Neither dectin-2 nor the mannose receptor is required for resistance to Coccidioides immitis in mice

Bioinformatics-led discovery of liver-specific genes and macrophage infiltration in acute liver injury

Background

Acute liver injury (ALI) is an important global health concern, primarily caused by widespread hepatocyte cell death, coupled with a complex immune response and a lack of effective remedies. This study explores the underlying mechanisms, immune infiltration patterns, and potential targets for intervention and treatment ALI.

Methods

The datasets of acetaminophen (APAP), carbon tetrachloride (CCl4), and lipopolysaccharide (LPS)-induced ALI were obtained from the GEO database. Differentially expressed genes (DEGs) were individually identified using the limma packages. Functional enrichment analysis was performed using KEGG, GO, and GSEA methods. The overlapping genes were extracted from the three datasets, and hub genes were identified using MCODE and CytoHubba algorithms. Additionally, PPI networks were constructed based on the String database. Immune cell infiltration analysis was conducted using ImmuCellAI, and the correlation between hub genes and immune cells was determined using the Spearman method. The relationship between hub genes, immune cells, and biochemical indicators of liver function (ALT, AST) was validated using APAP and triptolide (TP) -induced ALI mouse models.

Results

Functional enrichment analysis indicated that all three ALI models were enriched in pathways linked to fatty acid metabolism, drug metabolism, inflammatory response, and immune regulation. Immune analysis revealed a significant rise in macrophage infiltration. A total of 79 overlapping genes were obtained, and 10 hub genes were identified that were consistent with the results of the biological information analysis after screening and validation. Among them, Clec4n, Ms4a6d, and Lilrb4 exhibited strong associations with macrophage infiltration and ALI.

Antifungal immunity mediated by C-type lectin receptors may be a novel target in immunotherapy for urothelial bladder cancer

Immunotherapies, such as immune-checkpoint blockade and adoptive T-cell therapy, offer novel treatment options with good efficacy for patients with urothelial bladder cancer. However, heterogeneity and therapeutic resistance have limited the use of immunotherapy. Further research into immune-regulatory mechanisms in bladder cancer is urgently required. Emerging evidence demonstrates that the commensal microbiota and its interactions with host immunity play pivotal roles in a variety of physiological and pathological processes, including in cancer. The gut microbiota has been identified as a potentially effective target of treatment that can be synergized with immunotherapy. The urothelial tract is also a key site for multiple microbes, although the immune-regulatory role of the urinary microbiome in the process of carcinogenesis of bladder cancer remains to be elucidated. We performed a comprehensive analysis of the expression and biological functions of C-type lectin receptors (CLRs), which have been recognized as innate pathogen-associated receptors for fungal microbiota, in bladder cancer. In line with previous research on fungal colonization of the urothelial tract, we found that CLRs, including Dectin-1, Dectin-2, Dectin-3, and macrophage-inducible Ca²⁺-dependent lectin receptor (Mincle), had a significant association with immune infiltration in bladder cancer. Multiple innate and adaptive pathways are positively correlated with the upregulation of CLRs. In addition, we found a significant correlation between the expression of CLRs and a range of immune-checkpoint proteins in bladder cancer. Based on previous studies and our findings, we hypothesize that the urinary mycobiome plays a key role in the pathogenesis of bladder cancer and call for more research on CLR-mediated anti-fungal immunity against bladder cancer as a novel target for immunotherapy in urothelial bladder cancer.

Key thermally dimorphic fungal pathogens: shaping host immunity

Exposure to fungal pathogens from the environment is inevitable and with the number of at-risk populations increasing, the prevalence of invasive fungal infection is on the rise. An interesting group of fungal organisms known as thermally dimorphic fungi predominantly infects immunocompromised individuals. These potential pathogens are intriguing in that they survive in the environment in one form, mycelial phase, but when entering the host, they are triggered by the change in temperature to switch to a new pathogenic form. Considering the growing prevalence of infection and the need for improved diagnostic and treatment approaches, studies identifying key components of fungal recognition and the innate immune response to these pathogens will significantly contribute to our understanding of disease progression. This review focuses on key endemic dimorphic fungal pathogens that significantly contribute to disease, including Histoplasma, Coccidioides and Talaromyces species. We briefly describe their prevalence, route of infection and clinical presentation. Importantly, we have reviewed the major fungal cell wall components of these dimorphic fungi, the host pattern recognition receptors responsible for recognition and important innate immune responses supporting adaptive immunity and fungal clearance or the failure thereof.

