Trypanosoma cruzi trans-sialidase initiates a program independent of the transcription factors RORγt and Ahr that leads to IL-17 production by activated B cells. Nat Immunol. 2013;14:514-522. [PMID: 23563688 PMCID: PMC3631452 DOI: 10.1038/ni.2569]

Interleukin-17 and its implication in the regulation of differentiation and function of hematopoietic and mesenchymal stem cells

Adult stem cells have a great potential applicability in regenerative medicine and cell-based therapies. However, there are still many unresolved issues concerning their biology, and the influence of the local microenvironment on properties of stem cells has been increasingly recognized. Interleukin (IL-) 17, as a cytokine implicated in many physiological and pathological processes, should be taken into consideration as a part of a regulatory network governing tissue-associated stem cells' fate. This review is focusing on the published data on the effects of IL-17 on the properties and function of hematopoietic and mesenchymal stem cells and trying to discuss that IL-17 achieves many of its roles by acting on adult stem cells.

IL-17-producing CD4(+) T cells contribute to the loss of B-cell tolerance in experimental autoimmune myasthenia gravis

The role of Th17 cells in the pathogenesis of autoantibody-mediated diseases is unclear. Here, we assessed the contribution of Th17 cells to the pathogenesis of experimental autoimmune myasthenia gravis (EAMG), which is induced by repetitive immunizations with Torpedo californica acetylcholine receptor (tAChR). We show that a significant fraction of tAChR-specific CD4(+) T cells is producing IL-17. IL-17(ko) mice developed fewer or no EAMG symptoms, although the frequencies of tAChR-specific CD4(+) T cells secreting IL-2, IFN-γ, or IL-21, and the percentage of FoxP3(+) Treg cells were similar to WT mice. Even though the total anti-tAChR antibody levels were equal, the complement fixating IgG2b subtype was reduced in IL-17(ko) as compared to WT mice. Most importantly, pathogenic anti-murine AChR antibodies were significantly lower in IL-17(ko) mice. Furthermore, we confirmed the role of Th17 cells in EAMG pathogenesis by the reconstitution of TCR β/δ(ko) mice with WT or IL-17(ko) CD4(+) T cells. In conclusion, we show that the level of IgG2b and the loss of B-cell tolerance, which results in pathogenic anti-murine AChR-specific antibodies, are dependent on IL-17 production by CD4(+) T cells. Thus, we describe here for the first time how Th17 cells are involved in the induction of classical antibody-mediated autoimmunity.

Trypanosoma cruzi trans-sialidase prevents elicitation of Th1 cell response via interleukin 10 and downregulates Th1 effector cells

The trans-sialidases (TSs) from Trypanosoma cruzi, the agent of Chagas disease, are virulence factors shed to the bloodstream that induce strong alterations in the immune system. Here, we report that both enzymatically active TS (aTS) and its lectinlike isoform (iTS) disturb CD4 T cell physiology, inducing downregulation of Th1 cell functionality and in vivo cell expansion. By using ovalbumin-specific DO11.10 cells as tracers of clones developing the Th1 phenotype, we found that the infection induced significant amounts of gamma interferon (IFN-γ) but low levels of interleukin 2 (IL-2) and increased IL-4 production in vivo, in agreement with a mixed T helper response. The production of cytokines associated with the Th2 phenotype was prevented by passive transfer of anti-TS neutralizing antibodies. TSs also reduced the T cell receptor signaling as assayed by Zap-70 phosphorylation. TSs also reduced IL-2 and IFN-γ secretion, with a concomitant increase in IL-4 production and then an unbalancing of the CD4 T cell response toward the Th2 phenotype. This effect was prevented by using anti-IL-10 neutralizing antibodies or IL-10(-/-) antigen-presenting cells, supporting the subversion of this regulatory pathway. In support, TSs stimulated IL-10 secretion by antigen-presenting cells during their interaction with CD4 T cells. When polarized cells were stimulated in the presence of TSs, the secretion of IL-2 and IFN-γ was strongly downregulated in Th1 cells, while IL-2 production was upregulated in Th2 cells. Although the Th1 response is associated with host survival, it may simultaneously induce extensive damage to infected tissues. Thus, by delaying the elicitation of the Th1 response and limiting its effector properties, TSs restrain the cell response, supporting T. cruzi colonization and persistence while favoring host survival.

