. Here we studied the importance of IL-4 and IL-10 for the development of oral tolerance using mice genetically engineered to lack either one or both of these cytokines. In these animals we were able to protect against EAU only through the regimen inducing cytokine-independent tolerance. When these animals were fed a regimen that in the wild-type animal is thought to predominantly induce regulatory cells and is associated with cytokine secretion, they were not protected from EAU. Interestingly, both regimens were associated with reduced IL-2 production and proliferation in response to interphotoreceptor retinoid binding protein. These findings indicate that both IL-4 and IL-10 are required for induction of protective oral tolerance dependent on regulatory cytokines, and that one cytokine cannot substitute for the other in this process. These data also underscore the fact that oral tolerance, manifested as suppression of proliferation and IL-2 production, is not synonymous with protection from disease.

Interferon beta modulates experimental autoimmune encephalomyelitis by altering the pattern of cytokine secretion

The mechanism of action underlying the beneficial effect of IFNbeta in Multiple Sclerosis is poorly understood. Experimental Autoimmune Encephalomyelitis (EAE) is the experimental model for Multiple Sclerosis; therefore, we investigated the effects of recombinant mouse IFNbeta on the severity of EAE induced in SJL mice and on cytokine production by Th1 and Th2 lymphocytes. The results indicated that rmIFN beta reduced the disease activity with an I.P. dosage of 10,000 U/day every other day, and successfully treated EAE mice revealed reduced amounts of IFN gamma; no changes in the levels of IL4 were observed, although thera was a significant increase in IL10 and TGFbeta production. Beneficial effects on EAE are associated with inhibition of inflammatory cytokines and stimulation of anti-inflammatory cytokines.

Innate resistance to experimental Trypanosoma congolense infection: differences in IL-10 synthesis by macrophage cell lines from resistant and susceptible inbred mice

BALB/c and C57Bl/6 mice differ in resistance to T. congolense infections. We investigated the production of various cytokines (IL-10, IL-6, TNF-alpha and TGF-beta) by macrophages from these mice. Macrophage cell lines (BALB.BM cells) of BALB/c mice but not (ANA-I cells)of C57BL/6 mice constitutively produced IL-10. Challenge of these cells with trypanosomes induced the production of 50-100 times more IL-10 in BALB.BM cells than in ANA-1 cells. Pre-incubation of the cell lines with IFN-gamma. prior to the trypanosome challenge, further upregulated this IL-10 production in BALB.BM but not in ANA-1 cells. Primary cultures of bone marrow-derived macrophages (BMDM) from BALB/c mice also produced more IL-10 following challenge with IFN-gamma and opsonized trypanosomes than did the C57Bl/6 BMDM. Similarly after challenge with trypanosomes, BALB.BM and BALB/c BMDM produced significantly more IL-6 than did the analogous cells from the C57Bl/6 mice following such challenges. Higher steady state levels of TNF-alpha mRNA accumulated in ANA-1 cells than in BALB.BM cells following challenge with IFN-gamma and opsonized trypanosomes. Findings of this study for the first time indicate a differential regulation of cytokines (IL-10, IL-6 and TNF-alpha) in macrophages of mice that significantly differ in their susceptibility to infections with T. congolense.

Anti-TGF-β Treatment Promotes Rapid Healing of Leishmania major Infection in Mice by Enhancing In Vivo Nitric Oxide Production

CB6F1 mice display intermediate susceptibility to Leishmania major infection compared with the highly susceptible BALB/c and resistant C57BL/6 parental strains. During early weeks of infection, these mice develop dominant Th2 type responses to L. major, although they eventually exhibit a Th2 to Th1 switch and spontaneously resolve their infections. In this study, we have examined the effects of either IL-12 or anti-TGF-β therapy on the immune response and course of disease in chronically infected CB6F1 mice. Local treatment with IL-12 inoculated into the parasitized lesion at 4 wk of infection induced a marked increase in IFN-γ production but did not result in a significant reduction in numbers of parasite or promote more rapid healing. However, local treatment with an Ab to TGF-β led to both a decrease in parasite numbers and more rapid healing, despite the fact that such treatment did not significantly alter the pattern of IL-4 and IFN-γ production. Immunohistochemical studies showed that anti-TGF-β treatment resulted in increased nitric oxide production within parasitized lesions. Our results suggest that TGF-β may play an important regulatory role during chronic stages of a L. major infection by suppressing macrophage production of nitric oxide and that, in the absence of TGF-β, even the relatively low levels of IFN-γ observed in mice with dominant Th2-type responses are sufficient to activate macrophages to destroy amastigotes within parasitized lesions.

