Myeloid-derived suppressor cells (MDSCs Keywords: Inflammation r MDSCs r Nitric oxide r ROS r Trypanosoma cruziAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionMyeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population consisting of immature macrophages, granulocytes, and dendritic cells as well as myeloid progenitor cells. They are considered to be one of the major components of the immune suppressive network responsible for suppressing T-cell responses in pathological conditions [1,2] as well as in the regulation of the immune response in healthy individuals [3]. These Correspondence: Dr. Susana Gea e-mail: sgea@fcq.unc.edu.ar myeloid cells are commonly identified in mice by the co-expression of the surface markers CD11b and Gr1 (Ly6G/Ly6C) and have been divided into two subsets: granulocytic (G) MDSCs with a CD11b + LY6G + LY6C low phenotype and monocytic (M) MDSCs with CD11b + LY6G − LY6C high phenotype [3,4]. Despite their morphological similarities, G-MDSCs and neutrophils are functionally and phenotypically different. G-MDSCs, but not neutrophils, are immunosuppressive and express higher levels of arginase-1 and myeloperoxidase than neutrophils, and also have increased production of reactive oxygen species (ROS) [5,6]. Although * These authors contributed equally to this work.www.eji-journal.eu Eur. J. Immunol. 2014. 44: 184-194 Immunomodulation 185 M-MDSCs and inflammatory monocytes share the same phenotype and morphology, these cells are functionally distinct since M-MDSCs are highly immunosuppressive and they express high levels of both iNOS and arginase-1. Furthermore, although iNOS expression is a hallmark of a tumoricidal/microbicidal phenotype in M1 macrophages, iNOS promotes suppressive activities in M-MDSCs. This shift in iNOS activity most likely reflects the crosstalk of iNOS with other enzymes such as NADPH oxidase to promote the production of peroxynitrites, which inhibits the proliferation and effector function of T cells [2]. MDSCs use several mechanisms in addition to the production of ROS and NO, such as triggering apoptosis of activated T cells by depleting of L-arginine, via arginase [7][8][9][10]. There is also evidence that MDSCs may suppress immune activation by inducing T regulatory cell expansion [11]. Other suppressive mechanisms that have recently been proposed include the production of TGF-β [12,13], depletion of cysteine [8], induction of COX2 and prostaglandin E2 [1,[14][15][16].Trypanosoma cruzi an obligate intracellular protozoan, is the causative agent of Chagas disease. This disease affects about 20 million people in Latin America, with 120 million persons at risk. In the past decades, mainly as a result of increased migrations, the diagnosed cases have also increased in nonendemic countries such as Canada, United States of America, and Europe. This has led to an increased risk of transmission of the infection, mainly through blood transfusion and organ transplantation [17]. Pa...

Background: B cells play an important role in the development and maintenance of rheumatoid arthritis (RA). Although IL-10–producing B cells represent a major subset of regulatory B cells (Bregs) able to suppress autoimmune and inflammatory responses, recent reports showed that B cell-mediated immune suppression may also occur independent of IL-10. For instance, B cells can modulate T cell immune responses through the expression of regulatory molecules such as PD-L1. So far, PD-L1-expressing B cells have not been analyzed in RA patients.Objective: To analyze the frequency of PD-L1-expressing B cells in the peripheral blood of RA patients compared to healthy controls (HC) matched for sex and age, their function on T cell response and their changes in response to therapy.Methods: Fresh peripheral blood B cells from RA patients and HC were characterized by flow cytometry and their functionality assessed in a co-culture system with autologous T cells.Results: The frequencies of CD19+PD-L1+ B cells, CD24hiCD38−PD-L1+ and CD24hiCD38hiPD-L1+ B cells were significantly lower in untreated RA patients than in HC. In a follow-up study, the frequencies of PD-L1+ B cells (CD19+PD-L1+ B cells, CD24hiCD38−PD-L1+ and CD24hiCD38hiPD-L1+ B cells) increased significantly after treatment in good responder patients, although the frequency of total CD24hiCD38hi B cells decreased. CD19+ B cells from untreated RA patients and HC upregulated PD-L1 expression similarly upon stimulation with CpG plus IL-2 and were able to suppress, in vitro, CD8+ T cell proliferation and cytokine production in a PD-L1-dependent manner.Conclusions: Our results show that PD-L1+ B cells exhibiting T cell suppressive capacity are significantly decreased in untreated RA patients but increase in response to successful treatment. PD-L1 expression on B cells from RA patients can be modulated in vitro and PD-L1+ B cells could thus provide new perspectives for future treatment strategies.

