Interleukin-10 (IL-10) is elevated in cancer and is thought to contribute to immune tolerance and tumor growth. Defying these expectations, the adoptive transfer of IL-10 expressing T-cells to mice with polyposis attenuates microbial-induced inflammation and suppresses polyposis. To gain better insights into how IL-10 impacts polyposis, we genetically ablated IL-10 in T-cells in APCΔ468 mice and compared the effects of treatment with broad-spectrum antibiotics. We found that T-cells and Tregs were a major cellular source of IL-10 in both the healthy and polyp-bearing colon. Notably, T-cell-specific ablation of IL-10 produced pathologies that were identical to mice with a systemic deficiency in IL-10, in both cases increasing the numbers and growth of colon polyps. Eosinophils were found to densely infiltrate colon polyps, which were enriched similarly for microbiota associated previously with colon cancer. In mice receiving broad-spectrum antibiotics, we observed reductions in microbiota, inflammation, and polyposis. Together our findings establish that colon polyposis is driven by high densities of microbes that accumulate within polyps and trigger local inflammatory responses. Inflammation, local microbe densities, and polyp growth are suppressed by IL-10 derived specifically from T-cells and Tregs.
interleukin-10; polyposis; microbiota; inflammation; colon
Inflammatory bowel disease is associated with industrialization, and its incidence has increased markedly over time. The prospect of reversing these trends motivates the search for the agent(s) involved. Modernity entails several physical and behavioral modifications that compromise both the photosynthesis of cholecalciferol in the skin, and of its bioavailability. Although deficiency in this “vitamin” has therefore emerged as a leading candidate, and despite the publication of a randomized control trial that showed a trend towards statistically significant benefit in Crohn’s disease, its causal agency has yet to be demonstrated by an adequately powered study. We discuss the strengths and weaknesses of the case being made by epidemiologists, geneticists, clinicians and basic researchers, and consolidate their findings into a model that provides mechanistic plausibility to the claim. Specifically, converging data sets suggest that local activation of vitamin D coordinates the activity of the innate and adaptive arms of immunity, and of the intestinal epithelium, in a manner that promotes barrier integrity, facilitates the clearance of translocated flora and diverts CD4 T cell development away from inflammatory phenotypes. Since smoking is an important risk-altering exposure, we also discuss its newly established melanizing effect, as well as other emerging evidence linking tobacco use to immune function through vitamin D pathways.
Vitamin D; Inflammatory Bowel Disease; Crohn’s Disease; Ulcerative Colitis
The spleen regulatory B cell subset with the functional capacity to express IL-10 (B10 cells) modulates both immune responses and autoimmune disease severity. However, the peritoneal cavity also contains relatively high frequencies of functionally-defined IL-10-competent B10 cells. In this study, peritoneal cavity B10 cells shared similar cell surface phenotypes with their spleen counterparts. However, peritoneal cavity B10 cells were 10-fold more frequent among B cells than occurred within the spleen, intestinal track or mesenteric lymph nodes and were present at higher proportions among the phenotypically-defined peritoneal B1a>B1b>B2 cell subpopulations. The development or localization of B10 cells within the peritoneal cavity was not dependent on the presence of commensal microbiota, T cells, IL-10 or B10 cell IL-10 production, or differences between their fetal liver or adult bone marrow progenitor cell origins. The BCR repertoire of peritoneal cavity B10 cells was diverse, as occurs in the spleen, and predominantly included germline-encoded VH and VL regions commonly found in either the conventional or B1 B cell compartments. Thereby, the capacity to produce IL-10 appears to be an intrinsic functional property acquired by clonally diverse B cells. Importantly, IL-10 production by peritoneal cavity B cells significantly reduced disease severity in spontaneous and induced models of colitis by regulating neutrophil infiltration, colitogenic CD4+ T cell activation and pro-inflammatory cytokine production during colitis onset. Thus, the numerically small B10 cell subset within the peritoneal cavity has regulatory function and is important for maintaining homeostasis within gastrointestinal tissues and the immune system.
