Interleukin-17 and lung host defense against Klebsiella pneumoniae infection

Circulating IL-17 levels during the peri-transplant period as a predictor for early leukemia relapse after myeloablative allogeneic stem cell transplantation

IL-17 is involved in inducing and mediating pro-inflammatory responses. The association of IL-17 with tumor growth or graft-versus-host disease (GVHD) has become a subject of controversy. We hypothesized that serum IL-17 (sIL-17) levels during the peri-transplant period may affect alloreactive responses after allogeneic stem cell transplantation (SCT). sIL-17 levels of 95 patients with leukemia who had undergone myeloablative allogeneic SCT were measured using ELISA before conditioning and on day 0, +7, and +14 after transplantation. With a median follow-up of 17 months, the overall survival, disease-free survival, non-relapse mortality, and relapse incidence were 70.9%, 66.3%, 10.3%, and 23.4%, respectively. Ten patients relapsed within 180 days (early relapse, 10.5%) post-transplant. The cumulative incidence of acute GVHD over grade II and chronic GVHD was 55.8% and 69.0%, respectively. Analyses using repeated measures of ANOVA and mean values of sIL-17 revealed that patients relapsed within 180 days had higher sIL-17 levels, whereas no association existed between sIL-17 levels and other clinical outcomes, including acute GVHD. Receiver operating characteristic curve analyses also revealed that sIL-17 levels were available for the prediction of early relapse and that patients with higher sIL-17 levels at each time point had a significantly higher early relapse. Multivariate analyses and subgroup analyses with only standard disease status suggest the association of sIL-17 levels with subsequent early relapse independent of disease status at transplantation. This study is the first one demonstrating the early change in sIL-17 during the peri-transplant period and the association with early relapse in humans.

Th17 (IFNγ- IL17+) CD4+ T cells generated after burn injury may be a novel cellular mechanism for postburn immunosuppression

BACKGROUND

The mechanism responsible for initiating and controlling the immunosuppressive response after burn injury remains unknown. Interleukin-17 (IL-17) secreting Th17 (interferon [IFN]γ IL17) cells are a novel subset of CD4 T cells associated with a weak, proinflammatory response that antagonizes the proinflammatory Th1 (IFNγ IL17) response. Given that transforming growth factor-β and IL6 mediate Th17 cell development, we hypothesized that burn injury may generate Th17 cells that could mediate postburn immunosuppression.

METHODS

After a 20% total body surface area burn in female C57BL/6 mice, wound-draining lymph nodes were harvested 3 days, 7 days, or 14 days after injury. CD4 T cells were enriched by magnetic selection, and flow cytometry was used to identify intracellular IL17 and IFNγ in CD3CD4 T cells. Additional purified CD3CD4 T cells were cultured with Th17 polarizing IL6 and transforming growth factor-β for 4 days, and flow cytometry was again used to identify intracellular IL17 and IFNγ in CD4 T cells.

RESULTS

The number and percentage of preformed Th17 cells was significantly greater in burn mice compared with sham at all time points. In addition, the ratio of Th17 cells to Th1 cells was always significantly higher in burn mice compared with sham. These differences were eliminated in Th17 polarizing conditions in vitro. CD4 T cells never generated both IL17 and IFNγ.

CONCLUSION

These results demonstrate for the first time that Th17 cells (IFNγ IL17) are spontaneously generated after burn injury. Given that Th17 cells (IFNγ IL17) are antagonistic to Th1 (IFNγ IL17) cells, these results suggest a novel mechanism for initiating and controlling postburn immunosuppression that deserves further investigation.

Development of autoimmune diabetes in the absence of detectable IL-17A in a CD8-driven virally induced model

Recent studies have shown that IL-17 can contribute beneficially to pathogen defense but also that excessive IL-17 levels are associated with chronic inflammation and autoimmune disorders. To date, the role of IL-17 in viral infections and type 1 diabetes is ambiguous. In this study, we used IL-17A enhanced green fluorescent protein bicistronic reporter mouse strains to analyze in situ production of IL-17A. Upon Klebsiella pneumoniae bacterial infection, CD4(+) and γδ T cells produce IL-17A. In contrast, CD4(+) or CD8(+) T cells do not produce IL-17A in response to acute or protracted viral infection with lymphocytic choriomeningitis virus or during autoimmune diabetes development in the CD8-driven lymphocytic choriomeningitis virus-induced model of type 1 diabetes. We conclude that viral elimination and type 1 diabetes can occur in the absence of detectable IL-17A production, suggesting IL-17A is not essential in these settings.

Soluble extract from the nematode Strongyloides stercoralis induces CXCR2 dependent/IL-17 independent neutrophil recruitment

Neutrophil recruitment via CXCR2 is required for innate and adaptive protective immunity to the larvae of Strongyloides stercoralis in mice. The goal of the present study was to determine the mechanism of CXCR2-mediated neutrophil recruitment to S. stercoralis. Mice deficient in the receptor for IL-17A and IL-17F, upstream mediators of CXCR2 ligand production, were infected with S. stercoralis larvae; there was no difference in larval survival, neutrophil recruitment, or production of CXCR2 ligands compared with wild type mice. In vivo and in vitro stimulation of neutrophils with S. stercoralis soluble extract resulted in significant neutrophil recruitment. In vitro assays demonstrated that the recruitment functioned through both chemokinesis and chemotaxis, was specific for CXCR2, and was a G protein-coupled response involving tyrosine kinase and PI3K. Finally, neutrophil stimulation with S. stercoralis soluble extract induced release of the CXCR2 ligands MIP-2 and KC from neutrophils, thereby potentially enhancing neutrophil recruitment.

Interleukins, from 1 to 37, and interferon-γ: receptors, functions, and roles in diseases

Advancing our understanding of mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumor development, organ transplantation, and chronic infections could lead to effective and targeted therapies. Subsets of immune and inflammatory cells interact via ILs and IFNs; reciprocal regulation and counter balance among T(h) and regulatory T cells, as well as subsets of B cells, offer opportunities for immune interventions. Here, we review current knowledge about ILs 1 to 37 and IFN-γ. Our understanding of the effects of ILs has greatly increased since the discoveries of monocyte IL (called IL-1) and lymphocyte IL (called IL-2); more than 40 cytokines are now designated as ILs. Studies of transgenic or knockout mice with altered expression of these cytokines or their receptors and analyses of mutations and polymorphisms in human genes that encode these products have provided important information about IL and IFN functions. We discuss their signaling pathways, cellular sources, targets, roles in immune regulation and cellular networks, roles in allergy and asthma, and roles in defense against infections.

Chronic mucocutaneous candidiasis and congenital susceptibility to Candida

PURPOSE OF REVIEW

To give an overview on the clinical spectrum and the molecular background of host defence against Candida.

RECENT FINDINGS

For many decades the molecular causes and the pathogenesis for an increased susceptibility to Candida - and fungal infections in general - have been elusive. In 2009 and 2010 interesting reports on the genetic background and the pathomechanisms involved in chronic mucocutaneous candidiasis (CMC) have been published.

SUMMARY

The susceptibility to recurrent Candida infections can be a monogenetic Mendelian trait. The sensing of Candida cell wall components and the consecutive intracellular signalling in myeloid cells via CARD9, but also the role of Th17 cells and their cytokines take centre stage in the human host defence against Candida.

