Claudia C. Motrán

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 β-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.

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.

Trypanosoma cruzi-induced immunosuppression : B cells undergo spontaneous apoptosis and lipopolysaccharide (LPS) arrests their proliferation during acute infection

Acute infection with Trypanosoma cruzi is characterized by multiple manifestations of immunosuppression of both cellular and humoral responses. B cells isolated at the acute stage of infection have shown marked impairment in their response to polyclonal activators in vitro. The present work aims at studying the B cell compartment in the context of acute T. cruzi infection to provide evidence for B cell activation, spontaneous apoptosis and arrest of the cell cycle upon mitogenic stimulation as a mechanism underlying B cell hyporesponse. We found that B cells from acutely infected mice, which fail to respond to the mitogen LPS, showed spontaneous proliferation and production of IgM, indicating a high level of B cell activation. Furthermore, these activated B cells also exhibited an increase in Fas expression and apoptosis in cultures without an exogenous stimulus. On the other hand, B cells from early acute and chronic infected mice did not present activation or apoptosis, and were able to respond properly to the mitogen. Upon in vitro stimulation with LPS, B cells from hyporesponder mice failed to progress through the cell cycle (G0/G1 arrest), nor did they increase the levels of apoptosis. These results indicate that B cell apoptosis and cell cycle arrest could be the mechanisms that control intense B cell expansion, but at the same time could be delaying the emergence of a specific immune response against the parasite.

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.

Helminth Antigens Enable CpG-Activated Dendritic Cells to Inhibit the Symptoms of Collagen-induced Arthritis through Foxp3+ Regulatory T Cells

Dendritic cells (DC) have the potential to control the outcome of autoimmunity by modulating the immune response. In this study, we tested the ability of Fasciola hepatica total extract (TE) to induce tolerogenic properties in CpG-ODN (CpG) maturated DC, to then evaluate the therapeutic potential of these cells to diminish the inflammatory response in collagen induced arthritis (CIA). DBA/1J mice were injected with TE plus CpG treated DC (T/C-DC) pulsed with bovine collagen II (CII) between two immunizations with CII and clinical scores CIA were determined. The levels of CII-specific IgG2 and IgG1 in sera, the histological analyses in the joints, the cytokine profile in the draining lymph node (DLN) cells and in the joints, and the number, and functionality of CD4+CD25+Foxp3+ T cells (Treg) were evaluated. Vaccination of mice with CII pulsed T/C-DC diminished the severity and incidence of CIA symptoms and the production of the inflammatory cytokine, while induced the production of anti-inflammatory cytokines. The therapeutic effect was mediated by Treg cells, since the adoptive transfer of CD4+CD25+ T cells, inhibited the inflammatory symptoms in CIA. The in vitro blockage of TGF-β in cultures of DLN cells plus CII pulsed T/C-DC inhibited the expansion of Treg cells. Vaccination with CII pulsed T/C-DC seems to be a very efficient approach to diminish exacerbated immune response in CIA, by inducing the development of Treg cells, and it is therefore an interesting candidate for a cell-based therapy for rheumatoid arthritis (RA).

Indoleamine 2,3-dioxigenase (IDO) is critical for host resistance against Trypanosoma cruzi

Indoleamine 2,3‐dioxigenase (IDO) is an inflammatory cytokine‐inducible rate‐limiting enzyme of the tryptophan (Trp) catabolism, which is involved in the inhibition of intracellular pathogen replication as well as in immunomodulation. Here we demonstrated the effect of IDO‐dependent Trp catabolism on Trypanosoma cruzi resistance to acute infection. Infection with T. cruzi resulted in the systemic activation of IDO. The blocking of IDO activity in vivo impaired resistance to the infection and exacerbated the parasite load and infection‐associated pathology. In addition, IDO activity was critical to controlling the parasites replication in macrophages (Mos), despite the high production of nitric oxide produced by IDO‐blocked T. cruzi‐infected Mos. Analysis of the mechanisms by which IDO controls the parasite replication revealed that T. cruzi amastigotes were sensitive to l‐kynurenine downstream metabolites 3‐hydroxykynurenine (3‐HK) and 3‐hydroxyanthranilic acid, while 3‐HK also affected the trypomastigote stage. Finally, 3‐HK treatment of mice acutely infected with T. cruzi was able to control the parasite and to improve the survival of lethally infected mice. During infection, IDO played a critical role in host defense against T. cruzi; therefore, the intervention of IDO pathway could be useful as a novel antitrypanosomatid therapeutic strategy.—Knubel, C. P., Martínez, F. F., Fretes, R. E., Díaz Lujan, C., Theumer, M. G., Cervi, L., Motran, C. C. Indoleamine 2,3‐dioxigenase (IDO) is critical for host resistance against Trypanosoma cruzi. FASEB J. 24, 2689–2701 (2010). www.fasebj.org

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‐β. PSG1a also affected the maturation of DCs, preventing the up‐regulation of some costimulatory molecules, and inducing the secretion of TGF‐β 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.

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.

Trypanosoma cruzi Infection Beats the B-cell Compartment Favouring Parasite Establishment: Can we Strike First?

Abstract Trypanosoma cruzi, the causative agent of Chagas’ disease, may sabotage humoral response by affecting B cells at the different stages of its development. The present review highlights the contributions of our laboratory in understanding how T. cruzi hinders B‐cell generation and B‐cell expansion limiting host defence and favouring its chronic establishment. We discuss how homoeostatic mechanisms can be triggered to control exacerbated B‐cell proliferation that favour T. cruzi infection by eliminating parasite‐specific B cells. Specific targeting of evasion mechanisms displayed in T. cruzi infection, as in vivo Fas/FasL blockade or Gal‐3 expression inhibition, allowed us to modulate B‐cell responses enhancing the anti‐parasite humoral immune response. A comprehensive understanding of the biology of the B cell in health and disease is strictly required to devise immunointervention strategies aimed at enhancing protective immune responses during infections.

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.