The role of pattern recognition receptors in the innate recognition of Candida albicans

Fungal vaccines and adjuvants: a tool to reveal the interaction between host and fungi

Fungal infections are incurring high risks in a range from superficial mucosal discomforts (such as oropharyngeal candidiasis and vulvovaginal candidiasis) to disseminated life-threatening diseases (such as invasive pulmonary aspergillosis and cryptococcal meningitis) and becoming a global health problem in especially immunodeficient population. The major obstacle to conquer fungal harassment lies in the presence of increasing resistance to conventional antifungal agents used in newly clinically isolated strains. Although recombinant cytokines and mono-/poly-clonal antibodies are added into antifungal armamentarium, more effective antimycotic drugs are exceedingly demanded. It is comforting that the development of fungal vaccines and adjuvants opens up a window to brighten the prospective way in the diagnosis, prevention and treatment of fungal assaults. In this review, we focus on the progression of several major fungal vaccines devised for the control of Candida spp., Aspergillus spp., Cryptococcus spp., Coccidioides spp., Paracoccidioides spp., Blastomyces spp., Histoplasma spp., Pneumocystis spp. as well as the adjuvants adopted. We then expound the interaction between fungal vaccines/adjuvants and host innate (macrophages, dendritic cells, neutrophils), humoral (IgG, IgM and IgA) and cellular (Th1, Th2, Th17 and Tc17) immune responses which generally experience immune recognition of pattern recognition receptors, activation of immune cells, and clearance of invaded fungi. Furthermore, we anticipate an in-depth understanding of immunomodulatory properties of univalent and multivalent vaccines against diverse opportunistic fungi, providing helpful information in the design of novel fungal vaccines and adjuvants.

Controlling Candida: immune regulation of commensal fungi in the gut

The intestinal microbiome harbors fungi that pose a significant risk to human health as opportunistic pathogens and drivers of inflammation. Inflammatory and autoimmune diseases are associated with dysbiotic fungal communities and the expansion of potentially pathogenic fungi. The gut is also the main reservoir for disseminated fungal infections. Immune interactions are critical for preventing commensal fungi from becoming pathogenic. Significant strides have been made in defining innate and adaptive immune pathways that regulate intestinal fungi, and these discoveries have coincided with advancements in our understanding of the fungal molecular pathways and effectors involved in both commensal colonization and pathogenesis within the gut. In this review, we will discuss immune interactions important for regulating commensal fungi, with a focus on how specific cell types and effectors interact with fungi to limit their colonization or pathogenic potential. This will include how innate and adaptive immune pathways target fungi and orchestrate antifungal immune responses, in addition to how secreted immune effectors, such as mucus and antimicrobial peptides, regulate fungal colonization and inhibit pathogenic potential. These immune interactions will be framed around our current understanding of the fungal effectors and pathways regulating colonization and pathogenesis within this niche. Finally, we highlight important unexplored mechanisms by which the immune system regulates commensal fungi in the gut.

Role of CARD9 in Cell- and Organ-Specific Immune Responses in Various Infections

The caspase recruitment domain-containing protein 9 (CARD9) is an intracellular adaptor protein that is abundantly expressed in cells of the myeloid lineage, such as neutrophils, macrophages, and dendritic cells. CARD9 plays a critical role in host immunity against infections caused by fungi, bacteria, and viruses. A CARD9 deficiency impairs the production of inflammatory cytokines and chemokines as well as migration and infiltration, thereby increasing susceptibility to infections. However, CARD9 signaling varies depending on the pathogen causing the infection. Furthermore, different studies have reported altered CARD9-mediated signaling even with the same pathogen. Therefore, this review focuses on and elucidates the current literature on varied CARD9 signaling in response to various infectious stimuli in humans and experimental mice models.

Dectin-1 ligands produce distinct training phenotypes in human monocytes through differential activation of signaling networks

Cells of the innate immune system retain memory of prior exposures through a process known as innate immune training. β-glucan, a Dectin-1 ligand purified from the Candida albicans cell wall, has been one of the most widely utilized ligands for inducing innate immune training. However, many Dectin-1 ligands exist, and it is not known whether these all produce the same phenotype. Using a well-established in vitro model of innate immune training, we compared two commercially available Dectin-1 agonists, zymosan and depleted zymosan, with the gold standard β-glucan in the literature. We found that depleted zymosan, a β-glucan purified from Saccharomyces cerevisiae cell wall through alkali treatment, produced near identical effects as C. albicans β-glucan. However, untreated zymosan produced a distinct training effect from β-glucans at both the transcript and cytokine level. Training with zymosan diminished, rather than potentiated, induction of cytokines such as TNF and IL-6. Zymosan activated NFκB and AP-1 transcription factors more strongly than β-glucans. The addition of the toll-like receptor (TLR) ligand Pam3CSK4 was sufficient to convert the training effect of β-glucans to a phenotype resembling zymosan. We conclude that differential activation of TLR signaling pathways determines the phenotype of innate immune training induced by Dectin-1 ligands.

