Interleukin-17 and lung host defense against Klebsiella pneumoniae infection

Alcohol, signaling, and ECM turnover

Alcohol is recognized as a direct hepatotoxin, but the precise molecular pathways that are important for the initiation and progression of alcohol-induced tissue injury are not completely understood. The current understanding of alcohol toxicity to organs suggests that alcohol initiates injury by generation of oxidative and nonoxidative ethanol metabolites and via translocation of gut-derived endotoxin. These processes lead to cellular injury and stimulation of the inflammatory responses mediated through a variety of molecules. With continuing alcohol abuse, the injury progresses through impairment of tissue regeneration and extracellular matrix (ECM) turnover, leading to fibrogenesis and cirrhosis. Several cell types are involved in this process, the predominant being stellate cells, macrophages, and parenchymal cells. In response to alcohol, growth factors and cytokines activate many signaling cascades that regulate fibrogenesis. This mini-review brings together research focusing on the underlying mechanisms of alcohol-mediated injury in a number of organs. It highlights the various processes and molecules that are likely involved in inflammation, immune modulation, susceptibility to infection, ECM turnover and fibrogenesis in the liver, pancreas, and lung triggered by alcohol abuse.

Splenic autotransplantation restores IL-17 production and antibody response to Streptococcus pneumoniae in splenectomized mice

The high incidence of overwhelming postsplenectomy infection caused by Streptococcus pneumoniae can be reduced by splenic autotransplantation. In this study the effect of splenectomy and splenic autotransplantation on the immune response to S. pneumoniae infection was investigated. Balb/c mice were divided into three groups: splenectomized (SP), splenectomized and autotransplanted (AT), and sham operated control (CT). Five days post-infection the serum antibody levels were measured and the number of S. pneumoniae CFU, neutrophil accumulation and IL-17 production in the liver and lungs were investigated. SP mice showed greater number of bacteria in both organs and lower serum levels of S. pneumoniae-specific IgM, IgG1 and IgG2a antibodies. IL-17 production and neutrophil recruitment to the liver and lungs were lower in SP mice, in comparison with both the CT and the AT groups. Levels of S. pneumoniae-specific IgM, CFU counts, neutrophil accumulation and IL-17 production did not differ significantly between the CT and AT groups. These results suggest that splenic autotransplantation restores the capacity of splenectomized mice to fight S. pneumoniae infection.

Administration of IL-23 engages innate and adaptive immune mechanisms during fungal infection

IL-23 is a key cytokine in promotion of chronic inflammation. Here, we address if its pro-inflammatory potential can be harnessed to protect against chronic cryptococcosis. Mice were infected with Cryptococcus neoformans and treated with recombinant IL-23. Administration of IL-23 led to prolonged survival and reduced fungal burden but was inferior to IL-12 treatment. Independent of endogenous IL-23/IL-12, IL-23 treatment induced an altered cytokine profile accompanied by marked changes in composition of the inflammatory infiltrate characterized by T cell and dendritic cell recruitment. Although IL-23 induced hallmarks of the T(h)17 pathway, also non-T cells produced IL-17A and IL-22. IL-23 treatment of T-cell-deficient mice resulted in increased IL-17A and IL-22 production and modulation of the cellular response at the site of infection with elevated expression of CD86 on macrophages. Our data show that IL-23 treatment induces innate and adaptive tissue inflammation with limited impact on resistance to chronic cryptococcosis.

Altered peptide ligands inhibit arthritis induced by glucose-6-phosphate isomerase peptide

INTRODUCTION

Immunosuppressants, including anti-TNFalpha antibodies, have remarkable effects in rheumatoid arthritis; however, they increase infectious events. The present study was designed to examine the effects and immunological change of action of altered peptide ligands (APLs) on glucose-6-phosphate isomerase (GPI) peptide-induced arthritis.

METHODS

DBA/1 mice were immunized with hGPI325-339, and cells of draining lymph node (DLN) were stimulated with hGPI325-339 to investigate the T-cell receptor (TCR) repertoire of antigen-specific CD4+ T cells by flow cytometry. Twenty types of APLs with one amino acid substitution at a TCR contact site of hGPI325-339 were synthesized. CD4+ T cells primed with human GPI and antigen-presenting cells were co-cultured with each APL and cytokine production was measured by ELISA to identify antagonistic APLs. Antagonistic APLs were co-immunized with hGPI325-339 to investigate whether arthritis could be antigen-specifically inhibited by APL. After co-immunization, DLN cells were stimulated with hGPI325-339 or APL to investigate Th17 and regulatory T-cell population by flow cytometry, and anti-mouse GPI antibodies were measured by ELISA.

RESULTS

Human GPI325-339-specific Th17 cells showed predominant usage of TCRVbeta8.1 8.2. Among the 20 synthesized APLs, four (APL 6; N329S, APL 7; N329T, APL 12; G332A, APL 13; G332V) significantly reduced IL-17 production by CD4+ T cells in the presence of hGPI325-339. Co-immunization with each antagonistic APL markedly prevented the development of arthritis, especially APL 13 (G332V). Although co-immunization with APL did not affect the population of Th17 and regulatory T cells, the titers of anti-mouse GPI antibodies in mice co-immunized with APL were significantly lower than in those without APL.

CONCLUSIONS

We prepared antagonistic APLs that antigen-specifically inhibited the development of experimental arthritis. Understanding the inhibitory mechanisms of APLs may pave the way for the development of novel therapies for arthritis induced by autoimmune responses to ubiquitous antigens.

Precarious balance: Th17 cells in host defense

Lineage-specific responses from the effector T-cell repertoire form a critical component of adaptive immunity. The recent identification of Th17 cells-a third, distinct lineage of helper T cells-collapses the long-accepted paradigm in which Th1 and Th2 cells distinctly mediate cellular and humoral immunity, respectively. In this minireview, we discuss the involvement of the Th17 lineage during infection by extracellular bacteria, intracellular bacteria, and fungi. Emerging trends suggest that the Th17 population bridges innate and adaptive immunity to produce a robust antimicrobial inflammatory response. However, because Th17 cells mediate both host defense and pathological inflammation, elucidation of mechanisms that attenuate but do not completely abolish the Th17 response may have powerful implications for therapy.

T helper 17 cells promote cytotoxic T cell activation in tumor immunity

Although T helper 17 (Th17) cells have been found in tumor tissues, their function in cancer immunity is unclear. We found that interleukin-17A (IL-17A)-deficient mice were more susceptible to developing lung melanoma. Conversely, adoptive T cell therapy with tumor-specific Th17 cells prevented tumor development. Importantly, the Th17 cells retained their cytokine signature and exhibited stronger therapeutic efficacy than Th1 cells. Unexpectedly, therapy using Th17 cells elicited a remarkable activation of tumor-specific CD8(+) T cells, which were necessary for the antitumor effect. Th17 cells promoted dendritic cell recruitment into the tumor tissues and in draining lymph nodes increased CD8 alpha(+) dendritic cells containing tumor material. Moreover, Th17 cells promoted CCL20 chemokine production by tumor tissues, and tumor-bearing CCR6-deficient mice did not respond to Th17 cell therapy. Thus, Th17 cells elicited a protective inflammation that promotes the activation of tumor-specific CD8(+) T cells. These findings have important implications in antitumor immunotherapies.

Regulation of airway MUC5AC expression by IL-1beta and IL-17A; the NF-kappaB paradigm

Mucin over-production is one of the hallmarks of chronic airway diseases such as chronic obstructive pulmonary disease, asthma, and cystic fibrosis. NF-kappaB activation in airway epithelial cells has been shown to play a positive inflammatory role in chronic airway diseases; however, the role of NF-kappaB in mucin gene expression is unresolved. In this study, we have shown that the proinflammatory cytokines, IL-1beta and IL-17A, both of which utilize the NF-kappaB pathway, are potent inducers of mucin (MUC)5AC mRNA and protein synthesis by both well-differentiated primary normal human bronchial epithelial cells and the human bronchial epithelial cell line, HBE1. MUC5AC induction by these cytokines was both time- and dose-dependent and occurred at the level of promoter activation, as measured by a reporter gene assay. These effects were attenuated by the small molecule inhibitor NF-kappaB inhibitor III, as well as p65 small-interfering RNA, suggesting that the regulation of MUC5AC expression by these cytokines is via an NF-kappaB-based transcriptional mechanism. Further investigation of the promoter region identified a putative NF-kappaB binding site at position-3594/-3582 in the promoter of MUC5AC as critical for the regulation of MUC5AC expression by both IL-1beta and IL-17A. Chromatin immunoprecipitation analysis confirmed enhanced binding of the NF-kappaB subunit p50 to this region following cytokine stimulation. We conclude that an NF-kappaB-based transcriptional mechanism is involved in MUC5AC regulation by IL-1beta and IL-17A in the airway epithelium. This is the first demonstration of the participation of NF-kappaB and its specific binding site in cytokine-mediated airway MUC5AC expression.

