Lack of Toll IL-1R8 exacerbates Th17 cell responses in fungal infection

New Immunological Markers in Chromoblastomycosis-The Importance of PD-1 and PD-L1 Molecules in Human Infection

The pathogenesis of chromoblastomycosis (CBM) is associated with Th2 and/or T regulatory immune responses, while resistance is associated with a Th1 response. However, even in the presence of IFN-γ, fungi persist in the lesions, and the reason for this persistence is unknown. To clarify the factors associated with pathogenesis, this study aimed to determine the polarization of the cellular immune response and the densities of cells that express markers of exhaustion in the skin of CBM patients. In the skin of patients with CBM, a moderate inflammatory infiltrate was observed, characterized primarily by the occurrence of histiocytes. Analysis of fungal density allowed us to divide patients into groups that exhibited low and high fungal densities; however, the intensity of the inflammatory response was not related to mycotic loads. Furthermore, patients with CBM exhibited a significant increase in the number of CD4+ and CD8+ cells associated with a high density of IL-10-, IL-17-, and IFN-γ-producing cells, indicating the presence of a chronic and mixed cellular immune response, which was also independent of fungal load. A significant increase in the number of PD-1+ and PD-L1+ cells was observed, which may be associated with the maintenance of the fungus in the skin and the progression of the disease.

Fungal infections: Immune defense, immunotherapies and vaccines

Invasive fungal infection is an under recognized and emerging global health threat. Recently, the World Health Organization (WHO) released the first ever list of health-threatening fungi to guide research and public health interventions to strengthen global response to fungi infections and antifungal resistance. Currently, antifungal drugs only demonstrate partial success in improving prognosis of infected patients, and this is compounded by the rapid evolution of drug resistance among fungi species. The increased prevalence of fungal infections in individuals with underlying immunological deficiencies reflects the importance of an intact host immune system in controlling mycoses, and further highlights immunomodulation as a potential new avenue for the treatment of disseminated fungal diseases. In this review, we will summarize how host innate immune cells sense invading fungi through their pattern recognition receptors, and subsequently initiate a series of effector mechanisms and adaptive immune responses to mediate fungal clearance. In addition, we will discuss emerging preclinical and clinical data on antifungal immunotherapies and fungal vaccines which can potentially expand our antifungal armamentarium in future.

IL-1R8: A molecular brake of anti-tumor and anti-viral activity of NK cells and ILC

Interleukin-1 receptor family members (ILRs) and Toll-Like Receptors (TLRs) play pivotal role in immunity and inflammation and are expressed by most cell types including cells of both the innate and adaptive immune system. In this context, IL-1 superfamily members are also important players in regulating function and differentiation of adaptive and innate lymphoid cells. This system is tightly regulated in order to avoid uncontrolled activation, which may lead to detrimental inflammation contributing to autoimmune or allergic responses. IL-1R8 (also known as TIR8 or SIGIRR) is a member of the IL-1R family that acts as a negative regulator dampening ILR and TLR signaling and as a co-receptor for human IL-37. Human and mouse NK cells, that are key players in immune surveillance of tumors and infections, express high level of IL-1R8. In this review, we will summarize our current understanding on the structure, expression and function of IL-1R8 and we will also discuss the emerging role of IL-1R8 as an important checkpoint regulating NK cells function in pathological conditions including cancer and viral infections.

Regulation of CD18 stability by SIGIRR-modulated ubiquitination: new insights into the relationship between innate immune response and acute lung injury

Inappropriate accumulation of alveolar macrophages (AMs) and subsequent excessive production of immune responses play critical roles in the pathogenesis of acute lung injury (ALI), but the core negative regulators governing innate signalling in AMs are ill defined. We have previously shown that single immunoglobin IL-1 receptor-related protein (SIGIRR), a negative regulator of IL-1 receptor and Toll-like receptor signalling, inhibits lipopolysaccharide (LPS)-induced inflammatory responses in AMs. To address the biological relevance of SIGIRR in vivo, we generated a murine ALI model via intratracheal instillation of LPS. Intriguingly, SIGIRR expression was observed to be decreased in resident and recruited macrophages during ALI. This decrease was associated with parallel induction in CD18 protein levels in LPS-challenged lung tissues. Through intranasal injection of SIGIRR lentiviral particles studies, we showed that the overexpression of SIGIRR attenuated recruitment of macrophages and neutrophils, decreased production of inflammatory cytokines and ameliorated pathological changes in lungs. Whilst exploring the basis for this phenotype, SIGIRR was found to be coexpressed with CD18 in AMs, and SIGIRR potentiated the instability of CD18 protein via enhancement of its ubiquitination and proteasome degradation. Conversely, by using CD18^-/- mice, we further observed that CD18 deletion completely abolished the therapeutic effects of overexpression of SIGIRR on LPS-induced ALI. Mover, overexpression of CD18 in AMs promoted adhesion to ECM components, enhanced TLR4-mediated inflammasome activation and thereby potentiated IL-1β production. These data collectively identify SIGIRR/CD18 as a key negative regulatory circuit maintaining innate immune homeostasis in AMs along the pathogenesis of ALI.

Negative Regulation of the IL-1 System by IL-1R2 and IL-1R8: Relevance in Pathophysiology and Disease

Interleukin-1 (IL-1) is a primary cytokine of innate immunity and inflammation. IL-1 belongs to a complex family including ligands with agonist activity, receptor antagonists, and an anti-inflammatory cytokine. The receptors for these ligands, the IL-1 Receptor (IL-1R) family, include signaling receptor complexes, decoy receptors, and negative regulators. Agonists and regulatory molecules co-evolved, suggesting the evolutionary relevance of a tight control of inflammatory responses, which ensures a balance between amplification of innate immunity and uncontrolled inflammation. IL-1 family members interact with innate immunity cells promoting innate immunity, as well as with innate and adaptive lymphoid cells, contributing to their differentiation and functional polarization and plasticity. Here we will review the properties of two key regulatory receptors of the IL-1 system, IL-1R2, the first decoy receptor identified, and IL-1R8, a pleiotropic regulator of different IL-1 family members and co-receptor for IL-37, the anti-inflammatory member of the IL-1 family. Their complex impact in pathology, ranging from infections and inflammatory responses, to cancer and neurologic disorders, as well as clinical implications and potential therapeutic exploitation will be presented.

Combination Adjuvants Enhance Recombinant Protein Vaccine Protection against Fungal Infection

The development of effective vaccines against fungal infections requires the induction of protective, pathogen-specific cell-mediated immune responses. Here, we asked whether combination adjuvants based on delta inulin (Advax) formulated with Toll-like receptor (TLR) agonists could improve vaccine protection mediated by a fungal recombinant protein, Bl-Eng2 (i.e., Blastomyces endoglucanase 2), which itself harbors an immunodominant antigen and dectin-2 agonist/adjuvant. We found that Bl-Eng2 formulated with Advax3 containing TLR9 agonist or Advax8 containing TLR4 agonist provided the best protection against pulmonary infection with Blastomyces dermatitidis, being more effective than complete Freund’s adjuvant or Adjuplex. Advax3 was most efficient in inducing gamma interferon (IFN-γ)- and interleukin-17 (IL-17)-producing antigen-specific T cells that migrated to the lung upon Blastomyces dermatitidis infection. Mechanistic studies revealed Bl-Eng2/Advax3 protection was tempered by neutralization of IL-17 and particularly IFN-γ. Likewise, greater numbers of lung-resident T cells producing IFN-γ, IL-17, or both IFN-γ and IL-17 correlated with fewer fungi recovered from lung. Protection was maintained after depletion of CD4⁺ T cells, partially reduced by depletion of CD8⁺ T cells, and completely eliminated after depletion of both CD4⁺ and CD8⁺ T cells. We conclude that Bl-Eng2 formulated with Advax3 is promising for eliciting vaccine-induced antifungal immunity, through a previously uncharacterized mechanism involving CD8⁺ and also CD4⁺ T cells producing IFN-γ and/or IL-17. Although no licensed vaccine exists as yet against any fungal disease, these findings indicate the importance of adjuvant selection for the development of effective fungal vaccines.