Unveiling the hidden players: exploring the role of gut mycobiome in cancer development and treatment dynamics

The role of gut fungal species in tumor-related processes remains largely unexplored, with most studies still focusing on fungal infections. This review examines the accumulating evidence suggesting the involvement of commensal and pathogenic fungi in cancer biological process, including oncogenesis, progression, and treatment response. Mechanisms explored include fungal influence on host immunity, secretion of bioactive toxins/metabolites, interaction with bacterial commensals, and migration to other tissues in certain types of cancers. Attempts to utilize fungal molecular signatures for cancer diagnosis and fungal-derived products for treatment are discussed. A few studies highlight fungi's impact on the responsiveness and sensitivity to chemotherapy, radiotherapy, immunotherapy, and fecal microbiota transplant. Given the limited understanding and techniques in fungal research, the studies on gut fungi are still facing great challenges, despite having great potentials.

A Putative Role of Candida albicans in Promoting Cancer Development: A Current State of Evidence and Proposed Mechanisms

Candida albicans is a commensal fungal species that commonly colonizes the human body, but it is also a pervasive opportunistic pathogen in patients with malignant diseases. A growing body of evidence suggests that this fungus is not only coincidental in oncology patients, but may also play an active role in the development of cancer. More specifically, several studies have investigated the potential association between C. albicans and various types of cancer, including oral, esophageal, and colorectal cancer, with a possible role of this species in skin cancer as well. The proposed mechanisms include the production of carcinogenic metabolites, modulation of the immune response, changes in cell morphology, microbiome alterations, biofilm production, the activation of oncogenic signaling pathways, and the induction of chronic inflammation. These mechanisms may act together or independently to promote cancer development. Although more research is needed to fully grasp the potential role of C. albicans in carcinogenesis, the available evidence suggests that this species may be an active contributor and underscores the importance of considering the impact of the human microbiome on cancer pathogenesis. In this narrative review, we aimed to summarize the current state of evidence and offer some insights into proposed mechanisms.

The Interplay between Candida albicans, Vaginal Mucosa, Host Immunity and Resident Microbiota in Health and Disease: An Overview and Future Perspectives

Vulvovaginal candidiasis (VVC), which is primarily caused by Candida albicans, is an infection that affects up to 75% of all reproductive-age women worldwide. Recurrent VVC (RVVC) is defined as >3 episodes per year and affects nearly 8% of women globally. At mucosal sites of the vagina, a delicate and complex balance exists between Candida spp., host immunity and local microbial communities. In fact, both immune response and microbiota composition play a central role in counteracting overgrowth of the fungus and maintaining homeostasis in the host. If this balance is perturbed, the conditions may favor C. albicans overgrowth and the yeast-to-hyphal transition, predisposing the host to VVC. To date, the factors that affect the equilibrium between Candida spp. and the host and drive the transition from C. albicans commensalism to pathogenicity are not yet fully understood. Understanding the host- and fungus-related factors that drive VVC pathogenesis is of paramount importance for the development of adequate therapeutic interventions to combat this common genital infection. This review focuses on the latest advances in the pathogenic mechanisms implicated in the onset of VVC and also discusses novel potential strategies, with a special focus on the use of probiotics and vaginal microbiota transplantation in the treatment and/or prevention of recurrent VVC.

An organotypic oral mucosal infection model to study host-pathogen interactions

Early in vitro oral mucosal infection models (OMMs) failed to consider the suitability of the model environment to represent the host immune response. Denture stomatitis (DS) is mediated by Candida albicans, but the role of Staphylococcus aureus remains uncertain. A collagen hydrogel-based OMM containing HaCaT and HGF cell types was developed, characterised and employed to study of tissue invasion and pro-inflammatory cytokine production in response to pathogens. Models formed a robust epithelium. Despite their inflammatory baseline, 24-h infection with C. albicans, and/or S. aureus led to tissue invasion, and significantly upregulated IL-6 and IL-8 production by OMMs when compared to the unstimulated control. No significant difference in IL-6 or IL-8 production by OMMs was observed between single and dual infections. These attributes indicate that this newly developed OMM is suitable for the study of DS and could be implemented for the wider study of oral infection.