Innate immune responses to systemic Acinetobacter baumannii infection in mice: neutrophils, but not interleukin-17, mediate host resistance

Acinetobacter baumannii is a nosocomial pathogen with a high prevalence of multiple-drug-resistant strains, causing pneumonia and sepsis. The current studies further develop a systemic mouse model of this infection and characterize selected innate immune responses to the organism. Five clinical isolates, with various degrees of antibiotic resistance, were assessed for virulence in two mouse strains, and between male and female mice, using intraperitoneal infection. A nearly 1,000-fold difference in virulence was found between bacterial strains, but no significant differences between sexes or mouse strains were observed. It was found that microbes disseminated rapidly from the peritoneal cavity to the lung and spleen, where they replicated. A persistent septic state was observed. The infection progressed rapidly, with mortality between 36 and 48 h. Depletion of neutrophils with antibody to Ly-6G decreased mean time to death and increased mortality. Interleukin-17 (IL-17) promotes the response of neutrophils by inducing production of the chemokine keratinocyte-derived chemoattractant (KC/CXCL1), the mouse homolog of human IL-8. Acinetobacter infection resulted in biphasic increases in both IL-17 and KC/CXCL1. Depletion of neither IL-17 nor KC/CXCL1, using specific antibodies, resulted in a difference in bacterial burdens in organs of infected mice at 10 h postinfection. Comparison of bacterial burdens between IL-17a(-/-) and wild-type mice confirmed that the absence of this cytokine did not sensitize mice to Acinetobacter infection. These studies definitely demonstrate the importance of neutrophils in resistance to systemic Acinetobacter infection. However, neither IL-17 nor KC/CXCL1 alone is required for effective host defense to systemic infection with this organism.

Monocyte chemoattractant protein 1 regulates pulmonary host defense via neutrophil recruitment during Escherichia coli infection

Neutrophil accumulation is a critical event to clear bacteria. Since uncontrolled neutrophil recruitment can cause severe lung damage, understanding neutrophil trafficking mechanisms is important to attenuate neutrophil-mediated damage. While monocyte chemoattractant protein 1 (MCP-1) is known to be a monocyte chemoattractant, its role in pulmonary neutrophil-mediated host defense against Gram-negative bacterial infection is not understood. We hypothesized that MCP-1/chemokine (C-C motif) ligand 2 is important for neutrophil-mediated host defense. Reduced bacterial clearance in the lungs was observed in MCP-1(-/-) mice following Escherichia coli infection. Neutrophil influx, along with cytokines/chemokines, leukotriene B(4) (LTB(4)), and vascular cell adhesion molecule 1 levels in the lungs, was reduced in MCP-1(-/-) mice after infection. E. coli-induced activation of NF-κB and mitogen-activated protein kinases in the lung was also reduced in MCP-1(-/-) mice. Administration of intratracheal recombinant MCP-1 (rMCP-1) to MCP-1(-/-) mice induced pulmonary neutrophil influx and cytokine/chemokine responses in the presence or absence of E. coli infection. Our in vitro migration experiment demonstrates MCP-1-mediated neutrophil chemotaxis. Notably, chemokine receptor 2 is expressed on lung and blood neutrophils, which are increased upon E. coli infection. Furthermore, our findings show that neutrophil depletion impairs E. coli clearance and that exogenous rMCP-1 after infection improves bacterial clearance in the lungs. Overall, these new findings demonstrate that E. coli-induced MCP-1 causes neutrophil recruitment directly via chemotaxis as well as indirectly via modulation of keratinocyte cell-derived chemokine, macrophage inflammatory protein 2, and LTB(4).

Tim-3 ligand galectin-9 reduces IL-17 level and accelerates Klebsiella pneumoniae infection

T cell immunoglobulin and mucin domain (Tim)-3 is expressed on activated CD4(+) and CD8(+) T cells. Identification of galectin-9 as a ligand for Tim-3 has now firmly established the Tim-3/galectin-9 pathway, which results in apoptosis of effector CD4(+) and CD8(+) T cells. Moreover, Th17 cells are a recently discovered CD4(+) effector T cell, which are important in antimicrobial immunity. Whether the Tim-3/galectin-9 pathway affects Th17 immunity has not been elucidated. Here, we demonstrated expression of Tim-3 on Th17 cells by flow cytometry. Th17-skewed cells were sensitive to galectin-9-induced apoptosis. In vitro administration of galectin-9 decreased stimulated Th17 cells and inhibited production of IL-17. Interestingly, Klebsiella pneumoniae (K. pneumoniae) infection led to enhanced IL-17 levels. Recombinant galectin-9 significantly decreased IL-17 in vivo, which resulted in reduced bacterial clearance and high mortality. These observations suggest that the Tim-3/galectin-9 pathway plays an important role in termination of Th17-immune responses, and could be a therapeutic target for inflammatory diseases.

Role of Th17 cells and IL-17 in lung transplant rejection

In the past decade, advances in immunology have led to the recognition that T cell differentiation is not simply Th1 or Th2 but involves differentiation to other subsets, such as T regulatory cells, T follicular helper cells, and Th17 cells. Th17 cells, characterized by production of IL-17, IL-22, and IL-21, have been implicated in the pathogenesis of autoimmune diseases, like rheumatoid arthritis and multiple sclerosis, but also play an important role in host defense and mucosal immunity. IL-17, with its pleiotropic effects on stromal cells, as well as hematopoietic cells, has long been recognized as a possible mediator of rejection after lung transplantation. Recent data have implicated IL-17 and Th17 cells in the development of autoimmunity and chronic rejection after lung transplantation in both animal models and humans. In this review, we will discuss the current data on Th17 and the prospects for the future for lung transplantation.

Role of IL-17A on resolution of pulmonary C. neoformans infection

The current studies evaluated the role of interleukin (IL)-17A in the induction of protective immunity against pulmonary cryptococcosis in mice. Protection against pulmonary infection with C. neoformans strain H99γ was associated with increased IL-17A production. Signaling through the IFN-γ receptor (R) was required for increased IL-17A production, however, a Th17-type cytokine profile was not observed. Neutrophils were found to be the predominant leukocytic source of IL-17A, rather than T cells, suggesting that the IL-17A produced was not part of a T cell-mediated Th17-type immune response. Depletion of IL-17A in mice during pulmonary infection with C. neoformans strain H99γ resulted in an initial increase in pulmonary fungal burden, but had no effect on cryptococcal burden at later time points. Also, depletion of IL-17A did not affect the local production of other cytokines. IL-17RA⁻/⁻ mice infected with C. neoformans strain H99γ survived the primary infection as well as a secondary challenge with wild-type cryptococci. However, dissemination of the wild-type strain to the brain was noted in the surviving IL-17RA⁻/⁻ mice. Altogether, our results suggested that IL-17A may be important for optimal protective immune responsiveness during pulmonary C. neoformans infection, but protective Th1-type immune responses are sufficient for protection against cryptococcal infection.