Th17 cells are involved in mouse chronic obstructive pulmonary disease complicated with invasive pulmonary aspergillosis

BACKGROUND

The incidence of chronic obstructive pulmonary disease (COPD) complicated with invasive pulmonary aspergillosis (IPA) has increased in the last two decades. The mechanism underpinning susceptibility to and high mortality of COPD complicated with IPA is unclear, and the role of T helper cells 17 (Th17 cells) in the compound disease remains unknown. Therefore, this study aimed to assess the function of Th17 cells in COPD combined with IPA.

METHODS

COPD, IPA, and COPD+IPA mouse models were established in male wild type C57/BL6 mice. The amounts of Th17 cells and retinoic acid-related orphan receptors γt (RORγt) were tested by flow cytometry. Then, serum interleukin (IL)-17 and IL-23 levels were detected by enzyme-linked immunosorbent assay (ELISA) in the control, COPD, IPA and COPD+IPA groups. In addition, COPD+IPA was induced in IL-17 knockout (KO) mice, for determining the role of Th17 cells in COPD+IPA.

RESULTS

Compared with the COPD group, the COPD+IPA group showed higher amounts of blood RORγt ([35.09 ± 16.12]% vs. [17.92 ± 4.91]%, P = 0.02) and serum IL-17 (17.96 ± 9.59 pg/mL vs. 8.05 ± 4.44 pg/mL, P = 0.02), but blood ([5.18 ± 1.09]% vs. [4.15 ± 0.87]%, P = 0.28) and lung levels of Th17 cells ([1.98 ± 0.83]% vs. [2.03 ± 0.98]%, P = 0.91), lung levels of RORγt ([9.58 ± 6.93]% vs. [9.63 ± 5.98]%, P = 0.49) and serum IL-23 (51.55 ± 27.82 pg/mL vs. 68.70 ± 15.20 pg/mL, P = 0.15) showed no significant differences. Compared with the IPA group, the COPD+IPA group displayed lower amounts of blood ([5.18 ± 1.09]% vs. [9.21 ± 3.56]%, P = 0.01) and lung Th17 cells ([1.98 ± 0.83]% vs. [6.29 ± 1.11]%, P = 0.01) and serum IL-23 (51.55 ± 27.82 pg/mL vs. 154.90 ± 64.60 pg/mL, P = 0.01) and IL-17 (17.96 ± 9.59 pg/mL vs. 39.81 ± 22.37 pg/mL, P = 0.02), while comparable blood ([35.09 ± 16.12]% vs. [29.86 ± 15.42]%, P = 0.25) and lung levels of RORγt ([9.58 ± 6.93]% vs. [15.10 ± 2.95]%, P = 0.18) were found in these two groups. Finally, Aspergillus load in IL-17 KO COPD+IPA mice was almost 2 times that of COPD+IPA mice (1,851,687.69 ± 944,480.43 vs. 892,958.10 ± 686,808.80, t = 2.32, P = 0.02).

CONCLUSION

These findings indicate that Th17 cells might be involved in the pathogenesis of COPD combined with IPA, with IL-17 likely playing an antifungal role.

Immune response against Chlamydia trachomatis via toll-like receptors is negatively regulated by SIGIRR

Chlamydia trachomatis is the most common bacterial sexually-transmitted infection and the major cause of preventable blindness worldwide. The asymptomatic nature of many infections along with uncontrolled inflammation leads to irreversible damage in the upper genital tract and the tarsal conjunctivae, with the major complications of infertility and chronic pelvic pain, and blindness, respectively. Inflammation must, therefore, be tightly regulated to avoid an unrestrained immune response. The genetic factors that regulate inflammation through Toll-like receptor (TLR) signaling pathways during C. trachomatis infection have not been fully characterized. SIGIRR (also known as IL-1R8 or TIR8) can regulate inflammation in response to various pathogens and diseases. However, nothing is known about its role during C. trachomatis infection. Expression of the pro-inflammatory chemokine, IL-8, was measured in epithelial cells infected with C. trachomatis. The effect of SIGIRR was determined by depleting SIGIRR or over-expressing SIGIRR in the epithelial cells before infection. Our results indicate that, in the absence of SIGIRR, epithelial cells induce higher levels of the pro-inflammatory chemokine, IL-8, in response to C. trachomatis infection. In addition, SIGIRR associates with MyD88 in both infected and uninfected infected cells. Collectively, our data demonstrate that SIGIRR functions as a negative regulator of the immune response to C. trachomatis infection. This finding provides insights into the immuno-pathogenesis of C. trachomatis that can be used to treat and identify individuals at risk of uncontrolled inflammation during infection.

Pathogenic Fungal Infection in the Lung

Respiratory fungal infection is a severe clinical problem, especially in patients with compromised immune functions. Aspergillus, Cryptococcus, Pneumocystis, and endemic fungi are major pulmonary fungal pathogens that are able to result in life-threatening invasive diseases. Growing data being reported have indicated that multiple cells and molecules orchestrate the host's response to a fungal infection in the lung. Upon fungal challenge, innate myeloid cells including macrophages, dendritic cells (DC), and recruited neutrophils establish the first line of defense through the phagocytosis and secretion of cytokines. Natural killer cells control the fungal expansion in the lung via the direct and indirect killing of invading organisms. Adaptive immune cells including Th1 and Th17 cells confer anti-fungal activity by producing their signature cytokines, interferon-γ, and IL-17. In addition, lung epithelial cells (LEC) also participate in the resistance against fungal infection by internalization, inflammatory cytokine production, or antimicrobial peptide secretion. In the host cells mentioned above, various molecules with distinct functions modulate the immune defense signaling: Pattern recognition receptors (PRRs) such as dectin-1 expressed on the cell surface are involved in fungal recognition; adaptor proteins such as MyD88 and TRAF6 are required for transduction of signals to the nucleus for transcriptional regulation; inflammasomes also play crucial roles in the host's defense against a fungal infection in the lung. Furthermore, transcriptional factors modulate the transcriptions of a series of genes, especially those encoding cytokines and chemokines, which are predominant regulators in the infectious microenvironment, mediating the cellular and molecular immune responses against a fungal infection in the lung.

Lung-infiltrating T helper 17 cells as the major source of interleukin-17A production during pulmonary Cryptococcus neoformans infection

Background

IL-17A has emerged as a key player in the pathologies of inflammation, autoimmune disease, and immunity to microbes since its discovery two decades ago. In this study, we aim to elucidate the activity of IL-17A in the protection against Cryptococcus neoformans, an opportunistic fungus that causes fatal meningoencephalitis among AIDS patients. For this purpose, we examined if C. neoformans infection triggers IL-17A secretion in vivo using wildtype C57BL/6 mice. In addition, an enhanced green fluorescence protein (EGFP) reporter and a knockout (KO) mouse models were used to track the source of IL-17A secretion and explore the protective function of IL-17A, respectively.

Results

Our findings showed that in vivo model of C. neoformans infection demonstrated induction of abundant IL-17A secretion. By examining the lung bronchoalveolar lavage fluid (BALF), mediastinal lymph node (mLN) and spleen of the IL-17A–EGFP reporter mice, we showed that intranasal inoculation with C. neoformans promoted leukocytes lung infiltration. A large proportion (~ 50%) of the infiltrated CD4⁺ helper T cell population secreted EGFP, indicating vigorous T_H17 activity in the C. neoformans–infected lung. The infection study in IL-17A–KO mice, on the other hand, revealed that absence of IL-17A marginally boosted fungal burden in the lung and accelerated the mouse death.

Conclusion

Therefore, our data suggest that IL-17A is released predominantly from T_H17 cells in vivo, which plays a supporting role in the protective immunity against C. neoformans infection.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0269-5) contains supplementary material, which is available to authorized users.