Foxp3+ regulatory T (Treg) cells are a crucial immunosuppressive population of CD4+ T cells, yet the homeostatic processes and survival programs that maintain the Treg cell pool are poorly understood. Here we report that peripheral Treg cells markedly alter their proliferative and apoptotic rates to rapidly restore numerical deficit through an interleukin 2–dependent and costimulation-dependent process. By contrast, excess Treg cells are removed by attrition, dependent on the Bim-initiated Bak- and Bax-dependent intrinsic apoptotic pathway. The antiapoptotic proteins Bcl-xL and Bcl-2 were dispensable for survival of Treg cells, whereas Mcl-1 was critical for survival of Treg cells, and the loss of this antiapoptotic protein caused fatal autoimmunity. Together, these data define the active processes by which Treg cells maintain homeostasis via critical survival pathways.
Two models are proposed to explain Notch function during helper T (Th) cell differentiation. One argues that Notch instructs one Th cell fate over the other, whereas the other posits that Notch function is dictated by cytokines. Here we provide a detailed mechanistic study investigating the role of Notch in orchestrating Th cell differentiation. Notch neither instructed Th cell differentiation nor did cytokines direct Notch activity, but instead, Notch simultaneously regulated the Th1, Th2, and Th17 cell genetic programs independently of cytokine signals. In addition to regulating these programs in both polarized and non-polarized Th cells, we identified Ifng as a direct Notch target. Notch bound the Ifng CNS-22 enhancer, where it synergized with Tbet at the promoter. Thus, Notch acts as an unbiased amplifier of Th cell differentiation. Our data provide a paradigm for Notch in hematopoiesis, with Notch simultaneously orchestrating multiple lineage programs, rather than restricting alternate outcomes.
During the course of many chronic viral infections, the antiviral T cell response becomes attenuated through a process that is regulated in part by the host. While elevated expression of the immunosuppressive cytokine IL-10 is involved in the suppression of viral-specific T cell responses, the relevant cellular sources of IL-10, as well as the pathways responsible for IL-10 induction, remain unclear. In this study, we traced IL-10 production over the course of chronic lymphocytic choriomeningitis virus (LCMV) infection in an IL-10 reporter mouse line. Using this model, we demonstrated that virus-specific T cells with reduced inflammatory function, particularly Th1 cells, display elevated and sustained IL-10 expression during chronic LCMV infection. Furthermore, ablation of IL-10 from the T cell compartment partially restored T cell function and reduced viral loads in LCMV-infected animals. We found that viral persistence is needed for sustained IL-10 production by Th1 cells and that the transcription factor BLIMP-1 is required for IL-10 expression by Th1 cells. Restimulation of Th1 cells from LCMV-infected mice promoted BLIMP-1 and subsequent IL-10 expression, suggesting that constant antigen exposure likely induces the BLIMP-1/IL-10 pathway during chronic viral infection. Together, these data indicate that effector T cells self-limit their responsiveness during persistent viral infection via an IL-10–dependent negative feedback loop.
Bone marrow graft failure and poor graft function are frequent complications following hematopoietic stem cell transplantation and result in significant morbidity and mortality. Both conditions are associated with graft versus host disease (GVHD), although the mechanism remains undefined. Here we show in two distinct murine models of GVHD (complete MHC- and class II-disparate) that mimic human peripheral blood stem cell transplantation that Th1 CD4+ cells induce bone marrow failure in allogeneic recipients. Bone marrow failure following transplant of allogeneic naïve CD4+ T cells was associated with increased CD4+ Th1 cell development within bone marrow and lymphoid tissues. Using IFNγ-reporter mice, we found that Th1 cells generated during GVHD induced bone marrow failure following transfers into secondary recipients. Homing studies demonstrated that transferred Th1 cells express CXCR4, which was associated with accumulation within bone marrow and spleen. Allogeneic Th1 cells were activated by radiation-resistant host bone marrow cells and induced bone marrow failure through an IFNγ-dependent mechanism. Thus, allogeneic Th1 CD4+ cells generated during GVHD traffic to hematopoietic sites and induce bone marrow failure via IFNγ-mediated toxicity. These results have important implications for prevention and treatment of bone marrow graft failure following hematopoietic stem cell transplantation.
