The Evolving View of IL-17-Mediated Immunity in Defense Against Mucocutaneous Candidiasis in Humans

Mucocutaneous Candidiasis: Insights Into the Diagnosis and Treatment

Recent progress in the methods of genetic diagnosis of inborn errors of immunity has contributed to a better understanding of the pathogenesis of chronic mucocutaneous candidiasis (CMC) and potential therapeutic options. This review describes the latest advances in the understanding of the pathophysiology, diagnostic strategies, and management of chronic mucocutaneous candidiasis.

A Practical Guide to the Management of Oral Candidiasis in Patients with Plaque Psoriasis Receiving Treatments That Target Interleukin-17

Plaque psoriasis is an immune-mediated inflammatory skin disease associated with the dysregulation of cytokines, especially those involved in the interleukin (IL)-23/IL-17 pathways. In recent years, there has been growing interest in developing biologic therapies that target these pathways. However, inhibition of the cytokines of the IL-23/IL-17 pathways may increase patients' risk of developing fungal infections, particularly oral candidiasis. Therefore, it is important that dermatology practitioners can effectively diagnose and treat oral candidiasis. In this review, we examine the role of the IL-23/IL-17 pathways in antifungal host defense, and provide a practical guide to the diagnosis and treatment of oral candidiasis in patients with psoriasis. Overall, while treatment with anti-IL-17 medications leads to an increased incidence of oral candidiasis in patients with psoriasis, these cases are typically mild or moderate in severity and can be managed with standard antifungal therapy without discontinuing treatment for psoriasis. If applicable, patients with psoriasis should also be advised to practice good oral hygiene and manage or control co-existing diabetes, and should be provided with information on smoking cessation to prevent oral candidiasis.

Mucocutaneous mycoses in people living with human immunodeficiency virus in Indonesia

BACKGROUND

To date, integrated care for people living with human immunodeficiency virus (PLHIV) has improved. However, although the management of mucocutaneous mycosis cases has improved, disease progression might be different in immunocompromised patients, which leads to variable clinical manifestations.

OBJECTIVES

To describe the characteristics of mucocutaneous mycosis cases in the PLHIV population and its associated factors in Indonesia.

METHODS

This retrospective study was conducted from January 2014 to December 2018 in four academic hospitals. Data were acquired from medical records with the inclusion of mucocutaneous mycosis patients with concurrent HIV infection. Analysis with the chi-squared test was performed using Statistical Package for the Social Sciences (SPSS) version 20.0.

RESULTS

A total of 1,796 cases of mucocutaneous mycoses were identified in 1782 PLHIV. The most common types of infection were candidiasis (63%), followed by dermatophytosis (35.1%), and malasseziosis (1.9%), which were significantly higher in PLHIV with CD4 level <200 cells/mm³ . The proportions of male gender (78.6% vs. 56.3%, p < .001), high level of education (48.0% vs. 64.1%, p < .001), office workers (73.8% vs. 64.1%, p < .001), combination of topical and systemic antifungal agents (59.1% vs. 48.5%, p = .006) and not receiving antiretroviral therapy (63.2% vs. 7.8%, p < .001) were significantly higher in PLHIV with a CD4 level <200 cells/mm³ .

CONCLUSION

In Indonesia, the most common fungal infection in PLHIV is candidiasis. This study also addressed the important matters regarding mucocutaneous mycoses in PLHIV. Education is an important measure to prevent the incidence of cutaneous mycoses in PLHIV, especially in high-risk groups.

Candida albicans-The Virulence Factors and Clinical Manifestations of Infection

Candida albicans is a common commensal fungus that colonizes the oropharyngeal cavity, gastrointestinal and vaginal tract, and healthy individuals' skin. In 50% of the population, C. albicans is part of the normal flora of the microbiota. The various clinical manifestations of Candida species range from localized, superficial mucocutaneous disorders to invasive diseases that involve multiple organ systems and are life-threatening. From systemic and local to hereditary and environmental, diverse factors lead to disturbances in Candida's normal homeostasis, resulting in a transition from normal flora to pathogenic and opportunistic infections. The transition in the pathophysiology of the onset and progression of infection is also influenced by Candida's virulence traits that lead to the development of candidiasis. Oral candidiasis has a wide range of clinical manifestations, divided into primary and secondary candidiasis. The main supply of C. albicans in the body is located in the gastrointestinal tract, and the development of infections occurs due to dysbiosis of the residential microbiota, immune dysfunction, and damage to the muco-intestinal barrier. The presence of C. albicans in the blood is associated with candidemia-invasive Candida infections. The commensal relationship exists as long as there is a balance between the host immune system and the virulence factors of C. albicans. This paper presents the virulence traits of Candida albicans and clinical manifestations of specific candidiasis.