IL-17/Th17 promotes type 1 T cell immunity against pulmonary intracellular bacterial infection through modulating dendritic cell function

Although their contribution to host defense against extracellular infections has been well defined, IL-17 and Th17 are generally thought to have limited impact on intracellular infections. In this study, we investigated the role and mechanisms of IL-17/Th17 in host defense against Chlamydia muridarum, an obligate intracellular bacterium, lung infection. Our data showed rapid increase in IL-17 production and expansion of Th17 cells following C. muridarum infection and significant detrimental impact of in vivo IL-17 neutralization by anti-IL-17 mAb on disease course, immune response, and dendritic cell (DC) function. Specifically, IL-17-neutralized mice exhibited significantly greater body weight loss, higher organism growth, and much more severe pathological changes in the lung compared with sham-treated control mice. Immunological analysis showed that IL-17 neutralization significantly reduced Chlamydia-specific Th1 responses, but increased Th2 responses. Interestingly, the DC isolated from IL-17-neutralized mice showed lower CD40 and MHC II expression and IL-12 production, but higher IL-10 production compared with those from sham-treated mice. In two DC-T cell coculture systems, DC isolated from IL-17-neutralized mice induced higher IL-4, but lower IFN-gamma production by Ag-specific T cells than those from sham-treated mice in cell priming and reaction settings. Adoptive transfer of DC isolated from IL-17-neutralized mice, unlike those from sham-treated mice, failed to protect the recipients against challenge infection. These findings provide in vivo evidence that IL-17/Th17 plays an important role in host defense against intracellular bacterial infection, and suggest that IL-17/Th17 can promote type 1 T cell immunity through modulating DC function.

Regulation of gastric B cell recruitment is dependent on IL-17 receptor A signaling in a model of chronic bacterial infection

Th17-driven immune responses contribute to the pathogenesis of many chronic inflammatory diseases. In this study, we investigated the role of IL-17 signaling in chronic gastric inflammation induced by Helicobacter pylori, a Gram-negative bacterium that persistently colonizes the human stomach. Wild-type C57BL/6 mice and mice lacking IL-17RA (IL-17RA(-/-)) were orogastrically infected with H. pylori. Differences in bacterial colonization density and gastric inflammation were not apparent at 1 mo postinfection, but by 3 mo postinfection, H. pylori colonization density was higher and mononuclear gastric inflammation more severe in infected IL-17RA(-/-) mice than in infected wild-type mice. A striking feature was a marked increase in gastric B cells, plasma cells, and lymphoid follicles, along with enhanced H. pylori-specific serum Ab responses, in infected IL-17RA(-/-) mice. Fewer gastric neutrophils and lower levels of neutrophil-recruiting chemokines were detected in infected IL-17RA(-/-) mice than in infected wild-type mice. Gastric IL-17a and IL-21 transcript levels were significantly higher in infected IL-17RA(-/-) mice than in infected wild-type mice or uninfected mice, which suggested that a negative feedback loop was impaired in the IL-17RA(-/-) mice. These results underscore an important role of IL-17RA signaling in regulating B cell recruitment. In contrast to many chronic inflammatory diseases in which IL-17RA signaling promotes an inflammatory response, IL-17RA signaling down-regulates the chronic mononuclear inflammation elicited by H. pylori infection.

Development of allergen-induced airway inflammation in the absence of T-bet regulation is dependent on IL-17

Dysfunctional expression of T-bet, a transcription factor that is critical for IFN-gamma production, has been implicated in the development of asthma. To investigate in detail the mechanisms responsible for exacerbated disease in the absence of T-bet expression, BALB/c wild-type (WT) and T-bet(-/-) mice were used in a murine model of OVA-induced allergic lung inflammation. Following OVA challenge, T-bet(-/-) mice displayed increased histological inflammation in the lungs as well as greater thickening of the bronchiole linings, increased numbers of eosinophils and neutrophils in the lung, and enhanced airway hyperresponsiveness, compared with WT mice. However, the production of Th2 cytokines in T-bet(-/-) mice did not appear to be significantly greater than in WT mice. Interestingly, a marked increase in the levels of the proinflammatory cytokine IL-17 was observed in T-bet(-/-) mice. Neutralization of pulmonary IL-17 in T-bet(-/-) mice by anti-IL-17 mAb treatment during OVA challenge resulted in decreased levels of neutrophilic infiltration into the airways and decreased airway inflammation, essentially reversing the development of allergic asthma development. These findings indicate that IL-17 is a key mediator of airway inflammation in the absence of T-bet. The results of this study suggest a possible target for therapeutic intervention of human asthma.

Critical role of IL-17RA in immunopathology of influenza infection

Acute lung injury due to influenza infection is associated with high mortality, an increase in neutrophils in the airspace, and increases in tissue myeloperoxidase (MPO). Because IL-17A and IL-17F, ligands for IL-17 receptor antagonist (IL-17RA), have been shown to mediate neutrophil migration into the lung in response to LPS or Gram-negative bacterial pneumonia, we hypothesized that IL-17RA signaling was critical for acute lung injury in response to pulmonary influenza infection. IL-17RA was critical for weight loss and both neutrophil migration and increases in tissue myeloperoxidase (MPO) after influenza infection. However, IL-17RA was dispensable for the recruitment of CD8(+) T cells specific for influenza hemagglutinin or nucleocapsid protein. Consistent with this, IL-17RA was not required for viral clearance. However, in the setting of influenza infection, IL-17RA(-/-) mice showed significantly reduced levels of oxidized phospholipids, which have previously been shown to be an important mediator in several models of acute lung injury, including influenza infection and gastric acid aspiration. Taken together, these data support targeting IL-17 or IL-17RA in acute lung injury due to acute viral infection.

Mechanisms of neutrophil accumulation in the lungs against bacteria

Bacterial lung diseases are a major cause of morbidity and mortality both in immunocompromised and in immunocompetent individuals. Neutrophil accumulation, a pathological hallmark of bacterial diseases, is critical to host defense, but may also cause acute lung injury/acute respiratory distress syndrome. Toll-like receptors, nucleotide-binding oligomerization domain (NOD)-like receptors, transcription factors, cytokines, and chemokines play essential roles in neutrophil sequestration in the lungs. This review highlights our current understanding of the role of these molecules in the lungs during bacterial infection and their therapeutic potential. We also discuss emerging data on cholesterol and ethanol as environmentally modifiable factors that may impact neutrophil-mediated pulmonary innate host defense. Understanding the precise molecular mechanisms leading to neutrophil influx in the lungs during bacterial infection is critical for the development of more effective therapeutic and prophylactic strategies to control the excessive host response to infection.