Tyrphostin AG126 exerts neuroprotection in CNS inflammation by a dual mechanism

The putative protein tyrosine kinase (PTK) inhibitor tyrphostin AG126 has proven beneficial in various models of inflammatory disease. Yet molecular targets and cellular mechanisms remained enigmatic. We demonstrate here that AG126 treatment has beneficial effects in experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. AG126 alleviates the clinical symptoms, diminishes encephalitogenic Th17 differentiation, reduces inflammatory CNS infiltration as well as microglia activation and attenuates myelin damage. We show that AG126 directly inhibits Bruton's tyrosine kinase (BTK), a PTK associated with B cell receptor and Toll-like receptor (TLR) signaling. However, BTK inhibition cannot account for the entire activity spectrum. Effects on TLR-induced proinflammatory cytokine expression in microglia involve AG126 hydrolysis and conversion of its dinitrile side chain to malononitrile (MN). Notably, while liberated MN can subsequently mediate critical AG126 features, full protection in EAE still requires delivery of intact AG126. Its anti-inflammatory potential and especially interference with TLR signaling thus rely on a dual mechanism encompassing BTK and a novel MN-sensitive target. Both principles bear great potential for the therapeutic management of disturbed innate and adaptive immune functions.

B cells take the front seat: dysregulated B cell signals orchestrate loss of tolerance and autoantibody production

A significant proportion of autoimmune-associated genetic variants are expressed in B cells, suggesting that B cells may play multiple roles in autoimmune pathogenesis. In this review, we highlight recent studies demonstrating that even modest alterations in B cell signaling are sufficient to promote autoimmunity. First, we describe several examples of genetic variations promoting B cell-intrinsic initiation of autoimmune germinal centers and autoantibody production. We highlight how dual antigen receptor/toll-like receptor signals greatly facilitate this process and how activated, self-reactive B cells may function as antigen presenting cells, leading to loss of T cell tolerance. Further, we propose that B cell-derived cytokines may initiate and/or sustain autoimmune germinal centers, likely also contributing, in parallel, to programing of self-reactive T cells.

B cells expressing IFN-γ suppress Treg-cell differentiation and promote autoimmune experimental arthritis

Clinical efficacy in the treatment of rheumatoid arthritis with anti-CD20 (Rituximab)-mediated B-cell depletion has garnered interest in the mechanisms by which B cells contribute to autoimmunity. We have reported that B-cell depletion in a murine model of proteoglycan-induced arthritis (PGIA) leads to an increase in Treg cells that correlate with decreased autoreactivity. Here, we demonstrate that the increase in Treg cells after B-cell depletion is due to an increase in the differentiation of naïve CD4(+) T cells into Treg cells. Since the development of PGIA is dependent on IFN-γ and B cells are reported to produce IFN-γ, we hypothesized that B-cell-specific IFN-γ plays a role in the development of PGIA. Accordingly, mice with B-cell-specific IFN-γ deficiency were as resistant to the induction of PGIA as mice that were completely IFN-γ deficient. Importantly, despite a normal frequency of IFN-γ-producing CD4(+) T cells, B-cell-specific IFN-γ-deficient mice exhibited a higher percentage of Treg cells compared with that in WT mice. These data indicate that B-cell IFN-γ production inhibits Treg-cell differentiation and exacerbates arthritis. Thus, we have established that IFN-γ, specifically derived from B cells, uniquely contributes to the pathogenesis of autoimmunity through prevention of immunoregulatory mechanisms.

Pathogen manipulation of B cells: the best defence is a good offence

B cells have long been regarded as simple antibody production units, but are now becoming known as key players in both adaptive and innate immune responses. However, several bacteria, viruses and parasites have evolved the ability to manipulate B cell functions to modulate immune responses. Pathogens can affect B cells indirectly, by attacking innate immune cells and altering the cytokine environment, and can also target B cells directly, impairing B cell-mediated immune responses. In this Review, we provide a summary of recent advances in elucidating direct B cell-pathogen interactions and highlight how targeting this specific cell population benefits different pathogens.

Clinical implications of basic science discoveries: janus resurrected--two faces of B cell and plasma cell biology

B cells play a complex role in the immune response. In addition to giving rise to plasma cells (PCs) and promoting T cell responses via antigen presentation, they perform immunoregulatory functions. This knowledge has created concerns regarding nonspecific B cell depletional therapy because of the potential to paradoxically augment immune responses. Recent studies now indicate that PCs have immune functions beyond immunoglobulin synthesis. Evidence for a new role for PCs as potent regulatory cells (via IL-10 and IL-35 production) is discussed including the implications for PC-targeted therapies currently being developed for clinical transplantation.