Chronic obesity and Chagas disease (caused by the protozoan Trypanosoma cruzi) represent serious public health concerns. The interrelation between parasite infection, adipose tissue, immune system and metabolism in an obesogenic context, has not been entirely explored. A novel diet-induced obesity model (DIO) was developed in C57BL/6 wild type mice to examine the effect of chronic infection (DIO+I) on metabolic parameters and on obesity-related disorders. Dyslipidemia, hyperleptinemia, and cardiac/hepatic steatosis were strongly developed in DIO mice. Strikingly, although these metabolic alterations were collectively improved by infection, plasmatic apoB100 levels remain significantly increased in DIO+I, suggesting the presence of pro-atherogenic small and dense LDL particles. Moreover, acute insulin resistance followed by chronic hyperglycemia with hypoinsulinemia was found, evidencing an infection-related-diabetes progression. These lipid and glucose metabolic changes seemed to be highly dependent on TLR4 expression since TLR4−/− mice were protected from obesity and its complications. Notably, chronic infection promoted a strong increase in MCP-1 producing macrophages with a M2 (F4/80+CD11c-CD206+) phenotype associated to oxidative stress in visceral adipose tissue of DIO+I mice. Importantly, infection reduced lipid content but intensified inflammatory infiltrates in target tissues. Thus, parasite persistence in an obesogenic environment and the resulting host immunometabolic dysregulation may contribute to diabetes/atherosclerosis progression.

Infection with protozoan parasite Trypanosoma cruzi results in activation of nucleotide-binding domain and leucine-rich repeat containing receptors (NLRs). NLR activation leads to inflammasome formation, the activation of caspase-1, and the subsequent cleavage of IL-1β and IL-18. Considering that inflammasome activation and IL-1β induction by macrophages are key players for an appropriate T cell response, we investigated the relevance of NLR pyrin domain-containing 3 (NLRP3) and caspase-1/11 to elucidate their roles in the induction of different T cell phenotypes and the relationship with parasite load and hepatic inflammation during T. cruzi-Tulahuen strain acute infection. We demonstrated that infected nlrp3−/− and C57BL/6 wild type (WT) mice exhibited similar parasitemia and survival, although the parasite load was higher in the livers of nlrp3−/− mice than in those of WT mice. Increased levels of transaminases and pro-inflammatory cytokines were found in the plasma of WT and nlrp3−/− mice indicating that NLRP3 is dispensable to control the parasitemia but it is required for a better clearance of parasites in the liver. Importantly, we have found that NLRP3 and caspase-1/11-deficient mice differentially modulate T helper (Th1, Th2, and Th17) and cytotoxic T lymphocyte phenotypes. Strikingly, caspase-1/11−/− mice showed the most dramatic reduction in the number of IFN-γ- and IL-17-producing CD4+ and CD8+ T cells associated with higher parasitemia and lower survival. Additionally, caspase-1/11−/− mice demonstrated significantly reduced liver inflammation with the lowest alanine aminotransferase (ALT) levels but the highest hepatic parasitic load. These results unequivocally demonstrate that caspase-1/11 pathway plays an important role in the induction of liver adaptive immunity against this parasite infection as well as in hepatic inflammation.