Functionalized niosomes as a smart delivery device in cancer and fungal infection

Various diseases remain untreated due to lack of suitable therapeutic moiety or a suitable drug delivery device, especially where toxicities and side effects are the primary reason for concern. Cancer and fungal infections are diseases where treatment schedules are not completed due to severe side effects or lengthy treatment protocols. Advanced treatment approaches such as active targeting and inhibition of angiogenesis may be preferred method for the treatment for malignancy over the conventional method. Niosomes may be a better alternative drug delivery carrier for various therapeutic moieties (either hydrophilic or hydrophobic) and also due to ease of surface modification, non-immunogenicity and economical. Active targeting approach may be done by targeting the receptors through coupling of suitable ligand on niosomal surface. Moreover, various receptors (CD44, folate, epidermal growth factor receptor (EGFR) & Vascular growth factor receptor (VGFR)) expressed by malignant cells have also been reviewed. The preparation of suitable niosomal formulation also requires considerable attention, and its formulation depends upon various factors such as selection of non-ionic surfactant, method of fabrication, and fabrication parameters. A combination therapy (dual drug and immunotherapy) has been proposed for the treatment of fungal infection with special consideration for surface modification with suitable ligand on niosomal surface to sensitize the receptors (C-type lectin receptors, Toll-like receptors & Nucleotide-binding oligomerization domain-like receptors) present on immune cells involved in fungal immunity. Certain gene silencing concept has also been discussed as an advanced alternative treatment for cancer by silencing the mRNA at molecular level using short interfering RNA (si-RNA).

CARD9-Associated Dectin-1 and Dectin-2 Are Required for Protective Immunity of a Multivalent Vaccine against Coccidioides posadasii Infection

Coccidioides species are fungal pathogens that can cause a widely varied clinical manifestation from mild pulmonary symptom to disseminated, life-threatening disease. We have previously created a subunit vaccine by encapsulating a recombinant coccidioidal Ag (rCpa1) in glucan-chitin particles (GCPs) as an adjuvant-delivery system. The GCP-rCpa1 vaccine has shown to elicit a mixed Th1 and Th17 response and confers protection against pulmonary coccidioidomycosis in mice. In this study, we further delineated the vaccine-induced protective mechanisms. Depletion of IL-17A in vaccinated C57BL/6 mice prior to challenge abrogated the protective efficacy of GCP-rCpa1 vaccine. Global transcriptome and Ingenuity Pathway Analysis of murine bone marrow-derived macrophages after exposure to this vaccine revealed the upregulation of proinflammatory cytokines (TNF-α, IL-6, and IL-1β) that are associated with activation of C-type lectin receptors (CLR) Dectin-1- and Dectin-2-mediated CARD9 signaling pathway. The GCP formulation of rCpa1 bound soluble Dectin-1 and Dectin-2 and triggered ITAM signaling of corresponding CLR reporter cells. Furthermore, macrophages that were isolated from Dectin-1 -/-, Dectin-2 -/-, and CARD9 -/- mice significantly reduced production of inflammatory cytokines in response to the GCP-rCpa1 vaccine compared with those of wild-type mice. The GCP-rCpa1 vaccine had significantly reduced protective efficacy in Dectin-1 -/-, Dectin-2 -/-, and CARD9 -/- mice that showed decreased acquisition of Th cells in Coccidioides-infected lungs compared with vaccinated wild-type mice, especially Th17 cells. Collectively, we conclude that the GCP-rCpa1 vaccine stimulates a robust Th17 immunity against Coccidioides infection through activation of the CARD9-associated Dectin-1 and Dectin-2 signal pathways.