LncRNA: A Potential Target for Host-Directed Therapy of Candida Infection

Despite various drugs work against Candida, candidiasis represents clinical management challenges worldwide due to the rising incidence and recurrence rate, as well as epidemics, of new drug-resistant pathogens. Recent insights into interactions between Candida and hosts contribute to exploring novel therapeutic strategies, termed host-directed therapies (HDTs). HDTs are viable adjuncts with good efficacy for the existing standard antifungal regimens. However, HDTs induce other response unintendedly, thus requiring molecular targets with highly specificity. Long noncoding RNAs (lncRNAs) with highly specific expression patterns could affect biological processes, including the immune response. Herein, this review will summarize recent advances of HDTs based on the Candida–host interaction. Especially, the findings and application strategies of lncRNAs related to the host response are emphasized. We propose it is feasible to target lncRNAs to modulate the host defense during Candida infection, which provides a new perspective in identifying options of HDTs for candidiasis.

Host defense mechanisms induce genome instability leading to rapid evolution in an opportunistic fungal pathogen

The ability to generate genetic variation facilitates rapid adaptation in stressful environments. The opportunistic fungal pathogen Candida albicans frequently undergoes large-scale genomic changes, including aneuploidy and loss-of heterozygosity (LOH), following exposure to host environments. However, the specific host factors inducing C. albicans genome instability remain largely unknown. Here, we leveraged the genetic tractability of nematode hosts to investigate whether innate immune components, including antimicrobial peptides (AMPs) and reactive oxygen species (ROS), induced host-associated C. albicans genome instability. C. albicans associated with immunocompetent hosts carried multiple large-scale genomic changes including LOH, whole chromosome, and segmental aneuploidies. In contrast, C. albicans associated with immunocompromised hosts deficient in AMPs or ROS production had reduced LOH frequencies and fewer, if any, additional genomic changes. To evaluate if extensive host-induced genomic changes had long-term consequences for C. albicans adaptation, we experimentally evolved C. albicans in either immunocompetent or immunocompromised hosts and selected for increased virulence. C. albicans evolved in immunocompetent hosts rapidly increased virulence, but not in immunocompromised hosts. Taken together, this work suggests that host-produced ROS and AMPs induces genotypic plasticity in C. albicans which facilitates rapid evolution.

Metabolic Influences of Gut Microbiota Dysbiosis on Inflammatory Bowel Disease

Inflammatory bowel diseases (IBD) are chronic medical disorders characterized by recurrent gastrointestinal inflammation. While the etiology of IBD is still unknown, the pathogenesis of the disease results from perturbations in both gut microbiota and the host immune system. Gut microbiota dysbiosis in IBD is characterized by depleted diversity, reduced abundance of short chain fatty acids (SCFAs) producers and enriched proinflammatory microbes such as adherent/invasive E. coli and H₂S producers. This dysbiosis may contribute to the inflammation through affecting either the immune system or a metabolic pathway. The immune responses to gut microbiota in IBD are extensively discussed. In this review, we highlight the main metabolic pathways that regulate the host-microbiota interaction. We also discuss the reported findings indicating that the microbial dysbiosis during IBD has a potential metabolic impact on colonocytes and this may underlie the disease progression. Moreover, we present the host metabolic defectiveness that adds to the impact of symbiont dysbiosis on the disease progression. This will raise the possibility that gut microbiota dysbiosis associated with IBD results in functional perturbations of host-microbiota interactions, and consequently modulates the disease development. Finally, we shed light on the possible therapeutic approaches of IBD through targeting gut microbiome.

The Role of IL-17-Producing Cells in Cutaneous Fungal Infections

The skin is the outermost layer of the body and is exposed to many environmental stimuli, which cause various inflammatory immune responses in the skin. Among them, fungi are common microorganisms that colonize the skin and cause cutaneous fungal diseases such as candidiasis and dermatophytosis. The skin exerts inflammatory responses to eliminate these fungi through the cooperation of skin-component immune cells. IL-17 producing cells are representative immune cells that play a vital role in anti-fungal action in the skin by producing antimicrobial peptides and facilitating neutrophil infiltration. However, the actual impact of IL-17-producing cells in cutaneous fungal infections remains unclear. In this review, we focused on the role of IL-17-producing cells in a series of cutaneous fungal infections, the characteristics of skin infectious fungi, and the recognition of cell components that drive cutaneous immune cells.