Regulation of IL-2–producing CD4+ T cell numbers is controlled by a quorum-sensing feedback loop as regulatory T cells sense the IL-2 produced.
Many species of bacteria use quorum sensing to sense the amount of secreted metabolites and to adapt their growth according to their population density. We asked whether similar mechanisms would operate in lymphocyte homeostasis. We investigated the regulation of the size of interleukin-2 (IL-2)–producing CD4+ T cell (IL-2p) pool using different IL-2 reporter mice. We found that in the absence of either IL-2 or regulatory CD4+ T (T reg) cells, the number of IL-2p cells increases. Administration of IL-2 decreases the number of cells of the IL-2p cell subset and, pertinently, abrogates their ability to produce IL-2 upon in vivo cognate stimulation, while increasing T reg cell numbers. We propose that control of the IL-2p cell numbers occurs via a quorum sensing–like feedback loop where the produced IL-2 is sensed by both the activated CD4+ T cell pool and by T reg cells, which reciprocally regulate cells of the IL-2p cell subset. In conclusion, IL-2 acts as a self-regulatory circuit integrating the homeostasis of activated and T reg cells as CD4+ T cells restrain their growth by monitoring IL-2 levels, thereby preventing uncontrolled responses and autoimmunity.
The recent emergence of a new CD4+ T cell subset, Th17, has transformed our understanding of the pathogenetic basis of an increasing number of chronic immune-mediated diseases. Particularly in tissues that interface with the microbial environment — such as the intestinal and respiratory tracts, and skin — where most of the Th17 cells present in the body reside, dysregulated immunity to self, or the extended “self,” the diverse microbiota that normally colonize these tissues, can result in chronic inflammatory disease. In this review, we focus on recent advances in the biology of the Th17 pathway and genome-wide association studies (GWAS) implicating this immune pathway in human disease that are providing new insights into disease mechanisms in these and other tissues.
Th17 cells; Th22 cells; autoimmunity; inflammatory bowel disease; Crohn’s disease; ulcerative colitis; asthma; COPD; psoriasis; atopic dermatitis
Whereas thymic education eliminates most self-reactive T cells, additional mechanisms to promote tolerance in the periphery are critical to prevent excessive immune responses against benign environmental antigens and some self-antigens. Here we show that murine CD4+ recent thymic emigrants (RTEs) are programmed to facilitate tolerance in the periphery. Both in vitro and in vivo, naïve RTEs more readily up-regulate Foxp3 than mature naïve cells after stimulation under tolerogenic conditions. In RTEs, a relatively high sensitivity to retinoic acid contributes to decreased IFN-γ production, permitting the expression of Foxp3. Conversely, mature naïve CD4 cells have a lower sensitivity to retinoic acid, resulting in increased IFN-γ production and subsequent IFN-γ-mediated silencing of Foxp3 expression. Enhanced retinoic acid signaling and Foxp3 induction in RTEs upon antigen encounter in the periphery may serve as form of secondary education that complements thymic education and helps avoid inappropriate immune responses. This mechanism for tolerance may be particularly important in settings where RTEs comprise a large fraction of the peripheral T cell pool, such as in newborns or after umbilical cord blood transplant.