BackgroundThe immune mechanisms underlying experimental non-alcoholic steatohepatitis (NASH), and more interestingly, the effect of T. cruzi chronic infection on the pathogenesis of this metabolic disorder are not completely understood.Methodology/Principal FindingsWe evaluated immunological parameters in male C57BL/6 wild type and TLR4 deficient mice fed with a standard, low fat diet, LFD (3% fat) as control group, or a medium fat diet, MFD (14% fat) in order to induce NASH, or mice infected intraperitoneally with 100 blood-derived trypomastigotes of Tulahuen strain and also fed with LFD (I+LFD) or MFD (I+MFD) for 24 weeks. We demonstrated that MFD by itself was able to induce NASH in WT mice and that parasitic infection induced marked metabolic changes with reduction of body weight and steatosis revealed by histological studies. The I+MFD group also improved insulin resistance, demonstrated by homeostasis model assessment of insulin resistance (HOMA-IR) analysis; although parasitic infection increased the triglycerides and cholesterol plasma levels. In addition, hepatic M1 inflammatory macrophages and cytotoxic T cells showed intracellular inflammatory cytokines which were associated with high levels of IL6, IFNγ and IL17 plasmatic cytokines and CCL2 chemokine. These findings correlated with an increase in hepatic parasite load in I+MFD group demonstrated by qPCR assays. The recruitment of hepatic B lymphocytes, NK and dendritic cells was enhanced by MFD, and it was intensified by parasitic infection. These results were TLR4 signaling dependent. Flow cytometry and confocal microscopy analysis demonstrated that the reactive oxygen species and peroxinitrites produced by liver inflammatory leukocytes of MFD group were also exacerbated by parasitic infection in our NASH model.ConclusionsWe highlight that a medium fat diet by itself is able to induce steatohepatitis. Our results also suggest a synergic effect between damage associated with molecular patterns generated during NASH and parasitic infection, revealing an intense cross-talk between metabolically active tissues, such as the liver, and the immune system. Thus, T. cruzi infection must be considered as an additional risk factor since exacerbates the inflammation and accelerates the development of hepatic injury.

Inhibitory receptor expression on T cells from RA patients is inversely correlated with effector T cell function and disease activity and may predict response to treatment. Furthermore, different inhibitory pathways are functional and cooperatively suppress synovial T cells, providing a rationale for new treatment strategies to regulate acute local inflammation.

B cells, follicular helper T (Tfh) cells and follicular regulatory T (Tfr) cells are part of a circuit that may play a role in the development or progression of rheumatoid arthritis (RA). With the aim of providing further insight into this topic, here we evaluated the frequency of different subsets of Tfh and Tfr in untreated and long-term treated RA patients from a cohort of Argentina, and their potential association with particular human leukocyte antigen (HLA) class-II variants and disease activity. We observed that the frequency of total Tfh cells as well as of particular Tfh subsets and Tfr cells were increased in seropositive untreated RA patients. Interestingly, when analyzing paired samples, the frequency of Tfh cells was reduced in synovial fluid compared to peripheral blood, while Tfr cells levels were similar in both biological fluids. After treatment, a decrease in the CCR7loPD1hi Tfh subset and an increase in the frequency of Tfr cells was observed in blood. In comparison to healthy donors, seropositive patients with moderate and high disease activity exhibited higher frequency of Tfh cells while seropositive patients with low disease activity presented higher Tfr cell frequency. Finally, we observed that HLA-DRB1*09 presence correlated with higher frequency of Tfh and Tfr cells, while HLA-DRB1*04 was associated with increased Tfr cell frequency. Together, our results increase our knowledge about the dynamics of Tfh and Tfr cell subsets in RA, showing that this is altered after treatment.

Unraveling the immune signatures in rheumatoid arthritis (RA) patients receiving various treatment regimens can aid in comprehending the immune mechanisms’ role in treatment efficacy and side effects. Given the critical role of cellular immunity in RA pathogenesis, we sought to identify T‐cell profiles characterizing RA patients under specific treatments. We compared 75 immunophenotypic and biochemical variables in healthy donors (HD) and RA patients, including those receiving different treatments as well as treatment‐free patients. Additionally, we conducted in vitro experiments to evaluate the direct effect of tofacitinib on purified naïve and memory CD4+ and CD8+ T cells. Multivariate analysis revealed that tofacitinib‐treated patients segregated from HD at the expense of T‐cell activation, differentiation, and effector function‐related variables. Additionally, tofacitinib led to an accumulation of peripheral senescent memory CD4+ and CD8+ T cells. In vitro, tofacitinib impaired the activation, proliferation, and effector molecules expression and triggered senescence pathways in T‐cell subsets upon TCR‐engagement, with the most significant impact on memory CD8+ T cells. Our findings suggest that tofacitinib may activate immunosenescence pathways while simultaneously inhibiting effector functions in T cells, both effects likely contributing to the high clinical success and reported side effects of this JAK inhibitor in RA.