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      Candida Infections: An Update on Host Immune Defenses and Anti-Fungal Drugs

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          Abstract

          Infections by fungal pathogens such as Candida albicans and non- albicans Candida species are becoming increasing prevalent in the human population. Such pathogens cause life-threatening diseases with high mortality, particularly in immunocompromised patients. Host defenses against fungal infections are provided by an exquisite interplay between innate and adaptive immune responses. However, effective anti-fungal agents for Candida infections are limited, and fungal drug resistance is a significant treatment challenge. In this review, we summarize the current understanding of host–fungal interactions, discuss the modes action of anti-fungal drugs, explore host defense mechanisms, and define the new challenges for treating Candida infections.

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          Most cited references116

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          Signalling through C-type lectin receptors: shaping immune responses

          Key Points Crosstalk between pattern recognition receptors (PRRs) expressed by dendritic cells orchestrates T helper (TH) cell differentiation through the induction of specific cytokine expression profiles, tailored to invading pathogens. C-type lectin receptors (CLRs) have an important role in orchestrating the induction of signalling pathways that regulate adaptive immune responses. CLRs can control adaptive immunity at various levels by inducing signalling on their own, through crosstalk with other PRRs or by inducing carbohydrate-specific signalling pathways. DC-specific ICAM3-grabbing non-integrin (DC-SIGN) interacts with mannose-carrying pathogens including Mycobacterium tuberculosis, HIV-1, measles virus and Candida albicans to activate the serine/threonine protein kinase RAF1. RAF1 signalling leads to the acetylation of Toll-like receptor (TLR)-activated nuclear factor-κB (NF-κB) subunit p65 and affects cytokine expression, such as inducing the upregulation of interleukin-10 (IL-10). DC-associated C-type lectin 1 (dectin 1) triggering by a broad range of fungal pathogens, such as C. albicans, Aspergillus fumigatus and Pneumocystis carinii, results in protective antifungal immunity through the crosstalk of two independent signalling pathways — one through spleen tyrosine kinase (SYK) and one through RAF1 — that are essential for the expression of TH1 and TH17 cell polarizing cytokines. Crosstalk between the SYK and RAF1 pathways is both synergistic and antagonizing to fine-tune NF-κB activity: although Ser276 phosphorylation of p65 leads to enhanced transcriptional activity of p65 itself through acetylation, it also inhibits the transcriptional activity of the NF-κB subunit RELB by sequestering it in p65–RELB dimers, which are transcriptionally inactive. The diversity in CLR-mediated signalling provides some major challenges for the researches to elucidate and manipulate the signalling properties of this exciting family of receptors. However, the recent advances strongly support the use of CLR targeting vaccination strategies using dendritic cells to induce or redirect adaptive immune responses as well as improve antigen delivery.
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            Syk- and CARD9-dependent coupling of innate immunity to the induction of T helper cells that produce interleukin 17.

            The C-type lectin dectin-1 binds to yeast and signals through the kinase Syk and the adaptor CARD9 to induce production of interleukin 10 (IL-10) and IL-2 in dendritic cells (DCs). However, whether this pathway promotes full DC activation remains unclear. Here we show that dectin-1-Syk-CARD9 signaling induced DC maturation and the secretion of proinflammatory cytokines, including IL-6, tumor necrosis factor and IL-23, but little IL-12. Dectin-1-activated DCs 'instructed' the differentiation of CD4+ IL-17-producing effector T cells (T(H)-17 cells) in vitro, and a dectin-1 agonist acted as an adjuvant promoting the differentiation of T(H)-17 and T helper type 1 cells in vivo. Infection with Candida albicans induced CARD9-dependent T(H)-17 responses to the organism. Our data indicate that signaling through Syk and CARD9 can couple innate to adaptive immunity independently of Toll-like receptor signals and that CARD9 is required for the development of T(H)-17 responses to some pathogens.
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              Dectin-2 recognition of alpha-mannans and induction of Th17 cell differentiation is essential for host defense against Candida albicans.

              Dectin-2 (gene symbol Clec4n) is a C-type lectin expressed by dendritic cells (DCs) and macrophages. However, its functional roles and signaling mechanisms remain to be elucidated. Here, we generated Clec4n(-/-) mice and showed that this molecule is important for host defense against Candida albicans (C. albicans). Clec4n(-/-) DCs had virtually no fungal alpha-mannan-induced cytokine production. Dectin-2 signaling induced cytokines through an FcRgamma chain and Syk-CARD9-NF-kappaB-dependent signaling pathway without involvement of MAP kinases. The yeast form of C. albicans induced interleukin-1beta (IL-1beta) and IL-23 secretion in a Dectin-2-dependent manner. In contrast, cytokine production induced by the hyphal form was only partially dependent on this lectin. Both yeast and hyphae induced Th17 cell differentiation, in which Dectin-2, but not Dectin-1, was mainly involved. Because IL-17A-deficient mice were highly susceptible to systemic candida infection, this study suggests that Dectin-2 is important in host defense against C. albicans by inducing Th17 cell differentiation. Copyright 2010 Elsevier Inc. All rights reserved.
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                Author and article information

                Contributors
                Journal
                Infectious Diseases and Translational Medicine
                Infect. Dis. Transl. Med.
                Infect. Dis. Transl. Med.
                International Biological and Medical Journals Publishing House Co., Limited (Room E16, 3/f, Yongda Commercial Building, No.97, Bonham Stand (Sheung Wan), HongKong )
                2411-2917
                10 April 2016
                10 April 2016
                : 2
                : 1
                : 30-40
                Affiliations
                From Key Laboratory of Molecular Virology and Immunology, Unit of Pathogenic Fungal Infection and Host Immunity, Institute Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
                From Key Laboratory of Molecular Virology and Immunology, Unit of Pathogenic Fungal Infection and Host Immunity, Institute Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
                Author notes
                Correspondence to: Changbin Chen, Tel: (+86)02154923055, Fax: (+86)02154923056, Email: cbchen@ 123456ips.ac.cn .
                Article
                10.11979/idtm.201601005
                514a8d40-af90-4fb3-a046-3afbfe7f2c90

                This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                Page count
                Figures: 2, Tables: 1, References: 131, Pages: 11
                Product
                Categories
                Review

                Medicine,Infectious disease & Microbiology
                Candida spp.,Candida albicans,Drug resistance,Host immune defenses

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