Serum Cytokine Profile in Patients with Chronic Rhinosinusitis with Nasal Polyposis Infected by Aspergillus flavus

Background

Fungi, especially Aspergillus flavus, can cause chronic rhinosinusitis with nasal polyposis and modulate host innate immune components. The objective of this study was to examine the serum levels of T helper (Th) cell subset Th1, Th2, and Th17 cytokines and total IgE in patients having chronic rhinosinusitis with nasal polyposis and Aspergillus flavus infection.

Methods

A case-control study including 40 patients with chronic rhinosinusitis with nasal polyposis and 20 healthy controls was conducted. Aspergillus flavus infection was confirmed by standard potassium hydroxide (KOH) testing, culture, and PCR. Serum samples of all patients and controls were analyzed for various cytokines (interleukins [IL]-1β, IL-2, IL-4, IL-6, IL-17, IL-21, IL-27, TGF-β) and total IgE by ELISA. Data from patients with Aspergillus flavus infection and healthy volunteers were compared using the independent t-test and non-parametric Mann-Whitney U test.

Results

Aspergillus flavus infection was found in 31 (77.5%) patients with chronic rhinosinusitis with nasal polyposis. IL-1β, IL-17, IL-21, and TGF-β serum levels were significantly higher in these patients than in controls; however, IL-2, IL-4, IL-6, and IL-27 levels were lower. Compared with nine (22.5%) patients without Aspergillus flavus infection, IL-17 level was higher while IL-2 level was lower in patients with Aspergillus flavus infection. Total IgE was significantly higher in patients with Aspergillus flavus infection than in controls.

Conclusions

High levels of IL-17 and its regulatory cytokines in patients with chronic rhinosinusitis with nasal polyposis infected by Aspergillus flavus raise a concern about effective disease management and therapeutic recovery. Surgical removal of the nasal polyp being the chief management option, the choice of post-operative drugs may differ in eosinophilic vs. non-eosinophilic nasal polyposis. The prognosis is likely poor, warranting extended care.

Tuning inflammation and immunity by the negative regulators IL-1R2 and IL-1R8

Interleukin-1 receptor family members (ILRs) and Toll-Like Receptors (TLRs) are key players in immunity and inflammation and are tightly regulated at different levels. Most cell types, including cells of the innate and adaptive immune system express ILRs and TLRs. In addition, IL-1 family members are emerging as key players in the differentiation and function of innate and adaptive lymphoid cells. IL-1R2 and IL-1R8 (also known as TIR8 or SIGIRR) are members of the ILR family acting as negative regulators of the IL-1 system. IL-1R2 binds IL-1 and the accessory protein IL-1RAcP without activating signaling and can be released as a soluble form (sIL-1R2), thus modulating IL-1 availability for the signaling receptor. IL-1R8 dampens ILR- and TLR-mediated cell activation and it is a component of the receptor recognizing human IL-37. Here, we summarize our current understanding of the structure and function of IL-1R2 and IL-1R8, focusing on their role in different pathological conditions, ranging from infectious and sterile inflammation, to autoimmunity and cancer-related inflammation. We also address the emerging evidence regarding the role of IL-1R8 as a crucial checkpoint molecule in NK cells in anti-cancer and antiviral activity and the potential therapeutic implications of IL-1R8 blockade in specific pathological contexts.

The Multifaceted Role of T-Helper Responses in Host Defense against Aspergillus fumigatus

The ubiquitous opportunistic fungal pathogen Aspergillus fumigatus rarely causes infections in immunocompetent individuals. A healthy functional innate immune system plays a crucial role in preventing Aspergillus-infection. This pivotal role for the innate immune system makes it a main research focus in studying the pathogenesis of aspergillosis. Although sometimes overshadowed by the innate immune response, the adaptive immune response, and in particular T-helper responses, also represents a key player in host defense against Aspergillus. Virtually all T-helper subsets have been described to play a role during aspergillosis, with the Th1 response being crucial for fungal clearance. However; morbidity and mortality of aspergillosis can also be partly attributed to detrimental immune responses resulting from adaptive immune activation. Th2 responses benefit fungal persistence; and are the foundation of allergic forms of aspergillosis. The Th17 response has two sides; although crucial for granulocyte recruitment, it can be involved in detrimental immunopathology. Regulatory T-cells, the endogenous regulators of inflammatory responses, play a key role in controlling detrimental inflammatory responses during aspergillosis. The current knowledge of the adaptive immune response against A. fumigatus is summarized in this review. A better understanding on how T-helper responses facilitate clearance of Aspergillus-infection and control inflammation can be the fundamental basis for understanding the pathogenesis of aspergillosis and for the development of novel host-directed therapies.

Role of TLR1, TLR2 and TLR6 in the modulation of intestinal inflammation and Candida albicans elimination

Background

Toll-like receptors (TLRs) are the major pattern recognition receptors that mediate sensing of a wide range of microorganisms. TLR2 forms heterodimers with either TLR1 or TLR6, broadening its ligand diversity against pathogens. TLR1, TLR2 and TLR6 have been implicated in the recognition of Candida albicans, an opportunistic fungal pathogen that colonizes the gastrointestinal tract. In this study, we explored whether the deficiency in TLR1, TLR2 or TLR6 impacts C. albicans colonization and inflammation-associated colonic injury in the dextran sulfate sodium (DSS)-induced colitis in mice.

Results

DSS treatment and C. albicans challenge induced greater weight loss, worse clinical signs of inflammation, higher histopathologic scores, and increased mortality rates in TLR1^−/− and TLR2^−/− mice when compared to TLR6^−/− and wild-type mice. The number of C. albicans colonies in the stomach, colon and feces was decreased in TLR6^−/− mice as compared to TLR2^−/−, TLR1^−/− and wild-type mice. Interestingly, the population of E. coli in colonic luminal contents, intestinal permeability to FITC-dextran and cytokine expression were significantly increased in TLR1^−/− and TLR2^−/− mice, while they were decreased in TLR6^−/− mice.

Conclusion

In contrast to TLR6, both TLR1 and TLR2 deficiencies increased intestinal inflammation, and the overgrowth of C. albicans and E. coli populations in the colitis model, suggesting the involvement of TLR1 and TLR2 in epithelial homeostasis, and a role of TLR6 in increasing intestinal inflammation in response to pathogen-sensing.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-017-0158-0) contains supplementary material, which is available to authorized users.

Cytokine decoy and scavenger receptors as key regulators of immunity and inflammation

IL-1R2 was the first decoy receptor to be described. Subsequently receptors which act as pure decoys or scavengers or trigger dampening of cytokine signaling have been described for cytokines and chemokines. Here we review the current understanding of the mode of action and significance in pathology of the chemokine atypical receptor ACKR2, the IL-1 decoy receptor IL-1R2 and the atypical IL-1 receptor family IL-1R8. Decoy and scavenger receptors with no or atypical signaling have emerged as a general strategy conserved in evolution to tune the action of cytokines, chemokines and growth factors.

Regulatory Role of IL-1R8 in Immunity and Disease

Interleukin-1 receptor family members (ILRs) and toll-like receptors (TLRs) are characterized by the presence of a conserved intracellular domain and the toll-IL-1resistance (TIR) domain and are key players in immunity and inflammation. ILR and TLR signaling is tightly regulated at different levels. All cell types of the innate immune system express ILRs and TLRs. In addition, IL-1 family members are emerging as key players in the differentiation and function of innate and adaptive lymphoid cells. IL-1R8, also known as TIR8 or SIGIRR, is a fringe member of the ILR family and acts as a negative regulator of ILR and TLR signaling, which dampens ILR- and TLR-mediated cell activation. IL-1R8 is a component of the receptor recognizing human IL-37. Here, we summarize our current understanding of the structure and function of IL-1R8, focusing on its role in different pathological conditions, ranging from infectious and sterile inflammation to autoimmunity and cancer-related inflammation.