Nasal immunity to staphylococcal toxic shock is controlled by the nasopharynx-associated lymphoid tissue

The nasopharynx-associated lymphoid tissue (NALT) of humans and other mammals is associated with immunity against airborne infections, though it is generally considered to be a secondary component of the mucosa-associated lymphoid system. We found that protective immunity to a virulence factor of nasal mucosa-colonizing Staphylococcus aureus, staphylococcal enterotoxin B (SEB), requires a functional NALT. We examined the role of NALT using intranasal (IN) vaccination with a recombinant SEB vaccine (rSEBv) combined with an adjuvant in a mouse model of SEB-induced toxic shock. The rSEBv was rapidly internalized by NALT cells at the mucosal barrier, and transport into NALT was accelerated by inclusion of a Toll-like receptor 4 (TLR4) agonist. Vaccine-induced germinal centers of B cells formed within NALT, accompanied by elevated levels of IgA(+) and IgG(+) cells, and these were further increased by TLR4 activation. The NALT was the site of specific anti-rSEBv IgA and IgG production but was also influenced by intraperitoneal (IP) inoculation and perhaps other isolated lymphoid follicles observed within the nasal cavity. Vaccination by the IN route generated robust levels of anti-rSEBv IgA in saliva, nasal secretions, and blood compared to much lower levels after IP vaccination. IN vaccination also induced secretion of anti-rSEBv IgG in the blood and nasal secretions. Significantly, the efficacy of IN vaccination was dependent on NALT, as surgical removal resulted in greater sensitivity to IN challenge with wild-type SEB. Thus, protective immunity to SEB within the nasal sinuses was elicited by responses originating in NALT.

The role of interleukin-17 in the Helicobacter pylori induced infection and immunity

BACKGROUND

Helicobacter pylori infection is regarded as the major cause of various gastric diseases and induces the production of several cytokines including interleukin-17 (IL-17) recently recognized as an important player in the mammalian immune system.

OBJECTIVE

This review deals with the role of IL-17 on the H. pylori-induced infection and immunity in humans and experimental animals.

RESULTS

H. pylori infection increases IL-17 in the gastric mucosa of humans and experimental animals. In humans, IL-17 induces the secretion of IL-8 by activating the ERK 1/2 MAP kinase pathway and the released IL-8 attracts neutrophils promoting inflammation. IL-23 is increased in patients with H. pylori-related gastritis and regulates IL-17 secretion via STAT3 pathway. Studies in H. pylori-infected mice indicate that IL-17 is primarily associated with gastric inflammation. The early events in the immune response of immunized and challenged mice include the recruitment of T cells and the production of IL-17. Neutrophil attracting chemokines are released, and the bacterial load is considerably reduced. IL-17 plays a dual role in infection and vaccination. In infection, T regulatory cells (Tregs) suppress the inflammatory reaction driven by IL-17 thereby favoring bacterial persistence. Immunization produces Helicobacter-specific memory T-helper cells that can possibly alter the ratio between T-helper 17 and Treg responses so that the IL-17-driven inflammatory reaction can overcome the Treg response leading to bacterial clearance.

CONCLUSION

IL-17 plays an important role in H. pylori-related gastritis and in the reduction of Helicobacter infection in mice following immunization.

Influenza A inhibits Th17-mediated host defense against bacterial pneumonia in mice

Staphylococcus aureus is a significant cause of hospital and community acquired pneumonia and causes secondary infection after influenza A. Recently, patients with hyper-IgE syndrome, who often present with S. aureus infections of the lung and skin, were found to have mutations in STAT3, required for Th17 immunity, suggesting a potential critical role for Th17 cells in S. aureus pneumonia. Indeed, IL-17R(-/-) and IL-22(-/-) mice displayed impaired bacterial clearance of S. aureus compared with that of wild-type mice. Mice challenged with influenza A PR/8/34 H1N1 and subsequently with S. aureus had increased inflammation and decreased clearance of both virus and bacteria. Coinfection resulted in greater type I and II IFN production in the lung compared with that with virus infection alone. Importantly, influenza A coinfection resulted in substantially decreased IL-17, IL-22, and IL-23 production after S. aureus infection. The decrease in S. aureus-induced IL-17, IL-22, and IL-23 was independent of type II IFN but required type I IFN production in influenza A-infected mice. Furthermore, overexpression of IL-23 in influenza A, S. aureus-coinfected mice rescued the induction of IL-17 and IL-22 and markedly improved bacterial clearance. These data indicate a novel mechanism by which influenza A-induced type I IFNs inhibit Th17 immunity and increase susceptibility to secondary bacterial pneumonia.

IL-17A and TNF-α exert synergistic effects on expression of CXCL5 by alveolar type II cells in vivo and in vitro

CXCL5, a member of the CXC family of chemokines, contributes to neutrophil recruitment during lung inflammation, but its regulation is poorly understood. Because the T cell-derived cytokine IL-17A enhances host defense by triggering production of chemokines, particularly in combination with TNF-α, we hypothesized that IL-17A would enhance TNF-α-induced expression of CXCL5. Intratracheal coadministration of IL-17A and TNF-α in mice induced production of CXCL1, CXCL2, and CXCL5, which was associated with increased neutrophil influx in the lung at 8 and 24 h. The synergistic effects of TNF-α and IL17A were greatly attenuated in Cxcl5(-/-) mice at 24 h, but not 8 h, after exposure, a time when CXCL5 expression was at its peak in wild-type mice. Bone marrow chimeras produced using Cxcl5(-/-) donors and recipients demonstrated that lung-resident cells were the source of CXCL5. Using differentiated alveolar epithelial type II (ATII) cells derived from human fetal lung, we found that IL-17A enhanced TNF-α-induced CXCL5 transcription and stabilized TNF-α-induced CXCL5 transcripts. Whereas expression of CXCL5 required activation of NF-κB, IL-17A did not increase TNF-α-induced NF-κB activation. Apical costimulation of IL-17A and TNF-α provoked apical secretion of CXCL5 by human ATII cells in a transwell system, whereas basolateral costimulation led to both apical and basolateral secretion of CXCL5. The observation that human ATII cells secrete CXCL5 in a polarized fashion may represent a mechanism to recruit neutrophils in host defense in a fashion that discriminates the site of initial injury.

Klebsiella pneumoniae outer membrane protein A is required to prevent the activation of airway epithelial cells

Outer membrane protein A (OmpA) is a class of proteins highly conserved among the Enterobacteriaceae family and throughout evolution. Klebsiella pneumoniae is a capsulated gram-negative pathogen. It is an important cause of community-acquired and nosocomial pneumonia. Evidence indicates that K. pneumoniae infections are characterized by a lack of an early inflammatory response. Data from our laboratory indicate that K. pneumoniae CPS helps to suppress the host inflammatory response. However, it is unknown whether K. pneumoniae employs additional factors to modulate host inflammatory responses. Here, we report that K. pneumoniae OmpA is important for immune evasion in vitro and in vivo. Infection of A549 and normal human bronchial cells with 52OmpA2, an ompA mutant, increased the levels of IL-8. 52145-Δwca(K2)ompA, which does not express CPS and ompA, induced the highest levels of IL-8. Both mutants could be complemented. In vivo, 52OmpA2 induced higher levels of tnfα, kc, and il6 than the wild type. ompA mutants activated NF-κB, and the phosphorylation of p38, p44/42, and JNK MAPKs and IL-8 induction was via NF-κB-dependent and p38- and p44/42-dependent pathways. 52OmpA2 engaged TLR2 and -4 to activate NF-κB, whereas 52145-Δwca(K2)ompA activated not only TLR2 and TLR4 but also NOD1. Finally, we demonstrate that the ompA mutant is attenuated in the pneumonia mouse model. The results of this study indicate that K. pneumoniae OmpA contributes to attenuate airway cell responses. This may facilitate pathogen survival in the hostile environment of the lung.