Critical role of the interleukin-17/interleukin-17 receptor axis in regulating host susceptibility to respiratory infection with Chlamydia species

The specific contribution of interleukin-17/interleukin-17 receptor (IL-17/IL-17R)-mediated responses in regulating host susceptibility against obligatory intracellular Chlamydia infection was investigated in C57BL/6 and C3H/HeN mice during Chlamydia muridarum respiratory infection. We demonstrated that Chlamydia stimulated IL-17/IL-17R-associated responses in both Chlamydia-resistant C57BL/6 and Chlamydia-susceptible C3H/HeN mice. However, C3H/HeN mice developed a significantly greater IL-17/IL-17R-associated response than C57BL/6 mice did. This was reflected by an increase in IL-17 mRNA expression, a higher recall IL-17 production from splenocytes upon antigen restimulation, and higher production of Th17-related cytokines (IL-23 and IL-6) and chemokines (chemokine [C-X-C motif] ligand 2 [CXCL1]/keratinocyte-derived chemokine [KC] and CXCL2/macrophage inflammatory protein 1 [MIP2]) in C3H/HeN mice than in C57BL/6 mice. Furthermore, C3H/HeN mice displayed a massive accumulation of activated and preactivated neutrophils in the airway and lung parenchyma compared to their C57BL/6 counterparts. We further demonstrated that the skewed IL-17/Th17 profile in C3H/HeN mice was predisposed by a higher basal level of IL-17 receptor C (IL-17RC) expression and then further amplified by a higher inducible IL-17RA expression in lungs. Most importantly, in vivo delivery of IL-17RA antagonist that resulted in a 50% reduction in the neutrophilic infiltration in lungs was able to reverse the susceptible phenotype of C3H/HeN mice to respiratory Chlamydia infection. Thus, our data for the first time have demonstrated a critical role for the IL-17/IL-17R axis in regulating host susceptibility to Chlamydia infection in mice.

[Immune regulation by IL-27 for therapeutic usage]

Cytokine-mediated immunity plays a crucial role in the pathogenesis of various diseases including autoimmunity. Recently, IL-27 was identified, which along with IL-12, 23 and 35 belongs to the IL-12 cytokine family. These family members play roles in regulation of Th cell differentiation. IL-27 is unique in that while it induces Th1 differentiation, the same cytokine suppresses immune responses. In the absence of IL-27-mediated immunosuppression, hyper-production of various pro-inflammatory cytokines concomitant with severe inflammation in affected organs was observed in IL-27 receptor alpha chain (WSX-1)-deficient mice infected with Trypanosoma cruzi. Experimental allergic or inflammatory responses were also enhanced in WSX-1-deficient mice. The immunosuppressive effects of IL-27 depend on inhibition of the development of Th 17 cells (a newly identified inflammatory T helper population), and induction of IL-10 production. Moreover, administration of IL-27 or augmentation of IL-27 signaling suppresses some diseases of autoimmune or allergic origin, including encephalitis, arthritis, and systemic lupus erythematosus, demonstrating its potential in therapy of diseases mediated by inflammatory cytokines.

Mucosal immunization with iron receptor antigens protects against urinary tract infection

Uncomplicated infections of the urinary tract, caused by uropathogenic Escherichia coli, are among the most common diseases requiring medical intervention. A preventive vaccine to reduce the morbidity and fiscal burden these infections have upon the healthcare system would be beneficial. Here, we describe the results of a large-scale selection process that incorporates bioinformatic, genomic, transcriptomic, and proteomic screens to identify six vaccine candidates from the 5379 predicted proteins encoded by uropathogenic E. coli strain CFT073. The vaccine candidates, ChuA, Hma, Iha, IreA, IroN, and IutA, all belong to a functional class of molecules that is involved in iron acquisition, a process critical for pathogenesis in all microbes. Intranasal immunization of CBA/J mice with these outer membrane iron receptors elicited a systemic and mucosal immune response that included the production of antigen-specific IgM, IgG, and IgA antibodies. The cellular response to vaccination was characterized by the induction and secretion of IFN-gamma and IL-17. Of the six potential vaccine candidates, IreA, Hma, and IutA provided significant protection from experimental infection. In immunized animals, class-switching from IgM to IgG and production of antigen-specific IgA in the urine represent immunological correlates of protection from E. coli bladder colonization. These findings are an important first step toward the development of a subunit vaccine to prevent urinary tract infections and demonstrate how targeting an entire class of molecules that are collectively required for pathogenesis may represent a fundamental strategy to combat infections.

Th17 cells at the crossroads of innate and adaptive immunity against infectious diseases at the mucosa

T helper type 17 (Th17) cells are a distinct lineage of T cells that produce the effector molecules IL-17, IL-17F, IL-21, and IL-22. Although the role of Th17 cells in autoimmunity is well documented, there is growing evidence that the Th17 lineage and other interleukin (IL)-17-producing cells are critical for host defense against bacterial, fungal, and viral infections at mucosal surfaces. Here we summarize recent progress in our understanding of the function of IL-17-producing cells as a bridge between innate and adaptive immunity against infectious diseases at the mucosa.

Interleukin-17-producing gammadelta T cells selectively expand in response to pathogen products and environmental signals

Gammadelta T cells are an innate source of interleukin-17 (IL-17), preceding the development of the adaptive T helper 17 (Th17) cell response. Here we show that IL-17-producing T cell receptor gammadelta (TCRgammadelta) T cells share characteristic features with Th17 cells, such as expression of chemokine receptor 6 (CCR6), retinoid orphan receptor (RORgammat), aryl hydrocarbon receptor (AhR), and IL-23 receptor. AhR expression in gammadelta T cells was essential for the production of IL-22 but not for optimal IL-17 production. In contrast to Th17 cells, CCR6(+)IL-17-producing gammadelta T cells, but not other gammadelta T cells, express Toll-like receptors TLR1 and TLR2, as well as dectin-1, but not TLR4 and could directly interact with certain pathogens. This process was amplified by IL-23 and resulted in expansion, increased IL-17 production, and recruitment of neutrophils. Thus, innate receptor expression linked with IL-17 production characterizes TCRgammadelta T cells as an efficient first line of defense that can orchestrate an inflammatory response to pathogen-derived as well as environmental signals long before Th17 cells have sensed bacterial invasion.

Klebsiella pneumoniae triggers a cytotoxic effect on airway epithelial cells

BACKGROUND

Klebsiella pneumoniae is a capsulated Gram negative bacterial pathogen and a frequent cause of nosocomial infections. Despite its clinical relevance, little is known about the features of the interaction between K. pneumoniae and lung epithelial cells on a cellular level, neither about the role of capsule polysaccharide, one of its best characterised virulence factors, in this interaction.

RESULTS

The interaction between Klebsiella pneumoniae and cultured airway epithelial cells was analysed. K. pneumoniae infection triggered cytotoxicity, evident by cell rounding and detachment from the substrate. This effect required the presence of live bacteria and of capsule polysaccharide, since it was observed with isolates expressing different amounts of capsule and/or different serotypes but not with non-capsulated bacteria. Cytotoxicity was analysed by lactate dehydrogenase and formazan measurements, ethidium bromide uptake and analysis of DNA integrity, obtaining consistent and complementary results. Moreover, cytotoxicity of non-capsulated strains was restored by addition of purified capsule during infection. While a non-capsulated strain was avirulent in a mouse infection model, capsulated K. pneumoniae isolates displayed different degrees of virulence.

CONCLUSION

Our observations allocate a novel role to K. pneumoniae capsule in promotion of cytotoxicity. Although this effect is likely to be associated with virulence, strains expressing different capsule levels were not equally virulent. This fact suggests the existence of other bacterial requirements for virulence, together with capsule polysaccharide.

Neutrophil-mediated lung permeability and host defense proteins

Neutrophil recruitment to the alveolar space is associated with increased epithelial permeability. The present study investigated in mice whether neutrophil recruitment to the lung leads to accumulation of plasma-derived host defense proteins in the alveolar space and whether respiratory burst contributes to this increase in permeability. Albumin, complement C1q, and IgM were increased in bronchoalveolar lavage (BAL) fluid 6 h after intratracheal LPS challenge. Neutrophil depletion before LPS treatment completely prevented this increase in BAL fluid protein concentration. Respiratory burst was not detected in neutrophils isolated from BAL fluid, and BAL proteins were increased in mice deficient in a key subunit of the respiratory burst apparatus, gp91(phox), similar to wild-type mice. Neutrophil recruitment elicited by intratracheal instillation of the chemokines macrophage inflammatory protein-2 and keratinocyte-derived chemokine was also accompanied by accumulation of albumin, C1q, and IgM. During neutrophil recruitment to the alveolar space, epithelial permeability facilitates delivery of host defense proteins. The observed increase in epithelial permeability requires recruitment of neutrophils, but not activation of the respiratory burst, and occurs with chemokine-induced neutrophil migration independent of LPS exposure.