Gut mycobiome: The probable determinative role of fungi in IBD patients

Inflammatory bowel disease (IBD) is a multi-factorial autoimmune disorder that its causative agents are unknown. The gut microbiota comprises of bacteria, viruses, fungi and protozoa that its role in IBD has remained controversially. Bacteria constitute more than 99% of the gut microbiota composition, and the main core of the gut microbiota is composed from Bacteroidetes and Firmicutes. The gut microbiota plays an important role in training, development and haemostasis of the immune responses during the life. Fungi compose a very small portion of gut microbiota, but play determinative roles in homeostasis of the gut bacterial composition and the mucosal immune responses. An interkingdom correlation between bacteria and fungi has been suggested. For example, the presence of Salmonella enterica serovar Typhimurium reduces the viability and colonisation of C albicans. Alterations in the composition and function of the gut microbiota, which is known as dysbiosis, are a usual event in patients who suffer from IBD. Although the main reason for this alteration is not clear, the interaction between gut bacteria and gut fungi seems to be an important subject in IBD patients. This review covers new findings on the interaction between fungi and bacteria and the role of fungi in the pathophysiology of IBD.

Candida Pathogenicity and Interplay with the Immune System

Candida species are opportunistic fungal pathogens that are part of the normal skin and mucosal microflora. Overgrowth of Candida can cause infections such as thrush or life-threatening invasive candidiasis in immunocompromised patients. Though Candida albicans is highly prevalent, several non-albicans species are also isolated from nosocomial infections. Candida sp. are over presented in the gut of people with Crohn's disease and certain types of neurological disorders, with hyphal form and biofilms being the most virulent states. In addition, Candida uses several secreted and cell surface molecules such as pH related antigen 1, High affinity glucose transporter, Phosphoglycerate mutase 1 and lipases to establish pathogenicity. A strong innate immune response is elicited against Candida via dendritic cells, neutrophils and macrophages. All three complement pathways are also activated. Production of proinflammatory cytokines IL-10 and IL-12 signal differentiation of CD4⁺ cells into Th1 and Th2 cells, whereas IL-6, IL-17 and IL-23 induce Th17 cells. Importance of T-lymphocytes is reflected in depleted T-cell count patients being more prone to Candidiasis. Anti- Candida antibodies also play a role against candidiasis using various mechanisms such as targeting virulent enzymes and exhibiting direct candidacidal activity. However, the significance of antibody response during infection remains controversial. Furthermore, some of the Candida strains have evolved molecular strategies to evade the sophisticated host attack by proteolysis of components of immune system and interfering with immune signalling pathways. Emergence of several non-albicans species that are resistant to current antifungal agents makes treatment more difficult. Therefore, deeper insight into interactions between Candida and the host immune system is required for discovery of novel therapeutic options.

A comparative review of intelectins

Intelectin (ITLN) is a new type of glycan-binding lectin. It has been demonstrated to agglutinate bacteria probably due to its carbohydrate-binding capacity, suggesting its role in an innate immune response. It is involved not only in many physiological processes but also in some human diseases such as asthma, heart disease, inflammatory bowel disease, chronic obstructive pulmonary disease and cancer. Up to now, intelectin orthologs have been identified in placozoans, urochordatas, cephalochordates and several vertebrates, such as cyclostomata, fish, amphibians and mammals. Although the sequences of intelectins in different species are conserved, their expression patterns, quaternary structures and functions differ considerably among and within species. We summarize the evolution of the intelectin gene family, the tissue distribution, structure and functions of intelectins. We conclude that intelectin plays a role in innate immune response and there are still potential functions of intelectin awaiting discovery.

Upregulated miR-155 inhibits inflammatory response induced by C. albicans in human monocytes derived dendritic cells via targeting p65 and BCL-10

Background

Candida albicans (C. albicans) is one of the most common fungal pathogens causing superficial and systemic infections. The innate immune system is the first defense line against C. albicans infection. MiR-155, a multifunctional microRNA (miRNA), has been proved to be a crucial regulator in innate immune response against bacterial and virus. However, the biological function of miR-155 in innate immune response against C. albicans infection remains unknown.

Methods

The expression miR-155, as well as inflammatory factors [interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ)], in monocytes derived dendritic cells (DCs) during heat-killed C. albicans infection was detected by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). The biological functions of miR-155 were investigated with "gain- and loss-of-function" experiments. Potential targets of miR-155 were identified by bioinformatics analysis, luciferase assay and western blot. Small interfering RNA (siRNA) was used to validate the function of miR-155 target.

Results

C. albicans increased the expression of miR-155 and pro-inflammatory factors. MiR-155 induced by C. albicans was depended on Dectin-1-spleen tyrosine kinase (Syk)/Raf-1-MAPK signaling pathway. Furthermore, miR-155 suppressed the secretion of pro-inflammatory cytokines induced by C. albicans by targeting NF-κB p65 and B cell leukemia/lymphoma 10 (BCL-10).

