3-Hydroxykynurenine, a Tryptophan Metabolite Generated during the Infection, Is Active Against Trypanosoma cruzi.

The antiparasitic activity of 3-hydroxykynurenine (3-HK), one of the major tryptophan catabolites of the kynurenine pathway, against both Trypanosoma cruzi evolutive forms that are important for human infection, trypomastigotes (Tps) and amastigotes (Am), possible targets in the parasite and the drug toxicity to mammalian cells have been investigated. 3-HK showed a potent activity against Am with IC50 values in the micromolar concentration range, while the IC50 values to cause Tps death was ∼6000-times higher, indicating that the replicative form present in the vertebrate hosts is much more susceptible to 3-HK than bloodstream Tps. In addition, 3-HK showed activity against Tps and Am, at concentrations that did not exhibit toxicity to mammalian cells. Ultrastructural analysis and flow cytometry studies indicated that Am and Tps mitochondrion and nuclei contain 3-HK targets. The potency and selectivity of 3-HK, which is generated during T. cruzi infection in human and mice, suggest that 3-HK may be a suitable candidate for drug research and development for Chagas disease.

PD-L2 negatively regulates Th1-mediated immunopathology during Fasciola hepatica infection.

Macrophage plasticity is critical for controlling inflammation including those produced by helminth infections, where alternatively activated macrophages (AAM) are accumulated in tissues. AAM expressing the co-inhibitory molecule programmed death ligand 2 (PD-L2), which is capable of binding programmed death 1 (PD-1) expressed on activated T cells, have been demonstrated in different parasitic infections. However, the role of PD-L2 during F. hepatica infection has not yet been explored. We observed that F. hepatica infection or a F. hepatica total extract (TE) injection increased the expression of PD-L2 on peritoneal macrophages. In addition, the absence of PD-L2 expression correlated with an increase in susceptibility to F. hepatica infection, as evidenced by the shorter survival and increased liver damage observed in PD-L2 deficient (KO) mice. We assessed the contribution of the PD-L2 pathway to Th2 polarization during this infection, and found that the absence of PD-L2 caused a diminished Th2 type cytokine production by TE stimulated splenocytes from PD-L2 KO infected compared with WT mice. Besides, splenocytes and intrahepatic leukocytes from infected PD-L2 KO mice showed higher levels of IFN-γ than those from WT mice. Arginase expression and activity and IL-10 production were reduced in macrophages from PD-L2 KO mice compared to those from WT mice, revealing a strong correlation between PD-L2 expression and AAM polarization. Taken together, our data indicate that PD-L2 expression in macrophages is critical for AAM induction and the maintenance of an optimal balance between the Th1- and Th2-type immune responses to assure host survival during F. hepatica infection.

Fasciola hepatica Kunitz type molecule decreases dendritic cell activation and their ability to induce inflammatory responses.

The complete repertoire of proteins with immunomodulatory activity in Fasciola hepatica (Fh) has not yet been fully described. Here, we demonstrated that Fh total extract (TE) reduced LPS-induced DC maturation, and the DC ability to induce allogeneic responses. After TE fractionating, a fraction lower than 10 kDa (F<10 kDa) was able to maintain the TE properties to modulate the DC pro- and anti-inflammatory cytokine production induced by LPS. In addition, TE or F<10 kDa treatment decreased the ability of immature DC to stimulate the allogeneic responses and induced a novo allogeneic CD4+CD25+Foxp3+ T cells. In contrast, treatment of DC with T/L or F<10 kDa plus LPS (F<10/L) induced a regulatory IL-27 dependent mechanism that diminished the proliferative and Th1 and Th17 allogeneic responses. Finally, we showed that a Kunitz type molecule (Fh-KTM), present in F<10 kDa, was responsible for suppressing pro-inflammatory cytokine production in LPS-activated DC, by printing tolerogenic features on DC that impaired their ability to induce inflammatory responses. These results suggest a modulatory role for this protein, which may be involved in the immune evasion mechanisms of the parasite.

In vivo expression of recombinant pregnancy-specific glycoprotein 1a inhibits the symptoms of collagen-induced arthritis.