A MyD88-dependent early IL-17 production protects mice against airway infection with the obligate intracellular pathogen Chlamydia muridarum

We found that IL-17, a signature cytokine of Th17, was produced early in the innate immunity phase after an intranasal infection with the obligate intracellular pathogen Chlamydia muridarum. The airway IL-17, which peaked at 48 h after infection, was dependent on live chlamydial organism replication and MyD88-mediated signaling pathways. Treatment with antibiotics or knockout of the MyD88 gene, but not Toll/IL receptor domain-containing adapter-inducing IFN-beta, can block the early IL-17 production. Treatment of mice with an anti-IL-17-neutralizing mAb enhanced growth of chlamydial organisms in the lung, dissemination to other organs, and decreased mouse survival, whereas treatment with an isotype-matched control IgG had no effect. Although IL-17 did not directly affect chlamydial growth in cell culture, it enhanced the production of other inflammatory cytokines and chemokines by Chlamydia-infected cells and promoted neutrophil infiltration in mouse airways during chlamydial infection, which may contribute to the antichlamydial effect of IL-17. These observations suggest that an early IL-17 response as an innate immunity component plays an important role in initiating host defense against infection with intracellular bacterial pathogens in the airway.

The IL-23/Th17 axis in the immunopathogenesis of psoriasis

Abnormal production of inflammatory mediators is believed to play an important role in the pathogenesis of psoriasis. Emerging data, both in mice and in humans, put the spotlight on a new subset of T helper (Th) cells, in part characterized by their production of IL-17 and accordingly named Th17 cells. Here, we review the development, characterization, and function of human Th17 cells as well as the crucial role of IL-23 in the context of Th17-cell-dependent chronic inflammation in psoriasis. We further discuss recent clinical trials targeting the IL-23/Th17 axis in psoriasis.

Barrier immunity and IL-17

CD4+ T(H)17 cells display a featured role in barrier immunity. This effector population of T cells is important for clearance of microorganisms but can also promote autoimmunity at barrier sites. Recent work has indicated that these effector cells share a pathway with CD4+ regulatory T cells (T(R) cells) that also have a critical function in barrier protection and immune regulation. The development and function of T(H)17 cells, and their relationship with T(R) cells are discussed.

Functional interleukin-17 receptor A is expressed in central nervous system glia and upregulated in experimental autoimmune encephalomyelitis

BACKGROUND

Interleukin-17A (IL-17A) is the founding member of a novel family of inflammatory cytokines that plays a critical role in the pathogenesis of many autoimmune diseases, including multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). IL-17A signals through its receptor, IL-17RA, which is expressed in many peripheral tissues; however, expression of IL-17RA in the central nervous system (CNS) and its role in CNS inflammation are not well understood.

METHODS

EAE was induced in C57Bl/6 mice by immunization with myelin oligodendroglial glycoprotein. IL-17RA expression in the CNS was compared between control and EAE mice using RT-PCR, in situ hybridization, and immunohistochemistry. Cell-type specific expression was examined in isolated astrocytic and microglial cell cultures. Cytokine and chemokine production was measured in IL-17A treated cultures to evaluate the functional status of IL-17RA.

RESULTS

Here we report increased IL-17RA expression in the CNS of mice with EAE, and constitutive expression of functional IL-17RA in mouse CNS tissue. Specifically, astrocytes and microglia express IL-17RA in vitro, and IL-17A treatment induces biological responses in these cells, including significant upregulation of MCP-1, MCP-5, MIP-2 and KC chemokine secretion. Exogenous IL-17A does not significantly alter the expression of IL-17RA in glial cells, suggesting that upregulation of chemokines by glial cells is due to IL-17A signaling through constitutively expressed IL-17RA.

CONCLUSION

IL-17RA expression is significantly increased in the CNS of mice with EAE compared to healthy mice, suggesting that IL-17RA signaling in glial cells can play an important role in autoimmune inflammation of the CNS and may be a potential pathway to target for therapeutic interventions.

Lipocalin 2 is required for pulmonary host defense against Klebsiella infection

Antimicrobial proteins comprise a significant component of the acute innate immune response to infection. They are induced by pattern recognition receptors as well as by cytokines of the innate and adaptive immune pathways and play important roles in infection control and immunomodulatory homeostasis. Lipocalin 2 (siderocalin, NGAL, 24p3), a siderophore-binding antimicrobial protein, is critical for control of systemic infection with Escherichia coli; however, its role in mucosal immunity in the respiratory tract is unknown. In this study, we found that lipocalin 2 is rapidly and robustly induced by Klebsiella pneumoniae infection and is TLR4 dependent. IL-1beta and IL-17 also individually induce lipocalin 2. Mucosal administration of IL-1beta alone could reconstitute the lipocalin 2 deficiency in TLR4 knockout animals and rescue them from infection. Lipocalin 2-deficient animals have impaired lung bacterial clearance in this model and mucosal reconstitution of lipocalin 2 protein in these animals resulted in rescue of this phenotype. We conclude that lipocalin 2 is a crucial component of mucosal immune defense against pulmonary infection with K. pneumoniae.

A pathogenic role of IL- 17 at the early stage of corneal allograft rejection

PURPOSE

Th17, recently identified as a new subset of effector Th cells, has been shown to be involved in microbe infection and autoimmunity. However, the role of these cells in organ allograft rejection remains largely unknown. In this study, we investigate whether Th17 cells participate in allogeneic corneal rejection in a mouse model.

METHODS

Donor cornea (C57BL/6) was transplanted into orthotopic graft bed of Balb/c recipients. At different time points after keratoplasty, the expression of Th17 and Th1- related cytokines in draining cervical lymph nodes (LN) and grafted cornea was examined by flow cytometry and quantitative RT- PCR, respectively. Furthermore, IL- 17(-/-) Balb/c mice were used to determine the effects of Th17 cells on allogeneic cornea survival. Finally, the profiles of Th1 and proinflammatory cytokines in IL- 17(-/-) recipients after transplantation were examined.

RESULTS

Th17 expression was enhanced significantly in inflamed transplants and draining lymph nodes at the early stage of allocorneal rejection, while upregulation of Th1 producing IFN- gamma was seen in the late phase. Upon activation by allogeneic accessory cells, responder cells in draining LN from transplanted recipients secreted high levels of IL- 6, TGF- beta and IL- 21 compared to controls, which may drive naive T cells to differentiate into Th17 cells. Importantly, IL- 17 deficiency led to the delayed development of allogeneic rejection, but did not affect the overall survival time of transplants. This effect correlated with restrained Th1 polarization and decreased production of proinflammatory cytokines.

CONCLUSION

Th17 cells play a disease-promoting role at the early stage of corneal allograft rejection.

Interleukin-17 causes neutrophil mediated inflammation in ovalbumin-induced uveitis in DO11.10 mice

T cell-mediated uveitis is strongly associated with many systemic inflammatory disorders. Th17 cells are a novel T cell subset characterized by production of interleukin (IL)-17. In this study, we used DO11.10 mice to investigate the role of IL-17 in the pathogenesis of uveitis. CD4(+) T cells in DO11.10 mice are genetically engineered to react with ovalbumin (OVA). IL-17 expression was determined by real-time PCR and ELISPOT. Uveitis was induced by intravitreal injection of OVA, and ocular inflammation was evaluated by intravital microscopy. OVA challenge significantly induced IL-17 production by DO11.10 splenocytes in vitro. Next, we examined whether OVA challenge could elicit local inflammation and induce IL-17 in vivo. OVA elicited marked neutrophil-predominant inflammatory cell infiltration in the eyes. This leukocyte influx was mediated by CD4(+) lymphocytes as evidenced by significant inhibition of the ocular inflammation by CD4+ depleting antibody. Compared to control mice, OVA treatment induced IL-17 expression. Moreover, anti-IL-17 antibody markedly reduced OVA-mediated ocular inflammation. Finally, the neutralization of IL-17 attenuated ocular expression of CXCL2 and CXCL5, two cytokines which are chemotactic for neutrophils. Our study suggests that IL-17 is implicated in the pathogenesis of this T cell-mediated model of uveitis in part through neutrophil chemotaxis as a downstream effect of IL-17.