Conclusions

In conclusion, up-regulated miR-155 acts as a negative feedback regulator in the innate immune response against C. albicans infection.

Kruppel-like factor 6 promotes macrophage inflammatory and hypoxia response

Macrophages are the professional phagocytes that protect the host from infection or injury. Tissue microenvironment at the site of injury and inflammation is characterized by low oxygen concentration and poor supply of nutrients. The responding macrophages have to advance against oxygen and nutrient gradients to reach the site of inflammation to perform host protection, and tissue repair functions. Thus, evolution has fashioned macrophages to orchestrate a coordinated inflammatory and hypoxic gene program to mount an effective immune response. Here, we discovered that Kruppel‐like factor 6 (KLF6) governs macrophage functions by promoting inflammatory and hypoxic response gene programming. Our in vivo studies revealed that myeloid‐KLF6‐deficient mice were highly resistant to endotoxin‐induced systemic inflammatory response syndrome symptomatology and mortality. Using complementary gain‐ and loss‐of‐function studies, we observed that KLF6 overexpression elevate and KLF6 deficiency attenuate inducible HIF1α expression in macrophages. Our integrated transcriptomics and gene set enrichment analysis studies uncovered that KLF6 deficiency attenuates broad inflammatory and glycolytic gene expression in macrophages. More importantly, overexpression of oxygen stable HIF1α reversed attenuated proinflammatory and glycolytic gene expression in KLF6‐deficient macrophages. Collectively, our studies uncovered that KLF6 govern inflammatory and hypoxic response by regulating HIF1α expression in macrophage.

Pattern recognition receptors and their roles on the innate immune system of mud crab (Scylla paramamosain)

The innate immune system is the first line of defense protecting the hosts against invading pathogens. Mud crab (Scylla paramamosain) is widely distributed in China and Indo-west Pacific countries, which develops a very complicated innate immune system against pathogen invasions. Innate immunity involves the humoral and cellular responses that are linked to the pattern recognition receptors (PRRs). PRRs initially recognize the infection and trigger the activation of signaling cascades, leading to transcriptional regulation of inflammatory mediators that function in pathogenic control and clearance. In mud crab S. paramamosain, the Toll/Toll-like receptors, lipopolysaccharide and β-1,3-glucan binding proteins, C-type lectins, scavenger receptors, and down syndrome cell adhesion molecules have been identified as receptor families responsible for the recognition of bacteria, fungi, and viruses, and are important components in the innate immune system. In this review, we summarize the literature on the current knowledge and the roles of PRRs in the immune defenses of mud crab, which in an effort to provide much information for further researches.

Emerging Complexity and the Need for Advanced Drug Delivery in Targeting Candida Species

Background:

Candida species are the important etiologic agents for candidiasis, the most prevalent cause of opportunistic fungal infections. Candida invasion results in mucosal to systemic infections through immune dysfunction and helps in further invasion and proliferation at several sites in the host. The host defence system utilizes a wide array of the cells, proteins and chemical signals that are distributed in blood and tissues which further constitute the innate and adaptive immune system. The lack of antifungal agents and their limited therapeutic effects have led to high mortality and morbidity related to such infections.

Methods:

The necessary information collated on this review has been gathered from various literature published from 1995 to 2019.

Results:

This article sheds light on novel drug delivery approaches to target the immunological axis for several Candida species (C. albicans, C. glabrata, C. parapsilosis, C. tropicalis, C. krusei, C. rugose, C. hemulonii, etc.).

Conclusion:

It is clear that the novel drug delivery approaches include vaccines, adoptive transfer of primed immune cells, recombinant cytokines, therapeutic antibodies, and nanoparticles, which have immunomodulatory effects. Such advancements in targeting various underpinning mechanisms using the concept of novel drug delivery will provide a new dimension to the fungal infection clinic particularly due to Candida species with improved patient compliance and lesser side effects. This advancement in knowledge can also be extended to target various other similar microbial species and infections.

Research Progress of Mechanisms and Drug Therapy For Atherosclerosis on Toll-Like Receptor Pathway

Recent reports have established atherosclerosis (AS) as a major factor in the pathogenetic process of cardiovascular diseases such as ischemic stroke and coronary heart disease. Although the possible pathogenesis of AS remains to be elucidated, a large number of investigations strongly suggest that the inhibition of toll-like receptors (TLRs) alleviates the severity of AS to some extent by suppressing vascular inflammation and the formation of atherosclerotic plaques. As pattern recognition receptors, TLRs occupy a vital position in innate immunity, mediating various signaling pathways in infective and sterile inflammation. This review summarizes the available data on the research progress of AS and the latest antiatherosclerotic drugs associated with TLR pathway.