IL-1 receptor antagonist ameliorates inflammasome-dependent inflammation in murine and human cystic fibrosis

Dysregulated inflammasome activation contributes to respiratory infections and pathologic airway inflammation. Through basic and translational approaches involving murine models and human genetic epidemiology, we show here the importance of the different inflammasomes in regulating inflammatory responses in mice and humans with cystic fibrosis (CF), a life-threatening disorder of the lungs and digestive system. While both contributing to pathogen clearance, NLRP3 more than NLRC4 contributes to deleterious inflammatory responses in CF and correlates with defective NLRC4-dependent IL-1Ra production. Disease susceptibility in mice and microbial colonization in humans occurrs in conditions of genetic deficiency of NLRC4 or IL-1Ra and can be rescued by administration of the recombinant IL-1Ra, anakinra. These results indicate that pathogenic NLRP3 activity in CF could be negatively regulated by IL-1Ra and provide a proof-of-concept evidence that inflammasomes are potential targets to limit the pathological consequences of microbial colonization in CF.

IL-1-mediated inflammation contributes to the pathogenesis of cystic fibrosis. Here the authors show that this is largely due to NLRP3 activation, whereas NLRP4 induces IL-1Ra, limiting the overall inflammasome activity and providing a therapeutic angle to ameliorate the disease.

SIGIRR participates in negative regulation of LPS response and tolerance in human bladder epithelial cells

Background

The innate immune response of urinary tract is critically important in the defense to microbial attack. Toll-like receptor 4 (TLR4) controls initial mucosal response to uropathogenic Escherichia coli (UPEC). However, excessive and dysfunctional TLR signaling may result in severe inflammation and inappropriate tissue damage. Previous studies have demonstrated that single immunoglobulin IL-1R-related receptor/Toll IL-1 receptor 8 (SIGIRR/TIR8) is a member of the toll-interleukin-1 receptor (TIR) family that can negatively modulate TLR4 mediated signaling, but its role in the innate immunity of urinary tract infection remains incompletely defined. In this study, we investigated its cellular distribution and mechanisms involved within the human bladder epithelial cells after LPS stimulation.

Results

Immunostaining, reverse transcription PCR and Western blot results showed that SIGIRR was constitutively expressed in the human bladder epithelial cell lines and was downregulated after LPS stimulation. To further define the role of SIGIRR, cells were transiently transfected with SIGIRR siRNA and stimulated with LPS. SIGIRR gene silencing augmented chemokine expression in response to LPS, as indicated by increased levels of IL-6 and IL-8 secretions in the supernatants compared with negative control siRNA. Furthermore, LPS tolerance, a protective mechanism against second LPS stimulation, was significantly reduced in SIGIRR siRNA transfected cells. Moreover, transient gene silencing augmented LPS-induced NF-κB and MAPK activation.

Conclusions

In conclusion, our results suggest that SIGIRR plays an important role in the negative regulation of LPS response and tolerance in human bladder epithelial cells, possibly through its impact on TLR-mediated signaling.

Pathogenic NLRP3 Inflammasome Activity during Candida Infection Is Negatively Regulated by IL-22 via Activation of NLRC4 and IL-1Ra

Candida albicans is a well-tolerated resident of human mucosal tissues. This implies that host defense mechanisms cooperate to limit inflammation while controlling fungal burden. The cytokine IL-22 and inflammasomes are essential components of the mucosal responses to C. albicans. How these components cooperate to mediate the balance of inflammation and host defense is not explored. We find that NLRP3 inflammasome activation promotes neutrophil recruitment and inflammation during infection and that this activity is counteracted by IL-22. Mechanistically, IL-22 activated NLRC4 for sustained production of the IL-1 receptor antagonist IL-1Ra, which restrained NLRP3 activity. Symptomatic infection in mice and humans occurred under conditions of IL-1Ra deficiency and was rescued in mice by replacement therapy with the recombinant IL-1Ra anakinra. Thus, pathogenic inflammasome activity during Candida infection is negatively regulated by the IL-22/NLRC4/IL-1Ra axis. Our findings offer insights into the pathogenesis of C. albicans and suggest therapeutic avenues for candidiasis.

IL-37 requires the receptors IL-18Rα and IL-1R8 (SIGIRR) to carry out its multifaceted anti-inflammatory program upon innate signal transduction

Interleukin 37 (IL-37) and IL-1R8 (SIGIRR or TIR8) are anti-inflammatory orphan members of the IL-1 ligand family and IL-1 receptor family, respectively. Here we demonstrate formation and function of the endogenous ligand-receptor complex IL-37-IL-1R8-IL-18Rα. The tripartite complex assembled rapidly on the surface of peripheral blood mononuclear cells upon stimulation with lipopolysaccharide. Silencing of IL-1R8 or IL-18Rα impaired the anti-inflammatory activity of IL-37. Whereas mice with transgenic expression of IL-37 (IL-37tg mice) with intact IL-1R8 were protected from endotoxemia, IL-1R8-deficient IL-37tg mice were not. Proteomic and transcriptomic investigations revealed that IL-37 used IL-1R8 to harness the anti-inflammatory properties of the signaling molecules Mer, PTEN, STAT3 and p62(dok) and to inhibit the kinases Fyn and TAK1 and the transcription factor NF-κB, as well as mitogen-activated protein kinases. Furthermore, IL-37-IL-1R8 exerted a pseudo-starvational effect on the metabolic checkpoint kinase mTOR. IL-37 thus bound to IL-18Rα and exploited IL-1R8 to activate a multifaceted intracellular anti-inflammatory program.

Assessment of the cutaneous immune response during Arthroderma benhamiae and A. vanbreuseghemii infection using an experimental mouse model

BACKGROUND

Dermatophytoses are common but poorly understood skin infections. Most in vivo studies have been performed using the guinea pig as the experimental animal model, which has several limitations.

OBJECTIVES

To develop a mouse model of dermatophytosis suitable for multiple purposes, including the investigation of immunity against dermatophytes.

MATERIALS AND METHODS

Two peculiar fungal species, Arthroderma benhamiae and A. vanbreuseghemii, isolated from tinea in humans having contact with rodents were used for epicutaneous inoculation. During the infection, clinical and histopathological follow-up were performed. The recruitment of immune cells was evaluated by immunofluorescence staining and the levels of cytokine mRNA were quantified by quantitative reverse transcriptase-polymerase chain reaction in the skin of infected mice.

RESULTS

The skin symptoms and microscopic lesions, including the colonization of keratinized epidermal and follicular structures by both dermatophytes, were highly similar to those observed in guinea pig infection models and in natural infections, mimicking acute superficial tinea in humans. The dermal inflammatory cellular infiltrate consisted of macrophages, dendritic cells and especially polymorphonuclear neutrophils, which are one of the histological 'clues' to the diagnosis of dermatophytosis. The in situ cytokine profile was characterized by the overexpression of transforming growth factor-β, interleukin (IL)-1β and IL-6 mRNA during infection, suggesting a role of the T-helper 17 pathway in the establishment of immunity.

CONCLUSIONS

Our new reproducible and validated mouse model of dermatophytosis is a modern in vivo tool that allows a more in-depth understanding of the pathogenesis of human dermatophyte infections.

Indoleamine 2,3-dioxygenase controls fungal loads and immunity in Paracoccidioidomicosis but is more important to susceptible than resistant hosts

Background

Paracoccidioidomycosis, a primary fungal infection restricted to Latin America, is acquired by inhalation of fungal particles. The immunoregulatory mechanisms that control the severe and mild forms of paracoccidioidomycosis are still unclear. Indoleamine 2,3-dioxygenase (IDO), an IFN-γ induced enzyme that catalyzes tryptophan metabolism, can control host-pathogen interaction by inhibiting pathogen growth, T cell immunity and tissue inflammation.