PROBLEM: The contribution of Pregnancy-specific glycoproteins (PSG), the major variant of PSG released into the circulation during pregnancy, to the pregnancy-dependent improvement of rheumatoid arthritis (RA) has still not been elucidated. METHOD OF STUDY: Collagen-induced arthritis (CIA) was used to test the hypothesis that PSG1a when released into circulation has a modulatory role on the Th1-pathogenic response, thus improving the CIA symptoms. In vivo expression of PSG1a was induced by injection of the vaccinia (Vac)-based expression vector harboring the complete open-reading frame of PSG1a cDNA. RESULTS: In vivo PSG1a expression during the induction of CIA ameliorated the clinical symptoms, thereby reducing the arthritis score and incidence. Significantly lower levels of IL-17, IL-6, and IFN-γ, but higher levels of TGF-ß and IL-10 were secreted by collagen type II-stimulated spleen mononuclear cells from Vac-PSG1a-treated mice compared with control mice. Moreover, Vac-PSG1a treatment promoted the increase in splenic CD4+CD25+Foxp3+ Treg cells. CONCLUSION: Pre-clinical Vac-PSG1a treatment suppressed the Th1- and Th17-type-specific responses, leading to an increase in splenic Treg cells as well as IL-10- and TGF-ß-secreting cells, with the CIA symptoms being ameliorated.

The role of pregnancy-specific glycoprotein 1a (PSG1a) in regulating the innate and adaptive immune response.

Among several explanations for the acceptance of the fetus, the one that suggests that the maternal immune system is suppressed or modified has been the subject of many studies. Thus, it has been proposed that the cells of innate immune system might be able to distinguish the pregnant from the non-pregnant state producing a signal, the so-called signal P. We have previously proposed that pregnancy-specific glycoprotein 1a (PSG1a), a representative member of the main glycoprotein family secreted by placental trophoblast, may modulate the activation of antigen-presenting cells promoting the T-cell shift of the maternal cell immunity toward a less harmful phenotype. In this review, we summarize current knowledge concerning the contribution of pregnancy-specific glycoprotein 1a (PSG1a) to modulate the maternal innate and adaptive immune response in order to assure a successful pregnancy.

Pregnancy-specific glycoprotein 1a activates dendritic cells to provide signals for Th17-, Th2-, and Treg-cell polarization.

Because of their plasticity and central role in orchestrating immunity and tolerance, DCs can respond to pregnancy-specific signals, thus promoting the appropriate immune response in order to support pregnancy. Here, we show that pregnancy-specific glycoprotein (PSG1a), the major variant of PSG released into the circulation during pregnancy, targets DCs to differentiate into a subset with a unique phenotype and function. This semi-mature phenotype is able to secrete IL-6 and TGF-ß. PSG1a also affected the maturation of DCs, preventing the up-regulation of some costimulatory molecules, and inducing the secretion of TGF-ß or IL-10 and the expression of programmed death ligand 1 (PD-L1) in response to TLR-9 or CD40 ligation. In addition, PSG1a-treated DCs promoted the enrichment of Th2-type cytokines, IL-17-producing cells, and Treg cells from CD4(+) T cells from DO11.10 Tg mice. Moreover, in vivo expression of PSG1a promoted the expansion of Ag-specific CD4(+) CD25(+) Foxp3(+) Treg cells and IL-17-, IL-4-, IL-5-, and IL-10-secreting cells able to protect against Listeria monocytogenes infection. Taken together, our data indicate that DCs can be targeted by PSG1a to generate the signals necessary to mount an appropriate, well-balanced, and effective immune response able to protect against invading pathogens while at the same time being compatible with a successful pregnancy.

Adoptive transfer of dendritic cells pulsed with Fasciola hepatica antigens and lipopolysaccharides confers protection against fasciolosis in mice.

Dendritic cells (DCs) can function as adjuvants able to mediate protection against different pathogens. Given that successful vaccination against Fasciola hepatica is mostly related to the induction of Th1 responses, we studied the potential of DCs loaded with F. hepatica antigens and lipopolysaccharide (LPS) (which promote DCs maturation) as a vaccine against fasciolosis in BALB/c mice. However, only a semimature phenotype was achieved when DCs were simultaneously cultured with an F. hepatica total extract (TE) and LPS. The activation status of TE-loaded DCs was enhanced when these cells were treated with TE 90 minutes before being stimulated with LPS (TE90 DCs). More importantly, a single vaccination of mice with TE90 DCs stimulated a systemic Th1 response and conferred protection against hepatic damage induced by F. hepatica infection. Thus, TE90 DCs may prove to be a useful new tool for vaccination against F. hepatica.