Discovery of the T-helper 17 (Th17) subset heralded a major shift in T-cell biology and immune regulation. In addition to defining a new arm of the adaptive immune response, studies of the Th17 pathway have led to a greater appreciation of the developmental flexibility, or plasticity, that is a feature of T-cell developmental programs. Since the initial finding that differentiation of Th17 cells is promoted by transforming growth factor-β (TGFβ), it became clear that Th17 cell development overlapped that of induced regulatory T (iTreg) cells. Subsequent findings established that Th17 cells are also unusually flexible in their late developmental programming, demonstrating substantial overlap with conventional Th1 cells through mechanisms that are just beginning to be understood but would appear to have important implications for immunoregulation at homeostasis and in immune-mediated diseases. Herein we examine the developmental and functional features of Th17 cells in relation to iTreg cells, Th1 cells, and Th22 cells, as a basis for understanding the contributions of this pathway to host defense, immune homeostasis, and immune-mediated disease.
Th17 cells; Th1 cells; Treg cells; Th22 cells; T-cell development; plasticity; cytokines
Differentiation-dependent regulation of the Ifng cytokine gene locus in T helper (Th) cells has emerged as an excellent model for functional study of distal elements that control lineage-specific gene expression. We previously identified a cis-regulatory element located 22 kb upstream of the Ifng gene (Conserved Non-coding Sequence -22, or CNS-22) that is a site for recruitment of the transcription factors T-bet, Runx3, NF-κB and STAT4, which act to regulate transcription of the Ifng gene in Th1 cells. Here, we report the generation of mice with a conditional deletion of CNS-22 that has enabled us to define the epigenetic and functional consequences of its absence. Deletion of CNS-22 led to a defect in induction of Ifng by the cytokines IL-12 and IL-18, with a more modest effect on induction via T-cell receptor activation. To better understand how CNS-22 and other Ifng CNSs regulated Ifng transcription in response to these distinct stimuli, we examined activation-dependent changes in epigenetic modifications across the extended Ifng locus in CNS-22-deficient T cells. We demonstrate that in response to both cytokine and TCR driven activation signals, CNS-22 and other Ifng CNSs recruit increased activity of histone acetyl transferases (HATs) that transiently enhance levels of histones H3 and H4 acetylation across the extended Ifng locus. We also demonstrate that activation-responsive increases in histone acetylation levels are directly linked to the ability of Ifng CNSs to acutely enhance Pol II recruitment to the Ifng promoter. Finally, we show that impairment in IL-12+IL-18 dependent induction of Ifng stems from the importance of CNS-22 in coordinating locus-wide levels of histone acetylation in response to these cytokines. These findings identify a role for acute histone acetylation in the enhancer function of distal conserved cis-elements that regulate of Ifng gene expression.
Differentiation of multipotent naïve T cell precursors into functionally mature effector cells that control different types of immune responses is an excellent model to study lineage-specific regulation of gene expression. A number of cis-regulatory elements have been reported to control expression of the gene that encodes the cytokine IFN-γ which is a signature product of effector T cells of the Th1 lineage. However, none of these elements has been analyzed for effects on gene expression and chromatin remodeling through deletional analysis in the native Ifng gene locus. Here we have generated mice in which a key element previously implicated in control of Ifng gene expression (CNS-22) was conditionally deleted from the genome. Th1 cells in which CNS-22 was deleted had activation-specific deficits in Ifng expression and demonstrated defects in epigenetic changes across the Ifng locus. Mapping epigenetic consequences of CNS-22 deletion led to identification of acute hyperacetylation of histones immediately flanking this and other cis-regulatory elements that was associated with Ifng gene transcription, as well as more global defects in histone acetylation. These findings support a mechanism whereby regulatory sites that have acquired baseline histone acetylation marks during lineage specification undergo acute, activation-dependent increases in histone acetyl transferase activity that enhance transcription of inducible genes.
Interleukin-22 (IL-22) is central to host protection against bacterial infections at barrier sites. Both innate lymphoid cells (ILCs) and T cells produce IL-22. However, the specific contributions of CD4+ T cells and their developmental origins are unclear. We found that the enteric pathogen Citrobacter rodentium induced sequential waves of IL-22 producing ILCs and CD4+ T cells that were each critical to host defense during a primary infection. Whereas IL-22 production by ILCs was strictly IL-23–dependent, development of IL-22 producing CD4+ T cells occurred via an IL-6–dependent mechanism that was augmented by, but not dependent on, IL-23, and was dependent on both transcription factors T-bet and AhR. Transfer of CD4+ T cells differentiated with IL-6 in the absence of TGF-β (“Th22” cells) conferred protection of infected IL-22-deficient mice whereas transferred Th17 cells did not. These findings establish Th22 cells as an important component of mucosal anti-microbial host defense.
