Pathogenic Th17 Responses Research Articles

Differential c-type lectin receptor expression correlates with the magnitude of pathology in murine schistosomiasis (55.4)

Abstract In murine schistosomiasis, immunopathology and cytokine production in response to schistosome eggs is uneven and strain dependent. Infected CBA mice develop severe hepatic egg-induced granulomatous inflammation associated with prominent Th17 and Th1 cytokine responses, whereas in BL/6 mice milder lesions develop in a Th2-dominant cytokine environment. The pathogenic Th17 response in CBA mice is largely dependent on IL-1β and IL-23 produced by schistosome egg-stimulated dendritic cells (DC); by comparison, this pro-inflammatory cytokine pathway fails to materialize in low-pathology BL/6 mice. Whereas requirements for Th17 cell differentiation elicited by CBA DC are apparent, the reason for such a strain difference in APC reactivity to live eggs is not known. Initial gene profiling disclosed a significant difference in C-type lectin receptor (CLR) expression between CBA and BL/6 bone marrow derived DC. CLR are pattern recognition receptors capable of binding carbohydrates, including those secreted by schistosome eggs. A significant increase in CLR expression, particularly murine homologues of human DC-specific ICAM-3-grabbing non-integrin (DC-SIGN), was documented by real-time PCR and flow cytometry on tissues from infected CBA mice, including liver, spleen and granuloma cells. Current work is aimed at elucidating the functional implications of differential CLR expression on T cell subset differentiation, activation and pathogenicity during the schistosome infection.

Novel cytokine signaling pathways in inflammatory bowel disease: insight into the dichotomous functions of IL-33 during chronic intestinal inflammation

In 2010, four independent groups almost simultaneously reported the association of the novel interleukin-1 (IL-1) family member, IL-33, with inflammatory bowel disease (IBD). The findings were remarkably consistent and demonstrated that IL-33 is markedly upregulated in, and specific to, ulcerative colitis (UC). In addition, although a variety of gut-associated immune cell subsets express IL-33, the primary source appears to be the intestinal epithelium. IL-33's receptor, ST2, a formerly orphaned IL-1 receptor-related protein, was also found to be increased in UC patients, although the cellular source of ST2 appears to be somewhat more ambiguous. In fact, emerging evidence indicates that the IL-33/ST2 axis plays a critical role in several other chronic inflammatory and immune disorders. In the gut, IL-33 has been shown to be important in the clearance of intestinal parasites, and inducing epithelial cell hyperplasia, mucus production and mucosal eosinophilic infiltration. However, despite the established trend of increased IL-33 and ST2 expression during IBD, specifically UC, the precise pathophysiologic relevance of these findings has yet to be determined. Interestingly, IL-33 has the ability to potentiate pathogenic Th2 and Th17 responses in gut-associated lymphoid tissues, while also promoting healing of damaged mucosa following inflammatory insults. Indeed, further mechanistic studies are warranted to confirm the possible dichotomous functions of IL-33 during chronic intestinal inflammation and better define its precise role in the pathogenesis of IBD. Herein, we discuss what is currently known about IL-33/ST2 in the gut and speculate as to the potential role of the IL-33/ST2 system in IBD.

An essential protective role of IL-10 in the immunological mechanism underlying resistance vs susceptibility to lupus induction by dendritic cells and dying cells

Objective. To define the role of IL-10 in lupus pathogenesis, and to understand the immunological mechanisms underlying resistance vs susceptibility to lupus disease induction by dendritic cells (DCs) and dying cells.Methods. Groups of IL-10-deficient and normal C57BL/6 mice were injected with syngenic DCs that had ingested necrotic cells prepared by either freeze–thaw cycle (DC/necF/T) or heat shock (DC/necH/S) procedures, or with DC or necrotic cells alone, or with PBS only. Disease development, including proteinuria and renal pathological changes, was monitored. Levels of autoantibodies against different lupus-associated nuclear antigens were measured by ELISAs, and IC deposition in the kidneys was confirmed by immunostaining.Results. No significant proteinuria was detected in the mice. However, striking renal pathological changes typical of IC-mediated GN were consistently observed in the DC/necF/T-treated IL-10−/− mice. These included glomerular hypercellularity and macrophage infiltration, renal IC deposition, circulating kidney-reactive autoantibodies and the presence of immunoglobulin G2 isotype-specific antibody complexes in the diseased kidneys. We demonstrated further that host-derived IL-10 was primarily responsible for protecting against the induction of pathogenic Th1 type of autoantibody responses in the mice.Conclusion. IL-10 protects against the induction of lupus-like renal end-organ damage by down-regulating pathogenic Th1 responses.