Methodology/Principal Findings

In this study, we investigated the role of IDO in pulmonary paracoccidioidomycosis of susceptible and resistant mice. IDO was blocked by 1-methyl-dl-tryptophan (1MT), and fungal infection studied in vitro and in vivo. Paracoccidioides brasiliensis infection was more severe in 1MT treated than untreated macrophages of resistant and susceptible mice, concurrently with decreased production of kynurenines and IDO mRNA. Similar results were observed in the pulmonary infection. Independent of the host genetic pattern, IDO inhibition reduced fungal clearance but enhanced T cell immunity. The early IDO inhibition resulted in increased differentiation of dendritic and Th17 cells, accompanied by reduced responses of Th1 and Treg cells. Despite these equivalent biological effects, only in susceptible mice the temporary IDO blockade caused sustained fungal growth, increased tissue pathology and mortality rates. In contrast, resistant mice were able to recover the transitory IDO blockade by the late control of fungal burdens without enhanced tissue pathology.

Conclusions/Significance

Our studies demonstrate for the first time that in pulmonary paracoccidioidomycosis, IDO is an important immunoregulatory enzyme that promotes fungal clearance and inhibits T cell immunity and inflammation, with prominent importance to susceptible hosts. In fact, only in the susceptible background IDO inhibition resulted in uncontrolled tissue pathology and mortality rates. Our findings open new perspectives to understand the immunopathology of paracoccidioidomycosis, and suggest that an insufficient IDO activity could be associated with the severe cases of human PCM characterized by inefficient fungal clearance and excessive inflammation.

Immunoprotection to paracoccidiodomycosis, a systemic mycosis endemic in Latin America, is mediated by T cell immunity whereas immunosuppression characterizes the severe forms of the disease. Indoleamine 2,3-dioxygenase (IDO), an enzyme mainly induced by IFN-γ, catabolizes tryptophan along the kynurenines pathway. Tryptophan deficiency has been associated with reduced pathogen growth, while elevated levels of kynurenines with suppressed immune responses. In this study, the role of IDO in pulmonary paracoccidioidomycosis was investigated using resistant and susceptible mice. In both mouse strains, IDO blockade by 1-methyl tryptophan resulted in inefficient fungal clearance accompanied by enhanced T cell immunity. Despite these equivalent biological effects, only in susceptible mice IDO inhibition caused progressive fungal growth and tissue pathology resulting in increased mortality. Our findings demonstrate for the first time that IDO exert a yet unexplored immunoregulatory role in pulmonary paracoccidioidomycosis that can be particularly important in the severe cases of the disease.

IL-37 inhibits inflammasome activation and disease severity in murine aspergillosis

Since IL-37 transgenic mice possesses broad anti-inflammatory properties, we assessed whether recombinant IL-37 affects inflammation in a murine model of invasive pulmonary aspergillosis. Recombinant human IL-37 was injected intraperitoneally into mice prior to infection and the effects on lung inflammation and inflammasome activation were evaluated. IL-37 markedly reduced NLRP3-dependent neutrophil recruitment and steady state mRNA levels of IL-1β production and mitigated lung inflammation and damage in a relevant clinical model, namely aspergillosis in mice with cystic fibrosis. The anti-inflammatory activity of IL-37 requires the IL-1 family decoy receptor TIR-8/SIGIRR. Thus, by preventing activation of the NLRP3 inflammasome and reducing IL-1β secretion, IL-37 functions as a broad spectrum inhibitor of the innate response to infection-mediated inflammation, and could be considered to be therapeutic in reducing the pulmonary damage due to non-resolving Aspergillus infection and disease.

IL-37, firstly identified by in silico research in the year 2000, is a member of the IL-1 family. The biological properties of IL-37 are mainly those of down-regulating inflammation in models of septic shock, chemical colitis, cardiac ischemia and contact dermatitis. Whether and how IL-37 down-regulates the inflammation of infection, and its consequences, is not known. We observed that IL-37 limits inflammation and disease severity in murine invasive aspergillosis, an infection model in which cytokines of the IL-1 family have important roles. However, given that IL-1R1-deficient or caspase 1-deficient mice are resistant to lung inflammation during infection and that IL-1 signaling could drive the differentiation of antifungal inflammatory Th17 cells, the pro-inflammatory properties of IL 1-induced inflammation in aspergillosis is potentially dangerous for the host. IL-37 markedly reduced NLRP3-dependent neutrophil recruitment and steady state mRNA levels of IL-1β production and mitigated lung inflammation and damage in a relevant clinical model, namely aspergillosis in mice with cystic fibrosis. The anti-inflammatory activity of IL-37 requires the IL-1 receptor family decoy TIR-8/SIGIRR. Thus, IL-37 functions as a broad spectrum inhibitor of infection-mediated inflammation, and could be considered to be therapeutic in reducing the pulmonary damage due to non-resolving Aspergillus infection and disease.

Adaptive immunity to fungi

Life-threatening fungal infections have risen sharply in recent years, owing to the advances and intensity of medical care that may blunt immunity in patients. This emerging crisis has created the growing need to clarify immune defense mechanisms against fungi with the ultimate goal of therapeutic intervention. We describe recent insights in understanding the mammalian immune defenses that are deployed against pathogenic fungi. We focus on adaptive immunity to the major medically important fungi and emphasize three elements that coordinate the response: (1) dendritic cells and subsets that are mobilized against fungi in various anatomical compartments; (2) fungal molecular patterns and their corresponding receptors that signal responses and shape the differentiation of T-cell subsets and B cells; and, ultimately (3) the effector and regulatory mechanisms that eliminate these invaders while constraining collateral damage to vital tissue. These insights create a foundation for the development of new, immune-based strategies for prevention or enhanced clearance of systemic fungal diseases.

The decreased frequency of SIGIRR-positive CD4+ T cells in peripheral blood of patients with SLE and its correlation with disease activity

Recently, many studies have shown that Single immunoglobulin interleukin-1 receptor related protein (SIGIRR), a member of the IL-1R family acting as a negative regulator of TLR/IL-1R signaling, affects autoimmune responses in animal model of systemic lupus erythematosus (SLE). However, the role of SIGIRR in the pathogenesis of human SLE has not been widely explored. In this study, we analyzed the frequency of SIGIRR-positive CD4+ T cells in peripheral blood mononuclear cells (PBMCs) of SLE patients and its correlation with disease activity as well as the clinical data. Circulating SIGIRR-positive CD4+ T cells were quantified in 51 SLE patients and 38 healthy controls by using flow cytometer. Results showed that the percentages of SIGIRR-positive CD4+ T cells were decreased in the PBMCs of SLE patients compared with healthy controls (Z = -5.49, P < 0.001). The frequency of SIGIRR-positive CD4 + T cells were also significantly decreased in SLE patients with nephritis than those without nephritis (Z = -3.71, P < 0.001). In addition, there was significant correlation between the percentages of SIGIRR-positive CD4+ T cells and SLEDAI score (r s = -0.74, P < 0.001), 24-hour urine protein (r s = -0.62, P < 0.001), Scr (r s = -0.65, P < 0.001), ESR (r s = -0.60, P < 0.001), C3 (r s = 0.53, P < 0.001) as well as C4 (r s = 0.52, P < 0.001). However, there was no correlation between the proportion of SIGIRR-positive CD4+ T cells and glucocorticoid dose (P = 0.59). In summary, decreased numbers of SIGIRR-positive CD4+ T cells in SLE patients and its correlation with SLEDAI score as well as the clinical data suggest that SIGIRR may be involved in the pathogenesis of SLE.