Innate Immune Receptors and Defense Against Primary Pathogenic Fungi

The innate immune system is critical for natural resistance to all pathogenic microorganisms, including fungi. The innate response plays a vital role in resistance to infections before the antigen-specific immune response and also influences antigen-specific adaptive immunity. There are many different receptors for the innate immune response to fungi, and some receptors have been found to play a significant role in the response to human infections with opportunistic fungi. Most human infections are caused by opportunistic fungi, but a small number of organisms are capable of causing infections in normal hosts. The primary pathogenic fungi that cause invasive infections include Blastomyces spp., Cryptococcus gattii, Coccidioides spp., Histoplasma spp., and Paracoccidioides spp. In this review of innate immune receptors that play a role in infections caused by these organisms, we find that innate immunity differs between organisms.

Early Events in Coccidioidomycosis

Since its description nearly 130 years ago, hundreds of studies have deepened our understanding of coccidioidomycosis, also known as valley fever (VF), and provided useful diagnostic tests and treatments for the disease caused by the dimorphic fungi Coccidioides spp. In general, most of the literature has addressed well-established infections and has described patients who have experienced major complications. In contrast, little attention has been given to the earliest consequences of the pathogen-host interaction and its implications for disease manifestation, progression, and resolution. The purpose of this review is to highlight published studies on early coccidioidomycosis, identify gaps in our knowledge, and suggest new or former research areas that might be or remain fertile ground for insight into the early stages of this invasive fungal disease.

Host-Pathogen Interactions in Coccidioidomycosis: Prognostic Clues and Opportunities for Novel Therapies

PURPOSE

Coccidioidomycosis (CM) is a systemic fungal disease caused by the dimorphic fungi Coccidioides immitis and Coccidioides posadasii. In its endemic areas of the United States, CM is growing as a public health challenge with a marked increase in incidence in the last 15 years. Although Coccidioides infection is asymptomatic in most cases, symptomatic pulmonary disease occurs in ~40% and disseminated coccidioidomycosis (DCM) occurs in ~1% of previously healthy children and adults. DCM is markedly more common in immunocompromised people, who often experience life-threatening disease despite use of antifungal medications. Although options for antifungal therapy have improved, lifelong therapy is needed for those who develop coccidioidal meningitis. The purpose of this article was to review the state of antifungal therapy and recent studies of host-pathogen interactions in CM in light of advances in immunomodulatory therapy.

METHODS

The study included a review of PubMed and abstracts of the Coccidioidomycosis Study Group (years 2000-2019).

FINDINGS

Current therapy for CM relies upon azole and polyene antifungal agents. Murine models and studies of DCM in patients with monogenic primary immunodeficiency states and acquired immunodeficiency have revealed the importance of both innate and adaptive immune responses in the control of infections with Coccidioides species. In particular, defects in sensing of fungi and induction of cellular immune responses have been frequently reported. More recently, polymorphisms in key signaling pathways and in the generation of Th17 and Th1 immune responses have been linked with DCM.

IMPLICATIONS

Antifungal therapy is sufficient to control disease in most cases of CM, but treatment failure occurs in cases of severe pulmonary disease and nonmeningeal disseminated disease. Lifelong therapy is recommended for meningitis in view of the very high risk of recurrence. Corticosteroid therapy is advised by some experts for severe pulmonary disease and for some neurologic complications of DCM. DCM is only rarely the result of a severe monogenic immunodeficiency. Case studies suggest that reorienting cellular immune responses or augmenting effector immune responses may help resolve DCM. Systematic investigation of immunotherapy for coccidioidomycosis is advisable and may help to address the recent marked increase in reports of the disease in endemic areas.

The Rise of Coccidioides: Forces Against the Dust Devil Unleashed

Coccidioidomycosis (Valley fever) is a fungal disease caused by the inhalation of Coccidioides posadasii or C. immitis. This neglected disease occurs in the desert areas of the western United States, most notably in California and Arizona, where infections continue to rise. Clinically, coccidioidomycosis ranges from asymptomatic to severe pulmonary disease and can disseminate to the brain, skin, bones, and elsewhere. New estimates suggest as many as 350,000 new cases of coccidioidomycosis occur in the United States each year. Thus, there is an urgent need for the development of a vaccine and new therapeutic drugs against Coccidioides infection. In this review, we discuss the battle against Coccidioides including the development of potential vaccines, the quest for new therapeutic drugs, and our current understanding of the protective host immune response to Coccidioides infection.