The pathogenicity of an enteric Citrobacter rodentium Infection is enhanced by deficiencies in the antioxidants selenium and vitamin E

The pathogenesis of a Citrobacter rodentium infection was evaluated in mice fed diets with a single deficiency in either selenium or vitamin E or with a double deficiency in both selenium and vitamin E compared to mice on nutritionally adequate diets. Mice fed the selenium- and vitamin E-deficient diet for 6 weeks had increased loads of C. rodentium in the colon and spleen, which were not observed in mice fed either of the singly deficient diets or the adequate diet. Infected mice fed the doubly deficient diet had increased colon crypt hyperplasia and an influx of infiltrating cells along with gross changes to crypt architecture, including ulceration and denuding of the epithelial layer. Cytokine and chemokine mRNA levels in the colon were measured by real-time PCR. Expression of proinflammatory cytokines and chemokines was upregulated on day 12 after infection with C. rodentium in mice fed the doubly deficient diet compared to mice fed the control diet. Heme oxygenase 1, an enzyme upregulated by oxidative stress, also was more highly induced in infected mice fed the doubly deficient diet. Production of C. rodentium antigen-specific IgM and IgG antibodies was not affected by feeding the doubly deficient diet. The results indicated that selenium and vitamin E play an important role in host resistance and in the pathology induced by C. rodentium, an infection that mimics disease caused by common food-borne bacterial pathogens in humans.

Early production of IL-17 protects against acute pulmonary Pseudomonas aeruginosa infection in mice

Interleukin-17 (IL-17) is involved in protection against extracellular bacteria. However, IL-17 is likely to be deleterious to a host with chronic pulmonary Pseudomonas aeruginosa infection. The role of IL-17 during acute pulmonary P. aeruginosa infection remains unknown. Here, we evaluated the role that IL-17 plays in acute pulmonary P. aeruginosa infection and the source of the interleukin. The production of IL-17 increased rapidly after acute pulmonary P. aeruginosa infection in mice. We subsequently examined the role of IL-17 in acute infection and found 100 times more bacteria in the bronchoalveolar lavage fluid of mice treated with an IL-17-neutralizing antibody compared with the IgG(2a) -treated mice after 16 h of infection. The main infiltrating cells in the anti-IL-17-treated mice were lymphocytes rather than neutrophils. Consistently, more tissue damage and pathological changes in the lung were observed in the anti-IL-17-treated mice. We also found that Th17 cells are one of the sources of IL-17. We conclude that the early production of IL-17 plays a protective role during acute pulmonary P. aeruginosa infection in mice and that Th17 cells are one of the sources of IL-17 during acute pulmonary P. aeruginosa infection. Altogether, IL-17 and Th17 cells contribute to the pathogenesis of acute pulmonary P. aeruginosa infection in vivo.

An oral vaccine based on U-Omp19 induces protection against B. abortus mucosal challenge by inducing an adaptive IL-17 immune response in mice

As Brucella infections occur mainly through mucosal surfaces, the development of mucosal administered vaccines could be radical for the control of brucellosis. In this work we evaluated the potential of Brucella abortus 19 kDa outer membrane protein (U-Omp19) as an edible subunit vaccine against brucellosis. We investigated the protective immune response elicited against oral B. abortus infection after vaccination of mice with leaves from transgenic plants expressing U-Omp19; or with plant-made or E. coli-made purified U-Omp19. All tested U-Omp19 formulations induced protection against Brucella when orally administered without the need of adjuvants. U-Omp19 also induced protection against a systemic challenge when parenterally administered. This built-in adjuvant ability of U-Omp19 was independent of TLR4 and could be explained at least in part by its capability to activate dendritic cells in vivo. While unadjuvanted U-Omp19 intraperitoneally administered induced a specific Th1 response, following U-Omp19 oral delivery a mixed specific Th1-Th17 response was induced. Depletion of CD4(+) T cells in mice orally vaccinated with U-Omp19 resulted in a loss of the elicited protection, indicating that this cell type mediates immune protection. The role of IL-17 against Brucella infection has never been explored. In this study, we determined that if IL-17A was neutralized in vivo during the challenge period, the mucosal U-Omp19 vaccine did not confer mucosal protection. On the contrary, IL-17A neutralization during the infection did not influence at all the subsistence and growth of this bacterium in PBS-immunized mice. All together, our results indicate that an oral unadjuvanted vaccine based on U-Omp19 induces protection against a mucosal challenge with Brucella abortus by inducing an adaptive IL-17 immune response. They also indicate different and important new aspects i) IL-17 does not contribute to reduce the bacterial burden in non vaccinated mice and ii) IL-17 plays a central role in vaccine mediated anti-Brucella mucosal immunity.

IL-17 and Th17 cells in tuberculosis

Tuberculosis is primarily a disease of the lung. Constant expression of cellular immunity in this organ is required to control Mycobacterium tuberculosis growth, but this can also result in chronic inflammation and pathologic consequences. During primary tuberculosis both IFN-γ and IL-17 are induced: both are potent inflammatory cytokines capable of inducing expression of chemokines that promote cell recruitment and granuloma organization throughout infection. During the chronic phase, a balance between Th1 and Th17 responses needs to be achieved to control bacterial growth and limit immunopathology, as a shift of the response towards excessive IL-17 production may sustain extensive neutrophil recruitment and tissue damage. Thus, regulation of Th1 and Th17 responses during tuberculosis is essential to promote anti-mycobacterial immunity and prevent extensive immunopathological consequences.

Review: T helper 17 cells: their role in glomerulonephritis

T helper (Th) cells are an integral part of the host's immune response to eliminate invading pathogens. However, autoimmune or 'autoinflammatory' diseases can develop if Th cell responses are not effectively regulated. Several subsets of Th cells exist, including the Th17 subset that produces interleukin-17A, important in experimental models of organ-specific autoimmune inflammation. Its discovery has explained paradoxical observations in model systems thought to be Th1 mediated but were exacerbated in the absence of interferon-gamma, the prototypic Th1 effector cytokine. Th17 cells express unique transcription factors and secrete a unique pattern of cytokines. Interleukin-17A induces pro-inflammatory cytokines and chemokines and mediates neutrophil recruitment. Th17 cells have a reciprocal relationship with T regulatory cells and can also mediate suppression of Th1 responses. Recent studies also suggest that Th17 cells are not terminally differentiated but can switch into Th1 cells. Th17 cells have themselves been recently shown to induce antigen-specific cell-mediated proliferative glomerulonephritis. There is increasing evidence implicating Th17 cells in anti-glomerular basement membrane disease, lupus nephritis and pauci-immune glomerulonephritis. This review will review the discovery of the Th17 subset, its properties, its relationship with other Th subsets and assess the current evidence implicating Th17 cells in glomerulonephritis.

Revisiting human IL-12Rβ1 deficiency: a survey of 141 patients from 30 countries

Interleukin-12 receptor β1 (IL-12Rβ1) deficiency is the most common form of Mendelian susceptibility to mycobacterial disease (MSMD). We undertook an international survey of 141 patients from 102 kindreds in 30 countries. Among 102 probands, the first infection occurred at a mean age of 2.4 years. In 78 patients, this infection was caused by Bacille Calmette-Guérin (BCG; n = 65), environmental mycobacteria (EM; also known as atypical or nontuberculous mycobacteria) (n = 9) or Mycobacterium tuberculosis (n = 4). Twenty-two of the remaining 24 probands initially presented with nontyphoidal, extraintestinal salmonellosis. Twenty of the 29 genetically affected sibs displayed clinical signs (69%); however 8 remained asymptomatic (27%). Nine nongenotyped sibs with symptoms died. Recurrent BCG infection was diagnosed in 15 cases, recurrent EM in 3 cases, recurrent salmonellosis in 22 patients. Ninety of the 132 symptomatic patients had infections with a single microorganism. Multiple infections were diagnosed in 40 cases, with combined mycobacteriosis and salmonellosis in 36 individuals. BCG disease strongly protected against subsequent EM disease (p = 0.00008). Various other infectious diseases occurred, albeit each rarely, yet candidiasis was reported in 33 of the patients (23%). Ninety-nine patients (70%) survived, with a mean age at last follow-up visit of 12.7 years ± 9.8 years (range, 0.5-46.4 yr). IL-12Rβ1 deficiency is characterized by childhood-onset mycobacteriosis and salmonellosis, rare recurrences of mycobacterial disease, and more frequent recurrence of salmonellosis. The condition has higher clinical penetrance, broader susceptibility to infections, and less favorable outcome than previously thought.