Sensitization to fungi, such as the mold Aspergillus fumigatus, is increasingly becoming linked with asthma severity. We have previously shown that lung responses generated via the beta-glucan receptor Dectin-1 are required for lung defense during acute, invasive A. fumigatus infection. Unexpectedly, in an allergic model of chronic lung exposure to live A. fumigatus conidia, beta-glucan recognition via Dectin-1 led to the induction of multiple proallergic (Muc5ac, Clca3, CCL17, CCL22 and IL-33) and proinflammatory (IL-1β and CXCL1) mediators that compromised lung function. Attenuated proallergic and proinflammatory responses in the absence of Dectin-1 was not associated with changes in Ido (indoleamine 2,3-dioxygenase), Il12p35/Ebi3 (IL-35), IL-10 or TGF-β levels. Assessment of T helper responses demonstrated that purified lung CD4+ T cells produced IL-4, IL-13, IFN-γ and IL-17A, but not IL-22, in a Dectin-1 dependent manner. In contrast, we observed robust, Dectin-1 dependent IL-22 production by unfractionated lung digest cells. Intriguingly, the absence of IL-22 alone mimicked the attenuated proallergic and proinflammatory responses observed in the absence of Dectin-1, suggesting that Dectin-1 mediated IL-22 production potentiated responses that led to decrements in lung function. To this end, neutralization of IL-22 improved lung function in normal mice. Collectively, these results indicate that the beta-glucan receptor Dectin-1 contributes to lung inflammation and immunopathology associated with persistent fungal exposure via the production of IL-22.
γδ T cells contribute uniquely to host immune defense. However, how they function remains an enigma. Although it is unclear what most γδ T cells recognize, common dogma asserts that they recognize self-antigens. While they are the major initial Interleukin-17 (IL-17) producers in infections, it is unclear what is required to trigger these cells to act. Here, we report that a noted B cell antigen, the algae protein-phycoerythrin (PE) is an antigen for murine and human γδ T cells. PE also stained specific bovine γδ T cells. Employing this specificity, we demonstrated that antigen recognition, but not extensive clonal expansion, was required to activate naïve γδ T cells to make IL-17. In this activated state, γδ T cells gained the ability to respond to cytokine signals that perpetuated the IL-17 production. These results underscore the adaptability of lymphocyte antigen receptors and suggest a previously unrecognized antigen-driven rapid response in protective immunity prior to the maturation of classical adaptive immunity.
Levels of reactive free radicals are elevated in the airway during asthmatic exacerbations, but their roles in the pathophysiology of asthma remain unclear. We have identified subsets of myeloid-derived suppressor-like cells as key sources of nitric oxide and superoxide in the lungs of mice with evolving experimental allergic airway inflammation and established these cells as master regulators of the airway inflammatory response. The profiles of free radicals they produced depended on expression of iNOS, arginase, and NADPH oxidase. These radicals controlled the pro- and anti-inflammatory potential of these cells, and also regulated the reciprocal pattern of their infiltration into the lung. The nitric oxide-producing cells were Ly-6C+Ly-6G− and down-modulated T cell activation, recruited Treg cells, and dramatically down-regulated antigen-induced airway hyperresponsiveness. The superoxide-producing cells were Ly-6C−Ly-6G+ and expressed proinflammatory activities, exacerbating airway hyperresponsiveness in a superoxide-dependent fashion. A smaller population of Ly-6C+Ly-6G+ cells also suppressed T cell responses, but in an iNOS- and arginase-independent fashion. These regulatory myeloid cells represent important targets for asthma therapy.