Extracellular vesicles in parasitic diseases

Parasitic diseases affect billions of people and are considered a major public health issue. Close to 400 species are estimated to parasitize humans, of which around 90 are responsible for great clinical burden and mortality rates. Unfortunately, they are largely neglected as they are mainly endemic to poor regions. Of relevance to this review, there is accumulating evidence of the release of extracellular vesicles (EVs) in parasitic diseases, acting both in parasite–parasite inter-communication as well as in parasite–host interactions. EVs participate in the dissemination of the pathogen and play a role in the regulation of the host immune systems. Production of EVs from parasites or parasitized cells has been described for a number of parasitic infections. In this review, we provide the most relevant findings of the involvement of EVs in intercellular communication, modulation of immune responses, involvement in pathology, and their potential as new diagnostic tools and therapeutic agents in some of the major human parasitic pathogens.

The role of B cells and humoral immunity in Mycobacterium tuberculosis infection

Mycobacterium tuberculosis remains a major public health burden. It is generally thought that while B cell- and antibody-mediated immunity plays an important role in host defense against extracellular pathogens, the primary control of intracellular microbes derives from cellular immune mechanisms. Studies on the immune regulatory mechanisms during infection with M. tuberculosis, a facultative intracellular organism, has established the importance of cell-mediated immunity in host defense during tuberculous infection. Emerging evidence suggest a role for B cell and humoral immunity in the control of intracellular pathogens, including obligatory species, through interactions with the cell-mediated immune compartment. Recent studies have shown that B cells and antibodies can significantly impact on the development of immune responses to the tubercle bacillus. In this review, we present experimental evidence supporting the notion that the importance of humoral and cellular immunity in host defense may not be entirely determined by the niche of the pathogen. A comprehensive approach that examines both humoral and cellular immunity could lead to better understanding of the immune response to M. tuberculosis.

Re-thinking the functions of IgA(+) plasma cells

The intestinal mucosa harbors the largest population of antibody (Ab)-secreting plasma cells (PC) in the human body, producing daily several grams of immunoglobulin A (IgA). IgA has many functions, serving as a first-line barrier that protects the mucosal epithelium from pathogens, toxins and food antigens (Ag), shaping the intestinal microbiota, and regulating host-commensal homeostasis. Signals induced by commensal colonization are central for regulating IgA induction, maintenance, positioning and function and the number of IgA(+) PC is dramatically reduced in neonates and germ-free (GF) animals. Recent evidence demonstrates that the innate immune effector molecules tumor necrosis factor α (TNFα) and inducible nitric oxide synthase (iNOS) are required for IgA(+) PC homeostasis during the steady state and infection. Moreover, new functions ascribed to PC independent of Ab secretion continue to emerge, suggesting that PC, including IgA(+) PC, should be re-examined in the context of inflammation and infection. Here, we outline mechanisms of IgA(+) PC generation and survival, reviewing their functions in health and disease.

Dendritic cells and B cells: unexpected partners in Th2 development

Although we have known for decades that B cells contribute to immune responses by secreting Ab, it is now clear that they are more than simply factories for Ig production, and they also play key roles as modulators of T cell-dependent immunity. Indeed, the evidence showing that Ag-presenting and cytokine-producing B cells can alter the magnitude and quality of CD4 T cell responses continues to grow. In this article, we review the data showing that B cells, working in partnership with dendritic cells, regulate the development of Th2 cells and the subsequent allergic response.

Dysregulated cytokine production by dendritic cells modulates B cell responses in the NZM2410 mouse model of lupus