IL-17 and anti-bacterial immunity: protection versus tissue damage

IL-17 can impact health in a variety of ways. It is protective for some pathogens but it is also associated with tissue damaging inflammation. By examining the role of IL-17 in a variety of bacterial infections the mechanisms by which this cytokine mediates both protection and damage can be dissected. A key element in understanding the role of this cytokine is determining where and when it is acting. Dissecting its essential protective role from its immunopathologic role will allow for improved intervention in both acute and chronic disease.

Anti-inflammatory effects of IL-17A on Helicobacter pylori-induced gastritis

Helicobacter pylori-induced immune responses are skewed toward a T helper (Th) 1 phenotype. IL-17-producing Th17 cells have recently been discovered, and we examined the role of IL-17A in H. pylori-induced gastritis. Six months after inoculation with H. pylori, the mice received an intraperitoneal injection of recombinant IL-17A, anti-IL-17A antibody or irrelevant IgG(2a) for 3days. H. pylori infection markedly increased mRNA for IL-17A. Double immunofluorescence studies showed that IL-17A proteins were expressed on CD4(+) T cells, macrophages, and dendritic cells. H. pylori infection elevated mRNAs for IL-12, IFN-gamma, and TNF-alpha with increase in myeloperoxidase activity, whereas it did not affect mRNAs for IL-4 and IL-5. Neutralization of IL-17A elevated mRNAs for IFN-gamma and TNF-alpha, and myeloperoxidase activity, whereas recombinant IL-17A had a tendency to reduce these parameters. In conclusion, IL-17A exerts anti-inflammatory effects on H. pylori-induced gastritis through suppression of Th1 differentiation.

Regulation of immune responses by interleukin-27

Cytokine-mediated immunity plays a crucial role in the pathogenesis of various diseases including autoimmunity. Recently, interleukin-27 (IL-27) was identified, which, along with IL-12, IL-23, and IL-35, belongs to the IL-12 cytokine family. These family members play roles in the regulation of T helper (Th) cell differentiation. IL-27 is unique in that while it induces Th1 differentiation, the same cytokine suppresses immune responses. In the absence of IL-27-mediated immunosuppression, hyper-production of various pro-inflammatory cytokines concomitant with severe inflammation in affected organs was observed in IL-27 receptor alpha chain (WSX-1)-deficient mice infected with Trypanosoma cruzi. Experimental allergic or inflammatory responses were also enhanced in WSX-1-deficient mice. The immunosuppressive effects of IL-27 depend on inhibition of the development of Th17 cells (a newly identified inflammatory T-helper population) and induction of IL-10 production. Moreover, administration of IL-27 or augmentation of IL-27 signaling suppresses some diseases of autoimmune or allergic origin, demonstrating its potential in therapy of diseases mediated by inflammatory cytokines. In this review, we discuss recent studies on the role of IL-27 in immunity to parasitic and bacterial infections as well as in allergy and autoimmunity in view of its pro- and anti-inflammatory properties.

Neutrophil mobilization and clearance in the bone marrow

The bone marrow is the site of neutrophil production, a process that is regulated by the cytokine granulocyte colony-stimulating factor (G-CSF). Mature neutrophils are continually released into the circulation, with an estimated 10(11) neutrophils exiting the bone marrow daily under basal conditions. These leucocytes have a short half-life in the blood of approximately 6.5 hr, and are subsequently destroyed in the spleen, liver and indeed the bone marrow itself. Additionally, mature neutrophils are retained in the bone marrow by the stromal cell-derived factor (SDF-1alpha)/chemokine (C-X-C motif) receptor 4 (CXCR4) chemokine axis and form the bone marrow reserve. Following infection or inflammatory insult, neutrophil release from the bone marrow reserve is substantially elevated and this process is mediated by the co-ordinated actions of cytokines and chemokines. In this review we discuss the factors and molecular mechanisms regulating the neutrophil mobilization and consider the mechanisms and functional significance of neutrophil clearance via the bone marrow.

A novel IL-17-dependent mechanism of cross protection: respiratory infection with mycoplasma protects against a secondary listeria infection

Immune responses to pathogens occur within the context of current and previous infections. Cross protection refers to the phenomena where infection with a particular pathogen provides enhanced resistance to a subsequent unrelated pathogen in an antigen-independent manner. Proposed mechanisms of antigen-independent cross protection have involved the secretion of IFN-gamma, which activates macrophages, thus providing enhanced innate immunity against the secondary viral or bacterial pathogen. Here we provide evidence that a primary infection with the chronic respiratory pathogen, Mycoplasma pulmonis, provides a novel form of cross protection against a secondary infection with Listeria monocytogenes that is not mediated by IFN-gamma, but instead relies upon IL-17 and mobilization of neutrophils. Mice infected with M. pulmonis have enhanced clearance of L. monocytogenes from the spleen and liver, which is associated with increased numbers of Gr-1(+)CD11b(+) cells and higher levels of IL-17. This enhanced clearance of L. monocytogenes was absent in mice depleted of Gr-1(+) cells or in mice deficient in the IL-17 receptor. Additionally, both the IL-17 receptor and neutrophils were essential for optimal clearance of M. pulmonis. Thus, a natural component of the immune response directed against M. pulmonis was able to enhance clearance of L. monocytogenes.

Critical loss of the balance between Th17 and T regulatory cell populations in pathogenic SIV infection

Chronic immune activation and progression to AIDS are observed after SIV infection in macaques but not in natural host primate species. To better understand this dichotomy, we compared acute pathogenic SIV infection in pigtailed macaques (PTs) to non-pathogenic infection in African green monkeys (AGMs). SIVagm-infected PTs, but not SIVagm-infected AGMs, rapidly developed systemic immune activation, marked and selective depletion of IL-17-secreting (Th17) cells, and loss of the balance between Th17 and T regulatory (Treg) cells in blood, lymphoid organs, and mucosal tissue. The loss of Th17 cells was found to be predictive of systemic and sustained T cell activation. Collectively, these data indicate that loss of the Th17 to Treg balance is related to SIV disease progression.

Interleukin-17 in host defence against bacterial, mycobacterial and fungal pathogens

The mammalian immune system is intricately regulated, allowing for potent pathogen-specific immunity to be rapidly activated in response to infection with a broad and diverse array of potential pathogens. As a result of their ability to differentiate into distinct effector lineages, CD4 T cells significantly contribute to pathogen-specific adaptive immune responses. Through the production of effector cytokines, CD4 T helper (Th) cells orchestrate the precise mobilization of specific immune cells to eradicate infection. The protective effects of the newly identified lineage of Th17 cells against pathogens like Klebsiella pneumoniae, Citrobacter rodentium and Candida albicans indicate the capacity of Th17 cells to confer protection against extracellular bacterial and fungal pathogens, filling a critical void in host immunity not covered by the classically described Th1 lineage that activates immunity to intracellular pathogens or the Th2 lineage that is important in protection against mucosal parasitic pathogens. Host defence by Th17 cells extends beyond protection against extracellular bacterial and fungal pathogens, as demonstrated in infections against intracellular bacteria like Listeria monocytogenes and Salmonella enterica, as well as Mycobacterium tuberculosis. Herein, we summarize both experimental data from mouse infection models and epidemiological studies in humans that demonstrate the protective effects of interleukin-17 and Th17 CD4 T cells in immunity to bacterial, mycobacterial and fungal pathogens.

IL-17 contributes to CD4-mediated graft-versus-host disease

CD4(+) interleukin-17 (IL-17)(+) T cells (Th17 cells) have been implicated in allograft rejection of solid organs and several autoimmune diseases. However, the functional role of Th17 cells in the development of acute graft-versus-host disease (GVHD) has not been well-characterized. We detected significant numbers of alloreactive CD4(+) donor T cells expressing IL-17, IL-17F, or IL-22 in the lymphoid organs of recipients of an allogeneic bone marrow transplant. We found no differences in GVHD mortality or graft-versus-tumor (GVT) activity between wild type (WT) and IL-17(-/-) T-cell recipients. However, upon transfer of murine IL-17(-/-) CD4(+) T cells in an allogeneic BMT model, GVHD development was significantly delayed behind recipients of WT CD4(+) T cells, yet overall GVHD mortality was unaffected. Moreover, recipients of IL-17(-/-) CD4(+) T cells had significantly fewer Th1 cells during the early stages of GVHD. Furthermore, we observed a decrease in the number of IFN-gamma-secreting macrophages and granulocytes and decreased production of proinflammatory cytokines (interferon [IFN]-gamma, IL-4, and IL-6) in recipients of IL-17(-/-) CD4(+) T cells. We conclude that IL-17 is dispensable for GVHD and GVT activity by whole T cells, but contributes to the early development of CD4-mediated GVHD by promoting production of proinflammatory cytokines.