Development of T helper (Th) 17 cells requires transforming growth factor (TGF)-β and interleukin (IL)-6 and is independent of the Th1 pathway. Although T cells that produce interferon (IFN)-γ are a recognized feature of Th17 cell responses, mice deficient for STAT4 and T-bet—two prototypical Th1 transcription factors—are protected from autoimmunity associated with Th17 pathogenesis. To examine the fate and pathogenic potential of Th17 cells and origin of IFN-γ-producing T cells that emerge during Th17 immunity, we developed IL-17F reporter mice that identify cells committed to expression of IL-17F and IL-17A. Th17 cells required TGF-β for sustained expression of IL-17F and IL-17A. In the absence of TGF-β, both IL-23 and IL-12 acted to suppress IL-17 and enhance IFN-γ production in a STAT4- and T-bet-dependent manner, albeit with distinct efficiencies. These results support a model of late Th17 developmental plasticity with implications for auto-immunity and host defense.
Similar to hematopoietic stem cells, memory lymphocytes self renew, while their clonally expanded effector progeny differentiate to fight infection and tumors. Recently, Muranski et al. report in Immunity (2011) that a subset of Th17 effector cells functions as memory cells and retain stem cell properties.
Regulatory B cells that are functionally defined by their capacity to express IL-10 (B10 cells) downregulate inflammation and autoimmunity. In studies using well-defined IL-10-reporter mice, this rare B10 cell subset was also found to maintain a capacity for plasma cell differentiation. During a transient period of il10 transcription, the blimp1 and irf4 transcription factors were induced in B10 cells while pax5 and bcl6 were downregulated as a significant fraction of B10 cells completed the genetic and phenotypic program leading to antibody-secreting cell differentiation in vitro and in vivo. B10 cell-derived IgM reacted with both self and foreign Ags, whereas B10 cells generated Ag-specific IgG in response to immunizations. Moreover, B10 cells represented a significant source of serum IgM and IgG during adoptive transfer experiments, and produced Ag-specific, polyreactive and autoreactive antibody specificities that were consistent with their expression of a diverse Ag receptor repertoire. Thereby, B10 cells not only limit inflammation and immune responses by the transient production of IL-10, but may also facilitate clearance of their eliciting Ags through an inherent capacity to quickly generate polyreactive and/or Ag-specific antibodies during humoral immune responses.
Human neonates are at significantly greater risk of serious infection than immunocompetent adults. In particular, very low birth weight infants in the neonatal intensive care nursery are at high risk of developing life-threatening bacterial and fungal infections. Recent studies have identified Th17 cells as critical mediators of immunity to bacterial and fungal infections at epithelial barriers. Little is known, however, about the ontogeny of Th17 responses in humans. The frequency of serious bacterial infections in preterm infants and the importance of Th17 cells in providing protection against such infections in animal studies prompted us to study Th17 development in human neonates. NaÔve CD4 T cells from extremely preterm infants, term infants, and adults were assayed for their capacity to develop into Th17 effector cells. Surprisingly, Th17 capacity was inversely related to developmental age. Neonates expressed higher levels of IL-23R, RORγt, and STAT3 prior to activation and showed a significant Th17 bias after activation. In contrast, adult cells expressed more TBX21 with a corresponding Th1 bias. CD161 expression on Th17 precursors was also developmentally regulated. Our results suggest there is significant developmental regulation of CD4 effector lineages with a strong bias toward Th17 development early in life.