A review of innate and adaptive immunity to coccidioidomycosis

Coccidioidomycosis is a human fungal disease cause by inhalation of aerosol spores produced by Coccidioides posadasii or Coccidioides immitis. This disease is a common cause of community-acquired pneumonia in the endemic areas of the Southwestern United States. It also can present as a life-threatening disease as the fungal cells disseminate to skin, bone, and central nervous system. The outcome of coccidioidomycosis is largely determined by the nature of host immune response to the infection. Escalation of symptomatic infections and increased cost of long-term antifungal treatment warrant a concerted effort to better understand the innate and adaptive immune responses and the genetics associated with coccidioidomycosis susceptibility. This knowledge can be harnessed for development of a human vaccine against Coccidioides and advance clinic management of this disease. This review discusses recently reported studies on innate and adaptive immunity to Coccidioides infection, Mendelian susceptibility to disseminated disease and progress toward a human vaccine against this formidable disease.

The Interaction of Human Pathogenic Fungi With C-Type Lectin Receptors

Fungi, usually present as commensals, are a major cause of opportunistic infections in immunocompromised patients. Such infections, if not diagnosed or treated properly, can prove fatal. However, in most cases healthy individuals are able to avert the fungal attacks by mounting proper antifungal immune responses. Among the pattern recognition receptors (PRRs), C-type lectin receptors (CLRs) are the major players in antifungal immunity. CLRs can recognize carbohydrate ligands, such as β-glucans and mannans, which are mainly found on fungal cell surfaces. They induce proinflammatory immune reactions, including phagocytosis, oxidative burst, cytokine, and chemokine production from innate effector cells, as well as activation of adaptive immunity via Th17 responses. CLRs such as Dectin-1, Dectin-2, Mincle, mannose receptor (MR), and DC-SIGN can recognize many disease-causing fungi and also collaborate with each other as well as other PRRs in mounting a fungi-specific immune response. Mutations in these receptors affect the host response and have been linked to a higher risk in contracting fungal infections. This review focuses on how CLRs on various immune cells orchestrate the antifungal response and on the contribution of single nucleotide polymorphisms in these receptors toward the risk of developing such infections.

Myeloid Differentiation Factor 88 and Interleukin-1R1 Signaling Contribute to Resistance to Coccidioides immitis

Rodents are a natural host for the dimorphic pathogenic fungi Coccidioides immitis and Coccidioides posadasii, and mice are a good model for human infection. Humans and rodents both express Dectin-1 and Toll-like receptor 2 (TLR2) on myeloid cells, and those receptors collaborate to maximize the cytokine/chemokine responses to spherules (the tissue form of the fungi) and to formalin-killed spherules (FKS). We showed that Dectin-1 is necessary for resistance to pulmonary coccidioidomycosis, but the importance of TLR2 in vivo is uncertain. Myeloid differentiation factor 88 (MyD88) is the adapter protein for TLR2 and -4, interleukin-1R1 (IL-1R1), and IL-18R1. MyD88/TRIF^-/- and MyD88^-/- mice were equally susceptible to C. immitis infection, in contrast to C57BL/6 (B6) controls. Of the four surface receptors, only IL-1R1 was required for resistance to C. immitis, partially explaining the susceptibility of MyD88^-/- mice. We also found that FKS stimulated production of IL-1Ra by bone marrow-derived dendritic cells (BMDCs), independent of MyD88 and Dectin-1. There also was a very high concentration of IL-1Ra in the lungs of infected B6 mice, supporting the potential importance of this regulatory IL-1 family protein in the largely ineffective response of B6 mice to coccidioidomycosis. These results suggest that IL-1R1 signaling is important for defense against C. immitis infection.