Serum Amyloid A Activates the NLRP3 Inflammasome and Promotes Th17 Allergic Asthma in Mice

IL-1β is a cytokine critical to several inflammatory diseases in which pathogenic Th17 responses are implicated. Activation of the NLRP3 inflammasome by microbial and environmental stimuli can enable the caspase-1-dependent processing and secretion of IL-1β. The acute-phase protein serum amyloid A (SAA) is highly induced during inflammatory responses, wherein it participates in systemic modulation of innate and adaptive immune responses. Elevated levels of IL-1β, SAA, and IL-17 are present in subjects with severe allergic asthma, yet the mechanistic relationship among these mediators has yet to be identified. In this study, we demonstrate that Saa3 is expressed in the lungs of mice exposed to several mixed Th2/Th17-polarizing allergic sensitization regimens. SAA instillation into the lungs elicits robust TLR2-, MyD88-, and IL-1-dependent pulmonary neutrophilic inflammation. Furthermore, SAA drives production of IL-1α, IL-1β, IL-6, IL-23, and PGE(2), causes dendritic cell (DC) maturation, and requires TLR2, MyD88, and the NLRP3 inflammasome for secretion of IL-1β by DCs and macrophages. CD4(+) T cells polyclonally stimulated in the presence of conditioned media from SAA-exposed DCs produced IL-17, and the capacity of polyclonally stimulated splenocytes to secrete IL-17 is dependent upon IL-1, TLR2, and the NLRP3 inflammasome. Additionally, in a model of allergic airway inflammation, administration of SAA to the lungs functions as an adjuvant to sensitize mice to inhaled OVA, resulting in leukocyte influx after Ag challenge and a predominance of IL-17 production from restimulated splenocytes that is dependent upon IL-1R signaling.

Preferential induction of protective T cell responses to Theiler’s virus in resistant (C57BL/6 x SJL)F1 mice (67.14)

Abstract Infection of the CNS with Theiler's murine encephalomyelitis virus (TMEV) induces an immune-mediated demyelinating disease in susceptible mouse strains such as SJL/J (H-2(s)), but not in strains such as C57BL/6 (H-2(b)). In addition, it has been shown that (SJL/J x C57BL/6)F1 mice, which carry both resistant and susceptible MHC haplotypes (H-2(b/s)), are resistant to both viral persistence and TMEV-induced demyelinating disease. In this study, we further analyzed the immune responses underlying resistance of F1 mice. Our study shows that the resistance of F1 mice is associated with a higher level of the initial virus-specific H-2(b)-restricted CD8(+) T cell responses vs. the H-2(s)-restricted CD8(+) T cell responses. In contrast, pathogenic Th17 responses to viral epitopes are lower in F1 mice compared to that in susceptible SJL mice. Dominant effects of resistant genes expressed in antigen-presenting cells of F1 mice on regulating viral replication and inducing protective T cell responses appear to play a crucial role in disease resistance. Although the F1 mice are resistant to disease, the level of viral RNA in the CNS was intermediate between those of SJL/J and C57BL/6 mice, indicating the presence of a threshold of viral expression for pathogenesis.

Preferential Induction of Protective T Cell Responses to Theiler's Virus in Resistant (C57BL/6 × SJL)F1 Mice

Infection of the central nervous system (CNS) with Theiler's murine encephalomyelitis virus (TMEV) induces an immune-mediated demyelinating disease in susceptible mouse strains such as SJL/J (H-2(s)) but not in strains such as C57BL/6 (H-2(b)). In addition, it has been shown that (C57BL/6 × SJL/J)F1 mice (F1 mice), which carry both resistant and susceptible MHC haplotypes (H-2(b/s)), are resistant to both viral persistence and TMEV-induced demyelinating disease. In this study, we further analyzed the immune responses underlying the resistance of F1 mice. Our study shows that the resistance of F1 mice is associated with a higher level of the initial virus-specific H-2(b)-restricted CD8(+) T cell responses than of the H-2(s)-restricted CD8(+) T cell responses. In contrast, pathogenic Th17 responses to viral epitopes are lower in F1 mice than in susceptible SJL/J mice. Dominant effects of resistant genes expressed in antigen-presenting cells of F1 mice on regulation of viral replication and induction of protective T cell responses appear to play a crucial role in disease resistance. Although the F1 mice are resistant to disease, the level of viral RNA in the CNS was intermediate between those of SJL/J and C57BL/6 mice, indicating the presence of a threshold of viral expression for pathogenesis.