Th17 cell; premature infant; CD161; neonatal immunity; T-helper subsets
B cells contribute to the pathogenesis of chronic autoimmune disorders like systemic lupus erythematosus (SLE) via multiple effector functions. However, B cells are also implicated in regulating SLE and other autoimmune syndromes via release of IL-10. B cells secreting IL-10 have been termed “Breg” and have been proposed as a separate subset of cells, a concept that remains controversial. The balance between pro- and anti-inflammatory effects could determine the success of B cell targeted therapies for autoimmune disorders and it is therefore pivotal to understand the significance of B cell-secreted IL-10 in spontaneous autoimmunity. By lineage specific deletion of Il10 from B cells we demonstrate that B cell-derived IL-10 is ineffective in suppressing the spontaneous activation of self-reactive B and T cells during lupus. Correspondingly, severity of organ disease and survival rates in mice harboring Il10 deficient B cells are unaltered. Genetic marking of cells that transcribe Il10 illustrates that the pool of IL-10 competent cells is dominated by CD4 T cells and macrophages. IL-10 competent cells of the B lineage are rare in vivo and among them short-lived plasmablasts have the highest frequency, suggesting an activation rather than lineage-driven phenotype. Putative Breg phenotypic subsets such as CD1dhiCD5+ and CD21hiCD23hi B cells are not enriched in Il10 transcription. These genetic studies demonstrate that in a spontaneous model of murine lupus, IL-10 dependent B cell regulation does not restrain disease and thus the pathogenic effects of B cells are not detectably counterbalanced by their IL-10 dependent regulatory functions.
The interleukin-17 (IL-17) family of cytokines phylogenetically pre-dates the evolution of T cells in jawed vertebrates, suggesting that the ontogeny of the Th17 cell lineage must have arisen to confer an evolutionary advantage to the host over innate sources of IL-17. Using a model of mucosal immunization with the encapsulated bacteria Klebsiella pneumoniae, B cells largely recognized polysaccharide capsular antigens, which limited protection to only the vaccine strain. In contrast, memory Th17 cells proliferated in response to conserved outer membrane proteins and conferred protection against several serotypes of K. pneumoniae, including the recently described multi-drug resistant New Dehli metallolactamase strain. Notably, this heterologous, clade specific protection was antibody-independent, demonstrating the Th17 cell lineage confers a host advantage by providing heterologous mucosal immunity independent of serotype specific antibody.
We have previously reported that mice deficient in the beta-glucan receptor Dectin-1 displayed increased susceptibility to Aspergillus fumigatus lung infection in the presence of lower interleukin 23 (IL-23) and IL-17A production in the lungs and have reported a role for IL-17A in lung defense. As IL-23 is also thought to control the production of IL-22, we examined the role of Dectin-1 in IL-22 production, as well as the role of IL-22 in innate host defense against A. fumigatus. Here, we show that Dectin-1-deficient mice demonstrated significantly reduced levels of IL-22 in the lungs early after A. fumigatus challenge. Culturing cells from enzymatic lung digests ex vivo further demonstrated Dectin-1-dependent IL-22 production. IL-22 production was additionally found to be independent of IL-1β, IL-6, or IL-18 but required IL-23. The addition of recombinant IL-23 augmented IL-22 production in wild-type (WT) lung cells and rescued IL-22 production by lung cells from Dectin-1-deficient mice. In vivo neutralization of IL-22 in the lungs of WT mice resulted in impaired A. fumigatus lung clearance. Moreover, mice deficient in IL-22 also demonstrated a higher lung fungal burden after A. fumigatus challenge in the presence of impaired IL-1α, tumor necrosis factor alpha (TNF-α), CCL3/MIP-1α, and CCL4/MIP-1β production and lower neutrophil recruitment, yet intact IL-17A production. We further show that lung lavage fluid collected from both A. fumigatus-challenged Dectin-1-deficient and IL-22-deficient mice had compromised anti-fungal activity against A. fumigatus in vitro. Although lipocalin 2 production was observed to be Dectin-1 and IL-22 dependent, lipocalin 2-deficient mice did not demonstrate impaired A. fumigatus clearance. Moreover, lung S100a8, S100a9, and Reg3g mRNA expression was not lower in either Dectin-1-deficient or IL-22-deficient mice. Collectively, our results indicate that early innate lung defense against A. fumigatus is mediated by Dectin-1-dependent IL-22 production.