Up for Mischief? IL-17/Th17 in the tumour microenvironment

The role of interleukin (IL)-17 and the IL-17-producing T helper (Th)17 cells in cancer has recently become the focus of extensive investigation. An expanding body of literature implicates Th17 cells and their hallmark cytokine in both pro- and anti-tumourigenic processes. In this review we describe their biological activities and outline the reciprocal interactions between Th17 cells and other cells of the immune system. We also discuss the evidence regarding their dual role in the tumour microenvironment. An understanding of the processes that regulate the pro- or anti-tumour activities of Th17 cell and IL-17 will allow the development of more effective means for cancer immunotherapy.

Klebsiella pneumoniae subverts the activation of inflammatory responses in a NOD1-dependent manner

Klebsiella pneumoniae is an important cause of community-acquired and nosocomial pneumonia. Subversion of inflammation is essential for pathogen survival during infection. Evidence indicates that K. pneumoniae infections are characterized by lacking an early inflammatory response although the molecular bases are currently unknown. Here we unveil a novel strategy employed by a pathogen to counteract the activation of inflammatory responses. K. pneumoniae attenuates pro-inflammatory mediators-induced IL-8 secretion. Klebsiella antagonizes the activation of NF-κB via the deubiquitinase CYLD and blocks the phosphorylation of mitogen-activated protein kinases (MAPKs) via the MAPK phosphatase MKP-1. Our studies demonstrate that K. pneumoniae has evolved the capacity to manipulate host systems dedicated to control the immune balance. To exert this anti-inflammatory effect, Klebsiella engages NOD1. In NOD1 knock-down cells, Klebsiella neither induces the expression of CYLD and MKP-1 nor blocks the activation of NF-κB and MAPKs. Klebsiella inhibits Rac1 activation; and inhibition of Rac1 activity triggers a NOD1-mediated CYLD and MKP-1 expression which in turn attenuates IL-1β-induced IL-8 secretion. A capsule (CPS) mutant does not attenuate the inflammatory response. However, purified CPS neither reduces IL-1β-induced IL-8 secretion nor induces the expression of CYLD and MKP-1 thereby indicating that CPS is necessary but not sufficient to attenuate inflammation.

NF-κB mediates IL-1β- and IL-17A-induced MUC5B expression in airway epithelial cells

A major pathological feature of chronic airway diseases is the elevated expression of gel-forming mucins. NF-κB activation in airway epithelial cells has been shown to play a proinflammatory role in chronic airway diseases; however, the specific role of NF-κB in mucin gene expression has not been characterized. In this study, we show that the proinflammatory cytokines, IL-1β and IL-17A, both of which use the NF-κB pathway, are potent inducers of MUC5B mRNA expression in both well differentiated primary normal human bronchial epithelial cells and the human bronchial epithelial cell line, HBE1. MUC5B induction by these cytokines was both time- and dose-dependent, and was attenuated by the small molecule inhibitor, NF-κB inhibitor III, as well as p65 small interfering RNA, suggesting that the regulation of MUC5B expression by these cytokines is via an NF-κB-based transcriptional mechanism. Deletion analysis of the MUC5B promoter demonstrated that IL-1β- and IL-17A-induced promoter activity resides within the -4.17-kb to -2.56-kb region relative to the transcriptional start site. This region contains three putative κB-binding sites (NF-κB-1, -3,786/-3,774; NF-κB-2, -3,173/-3,161; and NF-κB-3, -2,921/-2,909). Chromatin immunoprecipitation analysis confirmed enhanced binding of the p50 NF-κB subunit to the NF-κB-3 site after cytokine stimulation. We conclude that an NF-κB-based transcriptional mechanism is involved in MUC5B regulation by IL-1β and IL-17A in airway epithelium. This is the first demonstration of the participation of NF-κB and its specific binding site in cytokine-mediated airway MUC5B expression.

Dyslipidemia induces opposing effects on intrapulmonary and extrapulmonary host defense through divergent TLR response phenotypes

Dyslipidemia influences innate immune responses in the bloodstream, but whether and how pulmonary innate immunity is sensitive to circulating lipoproteins is largely unknown. To define whether dyslipidemia impacts responses to bacteria in the airspace and, if so, whether differently from its effects in other tissues, airspace, bloodstream, and i.p. responses to LPS and Klebsiella pneumoniae were investigated using murine models of dyslipidemia. Dyslipidemia reduced neutrophil (PMN) recruitment to the airspace in response to LPS and K. pneumoniae by impairing both chemokine induction in the airspace and PMN chemotaxis, thereby compromising pulmonary bacterial clearance. Paradoxically, bacteria were cleared more effectively from the bloodstream during dyslipidemia. This enhanced systemic response was due, at least in part, to basal circulating neutrophilia and basal TLR4/MyD88-dependent serum cytokine induction and enhanced serum cytokine responses to systemically administered TLR ligands. Dyslipidemia did not globally impair PMN transvascular trafficking to, and host defense within all loci, because neutrophilia, cytokine induction, and bacterial clearance were enhanced within the infected peritoneum. Peritoneal macrophages from dyslipidemic animals were primed for more robust TLR responses, reflecting increased lipid rafts and increased TLR4 expression, whereas macrophages from the airspace, in which cholesterol was maintained constant during dyslipidemia, had normal responses and rafts. Dyslipidemia thus imparts opposing effects upon intra- and extrapulmonary host defense by inducing tissue-divergent TLR response phenotypes and dysregulating airspace/blood compartmental levels of PMNs and cytokines. We propose that the airspace is a "privileged" site, thereby uniquely sensitive to dyslipidemia.

Th-17 cells in the lungs?

Naive CD4 cells are capable of integrating signals from antigen-activated cells of the innate immune system and differentiating into effector CD4 cells, also termed T helper (Th) cells. According to the traditional paradigm explaining adaptive CD4 cell responses, there are two subsets of Th cells: the Th-1 and Th-2 subset. Each of these subsets undergoes a distinct differentiation pathway (a pathway that is characterized by a unique profile of cytokine production and has specific immunoregulatory functions). However, recent studies in mouse models have forwarded evidence of a third subset of Th cells: the Th-17 subset. As indicated predominantly in studies on mice, the Th-17 subset is characterized by an ability to produce the neutrophil-mobilizing cytokine IL-17 in response to stimulation with the cytokine IL-23, an IL-12-related cytokine released from antigen-presenting cells. There is now a growing body of evidence from animal models that the Th-17 subset plays an important role in host defence in the lungs and other organs. Altered IL-17 levels have also been demonstrated in human patients with asthma, exacerbations of cystic fibrosis or following lung transplantation. There is now also evidence that the Th-17 subset is functionally distinct from the Th-2 subset but little is known of the functional inter-relationship between the Th-1 and Th-17 cell subsets; this is particularly true in human lungs. It has been proposed that the Th-17 subset plays a unique role by linking the arms of innate and adaptive immunity. Thus, an improved understanding of the human correlate to the Th-17 subset may reveal new targets for pharmacotherapy against lung disorders that are characterized by aberrant innate responses in host defense.