The breakdown in tolerance of autoreactive B cells in the lupus-prone NZM2410-derived B6.Sle1.Sle2.Sle3 (TC) mice results in the secretion of autoantibodies. TC dendritic cells (DCs) enhance B cell proliferation and antibody secretion in a cytokine-dependent manner. However, the specific cytokine milieu by which TC DCs activate B cells was not known. In this study, we compared TC and C57BL/6 (B6) control for the distribution of DC subsets and for their production of cytokines affecting B cell responses. We show that TC DCs enhanced B cell proliferation through the production of IL-6 and IFN-γ, while antibody secretion was only dependent on IL-6. Pre-disease TC mice showed an expanded PDCA1(+) cells prior to disease onset that was localized to the marginal zone and further expanded with age. The presence of PDCA1(+) cells in the marginal zone correlated with a Type I Interferon (IFN) signature in marginal zone B cells, and this response was higher in TC than B6 mice. In vivo administration of anti-chromatin immune complexes upregulated IL-6 and IFN-γ production by splenic DCs from TC but not B6 mice. The production of BAFF and APRIL was decreased upon TC DC stimulation both in vitro and in vivo, indicating that these B cell survival factors do not play a role in B cell modulation by TC DCs. Finally, TC B cells were defective at downregulating IL-6 expression in response to anti-inflammatory apoptotic cell exposure. Overall, these results show that the TC autoimmune genetic background induces the production of B cell-modulating inflammatory cytokines by DCs, which are regulated by the microenvironment as well as the interplay between DC.

Histochemical fluorescent staining of Sendai virus-infected cells with a novel sialidase substrate

Sialidases, enzymes that remove terminal sialic acid residues, are pivotal in various biological processes such as malignancy and infection with pathogens. For histochemical staining of sialidase activity, we have developed a new synthetic sialidase substrate, sialic acid-conjugated fluorescent benzothiazolylphenol derivative (BTP3-Neu5Ac), for rapid, sensitive, and specific fluorescent staining of sialidase activity. Here, we showed the usefulness of BTP3-Neu5Ac for histochemical fluorescent staining of cells infected with Sendai virus (SV), which possesses sialidase activity. BTP3-Neu5Ac also visualised SV-infected regions of lung sections from SV-infected mice. We succeeded in histochemical fluorescent staining of SV both in vitro and in vivo. SV has been utilised in many virological and biotechnological studies such as developments of an oncolytic virus, a gene therapy vector, and a vaccine candidate. BTP3-Neu5Ac should contribute to rapid progress of such studies and researches on viral sialidase.

Human pleural B-cells regulate IFN-γ production by local T-cells and NK cells in a Mycobacterium tuberculosis-induced delayed hypersensitivity reaction

DTH (delayed type hypersensitivity) reactions are secondary cellular immune responses that appear 24-72 h after antigen exposure. Tuberculous pleurisy is a common manifestation of extrapulmonary TB (tuberculosis) and is considered a human model of Th1-mediated DTH. In order to identify functional cross-talk among cellular populations sited in this inflammatory microenvironment, we analysed phenotypic and functional features of human B-cells isolated from the PF (pleural fluid) of TB patients. Freshly isolated PF-B-cells displayed a lower expression of CD20, CD1d and HLA-DR, and a higher expression of CD95, CD38, CD25, CXCR3 (CXC chemokine receptor 3) and CXCR4 (CXC chemokine receptor 4) than their PB (peripheral blood) counterparts, suggesting a non-classical in situ activation. Although memory PF-T-cell frequencies were increased, the frequencies of memory PF-B-cells were not. We demonstrated that, upon stimulation with γ-irradiated M. tuberculosis, mycobacterially secreted proteins or a lectin mitogen, PF-B-cells had a strong activation and produced IL-10 by a mechanism that was dependent on bystander activation of CD19(-) PF cells. Besides, within PF cells, B-cells diminished in vitro M. tuberculosis-induced IFN (interferon)-γ production by T-cells and NK (natural killer) cells in an IL-10-dependent manner. Finally, we found that the lower the frequency of B-cells, the higher the ratio of IFN-γ/IL-10 within PF. Thus our results suggest that B-cells can regulate a human DTH reaction induced by M. tuberculosis.

IL-10 detection in murine B cells: pros and cons of the different techniques

With the recently increased understanding of the roles of B cells in immune response and autoimmune pathogenesis, various techniques have been used for the detection of IL-10 production in B cells. In this chapter, we describe several commonly used methods for the effective detection of IL-10 in B cells at both mRNA and protein levels, including quantitative PCR analysis, intracellular staining of IL-10 by flow cytometry, ELISA assay for secreted IL-10 detection, and ELISPOT assay of enumerating IL-10-producing B cells. Moreover, we provide a detailed protocol for the detection of IL-10-producing B cells in situ by immunofluorescence microscopy. Together, the application of these described methods for the detection of IL-10 will facilitate the characterization of B cell subsets with regulatory functions and enhance our current understanding on the critical roles of B cells in immune response and autoimmune development.