Interacting neuroendocrine and innate and acquired immune pathways regulate neutrophil mobilization from bone marrow following hemorrhagic shock

Polymorphonuclear neutrophils (PMN) are critical innate immune effector cells that either protect the host or exacerbate organ dysfunction by migrating to injured or inflamed tissues. Resuscitated hemorrhagic shock following major trauma promotes the development of organ inflammation by priming PMN migration and activation in response to a second, often trivial, stimulus (a so-called "two hit" phenomenon). PMN mobilization from bone marrow supports a sustained, hemorrhagic shock/resuscitation (HS/R)-primed migration of PMN. We addressed the role and mechanism of HS/R in regulating PMN egress from bone marrow. We demonstrate that HS/R through the alarmin HMGB1 induces IL-23 secretion from macrophages in an autocrine and TLR4 signaling-dependent manner. In turn IL-23, through an IL-17 G-CSF-mediated mechanism, induces PMN egress from bone marrow. We also show that beta-adrenergic receptor activation by catecholamine of macrophages mediates the HS/R-induced release of HMGB1. These data indicate that HS/R, a global ischemia/reperfusion stimulus, regulates PMN mobilization through a series of interacting pathways that include neuroendocrine and innate and acquired immune systems. Blocking this novel signaling axis may present a novel therapeutic target for posttrauma inflammation.

Interleukin-23 orchestrates mucosal responses to Salmonella enterica serotype Typhimurium in the intestine

Salmonella enterica serotype Typhimurium causes an acute inflammatory reaction in the ceca of streptomycin-pretreated mice that involves T-cell-dependent induction of gamma interferon (IFN-gamma), interleukin-22 (IL-22), and IL-17 expression (genes Ifn-gamma, Il-22, and Il-17, respectively). We investigated here the role of IL-23 in initiating these inflammatory responses using the streptomycin-pretreated mouse model. Compared to wild-type mice, the expression of IL-17 was abrogated, IL-22 expression was markedly reduced, but IFN-gamma expression was normal in the ceca of IL-23p19-deficient mice during serotype Typhimurium infection. IL-23p19-deficient mice also exhibited a markedly reduced expression of regenerating islet-derived 3 gamma, keratinocyte-derived cytokine, and reduced neutrophil recruitment into the cecal mucosa during infection. Analysis of CD3(+) lymphocytes in the intestinal mucosa by flow cytometry revealed that alphabeta T cells were the predominant cell type expressing the IL-23 receptor in naive mice. However, a marked increase in the number of IL-23 receptor-expressing gammadelta T cells was observed in the lamina propria during serotype Typhimurium infection. Compared to wild-type mice, gammadelta T-cell-receptor-deficient mice exhibited blunted expression of IL-17 during serotype Typhimurium infection, while IFN-gamma expression was normal. These data suggested that gammadelta T cells are a significant source, but not the sole source, of IL-17 in the acutely inflamed cecal mucosa of mice. Collectively, our results point to IL-23 as an important player in initiating a T-cell-dependent amplification of inflammatory responses in the intestinal mucosa during serotype Typhimurium infection.

Induction, function and regulation of IL-17-producing T cells

Recent reports have provided convincing evidence that IL-17-producing T cells play a key role in the pathogenesis of organ-specific autoimmune diseases, a function previously attributed exclusively to IFN-gamma-secreting Th1 cells. Furthermore, it appears that IL-17-producing T cells can also function with Th1 cells to mediate protective immunity to pathogens. Although much of the focus has been on IL-17-secreting CD4+ T cells, termed Th17 cells, CD8+ T cells, gammadelta T cells and NKT cells are also capable of secreting IL-17. The differentiation of Th17 cells from naïve T cells appears to involve signals from TGF-beta, IL-6, IL-21, IL-1beta and IL-23. Furthermore, IL-1alpha or IL-1beta in synergy with IL-23 can promote IL-17 secretion from memory T cells. The induction or function of Th17 cells is regulated by cytokines secreted by the other major subtypes of T cells, including IFN-gamma, IL-4, IL-10 and at high concentrations, TGF-beta. The main function of IL-17-secreting T cells is to mediate inflammation, by stimulating production of inflammatory cytokines, such as TNF-alpha, IL-1beta and IL-6, and inflammatory chemokines that promote the recruitment of neutrophils and macrophages.

IL-17 is involved in Helicobacter pylori-induced gastric inflammatory responses in a mouse model

BACKGROUND

Helicobacter pylori (H. pylori) is the major cause of chronic active gastritis and peptic ulcer disease. Recent studies have shown that H. pylori produces various cytokines that are related to neutrophil or mononuclear cell accumulation. Interleukin-17 (IL-17) is the founding member of an emerging family of inflammatory cytokines whose biological activities remain incompletely defined. In this study, the contributions of IL-17 to the induction of gastric inflammation and to the protection from H. pylori infection were investigated using IL-17 gene-knockout (IL-17(-/-)) mice.

MATERIALS AND METHODS

IL-17(-/-)and wild-type C57BL/6 mice were challenged with H. pylori CPY2052 (2 x 10(8) CFU/mL) and the histological and microbiological evaluation were carried out at specified times. IL-17 and myeloperoxidase (MPO) protein levels in tissues were assayed in duplicate using ELISA kits.

RESULTS

In wild-type mice, IL-17 was undetected at baseline; however, the protein expression of IL-17 was induced after infection with H. pylori. A severe infiltration of neutrophils appeared in the submucosa and the lamina propria in wild-type mice. In contrast, the degree of neutrophil infiltration in IL-17(-/-) mice was significantly lower than that in wild-type mice. Although wild-type mice infected with H. pylori showed drastically higher MPO activity compared with uninfected wild-type mice, any significant increase in the enzyme activity was not revealed in infected IL-17(-/-) mice. The number of H. pylori colonized in the stomach of IL-17(-/-) mice was significantly lower than that of wild-type mice from 1 to 6 months after infection.

CONCLUSIONS

These results suggest that IL-17 may play an important role in the inflammatory response to the H. pylori infection and ultimately influence the outcome of the H. pylori-associated disease.

IL-17 is a critical component of vaccine-induced protection against lung infection by lipopolysaccharide-heterologous strains of Pseudomonas aeruginosa

In a murine model of acute fatal pneumonia, we previously showed that nasal immunization with a live-attenuated aroA deletant of Pseudomonas aeruginosa strain PAO1 elicited LPS serogroup-specific protection, indicating that opsonic Ab to the LPS O Ag was the most important immune effector. Because P. aeruginosa strain PA14 possesses additional virulence factors, we hypothesized that a live-attenuated vaccine based on PA14 might elicit a broader array of immune effectors. Thus, an aroA deletant of PA14, denoted PA14DeltaaroA, was constructed. PA14DeltaaroA-immunized mice were protected against lethal pneumonia caused not only by the parental strain but also by cytotoxic variants of the O Ag-heterologous P. aeruginosa strains PAO1 and PAO6a,d. Remarkably, serum from PA14DeltaaroA-immunized mice had very low levels of opsonic activity against strain PAO1 and could not passively transfer protection, suggesting that an antibody-independent mechanism was needed for the observed cross-serogroup protection. Compared with control mice, PA14DeltaaroA-immunized mice had more rapid recruitment of neutrophils to the airways early after challenge. T cells isolated from P. aeruginosa DeltaaroA-immunized mice proliferated and produced IL-17 in high quantities after coculture with gentamicin-killed P. aeruginosa. Six hours following challenge, PA14DeltaaroA-immunized mice had significantly higher levels of IL-17 in bronchoalveolar lavage fluid compared with unimmunized, Escherichia coli-immunized, or PAO1DeltaaroA-immunized mice. Antibody-mediated depletion of IL-17 before challenge or absence of the IL-17 receptor abrogated the PA14DeltaaroA vaccine's protection against lethal pneumonia. These data show that IL-17 plays a critical role in antibody-independent vaccine-induced protection against LPS-heterologous strains of P. aeruginosa in the lung.