Prostaglandin E2-dependent IL-23 production in aged murine dendritic cells

CD4+ T cells of the Th17 subtype are over-represented in the aged immune system. Dendritic cells (DC) play a critical role in naïve CD4+ T cell differentiation. However, expression of cytokines by aged DC that promote differentiation or survival of Th17 cells has not been extensively investigated. Using bone marrow-derived DC from C57BL/6 mice of different ages we compared cytokine production after DC activation by Toll-like receptor agonists for TLR4 and/or TLR7/8. DC-derived TNF-α and IL-12p70 production and expression of DC co-stimulatory molecules did not vary significantly by age indicating that TLR expression, function and signal transduction were intact in aged DC. There were relatively minor age-related changes in TGF-β and IL-6 which promote Th17 differentiation, but IL-23, a Th17-suvival cytokine, increased more than 40-fold across the lifespan. DC-derived prostaglandin E2 (PGE2) also increased with age and the up-regulation of IL-23 expression by aged DC was blocked by indomethacin that prevents PGE2 production, and by antagonists of PGE2 receptors. Exogenous PGE2 added to DC cultures further enhanced IL-23 production from aged but not young DCs. These data indicate that age-related changes in DC PGE2 production are necessary, but not sufficient to induce DC IL-23 production. Such changes may play a role in the expansion of Th17 cells in the aged immune system.

Nonprogressive and progressive primate immunodeficiency lentivirus infections

Natural hosts for simian immunodeficiency virus (SIV) can be, and are often naturally, infected with species-specific SIVs, but do not develop acquired immunodeficiency syndrome (AIDS). These natural hosts maintain high SIV viral loads, but avoid immunodeficiency. Elucidating the mechanisms that allow natural hosts to coexist with SIV without overt disease may provide crucial information for understanding AIDS pathogenesis. Over the past few years, several key features of natural SIV infections have been described in studies conducted predominantly in sooty mangabeys (SMs), African green monkeys (AGMs), and mandrills. Natural SIV hosts are able to avoid the chronic, generalized immune system activation that is associated with disease progression in HIV-infected individuals and are known to downmodulate the expression of the receptors for SIV. In this perspective we propose that a critical factor that differentiates nonprogressive from progressive HIV or SIV infection is the maintenance of T cell immune competence in the face of a virus that infects and kills CD4(+) T cells. Elucidation of the mechanisms underlying the preservation of immune function during and after the acute phase of natural SIV infection may lead to the design of novel preventive and therapeutic interventions for treatment of chronic HIV infection.

Innate IL-17-producing cells: the sentinels of the immune system

The cytokine interleukin-17 (IL-17) has received considerable attention since the discovery of a distinct CD4(+) T helper (T(H)) cell subset that produces it, known as the T(H)17 cell subset. Despite the fact that most of the recent literature describes IL-17 as a T cell-secreted cytokine, much of the IL-17 released during an inflammatory response is produced by innate immune cells. In this Review, we explore the many innate immune cell populations that are an early source of IL-17 in response to stress, injury or pathogens. These early sources have been shown to have a central role in the initiation of IL-17-dependent immune responses, even before the first CD4(+)T cell sees its cognate antigen and initiates the T(H)17 cell developmental programme.

T cell pathways involving CTLA4 contribute to a model of acute lung injury

Acute lung injury (ALI) is a frequent pulmonary complication in critically ill patients. We characterized a murine model of LPS-induced ALI, focusing on Th cells. Following LPS administration, bronchoalveolar lavage lymphocytes, neutrophils, IL-6, TNF-alpha, and albumin were increased. Analysis of LPS-induced T cells revealed increased Th cell-associated cytokines (IL-17A, -17F, and -22), as well as increased expression of CD69 (a cell activation marker), Foxp3, and CTLA4 in CD4(+) T cells. Administration of anti-CTLA4 Ab decreased LPS-induced bronchoalveolar lavage albumin and IL-17A, while increasing CD4(+)Foxp3(+) cell number and Foxp3 expression in CD4(+)Foxp3(+) cells. These data suggest that pulmonary LPS administration promotes CD4(+) T cells and that T cell pathways involving CTLA4 contribute to ALI.

Inhibition of bleomycin-induced pulmonary fibrosis through pre-treatment with collagen type V

BACKGROUND

Tolerance to collagen structures has been shown to inhibit the progression of autoimmune scleroderma and rheumatoid arthritis. More recently, tolerance induction to collagen type V (colV) in experimental models of lung transplantation was shown to ameliorate the complex pathology known as "chronic rejection." The link between colV autoimmunity and progressive graft dysfunction and subsequent development of bronchiolitis obliterans syndrome (BOS) has been established in human lung transplant recipients. We hypothesized that intravenous injection of colV inhibits development of lung fibrosis in a bleomycin-induced lung injury mouse model.

METHODS

Experimental animals were injected intravenously with saline or colV 10 days before intratracheal instillation of bleomycin. Pulmonary inflammation was monitored and quantified for the presence of cells in the bronchoalveolar lavage (BAL) fluid by flow cytometry and histology of lung tissue.

RESULTS

ColV-pre-treated animals showed a significant reduction in lung inflammation compared with non-treated animals, according to histology and morphometry. The number of inflammatory cells in the BAL fluid was significantly reduced and associated with a lower proportion of gammadelta T cells and CD4(+) T cells in the colV-pre-treated group. Matrix metalloproteinase-2 and -9 (MMP-2 and -9; also known as gelatinase A and gelatinase B, respectively) levels in the BAL fluid were significantly reduced in colV-pre-treated mice compared with the non-treated mice. In addition, intravenous injection of colV was associated with a significant reduction in the relative expression of interleukin (IL)-6, IL-17 and IL-22 in cells present in BAL fluid at 7 and 14 days after bleomycin instillation.

CONCLUSIONS

Pre-treatment by intravenous injection of colV inhibits bleomycin-induced pulmonary fibrosis by inhibiting IL-6 and IL-17 production. Fibrosis treatment in this context therefore should target induction of colV tolerance and Th17 development.

T helper 17 cells: discovery, function, and physiological trigger

In the few years since their discovery, T helper 17 cells (T(H)17) have been shown to play an important role in host defense against infections, and in tissue inflammation during autoimmunity. T(H)17 cells produce IL-17, IL-21, IL-10, and IL-22 cytokines, and thus have broad effects on a variety of tissues. Notably, the requirement for the immunosuppressive cytokine TGF-beta along with the pro-inflammatory cytokine IL-6 for T(H)17 differentiation supports the intimate relationship between the T(H)17 subset and FOXP3(+) regulatory T cells. Here, we discuss current knowledge on effector functions and differentiation of the T(H)17 lineage. Furthermore, we now know of a physiological stimulus for T(H)17 differentiation: innate immune recognition of cells undergoing apoptosis as a direct result of infection induces unique development of this subset. As our knowledge of T(H)17 and T regulatory cells grows, we are building on a new framework for the understanding of effector T cell differentiation and the biology of CD4(+) T cell adaptive immune responses.