3-Hydroxy kynurenine treatment controls T. cruzi replication and the inflammatory pathology preventing the clinical symptoms of chronic Chagas disease.

BACKGROUND: 3-Hydroxy Kynurenine (3-HK) administration during the acute phase of Trypanosoma. cruzi infection decreases the parasitemia of lethally infected mice and improves their survival. However, due to the fact that the treatment with 3-HK is unable to eradicate the parasite, together with the known proapoptotic and immunoregulatory properties of 3-HK and their downstream catabolites, it is possible that the 3-HK treatment is effective during the acute phase of the infection by controlling the parasite replication, but at the same time suppressed the protective T cell response before pathogen clearance worsening the chronic phase of the infection. Therefore, in the present study, we investigated the effect of 3-HK treatment on the development of chronic Chagas' disease. PRINCIPAL FINDINGS: In the present study, we treated mice infected with T. cruzi with 3-HK at day five post infection during 5 consecutive days and investigated the effect of this treatment on the development of chronic Chagas disease. Cardiac functional (electrocardiogram) and histopathological studies were done at 60 dpi. 3-HK treatment markedly reduced the incidence and the severity of the electrocardiogram alterations and the inflammatory infiltrates and fibrosis in heart and skeletal muscle. 3-HK treatment modulated the immune response at the acute phase of the infection impairing the Th1- and Th2-type specific response and inducing TGF-ß-secreting cells promoting the emergence of regulatory T cells and long-term specific IFN-γ secreting cells. 3-HK in vitro induced regulatory phenotype in T cells from T. cruzi acutely infected mice. CONCLUSIONS: Our results show that the early 3-HK treatment was effective in reducing the cardiac lesions as well as altering the pattern of the immune response in experimental Chagas' disease. Thus, we propose 3-HK as a novel therapeutic treatment able to control both the parasite replication and the inflammatory response.

Excretory-secretory products (ESP) from Fasciola hepatica induce tolerogenic properties in myeloid dendritic cells.

Fasciola hepatica is a helminth trematode that migrates through the host tissues until reaching bile ducts where it becomes an adult. During its migration the parasite releases different excretory-secretory products (ESP), which are in contact with the immune system. In this study, we focused on the effect of ESP on the maturation and function of murine bone marrow derived-dendritic cells (DC). We found that the treatment of DC with ESP failed to induce a classical maturation of these cells, since ESP alone did not activate DC to produce any cytokines, although they impaired the ability of DC to be activated by TLR ligands and also their capacity to stimulate an allospecific response. In addition, using an in vitro ovalbumin peptide-restricted priming assay, ESP-treated DC exhibited a capacity to drive Th2 and regulatory T cell (Treg) polarization of CD4(+) cells from DO11.10 transgenic mice. This was characterized by increased IL-4, IL-5, IL-10 and TGF-beta production and the expansion of CD4(+)CD25(+)Foxp3(+) cells. Our results support the hypothesis that ESP from F. hepatica modulate the maturation and function of DC as part of a generalized immunosuppressive mechanism that involves a bias towards a Th2 response and Treg development.

Galectin-1 functions as a Th2 cytokine that selectively induces Th1 apoptosis and promotes Th2 function.

Galectin-1 has been implicated in regulating T-cell survival, function, and Th1/Th2 balance in several mouse models, though the molecular and cellular basis of its immuno-modulatory activity has not been completely elucidated. Therefore, we examined galectin-1 expression and activity within differentiated murine Th1 and Th2 subsets. While recombinant galectin-1 specifically bound to both T-cell subsets, Th1 and Th2 T cells expressed distinct combinations of galectin-1-reactive epitopes and were differentially responsive to galectin-1 exposure. Indeed, Th1 cells were more susceptible to galectin-1-induced death than Th2 cells. Th2 protection from apoptosis was correlated with expression of anti-apoptotic galectin-3. Further, galectin-1 promoted TCR-induced type 2 cytokine production by Th2 cells. Differentiated Th2 cells constitutively expressed high levels of galectin-1 and can be induced to produce even higher levels of galectin-1 with restimulation, whereas comparable levels of galectin-1 in Th1 cells were only observed after restimulation. Co-culturing experiments using galectin-1(-/-) and galectin-1+/+ Th1 and Th2 T cells demonstrated that Th2-derived galectin-1 induced Th1 apoptosis, whereas Th1-derived galectin-1 promoted Th2 cytokine production. These studies identify galectin-1 as a cross-regulatory cytokine that selectively antagonizes Th1 survival, while promoting TCR-induced Th2 cytokine production.