Retinoic Acid Increases Foxp3+ Regulatory T Cells and Inhibits Development of Th17 Cells by Enhancing TGF-β-Driven Smad3 Signaling and Inhibiting IL-6 and IL-23 Receptor Expression

The de novo generation of Foxp3+ regulatory T (Treg) cells in the peripheral immune compartment and the differentiation of Th17 cells both require TGF-beta, and IL-6 and IL-21 are switch factors that drive the development of Th17 cells at the expense of Treg cell generation. The major vitamin A metabolite all-trans retinoic acid (RA) not only enforces the generation of Treg cells but also inhibits the differentiation of Th17 cells. Herein we show that RA enhances TGF-beta signaling by increasing the expression and phosphorylation of Smad3, and this results in increased Foxp3 expression even in the presence of IL-6 or IL-21. RA also inhibits the expression of IL-6Ralpha, IRF-4, and IL-23R and thus inhibits Th17 development. In vitro, RA significantly promotes Treg cell conversion, but in vivo during the development of experimental autoimmune encephalomyelitis it does not increase the frequency of Treg cells in the face of an ongoing inflammation. However, RA suppresses the disease very efficiently by inhibiting proinflammatory T cell responses, especially pathogenic Th17 responses. These data not only identify the signaling mechanisms by which RA can affect both Treg cell and Th17 differentiation, but they also highlight that in vivo during an autoimmune reaction, RA suppresses autoimmunity mainly by inhibiting the generation of effector Th17 cells.

The new water‐soluble artemisinin derivative SM905 ameliorates collagen‐induced arthritis by suppression of inflammatory and Th17 responses

Our previous study showed that SM905, a novel artemisinin derivative, exhibited potent immunosuppressive activity. In this study, we evaluate preventive and therapeutic effect of SM905 on collagen-induced arthritis (CIA) in DBA/1 mice, and investigate its mechanisms both in inflammatory and autoimmune aspects of the disease. CIA was induced by type II bovine collagen (CII) in DBA/1 mice. SM905 was given orally either before (continuously 1 day before booster immunization) or after disease onset (continuously 14 days after booster immunization). Disease incidence and severity were monitored, mRNA expression of proinflammatory mediators was determined by real-time PCR, purified T cell proliferation was assessed using [(3)H]-thymidine incorporated assay, and T helper (Th) 17/Th1/Th2 type cytokine production was examined by ELISA. Oral treatment with SM905 delayed disease onset, reduced arthritis incidence and severity, and suppressed the enhanced expression of pro-inflammatory cytokines, chemokines and chemokine receptors in draining lymph nodes. The CII-induced T cell proliferation and production of interleukin (IL)-17A by T cells were strikingly inhibited. Correspondingly, the mRNA expression of IL-17A and RORgamma t (a specific transcription factor for Th17) was also reduced. This effect was coupled with a striking reduction of IL-6 production, which has a critical role in Th17 development. In established arthritis, SM905 profoundly inhibited disease progression, reduced IL-17A and RORgamma t mRNA expression, and suppressed pro-inflammatory mediator expression in arthritic joints. SM905 had beneficial effects on CIA by suppressing inflammatory and pathogenic Th17 responses.

Epicutaneous Immunization with Type II Collagen Inhibits both Onset and Progression of Chronic Collagen-Induced Arthritis

Epicutaneous immunization is a potential non-invasive technique for antigen-specific immune-modulation. Topical application of protein antigens to barrier-disrupted skin induces potent antigen-specific immunity with a strong Th2-bias. In this study, we investigate whether the autoimmune inflammatory response of chronic collagen-induced arthritis (CCIA) in DBA/1-TCR-β Tg mice can be modified by epicutaneous immunization. We show that epicutaneous immunization with type II collagen (CII) inhibited development and progression of CCIA and, importantly, also ameliorated ongoing disease as indicated by clinical scores of disease severity, paw swelling and joints histology. Treated mice show reduced CII-driven T cell proliferation and IFN-γ production, as well as significantly lower levels of CII-specific IgG2a serum antibodies. In contrast, CII-driven IL-4 production and IgE antibody levels were increased consistent with skewing of the CII response from Th1 to Th2 in treated mice. IL-4 production in treated mice was inversely correlated with disease severity. Moreover, T cells from treated mice inhibited proliferation and IFN-γ production by T cells from CCIA mice, suggesting induction of regulatory T cells that actively inhibit effector responses in arthritic mice. The levels of CD4+CD25+ T cells were however not increased following epicutaneous CII treatment. Together, these results suggest that epicutaneous immunization may be used as an immune-modulating procedure to actively re-programme pathogenic Th1 responses, and could have potential as a novel specific and simple treatment for chronic autoimmune inflammatory diseases such as rheumatoid arthritis.