ATP-binding cassette transporter G1 deficiency dysregulates host defense in the lung

RATIONALE

Mice with genetic deletion of the cholesterol efflux transporter, ATP-binding cassette (ABC) G1, have pulmonary lipidosis and chronic pulmonary inflammation. Whether ABCG1 regulates host defense is unknown.

OBJECTIVES

To determine whether ABCG1 regulates pulmonary innate immunity and host defense, and to investigate the underlying molecular/cellular mechanisms.

METHODS

Abcg1(+/+) and Abcg1(-/-) mice were challenged with intrapulmonary lipopolysaccharide (LPS) or Klebsiella pneumoniae, intravenous K. pneumoniae, or intraperitoneal LPS. Phenotypic responses were profiled. Bone marrow chimeras and in vitro assays were used to differentiate and characterize the role of hematopoietic versus nonhematopoietic ABCG1 in host defense.

MEASUREMENTS AND MAIN RESULTS

Unexposed Abcg1(-/-) mice had normal numbers of circulating neutrophils, but increased neutrophil recruitment to the airspace and lung parenchyma, and increased airspace cytokines and chemokines in the steady state. After intrapulmonary LPS or K. pneumoniae, Abcg1(-/-) mice displayed exaggerated further neutrophil recruitment to and degranulation in the airspace, and elevated airspace cytokine/chemokine induction. Alveolar macrophage ABCG1 was critical, as ABCG1 deficiency in hematopoietic cells was sufficient to enhance responses in vivo, and Abcg1(-/-) alveolar macrophages adopted a "foam cell" phenotype, and were hyperresponsive ex vivo. Pulmonary compartmentalization and clearance of K. pneumoniae were increased in Abcg1(-/-) mice, indicating enhanced host defense. By contrast, Abcg1(+/+) and Abcg1(-/-) mice had equivalent responses to intravenous K. pneumoniae and intraperitoneal LPS, suggesting that ABCG1 regulates innate immunity in a tissue-selective manner.

CONCLUSIONS

Abcg1(-/-) mice have an enhanced pulmonary host defense response driven predominantly by hematopoietic cells.

Interleukin-17 and its expanding biological functions

Interleukin-17 (IL-17) and IL-17-producing cells have been shown to play important roles in inflammation and the immune response. IL-17 is believed to be mainly produced by T helper 17 (Th17) cells, a unique helper T-cell subset different from Th1 and Th2 cells. Other subsets of T cells such as gammadeltaT and natural killer T (NKT) cells have also been found to produce IL-17 in response to innate stimuli. IL-17 acts as a proinflammatory cytokine that can induce the release of certain chemokines, cytokines, matrix metalloproteinases (MMPs) and antimicrobial peptides from mesenchymal and myeloid cells. This leads to the expansion and accumulation of neutrophils in the innate immune system and links innate and adaptive immunity in vivo. Furthermore, increasing evidence indicates that IL-17 and IL-17-producing cells are involved in the pathogenesis of various diseases such as allergies, autoimmune diseases, allograft transplantation and even malignancy. They may also play protective roles in host defense against infectious diseases and promote induction of cytotoxic T lymphocyte (CTL) responses against cancer. Targeting of the IL-17 axis is under investigation for the treatment of inflammatory disorders.

Cooperative interactions between TLR4 and TLR9 regulate interleukin 23 and 17 production in a murine model of gram negative bacterial pneumonia

Toll like receptors play an important role in lung host defense against bacterial pathogens. In this study, we investigated independent and cooperative functions of TLR4 and TLR9 in microbial clearance and systemic dissemination during Gram-negative bacterial pneumonia. To access these responses, wildtype Balb/c mice, mice with defective TLR4 signaling (TLR4^lps-d), mice deficient in TLR9 (TLR9^−/−) and TLR4/9 double mutant mice (TLR4^lps-d/TLR9^−/−) were challenged with K. pneumoniae, then time-dependent lung bacterial clearance and systemic dissemination determined. We found impaired lung bacterial clearance in TLR4 and TLR9 single mutant mice, whereas the greatest impairment in clearance was observed in TLR4^lps-d/TLR9^−/− double mutant mice. Early lung expression of TNF-α, IL-12, and chemokines was TLR4 dependent, while IFN-γ production and the later expression of TNF-α and IL-12 was dependent on TLR9. Classical activation of lung macrophages and maximal induction of IL-23 and IL-17 required both TLR4 and TLR9. Finally, the i.t. instillation of IL-17 partially restored anti-bacterial immunity in TLR4^lps-d/TLR9^−/− double mutant mice. In conclusion, our studies indicate that TLR4 and TLR9 have both non-redundant and cooperative roles in lung innate responses during Gram-negative bacterial pneumonia and are both critical for IL-17 driven antibacterial host response.

Th17 cell dynamics in HIV infection

PURPOSE OF REVIEW

Th17 cells are a newly identified subtype of CD4 T cells that respond to bacterial and fungal antigens and are important in mucosal immunology. Because HIV infection results in loss of CD4 T cells as well as disruption to the gastrointestinal tract that causes microbial translocation and immune activation, Th17 cells potentially play an important role in HIV pathogenesis. Here we examine the relationship between Th17 cells and HIV disease pathogenesis.

RECENT FINDINGS

Th17 cells are preferentially lost from the gastrointestinal tract of HIV-infected individuals, which is not entirely due to direct infection, as Th17 cells can be infected in vivo, but are not preferentially infected. Long-term highly active antiretroviral therapy (HAART) can result in restoration of Th17 cells in the gastrointestinal, which may be associated with better disease prognosis. Furthermore, other cells, such as Vdelta1 T cells, can make IL-17 in vivo during HIV infection and may contribute to antibacterial immunity after loss of Th17 cells.

SUMMARY

Recent studies have improved our understanding of the role for Th17 cells during HIV infection; however, more studies are needed to discern better the detrimental consequences of loss of Th17 cells during HIV infection.

Costimulation of Th17 cells: Adding fuel or putting out the fire in the inflamed gut?

Inflammatory bowel disease, typified by Crohn's disease and ulcerative colitis, is a common disorder characterized by recurrent and serious inflammation of the gastrointestinal tract. It is well documented that T cells play a pivotal role in the development of inflammatory bowel disease. Th17 cells are a unique T cell subpopulation implicated in inflammatory bowel disease and many other autoimmune/inflammatory diseases. However, the regulatory mechanism of Th17 activation and proliferation has not been defined completely. Recent studies have shown that the ligation of several costimulatory receptor-ligand pairs contributes to the activation, differentiation, and proliferation of T lymphocytes including the Th17 subset. In this review, we will discuss the emerging evidence on the role of Th17 cells in inflammatory bowel disease pathogenesis as well as the effect of costimulatory molecules on Th17 development and consider if the need for such costimulation of T lymphocytes provides a target for the development of novel therapeutic strategy.

New insights in the immunologic basis of psoriasis

Psoriasis vulgaris is a multifactorial heritable disease characterized by severe inflammation resulting in poorly differentiated, hyperproliferative keratinocytes. Recent advances in genetic analyses have implicated components regulating the interleukin (IL)-23 and nuclear factor-kappaB pathways as risk factors for psoriasis. These inflammatory pathways exhibit increased activity in skin lesions, and promote secretion of various cytokines, such as IL-17 and IL-22. Unrestrained, the activated inflammatory cytokine network in psoriasis may trigger a vicious cycle of inflammation and cellular proliferation that ultimately results in lesion formation. These advances in genetic analyses, together with the progress made in targeted biological therapy, pave the path to tailor treatment on the basis of an individual's genetic and immunologic profile.