The immune potential and immunopathology of cytokine-producing B cell subsets: a comprehensive review

B lymphocytes are generally recognized for their potential to mediate humoral immunity by producing different antibody isotypes and being involved in opsonization and complement fixation. Nevertheless, the non-classical, antibody-independent immune potential of B cell subsets has attracted much attention especially in the past decade. These B cells can release a broad variety of cytokines (such as IL-2, IL-4, IL-6, IL-10, IL-17, IFN-α, IFN-γ, TNF-α, TGF-β, LT), and can be classified into distinct subsets depending on the particular cytokine profile, thus emerging the concept of cytokine-producing B cell subsets. Although there is still controversy surrounding the key cell surface markers, intracellular factors and cellular origins of cytokine-producing B cell subsets, accumulating evidence indicates that these B cells are endowed with great potential to regulate both innate and adaptive arms of immune system though releasing cytokines. On the one hand, they promote immune responses through mounting Th1/Th2/Th17 and neutrophil response, inducing DC maturation and formation of lymphoid structures, increasing NK cell and macrophage activation, enhancing development of themselves and sustaining antibody production. On the other hand, they can negatively regulate immune responses by suppressing Th cell responses, inhibiting Tr1 cell and Foxp3(+) Treg differentiation, impairing APC function and pro-inflammatory cytokine release by monocytes, and inducing CD8(+) T cell anergy and CD4(+) T cell apoptosis. Therefore, cytokine-producing B cell subsets have multifunctional functions in health and diseases, playing pathologic as well as protective roles in autoimmunity, infection, allergy, and even malignancy. In this review, we revisit the history of discovering cytokine-producing B cells, describe the identification of cytokine-producing B cell subsets, introduce the origins of cytokine-producing B cell subsets as well as molecular and cellular mechanisms for their differentiation, and summarize the recent progress made toward understanding the unexpectedly complex and potentially opposing roles of cytokine-producing B cells in immunological disorders.

Plasma cells in immunopathology: concepts and therapeutic strategies

Plasma cells are terminally differentiated B cells that secrete antibodies, important for immune protection, but also contribute to any allergic and autoimmune disease. There is increasing evidence that plasma cell populations exhibit a considerable degree of heterogeneity with respect to their immunophenotype, migration behavior, lifetime, and susceptibility to immunosuppressive drugs. Pathogenic long-lived plasma cells are refractory to existing therapies. In contrast, short-lived plasma cells can be depleted by steroids and cytostatic drugs. Therefore, long-lived plasma cells are responsible for therapy-resistant autoantibodies and resemble a challenge for the therapy of antibody-mediated autoimmune diseases. Both lifetime and therapy resistance of plasma cells are supported by factors produced within their microenviromental niches. Current results suggest that plasma cell differentiation and survival factors such as IL-6 also signal via mammalian miRNAs within the plasma cell to modulate downstream transcription factors. Recent evidence also suggests that plasma cells and/or their immediate precursors (plasmablasts) can produce important cytokines and act as antigen-presenting cells, exhibiting so far underestimated roles in immune regulation and bone homeostasis. Here, we provide an overview on plasma cell biology and discuss exciting, experimental, and potential therapeutic approaches to eliminate pathogenic plasma cells.

B-cell modulation of dendritic-cell function: signals from the far side

An appropriate immune response against a specific pathogen requires finely orchestrated interactions between the various cell populations within the immune system. At the same time, immunological tolerance to self must be maintained. DCs play an essential role in achieving these dual requisites. They coordinate adaptive immunity by integrating signals directly emanating from both infectious agents and cells of the immune system. Many such signals, especially those from innate cells and T cells, have been extensively characterized. In contrast, little is known about how B cells modulate function of DCs. B cells produce a variety of cytokines, including IL-10 and IL-6, which are known to influence DC function. In addition, Igs constitute the major secretory products of terminally differentiated B cells (plasma cells). DCs express various types of receptors for binding Ig, such as Fc receptors and C-type lectin receptors. In accordance, Igs can regulate DC function depending on the receptors engaged. Here, we review the emerging immunomodulatory role of cytokines and Ig secreted by B cells. We discuss the evidence for how these B-cell-derived factors may shape the adaptive immune response by directly acting on DCs.