Interplay between effector Th17 and regulatory T cells

INTRODUCTION

Over two decades ago, T helper cells were classified into its functional subsets. Soon after the classical observation of Mosmann et al., immunologists agreed to accept the Th1/Th2 paradigm of the T helper subsets. Each subset is not only characterized by its specific cytokines pattern and effector functions but also by their properties to counter regulate each other's functions. This classification helped to understand the complex principles of T helper cell biology and allowed us to comprehend different immune reactions in context of Th1 and Th2 subsets.

DISCUSSION

Although Th1 subsets thought to be the crucial player for most of the organ-specific autoimmune diseases like multiple sclerosis and type-1 diabetes but the loss of Th1 dominant cytokine, IFN-gamma did not prevent the development of autoimmunity which raised the possibility of involvement of other Th subsets, different from Th1 cells in the induction of autoimmunity.

CONCLUSION

Recently, a new subset of Th cells that predominantly produce IL-17 and induce autoimmunity has been discovered, and it is believed that this subset may be the major cell type involved in orchestrating tissue inflammation and autoimmunity. Recent data propose that the differentiation factors of Th17 cells reveal a link with induction of Foxp3(+) regulatory T cells. Here, we review the interplay between Th17 and Foxp3(+) T-reg cells and Tr1 cells during autoimmune inflammatory reaction.

Interleukin-17A mediates acquired immunity to pneumococcal colonization

Although anticapsular antibodies confer serotype-specific immunity to pneumococci, children increase their ability to clear colonization before these antibodies appear, suggesting involvement of other mechanisms. We previously reported that intranasal immunization of mice with pneumococci confers CD4+ T cell–dependent, antibody- and serotype-independent protection against colonization. Here we show that this immunity, rather than preventing initiation of carriage, accelerates clearance over several days, accompanied by neutrophilic infiltration of the nasopharyngeal mucosa. Adoptive transfer of immune CD4+ T cells was sufficient to confer immunity to naïve RAG1^−/− mice. A critical role of interleukin (IL)-17A was demonstrated: mice lacking interferon-γ or IL-4 were protected, but not mice lacking IL-17A receptor or mice with neutrophil depletion. In vitro expression of IL-17A in response to pneumococci was assayed: lymphoid tissue from vaccinated mice expressed significantly more IL-17A than controls, and IL-17A expression from peripheral blood samples from immunized mice predicted protection in vivo. IL-17A was elicited by pneumococcal stimulation of tonsillar cells of children or adult blood but not cord blood. IL-17A increased pneumococcal killing by human neutrophils both in the absence and in the presence of antibodies and complement. We conclude that IL-17A mediates pneumococcal immunity in mice and probably in humans; its elicitation in vitro could help in the development of candidate pneumococcal vaccines.

The bacterium Streptococcus pneumoniae (pneumococcus) causes serious disease in children and the elderly, including pneumonia and meningitis (inflammation of the brain). Carriage of pneumococcus in the nose is a necessary first step for most infections. As children age, they carry pneumococcus for shorter periods of time and their risk of disease decreases also. The mechanisms underlying this age-related decrease of carriage are not well understood. A deeper understanding of resistance to colonization would enable us to develop better pneumococcal vaccines. Using experimental mouse models, we show that repeated exposure to pneumococci leads to a subsequent reduction in duration of pneumococcal carriage, similar to what is observed in humans. We identify the immune cells that are responsible for this process, so-called T_H17 cells, which release a factor that enables human blood cells to kill pneumococcus more efficiently. We show that these T_H17 cells exist in adults and children, but not in newborn babies, which suggests that they may arise as a consequence of humans being exposed to pneumococcus. We describe an assay for the measurement of these cells in humans. Such an assay could facilitate the development of novel vaccines directed against pneumococcal carriage.

IL-17A produced by gammadelta T cells plays a critical role in innate immunity against listeria monocytogenes infection in the liver

IL-17A is originally identified as a proinflammatory cytokine that induces neutrophils. Although IL-17A production by CD4(+) Th17 T cells is well documented, it is not clear whether IL-17A is produced and participates in the innate immune response against infections. In the present report, we demonstrate that IL-17A is expressed in the liver of mice infected with Listeria monocytogenes from an early stage of infection. IL-17A is important in protective immunity at an early stage of listerial infection in the liver because IL-17A-deficient mice showed aggravation of the protective response. The major IL-17A-producing cells at the early stage were TCR gammadelta T cells expressing TCR Vgamma4 or Vgamma6. Interestingly, TCR gammadelta T cells expressing both IFN-gamma and IL-17A were hardly detected, indicating that the IL-17A-producing TCR gammadelta T cells are distinct from IFN-gamma-producing gammadelta T cells, similar to the distinction between Th17 and Th1 in CD4(+) T cells. All the results suggest that IL-17A is a newly discovered effector molecule produced by TCR gammadelta T cells, which is important in innate immunity in the liver.

IL-17F/IL-17R interaction stimulates granulopoiesis in mice

OBJECTIVE

IL-17F, a member of the interleukin (IL)-17 cytokine family, most closely resembles IL-17A structurally. IL-17A is a potent stimulator of granulopoiesis; its expression is induced in response to microbial challenge. Although IL-17F is considered to be a weak IL-17A analog that is also mediating its effect via IL-17R, its exact role and in vivo functions are unknown. Our goal was to determine the in vivo activity of IL-17F on granulopoiesis as well as on release of granulopoiesis-stimulating downstream cytokines in mice and directly compare its effect to IL-17A.

MATERIALS AND METHODS

Murine IL-17A (mIL-17A) or IL-17F (mIL-17F) was expressed in vivo in C57BL6 mice using adenoviral gene transfer technology. Peripheral cell counts were assessed as well as hematopoietic precursors using colony-forming assays at set time points. Downstream cytokines were measured using enzyme-linked immunosorbent assay and reverse transcriptase polymerase chain reaction.

RESULTS

We found mIL-17F to have similar expression kinetics as mIL-17A in splenocytes in vitro and in vivo, following challenge with microbial agents. Overexpression of mIL-17F in vivo resulted in similar neutrophilia and only in slightly reduced myeloid progenitor expansion when compared to mIL-17A. In vivo, there was no difference in releases for granulocyte-macrophage colony-stimulating factor; regulated on activation, normal T expressed and secreted; interferon-inducible protein-10; IL-6; and monocyte chemotactic protein-1 between either cytokine. IL-1A, macrophage inflammatory protein -2 (MIP), KC, and granulocyte colony-stimulating factor expression was approximately half of that seen with mIL-17A.

CONCLUSION

Both IL-17A and IL-17F are induced by similar stimuli, have similar expression kinetics and despite only minimal in vitro activity for IL-17F, surprisingly they exert similar in vivo bioactivity. IL-17F bioactivity appears to be augmented in vivo through mechanisms that require further investigation.

Tracing functional antigen-specific CCR6 Th17 cells after vaccination

Background

The function of T helper cell subsets in vivo depends on their location, and one hallmark of T cell differentiation is the sequential regulation of migration-inducing chemokine receptor expression. CC-chemokine receptor 6 (CCR6) is a trait of tissue-homing effector T cells and has recently been described as a receptor on T helper type 17 (Th17) cells. Th17 cells are associated with autoimmunity and the defence against certain infections. Although, the polarization of Th cells into Th17 cells has been studied extensively in vitro, the development of those cells during the physiological immune response is still elusive.

Methodology/Principal Findings

We analysed the development and functionality of Th17 cells in immune-competent mice during an ongoing immune response. In naïve and vaccinated animals CCR6⁺ Th cells produce IL-17. The robust homeostatic proliferation and the presence of activation markers on CCR6⁺ Th cells indicate their activated status. Vaccination induces antigen-specific CCR6⁺ Th17 cells that respond to in vitro re-stimulation with cytokine production and proliferation. Furthermore, depletion of CCR6⁺ Th cells from donor leukocytes prevents recipients from severe disease in experimental autoimmune encephalomyelitis, a model for multiple sclerosis in mice.