Recurrent, Severe Aphthous Stomatitis and Mucosal Ulcers as Primary Manifestations of a Novel STAT1 Gain-of-Function Mutation

Chronic mucocutaneous candidiasis (CMC) characterized by persistent and recurrent Candida infection of the skin, nails, and the mucosa membranes has been proposed as the major infectious phenotype in patients with gain-of-function mutation of signal transducer and activator of transcription 1 (STAT1) 1. However, viral infections caused mostly by herpesviruses, and a broad range of autoimmune disorders may also be part of the clinical phenotype. We report here on a 31 years old female patient suffering from severe mucosal aphthous mucositis and ulcers and recurrent herpes simplex for decades. We found a previously unknown heterozygous sequence variant in STAT1 (c.1219C>G; L407V) affecting the DNA-binding domain of the protein in the patient and her 4 years old daughter. We found this mutation gain-of-function (GOF) by using immunoblot and luciferase assays. We detected low proportion of IL-17A-producing CD4+ T cell lymphocytes by using intracellular staining and flow cytometry. Candida-induced secretion of IL-17A and IL-22 by mononuclear cells from the patient was markedly decreased compared to controls. These data suggest that the novel mutant allele may result in impaired differentiation of CD4+ T cells to CD4+/IL-17+ cells. The clinical phenotype of the disease in this patient was unique as it was dominated primarily by severe aphthous stomatitis and ulcerative esophagitis and only partly by typical CMC resulting in diagnostic delay. We suggest that patients with severe recurrent aphthous stomatitis and esophagitis should be evaluated for STAT1 GOF mutation. Based on the broad clinical spectrum of the disease, we also suggest that CMC and CMC disease may not be an appropriate term to define clinically STAT1 GOF mutation.

Bacterial pathogenesis and interleukin-17: interconnecting mechanisms of immune regulation, host genetics, and microbial virulence that influence severity of infection

Interleukin-17 (IL-17) is a pro-inflammatory cytokine involved in the control of many different disorders, including autoimmune, oncogenic, and diverse infectious diseases. In the context of infectious diseases, IL-17 protects the host against various classes of microorganisms but, intriguingly, can also exacerbate the severity of some infections. The regulation of IL-17 expression stems, in part, from the activity of Interleukin-23 (IL-23), which drives the maturation of different classes of IL-17-producing cells that can alter the course of infection. In this review, we analyze IL-17/IL-23 signalling in bacterial infection, and examine the interconnecting mechanisms that link immune regulation, host genetics, and microbial virulence in the context of bacterial pathogenesis. We consider the roles of IL-17 in both acute and chronic bacterial infections, with a focus on mouse models of human bacterial disease that involve infection of mucosal surfaces in the lungs, urogenital, and gastrointestinal tracts. Polymorphisms in IL-17-encoding genes in humans, which have been associated with heightened host susceptibility to some bacterial pathogens, are discussed. Finally, we examine the implications of IL-17 biology in infectious diseases for the development of novel therapeutic strategies targeted at preventing bacterial infection.

Patient Susceptibility to Candidiasis-A Potential for Adjunctive Immunotherapy

Candida spp. are colonizing fungi of human skin and mucosae of the gastrointestinal and genitourinary tract, present in 30-50% of healthy individuals in a population at any given moment. The host defense mechanisms prevent this commensal fungus from invading and causing disease. Loss of skin or mucosal barrier function, microbiome imbalances, or defects of immune defense mechanisms can lead to an increased susceptibility to severe mucocutaneous or invasive candidiasis. A comprehensive understanding of the immune defense against Candida is essential for developing adjunctive immunotherapy. The important role of underlying genetic susceptibility to Candida infections has become apparent over the years. In most patients, the cause of increased susceptibility to fungal infections is complex, based on a combination of immune regulation gene polymorphisms together with other non-genetic predisposing factors. Identification of patients with an underlying genetic predisposition could help determine which patients could benefit from prophylactic antifungal treatment or adjunctive immunotherapy. This review will provide an overview of patient susceptibility to mucocutaneous and invasive candidiasis and the potential for adjunctive immunotherapy.