Directing traffic: IL-17 and IL-22 coordinate pulmonary immune defense

Respiratory infections and diseases are among the leading causes of death worldwide, and effective treatments probably require manipulating the inflammatory response to pathogenic microbes or allergens. Here, we review mechanisms controlling the production and functions of interleukin-17 (IL-17) and IL-22, cytokines that direct several aspects of lung immunity. Innate lymphocytes (γδ T cells, natural killer cells, innate lymphoid cells) are the major source of IL-17 and IL-22 during acute infections, while CD4(+) T-helper 17 (Th17) cells contribute to vaccine-induced immunity. The characterization of dendritic cell (DC) subsets has revealed their central roles in T-cell activation. CD11b(+) DCs stimulated with bacteria or fungi secrete IL-1β and IL-23, potent inducers of IL-17 and IL-22. On the other hand, recognition of viruses by plasmacytoid DCs inhibits IL-1β and IL-23 release, increasing susceptibility to bacterial superinfections. IL-17 and IL-22 primarily act on the lung epithelium, inducing antimicrobial proteins and neutrophil chemoattractants. Recent studies found that stimulation of macrophages and DCs with IL-17 also contributes to antibacterial immunity, while IL-22 promotes epithelial proliferation and repair following injury. Chronic diseases such as asthma and chronic obstructive pulmonary disease have been associated with IL-17 and IL-22 responses directed against innocuous antigens. Future studies will evaluate the therapeutic efficacy of targeting the IL-17/IL-22 pathway in pulmonary inflammation.

The interleukin-1 family: back to the future

Interleukin-1 (IL-1) is a central mediator of innate immunity and inflammation. The IL-1 family includes seven ligands with agonist activity (IL-1α and IL-1β, IL-18, IL-33, IL-36α, IL-36β, IL-36γ), three receptor antagonists (IL-1Ra, IL-36Ra, IL-38), and an anti-inflammatory cytokine (IL-37). Members of the IL-1 Receptor (IL-1R) family include six receptor chains forming four signaling receptor complexes, two decoy receptors (IL-1R2, IL-18BP), and two negative regulators (TIR8 or SIGIRR, IL-1RAcPb). A tight regulation via receptor antagonists, decoy receptors, and signaling inhibitors ensures a balance between amplification of innate immunity and uncontrolled inflammation. All cells of the innate immune system express and/or are affected by IL-1 family members. Moreover, IL-1 family members play a key role in the differentiation and function of polarized innate and adaptive lymphoid cells. Here we will review the key properties of IL-1 family members, with emphasis on pathways of negative regulation and orchestration of innate and adaptive immunity.

Single immunoglobulin interleukin-1 receptor-related molecule impairs host defense during pneumonia and sepsis caused by Streptococcus pneumoniae

Streptococcus pneumoniae is a common cause of pneumonia and sepsis. Toll-like receptors (TLRs) play a pivotal role in the host defense against infection. In this study, we sought to determine the role of single immunoglobulin interleukin-1 receptor-related molecule (SIGIRR a.k.a. TIR8), a negative regulator of TLR signaling, in pneumococcal pneumonia and sepsis. Wild-type and SIGIRR-deficient (sigirr-/-) mice were infected intranasally (to induce pneumonia) or intravenously (to induce primary sepsis) with S. pneumoniae and euthanized after 6, 24, or 48 h for analyses. Additionally, survival studies were performed. sigirr-/- mice showed delayed mortality during lethal pneumococcal pneumonia. Accordingly, sigirr-/- mice displayed lower bacterial loads in lungs and less dissemination of the infection 24 h after the induction of pneumonia. SIGIRR deficiency was associated with increased interstitial and perivascular inflammation in lung tissue early after infection, with no impact on neutrophil recruitment or cytokine production. sigirr-/- mice also demonstrated reduced bacterial burdens at multiple body sites during S. pneumoniae sepsis. sigirr-/- alveolar macrophages and neutrophils exhibited an increased capacity to phagocytose viable pneumococci. These results suggest that SIGIRR impairs the antibacterial host defense during pneumonia and sepsis caused by S. pneumoniae.

Influence of TLR-2 in the immune response in the infection induced by fungus Sporothrix schenckii

Toll-like receptors (TLRs) play an important role in immunity, since they bind to pathogen surface antigens and initiate the immune response. However, little is known about the role of TLR-2 in the recognition of S. schenckii and in the subsequent immune response. Therefore, the aim of this study was to evaluate the involvement of TLR-2 in the immune response induced by S. schenckii. C57BL/6 mice (WT) and C57BL/6 TLR-2 knockout (TLR-2-/-) were used to evaluate, over a period of 10 weeks of sporotrichotic infection, the influence of TLR-2 over macrophages production of IL-1β, IL-12 and TNF-α, their stimulation level by NO release and the production of IFN -γ, IL-6, IL-17 and TGF-β by spleen cells. The results showed that the production of pro-inflammatory mediators and NO, TLR-2 interference is striking, since its absence completely inhibited it. IL-17 production was independent of TLR-2. The absence of Th1 response in TLR2-/- animals was concomitant with IL-17 production. Therefore, it can be suggested that TLR-2 absence interferes with the course of the infection induced by the fungus S. schenckii.

Negative regulatory receptors of the IL-1 family

The IL-1 family of ligands and receptors has a central role in both innate and adaptive immune responses and is tightly controlled by antagonists, decoy receptors, scavengers, dominant negative molecules, miRNAs and other mechanisms, acting extracellularly or intracellularly. During evolution, the development of multiple mechanisms of negative regulation reveals the need for tight control of the biological consequences of IL-1 family ligands in order to balance local and systemic inflammation and limit immunopathology. Indeed, studies with gene targeted mice for negative regulators and genetic studies in humans provide evidence for their non-redundant role in controlling inflammation, tissue damage and adaptive responses. In addition, studies have revealed the need of negative regulation of the IL-1 family not only in disease, but also in homeostatic conditions. In this review, the negative regulation mediated by decoy receptors are presented and include IL-1R2 and IL-IL-18BP as well as atypical receptors, which include TIR8/SIGIRR, IL-1RAcPb, TIGIRR-1 and IL-1RAPL. Particular emphasis is given to IL-1R2, since its discovery is the basis for the formulation of the decoy paradigm, now considered a general strategy to counter the primary inflammatory activities of cytokines and chemokines. Emphasis is also given to TIR8, a prototypical negative regulatory receptor having non-redundant roles in limiting inflammation and adaptive responses.

Absence of Toll-IL-1 receptor 8/single immunoglobulin IL-1 receptor-related molecule reduces house dust mite-induced allergic airway inflammation in mice

Allergic asthma is a chronic inflammatory disease predominately associated with the activation of CD4(+) T helper Type 2 (Th2) cells. Innate pattern recognition receptors are widely acknowledged to shape the adaptive immune response. For example, the activation of airway epithelial Toll-like receptor-4 (TLR4) is necessary for the generation of house dust mite (HDM)-specific Th2 responses and the development of asthma in mice. Here we sought to determine whether the absence of Toll-interleukin-1 receptor (TIR)-8, a negative regulator of TLR4 signaling that is highly expressed in airway epithelial cells, would exacerbate HDM-induced asthma in a murine model. We found that Th2 but not Th1 or Th17 cytokine expression was significantly reduced in the lung and draining lymph nodes in HDM-sensitized/challenged TIR8 gene-deleted mice. Mucus-producing goblet cells, HDM-specific IgG1, and airway hyperreactivity were also significantly reduced in HDM-exposed, TIR8-deficient mice. Consistent with the attenuated Th2 response, eotaxin-2/CCL24 expression and airway and peribronchial eosinophils were significantly reduced in the absence of TIR8. In contrast, IL-17A-responsive chemokines and neutrophil numbers were unaffected. Similar findings were obtained for cockroach allergen. HDM sensitization alone up-regulated the expression of IL-1F5, a putative TIR8 ligand and inducer of IL-4. Of note, innate IL-4, IL-5, IL-13, and IL-33 cytokine expression was reduced during HDM sensitization in the absence of TIR8, as was the recruitment of conventional dendritic cells and basophils to the draining lymph nodes. Our findings suggest that TIR8 enhances the development of HDM-induced innate and adaptive Th2, but not Th1 or Th17 type immunity.