Influence of acute-phase parasite load on pathology, parasitism, and activation of the immune system at the late chronic phase of Chagas' disease

To obtain low and high parasite loads in the acute phase of Chagas' disease, A/J mice were infected with 10(3) or 10(5) Trypanosoma cruzi trypomastigotes of the Y strain and treated on day 6 with benznidazol. One year later, chronically infected mice were screened for subpatent parasitemias, tissue pathology, and immune response. Mice infected with the high parasite inoculum showed higher levels of chronic parasitemias, heart and striated muscle inflammation, and activation of the immune system than did mice infected with the low inoculum. Concerning the activation of the immune system, the main findings for high-dose-infected mice were (i) increased numbers of splenocytes, with preferential expansion of CD8(+) and B220(-) CD5(-) cells, many of them bearing a macrophage phenotype; (ii) higher frequencies of B (B220(+)), CD4(+), and CD8(+) large lymphocytes; (iii) a shift of CD4(+) cells towards a CD45RBLow phenotype; (iv) increased frequencies of both CD45RBLow and CD45RBHigh large CD4(+) cells; (v) augmented numbers of total immunoglobulin (Ig)-secreting cells, with predominance of IgG2a-producing cells; and (vi) increased production of gamma interferon and interleukin 4. In addition, these mice presented lower IgM and higher IgG2a and IgG1 parasite-specific serum antibody levels. Our results indicate that the parasite load at the acute phase of T. cruzi infection influences the activation of the immune system and development of Chagas' disease pathology at the late chronic phase of the disease.

How do protozoan parasites survive inside macrophages?

During infections with intracellular microbes, macrophages have two roles. On the one hand, they are important effector cells for the control and killing of intracellular bacteria and protozoan parasites by oxidative and non-oxidative mechanisms. On the other hand, macrophages may also serve as long-term host cells that facilitate the replication and survival of the pathogens, for example, by protecting them against toxic components of the extracellular milieu. In this review, Christian Bogdan and Martin Röllinghoff summarize some of the more recently discovered mechanisms by which intracellular protozoan parasites, such as Leishmania spp, Trypanosoma cruzi and Toxoplasma gondii, manage to exploit macrophages as safe target cells.

The Importance of TGF-β in Murine Visceral Leishmaniasis

IFN-γ is critical for the cure of leishmaniasis in humans and mice. BALB/c mice are genetically susceptible to infection with the visceralizing species of Leishmania, L. chagasi. We have evidence that a soluble factor(s) inhibits IFN-γ production by cultured liver granuloma cells from BALB/c mice during L. chagasi infection. In contrast, liver granulomas from C3H.HeJ mice, which are genetically resistant to L. chagasi infection, produce abundant IFN-γ. According to ELISAs and neutralization studies, there was not evidence that the Th2-type cytokines IL-10 or IL-4 contributed to IFN-γ suppression. However, both Ab neutralization and immunohistochemistry showed that granuloma-derived TGF-β was, at least in part, responsible for inhibiting IFN-γ release by CD4+ cells in BALB/c liver granuloma cultures. Consistently, TGF-β levels were high in liver granulomas from susceptible BALB/c mice but low in resistant C3H mice or in BALB/c mice that were immunized against L. chagasi disease. Administration of recombinant adenovirus expressing TGF-β (AdV-TGFβ) but not IL-10 (AdV-IL10) caused genetically resistant C3H mice to become significantly more susceptible to L. chagasi infection. In contrast, either AdV-TGFβ or AdV-IL10 could abrogate the protective immune response achieved by immunization of BALB/c mice. We conclude that locally secreted TGF-β inhibits Th1-associated cure of murine visceral leishmaniasis caused by L. chagasi, independently of Th2-type cytokines.

Regulation and function of T-cell-mediated immunity during Toxoplasma gondii infection

The intracellular protozoan Toxoplasma gondii is a widespread opportunistic parasite of humans and animals. Normally, T. gondii establishes itself within brain and skeletal muscle tissues, persisting for the life of the host. Initiating and sustaining strong T-cell-mediated immunity is crucial in preventing the emergence of T. gondii as a serious pathogen. The parasite induces high levels of gamma interferon (IFN-gamma) during initial infection as a result of early T-cell as well as natural killer (NK) cell activation. Induction of interleukin-12 by macrophages is a major mechanism driving early IFN-gamma synthesis. The latter cytokine, in addition to promoting the differentiation of Th1 effectors, is important in macrophage activation and acquisition of microbicidal functions, such as nitric oxide release. During chronic infection, parasite-specific T lymphocytes release high levels of IFN-gamma, which is required to prevent cyst reactivation. T-cell-mediated cytolytic activity against infected cells, while easily demonstrable, plays a secondary role to inflammatory cytokine production. While part of the clinical manifestations of toxoplasmosis results from direct tissue destruction by the parasite, inflammatory cytokine-mediated immunopathologic changes may also contribute to disease progression.