From the regulatory functions of B cells to the identification of cytokine-producing plasma cell subsets

B lymphocytes have a unique role as antibody-producing cells. Antibodies are key mediators of humoral immunity against infections, and are thought to account for the protection afforded by successful vaccines. B cells can also secrete cytokines and subsequently regulate immune responses mediated by T and innate cells. Remarkably, recent studies identified plasma blasts/plasma cells as the main types of activated B cells producing the cytokines interleukin (IL)-10, IL-35, tumor necrosis factor (TNF)-α, IL-17, and GM-CSF in various contexts in mice. Here, we discuss these observations, which suggest the existence of various subsets of plasma blast/plasma cells distinguishable through their cytokine expression pattern.

Parasites: what are they good for?

Parasitic diseases caused by helminth and protozoan infections remain one of the largest global public health problems for mankind. While natural immunity in man is rare or slow to develop for many parasites, the immune response is capable of recognizing and responding to infection by utilizing a number of different immunological mechanisms. This special topics journal issue examines many of the key findings in the recent literature regarding the immune response against helminth and protozoan infections, as well as highlighting areas in which our current knowledge falls short. The question of how we can tailor immune responses to prevent or reduce disease burden is a burning question within the field of immunoparasitology.

The Role of Sialic Acid-Binding Receptors (Siglecs) in the Immunomodulatory Effects of Trypanosoma cruzi Sialoglycoproteins on the Protective Immunity of the Host

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and is an important endemic infection in Latin America. Lately, it has also become a health concern in the United States and Europe. Most of the immunomodulatory mechanisms associated with this parasitic infection have been attributed to mucin-like molecules on the T. cruzi surface. Mucins are high molecular weight glycoproteins that are involved in regulating diverse cellular activities in both normal and pathological conditions. In Trypanosoma cruzi infection, the parasite-derived mucins are the main acceptors of sialic acid and it has been suggested that they play a role in various host-parasite interactions during the course of Chagas disease. Recently, we have presented evidence that sialylation of the mucins is required for the inhibitory effects on CD4(+) T cells. In what follows we propose that signaling via sialic acid-binding Ig-like lectin receptors for these highly sialylated structures on host cells contributes to the arrest of cell cycle progression in the G1 phase and may allow the parasite to modulate the immune system of the host.

Innate IFNγ-producing B cells

In a recent paper published in Cell Research, Yan Bao and colleagues characterize a new population of IFNγ-producing innate-like B cells that promotes innate immune responses and contributes to early pathogen control following intracellular bacterial infection.

B cells contribute to heterogeneity of IL-17 producing cells in rheumatoid arthritis and healthy controls

Secretion of the proinflammatory cytokine Interleukin-17A (IL-17A) is the hallmark of a unique lineage of CD4 T cells designated Th17 cells, which may play a crucial role in the pathogenesis of rheumatoid arthritis (RA) and many autoimmune diseases. Recently, IL-17-producing cells other than T cells have been described, including diverse innate immune cells. Here, we show that the cellular sources of IL-17A in RA include a significant number of non-T cells. Multicolour fluorescence analysis of IL-17-expressing peripheral blood mononuclear cells (PBMC) revealed larger proportions of IL-17⁺CD3^- non-T cells in RA patients than in healthy controls (constitutive, 13.6% vs. 8.4%, and after stimulation with PMA/ionomycin 17.4% vs. 7.9% p < 0.001 in both cases). The source of IL-17 included CD3^-CD56⁺ NK cells, CD3^-CD14⁺ myeloid cells as well as the expected CD3⁺CD4⁺ Th17 cells and surprisingly a substantial number of CD3^-CD19⁺ B cells. The presence of IL-17A-expressing B cells was confirmed by specific PCR of peripheral MACS-sorted CD19⁺ B cells, as well as by the analysis of different EBV-transformed B cell lines. Here we report for the first time that in addition to Th17 cells and different innate immune cells B cells also contribute to the IL-17A found in RA patients and healthy controls.