Antigen Presentation in the CNS by Myeloid Dendritic Cells Drives Progression of Relapsing Experimental Autoimmune Encephalomyelitis

Chronic progression of relapsing experimental autoimmune encephalomyelitis (R-EAE), a mouse model of multiple sclerosis (MS), is dependent on the activation of T cells to endogenous myelin epitopes, that is, epitope spreading. This review focuses on the cellular and molecular mechanisms underlying the process of epitope spreading. Surprisingly, activation of naïve T cells to endogenous myelin epitopes in SJL mice undergoing R-EAE occurs directly in the central nervous system (CNS), a site generally perceived to be immunologically privileged. Determination of the antigen presentation capacity of antigen-presenting cell (APC) populations purified from the CNS of mice with established R-EAE shows that peripherally derived CD11b(+)CD11c(+)CD45(hi) myeloid dendritic cells (mDCs) most efficiently present endogenous myelin antigens to activate both preactivated effector myelin-specific T cells and naïve T cells. The mDCs, which drive epitope spreading, preferentially polarize pathogenic Th17 responses correlating with their enhanced expression of TGF-beta1, IL-6, and IL-23. Both B220(+)CD11c(+) plasmacytoid (pDCs) and CD8alpha(+)CD11c(+) (CD8 DCs) were superior to CD11b(+)CD11c(-)CD45(hi) macrophages, but less efficient than mDCs at presenting endogenous peptide to induce Th17 cells. In contrast, CNS-resident CD11b(+)CD11c(-)CD45(low) microglia purified from the inflamed CNS were found to be largely incapable of activating either naïve or effector T cells.

Regulation of Protective and Pathogenic Th17 Responses

The recent description of a T helper lymphocyte subset (Th17) that is characterized by the production of IL-17, TNF-α , IL-6, IL-22, and GM-CSF has substantially influenced current concepts of the pathogenesis of inflammatory diseases such as arthritis or encephalitis. Contrasting with the prevailing dogma that held IFN-γ producing Th1 cells responsible for the pathogenesis of most organ-specific autoimmune diseases it had been noted for some time that IFN-γ-/- mice were more susceptible to arthritis and encephalitis than their wild-type, littermates and that IL-12 was dispensable for disease induction. Recently it has become clear, that Th17 cells are of central importance for the pathogenesis of inflammatory diseases. The differentiation of naive Th cells into Th17 is triggered by antigen recognition in the presence of both IL-6 and TGF-β . IL-23, a heterodimeric cytokine which shares the p40 chain with IL-12 is an important survival factor for Th17 whereas IL-27, another member of the IL-12 family strongly inhibits Th17 production. Here we review the protective and pathogenic functions of Th17 in host defense and inflammatory diseases. Keywords: IL-17, IL-23, Th17, infection, autoimmunity, arthritis

Regulation of Protective and Pathogenic Th17 Responses

Regulation of Protective and Pathogenic Th17 Responses

Peptide-Specific CD8 T Regulatory Cells Use IFN-γ to Elaborate TGF-β-Based Suppression

We identified a murine peptide-specific CD8 T regulatory cell population able to suppress responding CD4 T cells. Immunization with OVA, poly(I:C), and anti-4-1BB generated a population of SIINFEKL-specific CD8 T regulatory cells that profoundly inhibited peptide-responding CD4 T cells from cellular division. The mechanism of suppression required IFN-gamma, but IFN-gamma alone was not sufficient to suppress the responding CD4 T cells. The data show that CD8 T regulatory cells were unable to suppress unless they engaged IFN-gamma. Furthermore, even in the absence of recall with peptide, the CD8 T regulatory cells suppressed CD4 responses as long as IFN-gamma was present. To examine the effector mechanism of suppression, we showed that neutralizing TGF-beta inhibited suppression because inclusion of anti-TGF-beta rescued the proliferative capacity of the responding cells. TGF-beta-based suppression was dependent completely upon the CD8 T regulatory cells being capable of binding IFN-gamma. This was the case, although peptide recall of primed IFN-gamma (-/-) or IFN-gammaR(-/-) CD8 T cells up-regulated pro-TGF-beta protein as measured by surface latency-associated peptide expression but yet were unable to suppress. Finally, we asked whether the CD8 T regulatory cells were exposed to active TGF-beta in vivo and showed that only wild-type CD8 T regulatory cells expressed the TGF-beta-dependent biomarker CD103, suggesting that latency-associated peptide expression is not always congruent with elaboration of active TGF-beta. These data define a novel mechanism whereby IFN-gamma directly stimulates CD8 T regulatory cells to elaborate TGF-beta-based suppression. Ultimately, this mechanism may permit regulation of pathogenic Th1 responses by CD8 T regulatory cells.