Galectin-3 mediates IL-4-induced survival and differentiation of B cells: functional cross-talk and implications during Trypanosoma cruzi infection.

The role of transcription factors in B cell survival and differentiation has been delineated during the last years. However, little is known about the intermediate signals and the intracellular pathways that control these events. In this study, we provide evidence both in vitro and in vivo, showing that galectin-3 (Gal-3), a beta-galactoside-binding protein, is a critical mediator of B cell differentiation and survival. Although Gal-3 is not expressed in resting B cells from normal mice, its expression is markedly induced after activation with stimuli such as IL-4 and CD40 cross-linking. These signals promote survival and block the final differentiation of these cells, thus allowing the rising of a memory B cell phenotype. In addition, Gal-3 is expressed in B cells from Trypanosoma cruzi-infected mice, which received signals for activation and differentiation in vivo. By using an antisense strategy, we determined that Gal-3 is a critical signal mediating the effects of IL-4 on B cell fate. Blockade of intracellular Gal-3 in vitro abrogated IL-4-induced survival of activated B cells, favoring the differentiation toward a plasma cell pathway. Moreover, B cells with restrained endogenous Gal-3 expression failed to down-regulate the Blimp-1 transcription factor after IL-4 stimulation. Finally, inhibition of Gal-3 in vivo skewed the balance toward plasma cell differentiation, which resulted in increased Ig production and parasite clearance during T. cruzi infection. Thus, the present study provides evidence of a novel role for Gal-3 as an intracellular mediator of B cell survival and a checkpoint in IL-4-induced B cell commitment toward a memory phenotype.

In vivo expression of recombinant pregnancy-specific glycoprotein 1a induces alternative activation of monocytes and enhances Th2-type immune response.

It has been proposed that pregnancy-specific factors could be responsible for shift the balance of cytokine profiles during maternal immune response from Th1-type reactivity into a "less-damaging" Th2-type reactivity. In the present work, we investigated the in vivo function of human pregnancy-specific glycoprotein (PSG)1a, the major variant of PSG polypeptides released into the circulation during pregnancy, on the modulation of the innate and adaptive immune response. For this, BALB/c mice were injected with a vaccinia virus-based vector harboring the human PSG1a cDNA (Vac-PSG1a) 4 days before immunization with ovalbumin (OVA) in complete Freund's adjuvant, and the early specific T cell response against OVA was evaluated 8 days post-immunization. We also studied the activation status of spleen and peritoneal monocytes/macrophages (Mo) populations from Vac-PSG1a-treated mice, and explored whether PSG1a-targeted Mo could affect the Th-type commitment by investigating their impact on the differentiation of naive T cells. Our data show that the treatment with Vac-PSG1a is able to induce a state of alternative activation on Mo. Furthermore, the generation of the immune response in the context of these alternatively activated antigen-presenting cells may shift T cell differentiation to Th2-type immunity which is more compatible with a successful pregnancy.

Trypanosoma cruzi infection selectively renders parasite-specific IgG+ B lymphocytes susceptible to Fas/Fas ligand-mediated fratricide.

The control of B cell expansion has been thought to be solely regulated by T lymphocytes. We show in this study that Trypanosoma cruzi infection induces up-regulation of both Fas and Fas ligand (FasL) molecules on B cells and renders them susceptible to B cell-B cell killing (referred to as fratricide throughout this paper) mediated via Fas/FasL. Moreover, by in vivo administration of anti-FasL blocking mAb we demonstrate that Fas-mediated B cell apoptosis is an ongoing process during this parasitic infection. We also provide evidence that B cells that have switched to IgG isotype are the preferential targets of B cell fratricide. More strikingly, this death pathway selectively affects IgG(+) B cells reactive to parasite but not self Ags. Parasite-specific but not self-reactive B cells triggered during this response are rescued after either in vitro or in vivo FasL blockade. Fratricide among parasite-specific IgG(+) B lymphocytes could impair the immune control of T. cruzi and possibly other chronic protozoan parasites. Our results raise the possibility that the blockade of Fas/FasL interaction in the B cell compartment of T. cruzi-infected mice may provide a means for enhancing antiparasitic humoral immune response without affecting host tolerance.