Identification of IFN-γ-producing innate B cells

Although B cells play important roles in the humoral immune response and the regulation of adaptive immunity, B cell subpopulations with unique phenotypes, particularly those with non-classical immune functions, should be further investigated. By challenging mice with Listeria monocytogenes, Escherichia coli, vesicular stomatitis virus and Toll-like receptor ligands, we identified an inducible CD11a(hi)FcγRIII(hi) B cell subpopulation that is significantly expanded and produces high levels of IFN-γ during the early stage of the immune response. This subpopulation of B cells can promote macrophage activation via generating IFN-γ, thereby facilitating the innate immune response against intracellular bacterial infection. As this new subpopulation is of B cell origin and exhibits the phenotypic characteristics of B cells, we designated these cells as IFN-γ-producing innate B cells. Dendritic cells were essential for the inducible generation of these innate B cells from the follicular B cells via CD40L-CD40 ligation. Increased Bruton's tyrosine kinase activation was found to be responsible for the increased activation of non-canonical NF-κB pathway in these innate B cells after CD40 ligation, with the consequent induction of additional IFN-γ production. The identification of this new population of innate B cells may contribute to a better understanding of B cell functions in anti-infection immune responses and immune regulation.

Role of Th17 cells in the pathogenesis of rheumatoid arthritis

Since early description of CD4/CD8 T cell duality, continuous discovery of functional T lymphocyte subsets and their related cytokines constitutes major progress in our understanding of the immune response. T-lymphocyte derived lymphokines and environmental cytokines are essential for both innate and antigen-specific immune responses to a wide variety of agents. Following immune battle and aggression overcome, cytokines may return against neighbored cells/organs, causing pathogenic hypersensitivity reactions, including autoimmune diseases. Due to their cytokine production, CD4⁺ T helper lymphocyte subsets may be considered as one the major players of the immune response. Among CD4⁺ T cell subsets, the identification of interleukin-17-producing cells (Th17) led to better understanding of coordinated cytokine involvement during inflammatory reactions together with the subsequent clarification of complex interactions between these mediators. In this review, we discuss Th17 cell differentiation, functions, and the role of this cell subset during rheumatoid arthritis pathogenesis together with therapeutic strategies to control these cells.

Inhibitory effects of Trypanosoma cruzi sialoglycoproteins on CD4+ T cells are associated with increased susceptibility to infection

Background

The Trypanosoma cruzi infection is associated with severe T cell unresponsiveness to antigens and mitogens characterized by decreased IL-2 synthesis. Trypanosoma cruzi mucin (Tc Muc) has been implicated in this phenomenom. These molecules contain a unique type of glycosylation consisting of several sialylated O-glycans linked to the protein backbone via N-acetylglucosamine residues.

Methodology/Principal Findings

In this study, we evaluated the ability of Tc Muc to modulate the activation of CD4⁺ T cells. Our data show that cross-linking of CD3 on naïve CD4⁺ T cells in the presence of Tc Muc resulted in the inhibition of both cytokine secretion and proliferation. We further show that the sialylated O-Linked Glycan residues from tc mucin potentiate the suppression of T cell response by inducing G1-phase cell cycle arrest associated with upregulation of mitogen inhibitor p27^kip1. These inhibitory effects cannot be reversed by the addition of exogenous IL-2, rendering CD4⁺ T cells anergic when activated by TCR triggering. Additionally, in vivo administration of Tc Muc during T. cruzi infection enhanced parasitemia and aggravated heart damage. Analysis of recall responses during infection showed lower frequencies of IFN-γ producing CD4⁺ T cells in the spleen of Tc Muc treated mice, compared to untreated controls.

Conclusions/Significance

Our results indicate that Tc Muc mediates inhibitory efects on CD4⁺ T expansion and cytokine production, by blocking cell cycle progression in the G1 phase. We propose that the sialyl motif of Tc Muc is able to interact with sialic acid-binding Ig-like lectins (Siglecs) on CD4⁺ T cells, which may allow the parasite to modulate the immune system.

Therapeutic potential of interleukin-17 in inflammation and autoimmune diseases

INTRODUCTION

Interleukin-17 (IL-17) is a proinflammatory cytokine that mainly produced by T helper 17 (Th17) cells. In this article, we discussed the role of IL-17 in inflammation and autoimmune diseases, and the therapeutic strategies targeting IL-17.

AREAS COVERED

In this article, we discussed the proinflammatory cytokine IL-17 and IL-17 receptors signals, and their regulation. IL-17 expression was abnormal in the bacterium, virus and fungus infection, and its higher level caused the tissue inflammation. IL-17 was involved in the pathological process of autoimmune diseases, such as systemic sclerosis, rheumatoid arthritis, ankylosing spondylitis and systemic lupus erythematosus, and IL-17 has been put as a therapeutic target in the clinic.