Importance of Candida Antigenic Factors: Structure-Driven Immunomodulation Properties of Synthetically Prepared Mannooligosaccharides in RAW264.7 Macrophages

The incidence and prevalence of serious fungal infections is rising, especially in immunosuppressed individuals. Moreover, co-administration of antibiotics and immunosuppressants has driven the emergence of new multidrug-resistant pathogens. The significant increase of multidrug-resistant pathogens, together with their ability to form biofilms, is associated with morbidity and mortality. Research on novel synthetically prepared immunomodulators as potential antifungal immunotherapeutics is of serious interest. Our study demonstrated the immunobiological activity of synthetically prepared biotinylated mannooligosaccharides mimicking Candida antigenic factors using RAW264.7 macrophages. Macrophage exposure to the set of eight structurally different mannooligosaccharides induced a release of Th1, Th2, Th17, and Treg cytokine signature patterns. The observed immune responses were tightly associated with structure, dose, exposure time, and selected signature cytokines. The viability/cytotoxicity of the mannooligosaccharide formulas was assessed based on cell proliferation. The structure-based immunomodulatory activity of the formulas was evaluated with respect to the length, branching and conformation of the various formulas. Glycoconjugate formulas with terminal β-mannosyl-units tended to be more potent in terms of Candida relevant cytokines IL-12 p70, IL-17, GM-CSF, IL-6, and TNFα induction and cell proliferation, and this tendency was associated with structural differences between the studied glycoconjugate formulas. The eight tested mannooligosaccharide conjugates can be considered potential in vitro immunomodulative agents suitable for in vitro Candida diagnostics or prospectively for subcellular anti-Candida vaccine design.

C-type lectin receptor-mediated immune recognition and response of the microbiota in the gut

C-type lectin receptors (CLRs) are powerful pattern-recognition receptors that discern ‘self’ and ‘non-self’ in our body and protect us from invasive pathogens by mediating immune recognition and response. The gastrointestinal tract is very important for the maintenance of homeostasis; it is the largest shelter for the billions of microorganisms in the body and CLRs play a crucial regulatory role in this system. This study focuses on several CLRs, including Dectin-1, Dectin-2, Dectin-3 and Mincle. We summarize the roles of CLRs in maintaining gastrointestinal immune-system homeostasis, especially their functions in mediating immune recognition and responses in the gut, discuss their relationships to some diseases, highlight the significance of CLR-mediated sensing of microbial and non-microbial compounds in the gut immune system and identify new therapeutic targets.

Immunomodulatory Role of Capsular Polysaccharides Constituents of Cryptococcus neoformans

Cryptococcosis is a systemic fungal infection caused by Cryptococcus neoformans. In immunocompetent patients, cryptococcal infection is often confined to the lungs. In immunocompromised individuals, C. neoformans may cause life-threatening illness, either from novel exposure or through reactivation of a previously acquired latent infection. For example, cryptococcal meningitis is a severe clinical disease that can manifest in people that are immunocompromised due to AIDS. The major constituents of the Cryptococcus polysaccharide capsule, glucuronoxylomannan (GXM), and galactoxylomannan (GalXM), also known as glucuronoxylomanogalactan (GXMGal), are considered the primary virulence factors of Cryptococcus. Despite the predominance of GXM in the polysaccharide capsule, GalXM has more robust immunomodulatory effects on host cellular immunity. This review summarizes current knowledge regarding host-Crytococcus neoformans interactions and the role of capsular polysaccharides in host immunomodulation. Future studies will likely facilitate a better understanding of the mechanisms involved in antigenic recognition and host immune response to C. neoformans and lead to the development of new therapeutic pathways for cryptococcal infection.

Candida albicans at Host Barrier Sites: Pattern Recognition Receptors and Beyond

Over the last decades, fungal infections have emerged as a growing threat to human health. Although the human body is at potential risk, various body sites host several commensal fungal species, including Candida albicans. In healthy individuals, C. albicans colonizes different mucosal surfaces without causing harm, while under diverse circumstances the fungus can proliferate and cause disease. In this context, the understanding of host⁻C. albicans interactions in health and during infection may lead to novel therapeutic approaches. Importantly, host cells express pattern recognition receptors (PRRs), which sense conserved fungal structures and orchestrate innate immune responses. Herein, important findings on the topic of the recognition of C. albicans at host barrier sites are discussed. This review briefly summarizes the importance and functions of myeloid PRRs, reviews the fungal recognition and biology of stromal cells, and highlights important C. albicans virulence attributes during site-specific proliferation and invasion.