Toll IL-1R8/single Ig IL-1-related receptor regulates psoriasiform inflammation through direct inhibition of innate IL-17A expression by γδ T cells

Expression of the orphan receptor Toll IL-1R8/single Ig IL-1-related receptor has been reported to be reduced in the peripheral blood of psoriatic arthritis patients. However whether TIR8/SIGIRR activity plays a specific role in regulating psoriatic inflammation is unknown. We report that Tir8/Sigirr-deficient mice develop more severe psoriatic inflammation in both the chemical (Aldara)- and cytokine (rIL-23)-induced models of psoriasis. Increased disease severity was associated with enhanced infiltration of Vγ4⁺ γδ T cells that express significantly elevated levels of IL-17A. Critically, we also demonstrate that TIR8/SIGIRR activity directly suppressed innate IL-17A expression by γδ T cells in vitro and in vivo. Importantly, treatment of Tir8/Sigirr⁻/⁻ mice with an IL-17A neutralization Ab reversed the enhanced disease severity observed in these mice. This study identifies TIR8/SIGIRR as a novel intrinsic negative regulator of innate IL-17A expression and characterizes a novel mechanism involved in the regulation of psoriatic inflammation.

Innate immune recognition of molds and homology to the inner ear protein, cochlin, in patients with autoimmune inner ear disease

Autoimmune Inner Ear Disease (AIED) is characterized by bilateral, fluctuating sensorineural hearing loss with periods of hearing decline triggered by unknown stimuli. Here we examined whether an environmental exposure to mold in these AIED patients is sufficient to generate a pro-inflammatory response that may, in part, explain periods of acute exacerbation of disease. We hypothesized that molds may stimulate an aberrant immune response in these patients as both several Aspergillus species and penecillium share homology with the LCCL domain of the inner ear protein, cochlin. We showed the presence of higher levels of anti-mold IgG in plasma of AIED patients at dilution of 1:256 (p = 0.032) and anti-cochlin IgG 1:256 (p = 0.0094 and at 1:512 p = 0.024) as compared with controls. Exposure of peripheral blood mononuclear cells (PBMC) of AIED patients to mold resulted in an up-regulation of IL-1β mRNA expression, enhanced IL-1β and IL-6 secretion, and generation of IL-17 expressing cells in mold-sensitive AIED patients, suggesting mold acts as a PAMP in a subset of these patients. Naïve B cells secreted IgM when stimulated with conditioned supernatant from AIED patients' monocytes treated with mold extract. In conclusion, the present studies indicate that fungal exposure can trigger autoimmunity in a subset of susceptible AIED patients.

Decoys and Regulatory "Receptors" of the IL-1/Toll-Like Receptor Superfamily

Members of the IL-1 family play a key role in innate and adaptive immunity and in the pathogenesis of diverse diseases. Members of IL-1R like receptor (ILR) family include signaling molecules and negative regulators. The latter include decoy receptors (IL-1RII; IL-18BP) and “receptors” with regulatory function (TIR8/SIGIRR; IL-1RAcPb; DIGIRR). Structural considerations suggest that also TIGIRR-1 and IL-1RAPL may have regulatory function. The presence of multiple pathways of negative regulation of members of the IL-1/IL-1R family emphasizes the need for a tight control of members of this fundamental system.

Therapeutic potential of SIGIRR in systemic lupus erythematosus

Single immunoglobulin IL-1-related receptor (SIGIRR), which is also known as Toll/interleukin-1 receptor 8, is a member of the interleukin-1 receptor (IL-1R) family. Different from other typical IL-1R superfamily members, SIGIRR seems to exert negatively modulates in immune responses. Several previous studies demonstrated that SIGIRR influences chronic inflammatory or autoimmune diseases, such as intestinal inflammation, rheumatoid arthritis and psoriatic arthritis. Recent work has explored the role of SIGIRR in systemic lupus erythematosus (SLE), for example, the role of SIGIRR protects the mice from hydrocarbon oil-induced lupus has been reported. These results indicate that SIGIRR may represent a novel target for the treatment of SLE. In this review, we will discuss the SIGIRR and the therapeutic potential of modulating the pathway in SLE.

Complexity and dynamics of host-fungal interactions

Pathologies attributable to fungal infections represent a growing concern in both developed and developing countries. Initially discovered as opportunistic pathogens of immunocompromised hosts, fungi such as Candida albicans are now being placed at the centre of a more complex and dynamic picture in which the outcome of an infection is the result of an intricate network of molecular interactions between the fungus, the host and the commensal microflora co-inhabiting various host niches, and especially the gastrointestinal (GI) tract. The complexity of the host-fungal interaction begins with the numerous pathogen-associated molecular patterns (PAMPs) present on the fungal cell wall that are recognized by multiple pathogen-recognition receptors (PRRs), expressed by several types of host cells. PAMP-PRR interactions elicit a variety of intracellular signalling pathways leading to a wide array of immune responses, some of which promote fungal clearance while others contribute to pathogenesis. The picture is further complicated by the fact that numerous commensal bacteria normally co-inhabiting the host's GI tract produce molecules that either directly modulate the survival and virulence of commensal fungi such as C. albicans or indirectly modulate the host's antifungal immune responses. On top of this complexity, this host-microbiome-fungal interaction exhibits features of a dynamic system, in which the same fungi can easily switch between different morphological forms presenting different PAMPs at different moments of time. Furthermore, fungal pathogens can rapidly accumulate genomic alterations that further modify their recognition by the immune system, their virulence and their resistance to antifungal compounds. Thus, based on available molecular data alone, it is currently difficult to construct a coherent model able to explain the balance between commensalism and virulence and to predict the outcome of a fungal infection. Here, we review current advances in our understanding of this complex and dynamic system and propose new avenues of investigation to assemble a more complete picture of the host-fungal interaction, integrating microbiological and immunological data under the lens of systems biology and evolutionary genomics.

TIR8/SIGIRR is an Interleukin-1 Receptor/Toll Like Receptor Family Member with Regulatory Functions in Inflammation and Immunity

Interleukin-1R like receptors (ILRs) and Toll Like Receptors (TLRs) are key receptors of innate immunity, inflammation, and orientation of the adaptive response. They belong to a superfamily characterized by the presence of a conserved intracellular domain, the Toll/IL-1R (TIR) domain, which is involved in the activation of a signaling cascade leading to activation of transcription factors associated to inflammation. The activation of inflammatory responses and immunity by ILRs or TLRs signaling is potentially detrimental for the host in acute and chronic conditions and is tightly regulated at different levels by receptor antagonists, decoy receptors or signaling molecules, and miRNAs. Recent evidence suggests that the ILRs family member TIR8 (also known as SIGIRR) is a regulatory protein acting intracellularly to inhibit ILRs and TLRs signaling. In particular, current evidence suggests that TIR8/SIGIRR dampens TLRs-mediated activation and inhibits signaling receptor complexes of IL-1 family members associated with Th1 (IL-18), Th2 (IL-33), and Th17 (IL-1) differentiation. Studies with Tir8/Sigirr-deficient mice showed that the ability to dampen signaling from ILRs and TLRs family members makes TIR8/SIGIRR a key regulator of inflammation. Here, we summarize our current understanding of the structure and function of TIR8/SIGIRR, focusing on its role in different pathological conditions, ranging from infectious and sterile inflammation, to autoimmunity and cancer-related inflammation.

DAMP signaling in fungal infections and diseases

Fungal infections and diseases predominantly affect patients with deregulated immunity. Compelling experimental and clinical evidence indicate that severe fungal diseases belong to the spectrum of fungus-related inflammatory diseases. Some degree of inflammation is required for protection during the transitional response occurring temporally between the rapid innate and slower adaptive response. However, progressive inflammation worsens disease and ultimately prevents pathogen eradication. The challenge now is to elucidate cellular and molecular pathways distinguishing protective vs. pathogenic inflammation to fungi. In addition to fungal ligands of pattern recognition receptors (pathogen-associated molecular patterns, PAMPs), several host-encoded proteins, the damage-associated molecular patterns (DAMPs), are released during tissue injury and activate innate recognition receptors. DAMPs have been shown to regulate inflammation in fungal diseases. The DAMP/receptor for advanced glycation end-products axis integrated with the PAMP/Toll-like receptors axis in the generation of the inflammatory response in experimental and clinical fungal pneumonia. These emerging themes better accommodate fungal pathogenesis in the face of high-level inflammation seen in several clinical settings and point to DAMP targeting as a novel immunomodulatory strategy in fungal diseases.