EXPERT OPINION

IL-17/IL-17R signals and their application in inflammation process still need to be explored. Therapeutic strategies targeting IL-17 in autoimmune diseases ameliorated the inadequate response to anti-TNF-α therapy.

Identification of trans-sialidases as a common mediator of endothelial cell activation by African trypanosomes

Understanding African Trypanosomiasis (AT) host-pathogen interaction is the key to an "anti-disease vaccine", a novel strategy to control AT. Here we provide a better insight into this poorly described interaction by characterizing the activation of a panel of endothelial cells by bloodstream forms of four African trypanosome species, known to interact with host endothelium. T. congolense, T. vivax, and T. b. gambiense activated the endothelial NF-κB pathway, but interestingly, not T. b. brucei. The parasitic TS (trans-sialidases) mediated this NF-κB activation, remarkably via their lectin-like domain and induced production of pro-inflammatory molecules not only in vitro but also in vivo, suggesting a considerable impact on pathogenesis. For the first time, TS activity was identified in T. b. gambiense BSF which distinguishes it from the subspecies T. b. brucei. The corresponding TS were characterized and shown to activate endothelial cells, suggesting that TS represent a common mediator of endothelium activation among trypanosome species with divergent physiopathologies.

Molecular mechanisms and cell targets of Th17 cells in the gastrointestinal tract: an innate sense of adaptivity

T-helper (TH) 17 activation is crucial for protective immune responses against bacteria and fungi at mucosal surfaces, but it can also be implicated in the pathogenesis of several autoimmune and chronic inflammatory diseases, such as inflammatory bowel diseases (IBD). Although rapid progress was made elucidating induction and functional heterogeneity of Th17 responses, the underlying molecular effects of Th17 response including the most relevant different cell targets of Th17 cytokines remain poorly understood. Cytokines produced by Th17 cells have broad effects on both hematopoietic and nonhematopoietic cells and can act in synergy with various inflammatory factors. In this review, we will focus on the effects of Th17-derived cytokines in the gastrointestinal tract and discuss how Th17 responses can affect both innate and adaptive immunity and may contribute to the pathogenesis of inflammatory GI processes.

IL-17 family: cytokines, receptors and signaling

The interleukin 17 (IL-17) family, a subset of cytokines consisting of IL-17A-F, plays crucial roles in host defense against microbial organisms and in the development of inflammatory diseases. Although IL-17A is the signature cytokine produced by T helper 17 (Th17) cells, IL-17A and other IL-17 family cytokines have multiple sources ranging from immune cells to non-immune cells. The IL-17 family signals via their correspondent receptors and activates downstream pathways that include NFκB, MAPKs and C/EBPs to induce the expression of anti-microbial peptides, cytokines and chemokines. The proximal adaptor Act1 is a common mediator during the signaling of all IL-17 cytokines so far and is thus involved in IL-17 mediated host defense and IL-17-driven autoimmune conditions. This review will give an overview and recent updates on the IL-17 family, the activation and regulation of IL-17 signaling as well as diseases associated with this cytokine family.

IL-17 family cytokines mediated signaling in the pathogenesis of inflammatory diseases

Inflammation is the immediate protective response of the body to pathogen invasions, allergen challenges, chemical exposures or physical injuries. Acute inflammation usually accompanies with transient infiltration of leukocytes, removal of danger signals and eventually tissue repair, while persistent and uncontrolled inflammation becomes a major stimulator in the progression of many chronic diseases in human, including autoimmune diseases, metabolic disorders and cancer. Interleukin (IL)-17 family is a recent classified subset of cytokines, playing critical roles in both acute and chronic inflammatory responses. In this review, we will summarize recent progresses on the signalings of this family cytokines and their impacts on the inflammatory responses or disorders.

IL-17 in the rheumatologist's line of sight

Over the past decades, the identification of several new cytokines, including interleukin (IL)-17 and IL-23, and of new T helper cell subsets, including Th17 cells, has changed the vision of immunological processes. The IL-17/Th17 pathway plays a critical role during the development of inflammation and autoimmunity, and targeting this pathway has become an attractive strategy for a number of diseases. This review aims to describe the effects of IL-17 in the joint and its roles in the development of autoimmune and inflammatory arthritis. Furthermore, biotherapies targeting directly or indirectly IL-17 in inflammatory rheumatisms will be developed.