The first line of defence: insights into mechanisms and relevance of phagocytosis in epithelial cells

Epithelial tissues cover most of the external and internal surfaces of the body and its organs. Inevitably, these tissues serve as first line of defence against inorganic, organic, and microbial intruders. Epithelial cells are the main cell type of these tissues. Besides their function as cellular barrier, there is growing evidence that epithelial cells are of particular relevance as initial sensors of danger and also as executers of adequate defence responses. These cells feature various essential functions to maintain tissue integrity in health and disease. In this review, we survey some of the different innate immune functions of epithelial cells in mucosal tissues being constantly exposed to a plethora of harmless contaminants but also of pathogens. We discuss how epithelial cells avoid inadequate immune responses in such conditions. In particular, we will focus on the diverse types and mechanisms of phagocytosis used by epithelial cells to not only maintain homeostasis but to also harness the host response against invading pathogens.

Pharmacodynamic and Immunomodulatory Effects of Micafungin on Host Responses against Biofilms of Candida parapsilosis in Comparison to Those of Candida albicans

Micafungin (MFG) demonstrates potent activity against biofilms of Candida albicans and Candida parapsilosis, the most frequent opportunistic fungal pathogens. Little is known about its immunopharmacologic effect on antibiofilm activity of phagocytic cells following exposure to Candida biofilms. In this study, we investigated the effects of MFG on human neutrophil-mediated damage of C. albicans and C. parapsilosis biofilms by XTT [2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide] and the potential mechanisms underlying the immunomodulatory MFG activities on cultured monocyte-derived THP-1 cells in response to these biofilms by reverse transcription-PCR and sandwich and multiplex enzyme-linked immunosorbent assay. Preexposure of C. albicans to subinhibitory MFG concentrations significantly enhanced neutrophil-mediated biofilm damage, an effect that appears to be species specific since a comparable effect was not observed with drug-pretreated C. parapsilosis biofilms. Human THP-1 cells responded to both Candida biofilms through Toll-like receptor 2 (TLR2) and TLR4 upregulation, modest TLR6 involvement, and enhanced NLRP3 activation, whereas the signal was relayed to the nucleus via NF-κB p65 activation. MFG caused 2- to 3-fold lower TLR2 and TLR4 mRNA levels than those caused by either organism. C. albicans biofilms induced a robust proinflammatory response, whereas C. parapsilosis biofilms either alone or in the presence of MFG caused increased interleukin-1β (IL-1β) production, but small amounts of IL-8, IL-23, and tumor necrosis factor alpha. In conclusion, MFG may condition THP-1 cells toward an inflammatory response through TLR2/TLR4 recruitment. Inflammatory signals observed with C. albicans biofilms are considerably reduced upon exposure of THP-1 cells to C. parapsilosis biofilms, possibly enhancing fungal survival and increasing biofilm pathogenicity.

Innate Immune Responses to Fungal Allergens

PURPOSE OF REVIEW

In this review, we describe innate immunity to fungi and the ability of pattern recognition receptors (PRRs) to recognize fungal-associated molecular patterns (FAMPs) and danger-associated molecular patterns (DAMPs).

RECENT FINDINGS

Protective responses against fungal antigens can be divided into two parts: innate immunity and adaptive immunity. Detection of foreign substance by the innate immune system is mediated by a variety of genetically encoded receptors known as pattern recognition receptors (PRRs). These PRRs bind to PAMPs (pathogen-associated molecular patterns) and more specifically to fungal-associated molecular patterns or FAMPs on target microorganisms. They also bind to DAMPs (damage-associated molecular patterns) which are substances released due to tissue and cell damage. PRRs can be divided into several families including Toll-like receptors (TLRs), nucleotide-oligomerization domain (NOD)-like receptors (NLRs), and C-type lectin receptors. Fungal PRRs can respond to internal and external components found in fungi. In addition, a number of fungal products, including some fungal allergens, seem to mimic or represent DAMPs. Collectively, activation of these fungal PRRs alerts the innate immune system to the presence of fungal exposure and can promote both innate and adaptive immune responses.

Mold allergy: is it real and what do we do about it?