Inflammatory and Anti-inflammatory Responses Co-exist Inside Lung Granuloma of Fatal Cases of Coccidioidomycosis: A Pilot Report

Coccidioidomycosis is a fungal disease caused by Coccidioides immitis or Coccidioides posadasii. These fungi are endemic in the southern USA and northern Mexico. Immunocompromised patients are susceptible to develop severe forms of this fungal infection. Cytokines play an important role in controlling the fungal infection, but little is known about the predominant immunological environment in human lung tissue from fatal cases. Our aim was to analyze the pro-inflammatory and anti-inflammatory cytokines and monocyte/macrophages markers (CD14 and CD206) in the granulomas of six fatal cases of coccidioidomycosis. Cytokines and surface markers were higher in coccidioidomycosis cases when compared to control (P < 0.05). CD14 positive cells were increased inside the coccidioidal granuloma when compared to the outside (P < 0.05). No differences were found in the number of CD206+ cells inside the granuloma when compared to the outer population (P > 0.05). Interestingly, an analysis of stain intensity signals showed an increased signaling of CD14, CD206, IL-10 and TNFα inside the granuloma when compared to the outside (P < 0.05). iNOS and IL-12 gene expression were not detected in coccidioidomycosis cases, while IL-10, IL-6 and TGFβ gene expression were detected, but the differences when compared to healthy lungs were not significant (P > 0.05). TNFα gene expression was lower in coccidioidomycosis cases when compared to healthy lung (P = 0.05). In conclusion, pro- and anti-inflammatory responses co-exist inside of the granulomas of fatal cases of coccidioidomycosis and the absent of iNOS and IL-12 gene expression may be related with patient's outcome.

Dectin-2 Is a C-Type Lectin Receptor that Recognizes Pneumocystis and Participates in Innate Immune Responses

Pneumocystis is an important fungal pathogen that causes life-threatening pneumonia in patients with AIDS and malignancy. Lung fungal pathogens are recognized by C-type lectin receptors (CLRs), which bind specific ligands and stimulate innate immune responses. The CLR Dectin-1 was previously shown to mediate immune responses to Pneumocystis spp. For this reason, we investigated a potential role for Dectin-2. Rats with Pneumocystis pneumonia (PCP) exhibited elevated Dectin-2 mRNA levels. Soluble Dectin-2 carbohydrate-recognition domain fusion protein showed binding to intact Pneumocystis carinii (Pc) and to native Pneumocystis major surface glycoprotein/glycoprotein A (Msg/gpA). RAW macrophage cells expressing V5-tagged Dectin-2 displayed enhanced binding to Pc and increased protein tyrosine phosphorylation. Furthermore, the binding of Pc to Dectin-2 resulted in Fc receptor-γ-mediated intracellular signaling. Alveolar macrophages from Dectin-2-deficient mice (Dectin-2^-/-) showed significant decreases in phospho-Syk activation after challenge with Pc cell wall components. Stimulation of Dectin-2^-/- alveolar macrophages with Pc components showed significant decreases in the proinflammatory cytokines IL-6 and TNF-α. Finally, during infection with Pneumocystis murina, Dectin-2^-/- mice displayed downregulated mRNA expression profiles of other CLRs implicated in fungal immunity. Although Dectin-2^-/- alveolar macrophages had reduced proinflammatory cytokine release in vitro, Dectin-2^-/- deficiency did not reduce the overall resistance of these mice in the PCP model, and organism burdens were statistically similar in the long-term immunocompromised and short-term immunocompetent PCP models. These results suggest that Dectin-2 participates in the initial innate immune signaling response to Pneumocystis, but its deficiency does not impair resistance to the organism.

Regulation of C-Type Lectin Receptor-Mediated Antifungal Immunity

Of all the pathogen recognition receptor families, C-type lectin receptor (CLR)-induced intracellular signal cascades are indispensable for the initiation and regulation of antifungal immunity. Ongoing experiments over the last decade have elicited diverse CLR functions and novel regulatory mechanisms of CLR-mediated-signaling pathways. In this review, we highlight novel insights in antifungal innate and adaptive-protective immunity mediated by CLRs and discuss the potential therapeutic strategies against fungal infection based on targeting the mediators in the host immune system.