Alpha-2-macroglobulin receptor is differently expressed in peritoneal macrophages from C3H and C57/B16 mice and up-regulated during Trypanosoma cruzi infection

Chagas' disease is caused by the protozoan Trypanosoma cruzi. The acute phase of T. cruzi infection, which can be conveniently studied in mouse models, is thought to be a determinant of survival and of the pathological features of the chronic phase. With regard to the occurrence of early death and parasitaemia levels C3H and C57/B16 mice are classically classified as 'susceptible' and 'resistant' to T. cruzi infection, respectively. Alpha-2-macroglobulin (A2M) is a physiological proteinase inhibitor found in tissues and in the plasma of mammals. Previous studies showed that A2M plasma levels increase in C3H mice acutely infected by T. cruzi but do not change in C57/B16 mice. This difference might involve two possible phenomena, concerning A2M synthesis and/or clearance by its receptor (A2M-R). In this study, we examined by flow cytometry the binding of A2M-trypsin conjugated with FITC to macrophages from normal and T. cruzi-infected C3H and C57/B16 mice. Our present results show for the first time that A2M-R is expressed more (by approximately 33%) in the surface of cells from normal C57/B16 as compared to C3H mice. We also show that A2M-R expression is up-regulated in both strains during acute T. cruzi infection, but at higher levels and earlier in C57/B16 mice. At the same time, peritoneal cells become activated as judged by: (1) increase of their size and granularity; (2) gradual increase of Fc gamma RII/III expression assayed by 2.4G2 binding; (3) down-modulation of F4/80 binding, a mAb that recognizes an antigen typically expressed in resident macrophages. Finally, our results indicate that as macrophages become activated in vivo a higher expression of A2M-R is observed.

Transforming growth factor beta production is inversely correlated with severity of murine malaria infection

We have examined the role of the immunomodulatory cytokine transforming growth factor (TGF)-beta in the resolution and pathology of malaria in BALB/c mice. Circulating levels of TGF-beta, and production of bioactive TGF-beta by splenocytes, were found to be low in lethal infections with Plasmodium berghei. In contrast, resolving infections with P. chabaudi chabaudi or P. yoelii were accompanied by significant TGF-beta production. A causal association between the failure to produce TGF-beta and the severity of malaria infection was demonstrated by treatment of infected mice with neutralizing antibody to TGF-beta, which exacerbated the virulence of P. berghei and transformed a resolving P. chabaudi chabaudi infection into a lethal infection, but had little effect on the course of P. yoelii infection. Parasitemia increased more rapidly in anti-TGF-beta-treated mice but this did not seem to be the explanation for the increased pathology of infection as peak parasitemias were unchanged. Treatment of P. berghei-infected mice with recombinant TGF-beta (rTGF-beta) slowed the rate of parasite proliferation and prolonged their survival from 15 to up to 35 d. rTGF-beta treatment was accompanied by a significant decrease in serum tumor necrosis factor alpha and an increase in interleukin 10. Finally, we present evidence that differences in TGF-beta responses in different malaria infections are due to intrinsic differences between species of malaria parasites in their ability to induce production of TGF-beta. Thus, TGF-beta seems to induce protective immune responses, leading to slower parasite growth, early in infection, and, subsequently, appears to downregulate pathogenic responses late in infection. This duality of effect makes TGF-beta a prime candidate for a major immunomodulatory cytokine associated with successful control of malaria infection.

Role of T lymphocytes and cytokines in coccidiosis

Development of a vaccine for avian coccidiosis has been hampered by lack of understanding of the various components of the host immune system leading to protective immunity. Clear understanding of the cellular dichotomy in cytokine production in mice and the availability of immunological reagents, as well as gene knock-out mice, now makes in-depth immunological study in this species feasible. From studies of various parasitic infection models in mice, it is becoming clear that complex regulation by cytokines is involved in host immunity. Furthermore, the studies in mice clearly indicated an important role of various effector mechanisms involving T lymphocytes, macrophages, natural killer (NK) cells and cytokines in resistance to coccidiosis. In comparative studies of coccidiosis in chickens, in-vivo and in-vitro studies revealed that interferon-gamma, tumor necrosis factor and transforming growth factor-beta are induced following Eimeria infection. Depletion studies revealed the importance of CD8+TCR-alpha-beta+ T lymphocytes in host protective immunity to avian coccidiosis. Taken together, studies in mice and chickens are providing a better understanding of the role of effector cells and soluble factors which control immune responses to Eimeria parasites.

Regulation of immune responses by TGF-beta

The transforming growth factor beta (TGF-beta) family of proteins are a set of pleiotropic secreted signaling molecules with unique and potent immunoregulatory properties. TGF-beta 1 is produced by every leukocyte lineage, including lymphocytes, macrophages, and dendritic cells, and its expression serves in both autocrine and paracrine modes to control the differentiation, proliferation, and state of activation of these immune cells. TGF-beta can modulate expression of adhesion molecules, provide a chemotactic gradient for leukocytes and other cells participating in an inflammatory response, and inhibit them once they have become activated. Increased production and activation of latent TGF-beta have been linked to immune defects associated with malignancy and autoimmune disorders, to susceptibility to opportunistic infection, and to the fibrotic complications associated with chronic inflammatory conditions. In addition to these roles in disease pathogenesis, TGF-beta is now established as a principal mediator of oral tolerance and can be recognized as the sine qua non of a unique subset of effector cells that are induced in this process. The accumulated knowledge gained through extensive in vitro functional analyses and from in vivo animal models, including newly established TGF-beta gene knockout and transgenic mice, supports the concept that clinical therapies based on modulation of this cytokine represent an important new approach to the treatment of disorders of immune function.