INTRODUCTION

fungi produce substances that contain pathogen-associated molecular patterns (pamps) and damage-associated molecular patterns (damps) which bind to pattern recognition receptors, stimulating innate immune responses in humans. they also produce allergens that induce production of specific ige. Areas covered: In this review we cover both innate and adaptive immune responses to fungi. Some fungal products can activate both innate and adaptive responses and in doing so, cause an intense and complex health effects. Methods of testing for fungal allergy and evidence for clinical treatment including environmental control are also discussed. In addition, we describe controversial issues including the role of Stachybotrys and mycotoxins in adverse health effects. Expert commentary: Concerns about long-term exposure to fungi have led some patients, attorneys and fungus advocates to promote fears about a condition that has been termed toxic mold syndrome. This syndrome is associated with vague symptoms and is believed to be due to exposure to mycotoxins, though this connection has not been proven. Ultimately, more precise methods are needed to measure both fungal exposure and the resulting health effects. Once that such methods become available, much of the speculation will be replaced by knowledge.

Binding of Candida albicans to Human CEACAM1 and CEACAM6 Modulates the Inflammatory Response of Intestinal Epithelial Cells

Candida albicans colonizes human mucosa, including the gastrointestinal tract, as a commensal. In immunocompromised patients, C. albicans can breach the intestinal epithelial barrier and cause fatal invasive infections. Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1; CD66a), CEACAM5 (CEA), and CEACAM6 (CD66c) are immunomodulatory receptors expressed on human mucosa and are recruited by bacterial and viral pathogens. Here we show for the first time that a fungal pathogen (i.e., C. albicans) also binds directly to the extracellular domain of human CEACAM1, CEACAM3, CEACAM5, and CEACAM6. Binding was specific for human CEACAMs and mediated by the N-terminal IgV-like domain. In enterocytic C2BBe1 cells, C. albicans caused a transient tyrosine phosphorylation of CEACAM1 and induced higher expression of membrane-bound CEACAM1 and soluble CEACAM6. Lack of the CEACAM1 receptor after short hairpin RNA (shRNA) knockdown abolished CXCL8 (interleukin-8) secretion by C2BBe1 cells in response to C. albicans In CEACAM1-competent cells, the addition of recombinant soluble CEACAM6 reduced the C. albicans-induced CXCL8 secretion.IMPORTANCE The present study demonstrates for the first time that fungal pathogens can be recognized by at least four members of the immunomodulatory CEACAM receptor family: CEACAM1, -3, -5, and -6. Three of the four receptors (i.e., CEACAM1, -5, and -6) are expressed in mucosal cells of the intestinal tract, where they are implicated in immunomodulation and control of tissue homeostasis. Importantly, the interaction of the major fungal pathogen in humans Candida albicans with CEACAM1 and CEACAM6 resulted in an altered epithelial immune response. With respect to the broad impact of CEACAM receptors on various aspects of the innate and the adaptive immune responses, in particular epithelial, neutrophil, and T cell behavior, understanding the role of CEACAMs in the host response to fungal pathogens might help to improve management of superficial and systemic fungal infections.

Candida albicans infection and intestinal immunity

Fungal infections cause high rates of morbidity and mortality in intensive care and immunocompromised patients, and can represent a life-threatening disease. As a microorganism commonly found in the intestine, Candida albicans (C. albicans) can invade the gut epithelium barrier via microfold cells and enter the bloodstream. The defensive potential of the intestinal barrier against invasive C. albicans is dependent on innate and adaptive immune responses which enable the host to eliminate pathogenic fungi. The lamina propria layer of the intestine contains numerous immune cells capable of inducing an innate cellular immune response against invasive fungi. This review focuses on the immune response triggered by a C. albicans infection in the intestine.

Candida albicans Targets a Lipid Raft/Dectin-1 Platform to Enter Human Monocytes and Induce Antigen Specific T Cell Responses

Several pathogens have been described to enter host cells via cholesterol-enriched membrane lipid raft microdomains. We found that disruption of lipid rafts by the cholesterol-extracting agent methyl-β-cyclodextrin or by the cholesterol-binding antifungal drug Amphotericin B strongly impairs the uptake of the fungal pathogen Candida albicans by human monocytes, suggesting a role of raft microdomains in the phagocytosis of the fungus. Time lapse confocal imaging indicated that Dectin-1, the C-type lectin receptor that recognizes Candida albicans cell wall-associated β-glucan, is recruited to lipid rafts upon Candida albicans uptake by monocytes, supporting the notion that lipid rafts act as an entry platform. Interestingly disruption of lipid raft integrity and interference with fungus uptake do not alter cytokine production by monocytes in response to Candida albicans but drastically dampen fungus specific T cell response. In conclusion, these data suggest that monocyte lipid rafts play a crucial role in the innate and adaptive immune responses to Candida albicans in humans and highlight a new and unexpected immunomodulatory function of the antifungal drug Amphotericin B.