LC3-Associated Phagocytosis Is Required for Dendritic Cell Inflammatory Cytokine Response to Gut Commensal Yeast Saccharomyces cerevisiae

The human fungal microbiota known as mycobiota is increasingly recognized as a critical factor in human gut health and disease. Non-pathogenic commensal yeasts such as Saccharomyces cerevisiae promote homeostasis in the gut, whereas dysbiosis of the gut mycobiota is associated with inflammation. Glycan-binding receptors (lectins) are key host factors in host-mycobiota interaction in the gut. They are expressed on immune cells such as dendritic cells (DCs) and recognize fungal polysaccharides. This interaction is imperative to mount appropriate immune responses for immune homeostasis in the gut as well as clearance of fungal pathogens. Recent studies demonstrate that microtubule-associated protein light-chain 3 (LC3)-associated phagocytosis (LAP) is involved in lectin-fungi interactions. Yet, the biological impact of LAP on the lectin function remains largely elusive. In this report, we demonstrate that in mouse LAP is linked to dendritic cell-associated lectin 2 (Dectin-2), a C-type lectin specific to fungal α-mannan polysaccharide. We found that mouse Dectin-2 recognizes commensal yeast S. cerevisiae and Kazachstania unispora. Mouse bone marrow-derived DCs (BMDCs) produced inflammatory cytokines TNFα and IL-1β in response to the yeasts in a Dectin-2 and spleen tyrosine kinase (Syk)-dependent manner. We found that S. cerevisiae and K. unispora induced LAP in mouse BMDCs upon internalization. Furthermore, LC3 was activated by stimulation of BMDCs with the yeasts in a Dectin-2 and Syk-dependent manner. To address the biological impact of LAP on Dectin-2 yeast interaction, we established a knock-in mouse strain (Atg16L1^E230, thereafter called E230), which BMDCs exhibit autophagy-active and LAP-negative phenotypes. When stimulated with yeasts, E230 BMDCs produced significantly less amounts of TNFα and IL-1β. Taken together, we revealed a novel link between Dectin-2 and LAP that enables host immune cells to respond to mycobiota.

Contact, Collaboration, and Conflict: Signal Integration of Syk-Coupled C-Type Lectin Receptors

Several spleen tyrosine kinase-coupled C-type lectin receptors (CLRs) have emerged as important pattern recognition receptors for infectious danger. Because encounter with microbial pathogens leads to the simultaneous ligation of several CLRs and TLRs, the signals emanating from different pattern recognition receptors have to be integrated to achieve appropriate biological responses. In this review, we briefly summarize current knowledge about ligand recognition and core signaling by Syk-coupled CLRs. We then address mechanisms of synergistic and antagonistic crosstalk between different CLRs and with TLRs. Emerging evidence suggests that signal integration occurs through 1) direct interaction between receptors, 2) regulation of expression levels and localization, and 3) collaborative or conflicting signaling interference. Accordingly, we aim to provide a conceptual framework for the complex and sometimes unexpected outcome of CLR ligation in bacterial and fungal infection.

Immune Response to Coccidioidomycosis and the Development of a Vaccine

Coccidioidomycosis is a fungal infection caused by Coccidioides posadasii and Coccidioides immitis. It is estimated that 150,000 new infections occur in the United States each year. The incidence of this infection continues to rise in endemic regions. There is an urgent need for the development of better therapeutic drugs and a vaccine against coccidioidomycosis. This review discusses the features of host innate and adaptive immune responses to Coccidioides infection. The focus is on the recent advances in the immune response and host-pathogen interactions, including the recognition of spherules by the host and defining the signal pathways that guide the development of the adaptive T-cell response to Coccidioides infection. Also discussed is an update on progress in developing a vaccine against these fungal pathogens.