Staged development of long-lived T-cell receptor αβ TH17 resident memory T-cell population to Candida albicans after skin infection

BACKGROUND

Candida albicans is a dimorphic fungus to which human subjects are exposed early in life, and by adulthood, it is part of the mycobiome of skin and other tissues. Neonatal skin lacks resident memory T (T_RM) cells, but in adults the C albicans skin test is a surrogate for immunocompetence. Young adult mice raised under specific pathogen-free conditions are naive to C albicans and have been shown recently to have an immune system resembling that of neonatal human subjects.

OBJECTIVE

We studied the evolution of the adaptive cutaneous immune response to Candida species.

METHODS

We examined both human skin T cells and the de novo and memory immune responses in a mouse model of C albicans skin infection.

RESULTS

In mice the initial IL-17-producing cells after C albicans infection were dermal γδ T cells, but by day 7, αβ T_H17 effector T cells were predominant. By day 30, the majority of C albicans-reactive IL-17-producing T cells were CD4 T_RM cells. Intravital microscopy showed that CD4 effector T cells were recruited to the site of primary infection and were highly motile 10 days after infection. Between 30 and 90 days after infection, these CD4 T cells became increasingly sessile, acquired expression of CD69 and CD103, and localized to the papillary dermis. These established T_RM cells produced IL-17 on challenge, whereas motile migratory memory T cells did not. T_RM cells rapidly clear an infectious challenge with C albicans more effectively than recirculating T cells, although both populations participate. We found that in normal human skin IL-17-producing CD4⁺ T_RM cells that responded to C albicans in an MHC class II-restricted fashion could be identified readily.

CONCLUSIONS

These studies demonstrate that C albicans infection of skin preferentially generates CD4⁺ IL-17-producing T_RM cells, which mediate durable protective immunity.

Podoplanin is a negative regulator of Th17 inflammation

Recent data indicate that there are different subpopulations of Th17 cells that can express a regulatory as opposed to an inflammatory gene signature. The transmembrane glycoprotein PDPN is critical in the development of multiple organs including the lymphatic system and has been described on T cells in mouse models of autoimmune Th17 inflammation. Here, we demonstrate that unlike in mice, PDPN+ T cells induced under classic Th17-polarizing conditions express transcription factors associated with Th17 cells but do not produce IL-17. Moreover, these cells express a transcriptional profile enriched for immunosuppressive and regulatory pathways and express a distinct cytokine profile compared with potentially pathogenic PDPN- Th17 cells. Ligation of PDPN by its ligand CLEC-2 ameliorates the Th17 inflammatory response. IL-17 secretion is restored with shRNA gene silencing of PDPN. Furthermore, PDPN expression is reduced via an Sgk1-mediated pathway under proinflammatory, high sodium chloride conditions. Finally, CD3+PDPN+ T cells are devoid of IL-17 in skin biopsies from patients with candidiasis, a prototypical Th17-driven skin disease. Thus, our data support the hypothesis that PDPN may serve as a marker of a nonpathogenic Th17 cell subset and may also functionally regulate pathogenic Th17 inflammation.

Immunomodulation and Disease Tolerance to Staphylococcus aureus

The Gram-positive bacterium Staphylococcus aureus is one of the most frequent pathogens that causes severe morbidity and mortality throughout the world. S. aureus can infect skin and soft tissues or become invasive leading to diseases such as pneumonia, endocarditis, sepsis or toxic shock syndrome. In contrast, S. aureus is also a common commensal microbe and is often part of the human nasal microbiome without causing any apparent disease. In this review, we explore the immunomodulation and disease tolerance mechanisms that promote commensalism to S. aureus.