Regulatory T (Treg) cells are plastic, but the in vivo mechanisms by which they are converted into Foxp3+interferon (IFN)-γ+ T cells, and whether these converted cells retain the ability to inhibit colitis, are not clear.
Foxp3+ Treg cells were generated by culture of naïve CD4+ T cells from Foxp3GFP CBir1 T-cell receptor (TCR) transgenic (CBir1-Tg) mice, which are specific for CBir1 flagellin (an immunodominant microbiota antigen), with transforming growth factor (TGF)-β. Foxp3GFP+ CBir1-Tg Treg cells were isolated by fluorescence-activated cell sorting and transferred into TCRβxδ−/− mice. Colitis was induced by transfer of naïve CBir1-Tg CD4+ T cells into immunodeficient mice.
Microbiota antigen-specific Foxp3+ Treg cells were converted, in the intestine, to IFN-γ+ T-helper (Th)1 cells, interleukin (IL)-17+ Th17 cells, and Foxp3+ T cells that coexpress IFN-γ and/or IL-17. Conversion of Treg cells into IFN-γ-producing Th1 cells and Foxp3+IFN-γ+ T cells required innate cell production of IL-12 in the intestine; blocking IL-12 with an antibody inhibited their conversion to Th1 and Foxp3+IFN-γ+ T cells in the intestines of mice that were recipients of Treg cells. Addition of IL-12, but not IL-23, promoted conversion of Treg cells into Th1 and Foxp3+IFN-γ+ T cells, in vitro. Foxp3+IFN-γ+ T cells had regulatory activity, because they suppressed proliferation of naïve T cells, in vitro, and inhibited induction of colitis by microbiota antigen-specific T cells. IFN-γ+ Th1 cells were not converted into Treg cells; Foxp3+IFN-γ+ T cells differentiated into IFN-γ+ but not Foxp3+ T cells.
IL-12 promotes conversion of Treg cells into IFN-γ-expressing cells; Foxp3+IFN-γ+ T cells retain their regulatory functions and develop during the transition of Foxp3+ Treg cells into IFN-γ+ Th1 cells.
IBD; immune regulation; inflammation; Crohn’s disease
We have previously reported that compromised interleukin 17A (IL-17A) production in the lungs increased susceptibility to infection with the invasive fungal pathogen Aspergillus fumigatus. Here we have shown that culturing lung cells from A. fumigatus-challenged mice ex vivo demonstrated Dectin-1-dependent IL-17A production. In this system, neutralization of IL-23 but not IL-6, IL-1β, or IL-18 resulted in attenuated IL-17A production. Il23 mRNA expression was found to be lower in lung cells from A. fumigatus-challenged Dectin-1-deficient mice, whereas bone marrow-derived dendritic cells from Dectin-1-deficient mice failed to produce IL-23 in response to A. fumigatus in vitro. Addition of recombinant IL-23 augmented IL-17A production by wild-type (WT) and Dectin-1-deficient lung cells, although the addition of IL-6 or IL-1β did not augment the effect of IL-23. Intracellular cytokine staining of lung cells revealed lower levels of CD11b+ IL-17A+ and Ly-6G+ IL-17A+ cells in A. fumigatus-challenged Dectin-1-deficient mice. Ly-6G+ neutrophils purified from the lungs of A. fumigatus-challenged Dectin-1-deficient mice displayed lower Il17a mRNA expression but surprisingly had intact Rorc and Rora mRNA expression. We further demonstrated that Ly-6G+ neutrophils required the presence of myeloid cells for IL-17A production. Finally, upon in vitro stimulation with A. fumigatus, thioglycolate-elicited peritoneal neutrophils were positive for intracellular IL-17A expression and produced IL-17A in a Dectin-1- and IL-23-dependent manner. In summary, Dectin-1-dependent IL-17A production in the lungs during invasive fungal infection is mediated in part by CD11b+ Ly-6G+ neutrophils in an IL-23-dependent manner.