Card9- and MyD88-Mediated Gamma Interferon and Nitric Oxide Production Is Essential for Resistance to Subcutaneous Coccidioides posadasii Infection

Coccidioidomycosis is a potentially life-threatening respiratory disease which is endemic to the southwestern United States and arid regions of Central and South America. It is responsible for approximately 150,000 infections annually in the United States alone. Almost every human organ has been reported to harbor parasitic cells of Coccidioides spp. in collective cases of the disseminated form of this mycosis. Current understanding of the mechanisms of protective immunity against lung infection has been largely derived from murine models of pulmonary coccidioidomycosis. However, little is known about the nature of the host response to Coccidioides in extrapulmonary tissue. Primary subcutaneous coccidioidal infection is rare but has been reported to result in disseminated disease. Here, we show that activation of MyD88 and Card9 signal pathways are required for resistance to Coccidioides infection following subcutaneous challenge of C57BL/6 mice, which correlates with earlier findings of the protective response to pulmonary infection. MyD88(-/-) andCard9(-/-) mice recruited reduced numbers of T cells, B cells, and neutrophils to the Coccidioides-infected hypodermis com pared to wild-type mice; however, neutrophils were dispensable for resistance to skin infection. Further studies have shown that gamma interferon (IFN-γ) production and activation of Th1 cells characterize resistance to subcutaneous infection. Furthermore, activation of a phagosomal enzyme, inducible nitric oxide synthase, which is necessary for NO production, is a requisite for fungal clearance in the hypodermis. Collectively, our data demonstrate that MyD88- and Card9-mediated IFN-γ and nitric oxide production is essential for protection against subcutaneous Coccidioides infection.

Immune Interactions with Pathogenic and Commensal Fungi: A Two-Way Street

We are exposed to a wide spectrum of fungi including innocuous environmental organisms, opportunistic pathogens, commensal organisms, and fungi that can actively and explicitly cause disease. Much less is understood about effective host immunity to fungi than is generally known about immunity to bacterial and viral pathogens. Innate and adaptive arms of the immune system are required for effective host defense against Candida, Aspergillus, Cryptococcus, and others, with specific elements of the host response regulating specific types of fungal infections (e.g., mucocutaneous versus systemic). Here we will review themes and controversies that are currently shaping investigation of antifungal immunity (primarily to Candida and Aspergillus) and will also examine the emerging field of the role of fungi in the gut microbiome.

Dectin-2 deficiency promotes Th2 response and mucin production in the lungs after pulmonary infection with Cryptococcus neoformans

Dectin-2 is a C-type lectin receptor that recognizes high mannose polysaccharides. Cryptococcus neoformans, a yeast-form fungal pathogen, is rich in polysaccharides in its cell wall and capsule. In the present study, we analyzed the role of Dectin-2 in the host defense against C. neoformans infection. In Dectin-2 gene-disrupted (knockout) (Dectin-2KO) mice, the clearance of this fungus and the inflammatory response, as shown by histological analysis and accumulation of leukocytes in infected lungs, were comparable to those in wild-type (WT) mice. The production of type 2 helper T (Th2) cytokines in lungs was higher in Dectin-2KO mice than in WT mice after infection, whereas there was no difference in the levels of production of Th1, Th17, and proinflammatory cytokines between these mice. Mucin production was significantly increased in Dectin-2KO mice, and this increase was reversed by administration of anti-interleukin 4 (IL-4) monoclonal antibody (MAb). The levels of expression of β1-defensin, cathelicidin, surfactant protein A (Sp-A), and Sp-D in infected lungs were comparable between these mice. In in vitro experiments, IL-12p40 and tumor necrosis factor alpha (TNF-α) production and expression of CD86 and major histocompatibility complex (MHC) class II by bone marrow-derived dendritic cells and alveolar macrophages were completely abrogated in Dectin-2KO mice. Finally, the disrupted lysates of C. neoformans, but not of whole yeast cells, activated Dectin-2-triggered signaling in an assay with nuclear factor of activated T cells (NFAT)-green fluorescent protein (GFP) reporter cells expressing this receptor. These results suggest that Dectin-2 may oppose the Th2 response and IL-4-dependent mucin production in the lungs after infection with C. neoformans, and it may not be required for the production of Th1, Th17, and proinflammatory cytokines or for clearance of this fungal pathogen.