The galactosaminogalactan (GAG) is a cell wall component of Aspergillus fumigatus that has potent anti-inflammatory effects in mice. However, the mechanisms responsible for the anti-inflammatory property of GAG remain to be elucidated. In the present study we used in vitro PBMC stimulation assays to demonstrate, that GAG inhibits proinflammatory T-helper (Th)1 and Th17 cytokine production in human PBMCs by inducing Interleukin-1 receptor antagonist (IL-1Ra), a potent anti-inflammatory cytokine that blocks IL-1 signalling. GAG cannot suppress human T-helper cytokine production in the presence of neutralizing antibodies against IL-1Ra. In a mouse model of invasive aspergillosis, GAG induces IL-1Ra in vivo, and the increased susceptibility to invasive aspergillosis in the presence of GAG in wild type mice is not observed in mice deficient for IL-1Ra. Additionally, we demonstrate that the capacity of GAG to induce IL-1Ra could also be used for treatment of inflammatory diseases, as GAG was able to reduce severity of an experimental model of allergic aspergillosis, and in a murine DSS-induced colitis model. In the setting of invasive aspergillosis, GAG has a significant immunomodulatory function by inducing IL-1Ra and notably IL-1Ra knockout mice are completely protected to invasive pulmonary aspergillosis. This opens new treatment strategies that target IL-1Ra in the setting of acute invasive fungal infection. However, the observation that GAG can also protect mice from allergy and colitis makes GAG or a derivative structure of GAG a potential treatment compound for IL-1 driven inflammatory diseases.

IL-1 drives Th responses, particularly Th17, in host defense. Sharing the same coreceptor, the IL-1 family member IL-36 exhibits properties similar to those of IL-1. In the present study, we investigated the role of IL-36 in Aspergillus fumigatus-induced human Th responses. We observed that different morphological forms of A. fumigatus variably increase steady-state mRNA of IL-36 subfamily members. IL-36α is not significantly induced by any morphological form of Aspergillus. Most strikingly, IL-36γ is significantly induced by live A. fumigatus conidia and heat-killed hyphae, whereas IL-36Ra (IL-36 receptor antagonist) is significantly induced by heat-killed conidia, hyphae, and live conidia. We also observed that IL-36γ expression is dependent on the dectin-1/Syk and TLR4 signaling pathway. In contrast, TLR2 and CR3 inhibit IL-36γ expression. IntroductionThe IL-1 family (IL-1F) consists of 11 members [1]. The in silico discovery of IL-1 family members IL-1F5, IL-1F6, IL-1F8, and IL-1F9 have recently been renamed IL-36 receptor antagonist (IL-36Ra), IL-36α, IL-36β, and IL-36γ, respectively. Presently, there is a paucity of data on the biological properties and functional roles of the IL-36 subfamily in health and disease. The clasCorrespondence: Dr. Frank L. van de Veerdonk e-mail: f.veerdonk@aig.umcn.nl sic IL-1 family members IL-1α and IL-1β as well as IL-18 and IL-33 polarize Th responses [1]. However, little is known about the role of the IL-36 subfamily (IL-36α, IL-36β, and IL-36γ) and the IL-36Ra in antimicrobial host defense. Each member of the IL-36 subfamily binds to IL-1Rrp2 (now renamed IL-36 receptor, IL-36R) and recruits the co-receptor for signal transduction, IL-1RAcP [2,3]. The IL-36R is expressed on dendritic cells (DCs) [4,5] and T cells [5]. Stimulation of T cells by IL-36R ligands results in the induction of , and DCs primed with IL-36 ligands are inducers of Th1 cells. Although the synthetic TLR3 ligand polyI:C induces IL-36γ secretion [6], nothing is known about the innate pattern recognition pathways that induce IL-36R ligands in the antimicrobial host defense.www.eji-journal.eu Eur. J. Immunol. 2013. 43: 416-426 Immunity to infection 417The opportunistic fungus Aspergillus fumigatus is ubiquitous; Aspergillus spores are inhaled daily by humans. Inhaled Aspergillus spores (conidia) are efficiently cleared in healthy individuals [7]. However, in immunocompromised persons, or in patients with preexisting lung injury, Aspergillus conidia germinate resulting in invasive infections associated with high mortality [8]. Th responses are important in the host defense against invasive aspergillosis [9], and the major known cytokine pathways that are involved in the induction of Th1 and Th17 responses are IL-12/IL-18 and IL-1/IL-23, respectively [9,10]. Next to the induction of the specific Th-axis, there is also interplay between these cytokine pathways. IFN-γ-induced IL-18 binding protein was found to downregulate the Th17 response [11], and in several cases the induction of Th17 or IL-17 produc...

A large variety of fungi are present in the environment, among which a proportion colonizes the human body, usually without causing any harm. However, depending on the host immune status, commensals can become opportunistic pathogens that induce diseases ranging from superficial non-harmful infection to life-threatening systemic disease. The interplay between the host and the fungal commensal flora is being orchestrated by an efficient recognition of the microorganisms, which in turn ensures a proper balance between tolerance of the normal fungal flora and induction of immune defense mechanisms when invasion occurs. Pattern recognition receptors (PRRs) play a significant role in maintaining this balance due to their capacity to sense fungi and induce host responses such as the induction of proinflammatory cytokines involved in the activation of innate and adaptive immune responses. In the present review, we will discuss the most recent findings regarding the recognition of Candida albicans and Aspergillus fumigatus and the different types of immune cells that play a role in antifungal host defense.

Aspergillus conidia are unique in triggering Th2 responses in human PBMCs, through a CR3-dependent pathway. ABPA patients display a significantly increased Aspergillus-induced Th2/Th1 ratio that can be modulated by biologicals. These data provide a rationale to explore IFNγ therapy in ABPA as a corticosteroid-sparing treatment option, by dampening Th2 responses and supplementing the IFNγ deficiency at the same time.

Chitin is an important cell wall component of Aspergillus fumigatus conidia, of which hundreds are inhaled on a daily basis. Previous studies have shown that chitin has both anti- and proinflammatory properties; however the exact mechanisms determining the inflammatory signature of chitin are poorly understood, especially in human immune cells. Human peripheral blood mononuclear cells were isolated from healthy volunteers and stimulated with chitin from Aspergillus fumigatus. Transcription and production of the proinflammatory cytokine interleukin-1β (IL-1β) and the anti-inflammatory cytokine IL-1 receptor antagonist (IL-1Ra) were measured from the cell culture supernatant by quantitative PCR (qPCR) or enzyme-linked immunosorbent assay (ELISA), respectively. Chitin induced an anti-inflammatory signature characterized by the production of IL-1Ra in the presence of human serum, which was abrogated in immunoglobulin-depleted serum. Fc-γ-receptor-dependent recognition and phagocytosis of IgG-opsonized chitin was identified as a novel IL-1Ra-inducing mechanism by chitin. IL-1Ra production induced by chitin was dependent on Syk kinase and phosphatidylinositol 3-kinase (PI3K) activation. In contrast, costimulation of chitin with the pattern recognition receptor (PRR) ligands lipopolysaccharide, Pam3Cys, or muramyl dipeptide, but not β-glucan, had synergistic effects on the induction of proinflammatory cytokines by human peripheral blood mononuclear cells (PBMCs). In conclusion, chitin can have both pro- and anti-inflammatory properties, depending on the presence of pathogen-associated molecular patterns and immunoglobulins, thus explaining the various inflammatory signatures reported for chitin.