Th17 cytokines in mucosal immunity and inflammation

PURPOSE OF REVIEW

Compelling evidence suggests that the Th17 lineage and other IL-17-producing cells play critical roles in host defense against pathogens at mucosal sites. However, IL-17 can also contribute to inflammatory responses at mucosal sites. In this review, we will discuss the recent progress in our understanding of the role of Th17 and other IL-17-producing cells in defining the fine balance between immunity and inflammation at different mucosal sites. RECENT FNDINGS: Recent findings have highlighted that Th17 cytokines are important for the induction of innate and adaptive host responses and contribute to host defense against pathogens at mucosal sites. More recent developments have probed how the Th17 responses are generated in vivo in response to infections and their requirement in maintaining barrier function at mucosal sites. Most importantly, it is becoming apparent that there is a fine balance between protective and pathological manifestation of Th17 responses at mucosal sites that defines immunity or inflammation.

SUMMARY

In this review, we have summarized the recent advances in our understanding of Th17 cytokines and how they contribute to immunity versus inflammation at mucosal sites.

Th17 and regulatory T cells: implications for AIDS pathogenesis

PURPOSE OF REVIEW

The present review discusses recent reports showing that reciprocal changes in T helper interleukin-17-secreting CD4 Th17 cells and CD4CD25FoxP3 regulatory T cells (Tregs) may play a role in the progressive disease caused by the HIV and by simian immunodeficiency virus.

RECENT FINDINGS

Studies in nonhuman primate models of lentiviral infection and in HIV-infected human individuals have shown that pathogenic infection is associated with loss of Th17 cells and an increase in the frequency of Tregs. Because interleukin-17 serves to maintain the integrity of the mucosal barrier, loss of Th17 cells may permit the increase in microbial translocation across the gastrointestinal mucosa that is observed in pathogenic lentiviral disease. It remains unclear, however, whether Th17 cells are preferentially infected or if, instead, their loss is induced by bystander effects of lentiviral infection, for example, the induction of indoleamine 2,3-dioxygenase.

SUMMARY

Progressive lentiviral disease is associated with preferential depletion of Th17 cells and loss of Th17/Treg balance. Further analysis of such changes in the composition of subset CD4 T helper and Tregs may shed new light on the immunopathology of HIV disease and suggest new strategies for therapeutic and preventive interventions.

Th1 cytokine responses fail to effectively control Chlamydia lung infection in ICOS ligand knockout mice

ICOS ligand (ICOSL) plays an important role in controlling specific aspects of T cell activation, differentiation, and function. Th1-type immune responses have been shown to be critical in host defense against chlamydial infections. To assess the role of ICOSL-ICOS interaction in host defense against chlamydial infection, we compared the immune responses and pathological reactions in ICOSL gene knockout (KO) and wild-type (WT) mice following Chlamydia muridarum lung infection. The results showed that ICOSL KO mice exhibited greater body weight loss, higher pathogen burden, and more severe histopathology in their lung than did WT mice. Cytokine analysis revealed that ICOSL KO mice produced lower levels of Th2 (IL-4 and IL-5) and anti-inflammatory (TGF-beta1 and IL-10) cytokines, but higher Th1-related (IFN-gamma and IL-12p40/IL-23) and proinflammatory (IL-6 and TNF-alpha) cytokines. ICOSL KO mice also showed reduced Chlamydia-specific Ab levels in their sera and lung homogenates. In addition, ICOSL KO mice demonstrated significantly lower ICOS expression in T cells and lower Th17 responses than did WT mice. Finally, we showed that ICOS-ICOSL interaction and cell-cell contact are essential for CD4(+) T cells to inhibit chlamydial growth in the cultured lung fibroblasts. The data suggest that ICOSL plays a significant role in immunoregulation and protective immunity against Chlamydia infections and that the Th1 skew in cytokine responses per se is not sufficient for effective control of Chlamydia infections.

Translational mini-review series on Th17 cells: development of mouse and human T helper 17 cells

There has been a considerable amount of interest in the immunological community about new phenotypic subsets of CD4(+) T cells, particularly cells that produce the cytokine interleukin (IL)-17 [named T helper type 17 (Th17) cells]. While the initial discovery of Th17 cells and the pathways that controlled their development was in the mouse, recent attention has shifted to the existence of these cells and the relevant upstream cytokine signals in humans. While it is clear that CD4(+) T cells producing IL-17 exist in vivo, their relevance to disease pathogenesis is only just being understood. In this paper, we review the data regarding the generation of human Th17 cells in vitro and the evidence that this effector population is important in human disease states.

IL-6 promotes NK cell production of IL-17 during toxoplasmosis

Previous studies have implicated T cell production of IL-17 in resistance to Toxoplasma gondii as well as the development of immune-mediated pathology during this infection. Analysis of C57BL/6 and C57BL/6 RAG(-/-) mice challenged with T. gondii-identified NK cells as a major innate source of IL-17. The ability of soluble Toxoplasma Ag to stimulate NK cells to produce IL-17 was dependent on the presence of accessory cells and the production of IL-6, IL-23, and TGF-beta. In contrast, these events were inhibited by IL-2, IL-15, and IL-27. Given that IL-6 was one of the most potent enhancers of NK cell production of IL-17, further studies revealed that only a subset of NK cells expressed both chains of the IL-6R, IL-6 upregulated expression of the Th17-associated transcription factor RORgammat, and that IL-6(-/-) mice challenged with T. gondii had a major defect in NK cell production of IL-17. Together, these data indicate that many of the same cytokines that regulate Th17 cells are part of a conserved pathway that also control innate production of IL-17 and identify a major role for IL-6 in the regulation of NK cell responses.

Transfer of tolerance to collagen type V suppresses T-helper-cell-17 lymphocyte-mediated acute lung transplant rejection

BACKGROUND

Rat lung allograft rejection is mediated by collagen type V (col(V)) specific T-helper-cell 17 (Th17) cells. Adoptive transfer of these cells is sufficient to induce rejection pathology in isografts, whereas tolerance to col(V) suppresses allograft rejection. Therefore, we tested whether regulatory T cells from tolerant rats could suppress the Th17-mediated rejection in the syngeneic model of lung transplantation.

METHODS

Rats were subjected to syngeneic left lung transplantation, and acute rejection was induced by adoptive transfer of lymph node cells from col(V)-immunized rats. Tolerance was induced by intravenous injection of col(V), and spleen lymphocytes were used for adoptive transfer. CD4+ T cells were depleted using magnetic beads. Lung isografts were analyzed using micro-positron emission tomography imaging and histochemistry. The transvivo delayed type hypersensitivity assay was used to analyze the Th17 response.

RESULTS

Adoptive cotransfer of col(V)-specific effector cells with cells from col(V)-tolerized rats suppressed severe vasculitis and bronchiolitis with parenchymal inflammation, and the expression of interleukin (IL)-17 transcripts in mediastinal lymph nodes induced by effector cells alone. Analysis by transvivo delayed type hypersensitivity showed that the reactivity to col(V) was dependent on the presence of tumor necrosis factor-alpha and IL-17 but not interferon-gamma. Depletion of CD4+ T cells from the suppressor cell population abrogated the col(V)-specific protection.

CONCLUSION

Th17-mediated acute rejection after lung transplantation is ameliorated by CD4+ col(V)-specific regulatory T cells. The mechanism for this Th17 suppression is consistent with tolerance induction to col(V). The goal of transplantation treatment, therefore, should target Th17 development and not suppression of T-cell activation by suppressing IL-2.