Conclusions/Significance

In conclusion, we defined CCR6 as a specific marker for functional antigen-specific Th17 cells during the immune response. Since IL-17 production reaches the highest levels during the immediate early phase of the immune response and the activation of Th17 cells precedes the Th1 cell differentiation we tent to speculate that this particular Th cell subset may represent a first line effector Th cell subpopulation. Interference with the activation of this Th cell subtype provides an interesting strategy to prevent autoimmunity as well as to establish protective immunity against infections.

IFN-gamma regulated chemokine production determines the outcome of Staphylococcus aureus infection

Immunomodulatory therapy represents an attractive approach in treating multidrug-resistant infections. Developing this therapy necessitates a lucid understanding of host defense mechanisms. Neutrophils represent the first line of systemic defense during Staphylococcus aureus infections. However, recent research suggests that survival of S. aureus inside neutrophils may actually contribute to pathogenesis, indicating that neutrophil trafficking to the infection site must be tightly regulated to ensure efficient microbial clearance. We demonstrate that neutrophil-regulating T cells are activated during S. aureus infection and produce cytokines that control the local neutrophil response. S. aureus capsular polysaccharide activates T cell production of IFN-gamma in a novel MHC class II-dependent mechanism. During S. aureus surgical wound infection, the presence of IFN-gamma at the infection site depends upon alphabetaTCR+ cells and functions to regulate CXC chemokine production and neutrophil recruitment in vivo. We note that the reduced neutrophil response seen in IFN-gamma-/- mice during S. aureus infection is associated with reduced tissue bacterial burden. CXC chemokine administration to the infection site resulted in an increased survival of viable S. aureus inside neutrophils isolated from the wound. These data demonstrate that T cell-derived IFN-gamma generates a neutrophil-rich environment that can potentiate S. aureus pathogenesis by facilitating bacterial survival within the neutrophil. These findings suggest avenues for novel immunomodulatory approaches to control S. aureus infections.

IL-17A inhibits the expansion of IL-17A-producing T cells in mice through "short-loop" inhibition via IL-17 receptor

IL-23 and IL-17A regulate granulopoiesis through G-CSF, the main granulopoietic cytokine. IL-23 is secreted by activated macrophages and dendritic cells and promotes the expansion of three subsets of IL-17A-expressing neutrophil-regulatory T (Tn) cells; CD4(-)CD8(-)alphabeta(low), CD4(+)CD8(-)alphabeta(+) (Th17), and gammadelta(+) T cells. In this study, we investigate the effects of IL-17A on circulating neutrophil levels using IL-17R-deficient (Il17ra(-/-)) mice and Il17ra(-/-)Itgb2(-/-) mice that lack both IL-17R and all four beta(2) integrins. IL-17R deficiency conferred a reduction in neutrophil numbers and G-CSF levels, as did Ab blockade against IL-17A in wild-type mice. Bone marrow transplantation revealed that IL-17R expression on nonhemopoietic cells had the greatest effects on regulating blood neutrophil counts. Although circulating neutrophil numbers were reduced, IL-17A expression, secretion, and the number of IL-17A-producing Tn cells were elevated in Il17ra(-/-) and Il17ra(-/-)Itgb2(-/-) mice, suggesting a negative feedback effect through IL-17R. The negative regulation of IL-17A-producing T cells and IL-17A and IL-17F gene expression through the interactions of IL-17A or IL-17F with IL-17R was confirmed in splenocyte cultures in vitro. We conclude that IL-17A regulates blood neutrophil counts by inducing G-CSF production mainly in nonhemopoietic cells. IL-17A controls the expansion of IL-17A-producing Tn cell populations through IL-17R.

IL-17A is produced by Th17, gammadelta T cells and other CD4- lymphocytes during infection with Salmonella enterica serovar Enteritidis and has a mild effect in bacterial clearance

T(h)17 cells represent a new pro-inflammatory T(h) cell lineage distinct from T(h)1 and T(h)2 cells. T(h)17 cells have been shown to be involved in extracellular bacterial infection but their role in intracellular infection remains unclear. We found antigen-specific IL-17A production during a systemic infection of mice with the facultative intracellular bacterium Salmonella enterica serovar Enteritidis (S. Enteritidis) and examined the function and cellular source of IL-17A during the adaptive immune response to S. Enteritidis. Infected IL-17A-/- mice survived completely after inoculation with the highest infection dose found to be sub-lethal for wild-type (WT) C57BL/6 mice. However, at 20 and 80 days post-infection (d.p.i.), we repeatedly found mildly elevated bacterial burden in spleen and liver of IL-17A-/- mice as compared with WT mice. Overall, IL-17A-/- mice showed reduced clearance of S. Enteritidis. S. Enteritidis-specific IL-17A production was induced in splenocytes and lymph node cells of infected WT mice at both time points, 20 and 80 d.p.i. Classical CD4+ T(h)17 cells developed upon infection with Salmonella. CD4- gammadelta TCR+ and CD4- gammadelta TCR- cells were found to be additional IL-17A-producing cell populations. In infected IL-17A-/- mice, a normal T(h)1 cytokine profile was observed consistent with the overall subtle phenotype. Nevertheless, in the absence of IL-17A, recruitment of neutrophils and delayed-type hypersensitivity (DTH) reactivity was significantly compromised. Our data indicate that IL-17A responses are induced by Salmonella and mildly contribute to protective immunity during S. Enteritidis infection. Thus, IL-17A complements the IL-12/IFN-gamma axis which is essential for protective immunity against salmonellosis in mice and men.

The role of the bone marrow in neutrophil clearance under homeostatic conditions in the mouse

In humans, 10(11) neutrophils are released from the bone marrow per day, and these cells have a half-life in the blood of only approximately 6.5 h. Although it is generally believed that neutrophils are cleared from the circulation via the liver and spleen, in this study using (111)In-labeled senescent neutrophils, we show that in mice, 32% of neutrophils are cleared from the circulation via the bone marrow. We have previously shown that senescent neutrophils home to the bone marrow in a CXCR4-dependent manner, and we show here that pretreatment of neutrophils with pertussis toxin significantly inhibits neutrophil clearance via the bone marrow (75%), consistent with a role for chemokines in this process. By labeling senescent neutrophils with inert fluorescent microspheres, we have tracked their fate and shown that in vivo, they are ultimately phagocytosed by bone marrow stromal macrophages. Finally, we show that under noninflammatory conditions, circulating levels of neutrophils are regulated by granulocyte-colony stimulating factor (G-CSF), but not interleukin-17. Interestingly, we report that the uptake of apoptotic neutrophils by bone marrow macrophages stimulates their production of G-CSF in vitro. Taken together, these data provide evidence that the bone marrow represents a major site of neutrophil clearance in mice.

Respiratory Francisella tularensis live vaccine strain infection induces Th17 cells and prostaglandin E2, which inhibits generation of gamma interferon-positive T cells

Two key routes of Francisella tularensis infection are through the skin and airway. We wished to understand how the route of inoculation influenced the primary acute adaptive immune response. We show that an intranasal inoculation of the F. tularensis live vaccine strain (LVS) with a 1,000-fold-smaller dose than an intradermal dose results in similar growth kinetics and peak bacterial burdens. In spite of similar bacterial burdens, we demonstrate a difference in the quality, magnitude, and kinetics of the primary acute T-cell response depending on the route of inoculation. Further, we show that prostaglandin E(2) secretion in the lung is responsible for the difference in the gamma interferon (IFN-gamma) response. Intradermal inoculation led to a large number of IFN-gamma(+) T cells 7 days after infection in both the spleen and the lung. In contrast, intranasal inoculation induced a lower number of IFN-gamma(+) T cells in the spleen and lung but an increased number of Th17 cells in the lung. Intranasal infection also led to a significant increase of prostaglandin E(2) (PGE(2)) in the bronchoalveolar lavage fluid. Inhibition of PGE(2) production with indomethacin treatment resulted in increased numbers of IFN-gamma(+) T cells and decreased bacteremia in the lungs of intranasally inoculated mice. This research illuminates critical differences in acute adaptive immune responses between inhalational and dermal infection with F. tularensis LVS mediated by the innate immune system and PGE(2).