Modulation of the immune response by the cholera-like enterotoxins.

Cholera toxins and heat labile enterotoxin from E. coli differ from most soluble proteins in eliciting systemic immunity both against themselves and unrelated admixed antigens, rather than tolerance following administration to a mucosal surface. Several reports have also demonstrated preferential induction of Th2-type responses when these molecules are used as adjuvants. Conversely, these proteins and their non-toxic derivatives, including the B sub-units are also able prevent and alleviate autoimmune diseases in naïve and systemically immune hosts demonstrating wide-ranging effects on the immune system. The recent observation that amelioration of autoimmune disease is associated with the generation of regulatory T cells which inhibit pathogenic Th1 responses may also help to consolidate these two apparently contradictory outcomes of exposure to the cholera-like enterotoxins. Furthermore, the observation that EtxB is able to alleviate autoimmune disease in the absence of conjugation to autoantigen highlights its potential for use in the clinical setting where the target antigen is often unknown. Direct effects on T cells, B cells and APC have been demonstrated in vitro which have provided insights into how these molecules may elicit these diverse effects. Further investigation is required for elucidation of the mechanisms of action of adjuvanticity and tolerance induction by these molecules to realise their potential for use in vaccines and therapies for autoimmune disease in humans.

A critical role for transforming growth factor-beta but not interleukin 4 in the suppression of T helper type 1-mediated colitis by CD45RB(low) CD4+ T cells.

A T helper type 1 (Th1)-mediated colitis with similarities to inflammatory bowel disease in humans developed in severe combined immunodeficiency mice reconstituted with CD45RB(high) CD4+ splenic T cells and could be prevented by cotransfer of CD45RB(low) CD4+ T cells. Inhibition of this Th1 response by the CD45RB(low) T cell population could be reversed in vivo by an anti-transforming growth factor (TGF) beta antibody. Interleukin (IL) 4 was not required for either the differentiation of function of protective cells as CD45RB(low) CD4+ cells from IL-4-deficient mice were fully effective. These results identify a subpopulation of peripheral CD4+ cells and TGF-beta as critical components of the natural immune regulatory mechanism, which prevents the development of pathogenic Th1 responses in the gut, and suggests that this immunoregulatory population is distinct from Th2 cells.

Regulatory interactions between CD45RBhigh and CD45RBlow CD4+ T cells are important for the balance between protective and pathogenic cell-mediated immunity.

BALB/c mice infected with the intracellular protozoan Leishmania major mount a T helper cell 2 (Th2) response that fails to control growth of the parasite and results in the development of visceral leishmaniasis. Separation of CD4+ T cells into CD45RBhigh and CD45RBlow subsets showed that the L. major-specific Th2 cells were contained within the CD45RBlow population as these cells produced high levels of antigen-specific interleukin 4 (IL-4) in vitro and transferred a nonhealing response to L. major-infected C.B-17 scid mice. In contrast, the CD45RBhighCD4+ population contained L. major-reactive cells that produced interferon gamma (IFN-gamma) in vitro and transferred a healing Th1 response to L. major-infected C.B-17 scid mice. Transfer of the Th1 response by the CD45RBhigh population was inhibited by the CD45RBlow population by a mechanism that was dependent on IL-4. These data indicate that L. major-specific Th1 cells do develop in BALB/c mice, but their functional expression is actively inhibited by production of IL-4 by Th2 cells. In this response, the suppressed Th1 cells can be phenotypically distinguished from the suppressive Th2 cells by the level of expression of CD45RB. Although the CD45RBhigh population mediated a protective response to L. major, C.B-17 scid mice restored with this population developed a severe inflammatory response in the colon that was independent of L. major infection, and was prevented by cotransfer of the CD45RBlow population. The colitis appeared to be due to a dysregulated Th1 response as anti-IFN-gamma, but not anti-IL-4, prevented it. Taken together, the data show that the CD4+ T cell population identified by high level expression of the CD45RB antigen contains cells that mediate both protective and pathogenic Th1 responses and that the reciprocal CD45RBlow population can suppress both of these responses. Whether suppression of cell-mediated immunity is beneficial or not depends on the nature of the stimulus, being deleterious during L. major infection but crucial for control of potentially pathogenic inflammatory responses developing in the gut.