The toll interleukin-1 receptor (IL-1R) 8/single Ig domain IL-1R-related molecule modulates the renal response to bacterial infection

Our immune system has to constantly strike a balance between activation and inhibition of an inflammatory response to combat invading pathogens and avoid inflammation-induced collateral tissue damage. Toll interleukin-1 receptor 8 (IL-1R-8)/single Ig domain IL-1R-related molecule (TIR8/SIGIRR) is an inhibitor of Toll-like receptor (TLR)/IL-1R signaling, which is predominantly expressed in the kidney. The biological role of renal TIR8 during infection is, however, unknown. We therefore evaluated renal TIR8 expression during Escherichia coli pyelonephritis and explored its role in host defense using TIR8(-/-) versus TIR8(+/+) mice. We found that TIR8 protein is abundantly present in the majority of cortical tubular epithelial cells. Pyelonephritis resulted in a significant downregulation of TIR8 mRNA in kidneys of TIR8(+/+) mice. TIR8 inhibited an effective host response against E. coli, as indicated by diminished renal bacterial outgrowth and dysfunction in TIR8(-/-) mice. This correlated with increased amounts of circulating and intrarenal neutrophils at the early phase of infection. TIR8(-/-) tubular epithelial cells had increased cytokine/chemokine production when stimulated with lipopolysaccharide (LPS) or heat-killed E. coli, suggesting that TIR8 played an anti-inflammatory role during pathogen stimulation by inhibiting LPS signaling. These data suggest that TIR8 is an important negative regulator of an LPS-mediated inflammatory response in tubular epithelial cells and dampens an effective antibacterial host response during pyelonephritis caused by uropathogenic E. coli.

Diagnosis and inflammatory response of patients with candiduria

Candiduria is common in hospitalised patients, but the clinical relevance is still unclear. This study was done to further our knowledge on detection of and host responses to candiduria. Urines and clinical data from 136 patients in whom presence of yeast was diagnosed by microscopic urinalysis were collected. Diagnosis by standard urine culture methods on blood and MacConkey agar as well as on fungal culture medium (Sabouraud dextrose agar) was compared. Inflammatory parameters (IL-6 and IL-17, Ig) were quantified in the urine and compared with levels in control patients without candiduria. Standard urine culture methods detected only 37% of Candida spp. in urine. Sensitivity was especially low (23%) for C. glabrata and was independent of fungal burden. Candida specific IgG but not IgA was significantly elevated when compared with control patients (P < 0.0001 and 0.07 respectively). In addition, urine levels of IL-6 and IL-17 were significantly higher in candiduric patients when compared with control patients (P < 0.001). Multivariate analysis documented an independent association between an increased IgG (odds ratio (OR) 136.0, 95% confidence interval (CI) 25.7-719.2; P < 0.0001), an increased IL-17 (OR 17.4, 95% CI 5.3-57.0; P < 0.0001) and an increased IL-6 level (OR 4.9, 95% CI 1.9-12.4; P = 0.001) and candiduria. In summary, our data indicate that clinical studies on candiduria should include fungal urine culture and that inflammatory parameters may be helpful to identify patients with clinically relevant candiduria.

SIGIRR, a negative regulator of colon tumorigenesis

Inappropriate activation of the Toll-IL-1R (TL-IL-1) signaling by commensal bacteria contributes to the pathogenesis of inflammatory bowel diseases and colitis-associated cancer. Recent studies have identified SIGIRR as a negative regulator of TL-IL-1 signaling. It dampens intestinal inflammation and tumorigenesis in the colon. In this review, we will discuss the role of SIGIRR in different cell types and the mechanisms underlying its tumor suppressor function.

Common polymorphisms in the PKP3-SIGIRR-TMEM16J gene region are associated with susceptibility to tuberculosis

BACKGROUND

Tuberculosis has been associated with genetic variation in host immunity. We hypothesized that single-nucleotide polymorphisms (SNPs) in SIGIRR, a negative regulator of Toll-like receptor/IL-1R signaling, are associated with susceptibility to tuberculosis.

METHODS

We used a case-population study design in Vietnam with cases that had either tuberculous meningitis or pulmonary tuberculosis. We genotyped 6 SNPs in the SIGIRR gene region (including the adjacent genes PKP3 and TMEM16J) in a discovery cohort of 352 patients with tuberculosis and 382 controls. Significant associations were genotyped in a validation cohort (339 patients with tuberculosis, 376 controls).

RESULTS

Three SNPs (rs10902158, rs7105848, rs7111432) were associated with tuberculosis in discovery and validation cohorts. The polymorphisms were associated with both tuberculous meningitis and pulmonary tuberculosis and were strongest with a recessive genetic model (odds ratios, 1.5-1.6; P = .0006-.001). Coinheritance of these polymorphisms with previously identified risk alleles in Toll-like receptor 2 and TIRAP was associated with an additive risk of tuberculosis susceptibility.

CONCLUSIONS

These results demonstrate a strong association of SNPs in the PKP3-SIGIRR-TMEM16J gene region and tuberculosis in discovery and validation cohorts. To our knowledge, these are the first associations of polymorphisms in this region with any disease.

Adaptive immunity to fungi

Only a handful of the more than 100,000 fungal species on our planet cause disease in humans, yet the number of life-threatening fungal infections in patients has recently skyrocketed as a result of advances in medical care that often suppress immunity intensely. This emerging crisis has created pressing needs to clarify immune defense mechanisms against fungi, with the ultimate goal of therapeutic applications. Herein, we describe recent insights in understanding the mammalian immune defenses deployed against pathogenic fungi. The review focuses on adaptive immune responses to the major medically important fungi and emphasizes how dendritic cells and subsets in various anatomic compartments respond to fungi, recognize their molecular patterns, and signal responses that nurture and shape the differentiation of T cell subsets and B cells. Also emphasized is how the latter deploy effector and regulatory mechanisms that eliminate these nasty invaders while also constraining collateral damage to vital tissue.

A mouse model of clonal CD8+ T lymphocyte-mediated alopecia areata progressing to alopecia universalis

Alopecia areata is among the most prevalent autoimmune diseases, yet compared with other autoimmune conditions, it is not well studied. This in part results from limitations in the C3H/HeJ mouse and DEBR rat model systems most commonly used to study the disease, which display a low frequency and late onset. We describe a novel high-incidence model for spontaneous alopecia areata. The 1MOG244 T cell expresses dual TCRA chains, one of which, when combined with the single TCRB present, promotes the development of CD8(+) T cells with specificity for hair follicles. Retroviral transgenic mice expressing this TCR develop spontaneous alopecia areata at nearly 100% incidence. Disease initially follows a reticular pattern, with regionally cyclic episodes of hair loss and regrowth, and ultimately progresses to alopecia universalis. Alopecia development is associated with CD8(+) T cell activation, migration into the intrafollicular region, and hair follicle destruction. The disease may be adoptively transferred with T lymphocytes and is class I and not class II MHC-dependent. Pathologic T cells primarily express IFNG and IL-17 early in disease, with dramatic increases in cytokine production and recruitment of IL-4 and IL-10 production with disease progression. Inhibition of individual cytokines did not significantly alter disease incidence, potentially indicating redundancy in cytokine responses. These results therefore characterize a new high-incidence model for alopecia areata in C57BL/6J mice, the first to our knowledge to apply a monoclonal TCR, and indicate that class I MHC-restricted CD8(+) T lymphocytes can independently mediate the pathologic response.