Assessment of the cutaneous immune response during Arthroderma benhamiae and A. vanbreuseghemii infection using an experimental mouse model

Dermatophyte infection: from fungal pathogenicity to host immune responses

Dermatophytosis is a common superficial infection caused by dermatophytes, a group of pathogenic keratinophilic fungi. Apart from invasion against skin barrier, host immune responses to dermatophytes could also lead to pathologic inflammation and tissue damage to some extent. Therefore, it is of great help to understand the pathogenesis of dermatophytes, including fungal virulence factors and anti-pathogen immune responses. This review aims to summarize the recent advances in host-fungal interactions, focusing on the mechanisms of anti-fungal immunity and the relationship between immune deficiency and chronic dermatophytosis, in order to facilitate novel diagnostic and therapeutic approaches to improve the outcomes of these patients.

Review on host-pathogen interaction in dermatophyte infections

Dermatophytosis is a common superficial fungal infection of the skin and its appendages caused by dermatophytes. Recent times have witnessed a dynamic evolution of dermatophytes driven by their ecology, reproduction, pathogenicity and host immune response, influenced by population migration and socioeconomic status. Dermatophytes establish infection following successful adherence of arthroconidia to the surface of keratinized tissues. The proteolytic enzymes released during adherence and invasion not only ascertain their survival but also allow the persistence of infection in the host. While the cutaneous immune surveillance mechanism, after antigen exposure and presentation, leads to activation of T lymphocytes and subsequent clonal expansion generating effector T cells that differentially polarize to a predominant Th17 response, the response fails to eliminate the pathogen despite the presence of high levels of IFN-γ. In chronic dermatophytosis, antigens are a constant source of stimulus promoting a dysregulated Th17 response causing inflammation. The host-derived iTreg response fails to counterbalance the inflammation and instead polarizes to Th17 lineage, aggravating the chronicity of the infection. Increasing antifungal resistance and recalcitrant dermatophytosis has impeded the overall clinical remission. Human genetic research has the potential to generate knowledge to explore new therapeutic targets. The review focuses on understanding specific virulence factors involved in pathogenesis and defining the role of dysregulated host immune response against chronic dermatophytic infections for future management strategies.

Exposure to itraconazole influences the susceptibility to antifungals, physiology, and virulence of Trichophyton interdigitale

Dermatophytosis is the most common human skin infection worldwide caused by dermatophytes, such as Trichophyton interdigitale and Trichophyton rubrum. Itraconazole (ITZ) is one of the main antifungals used to treat these infections. However, especially for onychomycosis, the treatment requires long-term regimens, increasing the possibility of drug resistance. We evaluated the effects of ITZ in the physiology, virulence, and interaction of T. interdigitale with phagocytes and mice cutaneous infection. In a screening test, fungal growth in the presence of ITZ led to the spontaneous selection of less susceptible T. interdigitale and T. rubrum strains. Interestingly, this phenotype was permanent for some T. interdigitale strains. Then, we studied three T. interdigitale strains: one susceptible and two ITZ-adapted. The ITZ-adapted strains were also less susceptible to the cell wall and membrane stressors, suggesting a multidrug resistance (MDR) phenotype associated with the increased ERG11 and MDR3 expression. These strains also presented substantial alterations in ergosterol content, lipid peroxidation, biofilm, and extracellular matrix production. During interaction with macrophages, ITZ-adapted strains were less engulfed but increased the intracellular oxidative and nitrosative bursts. In addition, ITZ-adapted strains presented a reduced ability to grow in a murine model of dermatophytosis, although causing the same tissue damage as the parental strain. In conclusion, the T. interdigitale ITZ adaptation increases tolerance to antifungals and alters the interaction with macrophages and a mammalian host. We hypothesized that successive exposure to ITZ may influence the emergence of adapted strains and lead to the recalcitrance of dermatophytosis.

Microsporum gypseum Isolated from Ailuropoda melanoleuca Provokes Inflammation and Triggers Th17 Adaptive Immunity Response

Microsporum gypseum causes dermatomycoses in giant pandas (Ailuropoda melanoleuca). This study aimed to investigate the immune response of M. gypseum following deep infection. The degree of damage to the heart, liver, spleen, lungs, and kidneys was evaluated using tissue fungal load, organ index, and histopathological methods. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) detected the mRNA expression of receptors and cytokines in the lung, and immunofluorescence staining and flow cytometry, were used to assess immune cells in the lung. The results indicated that conidia mainly colonized the lungs and caused serious injury with M. gypseum infection. Furthermore, dectin-1, TLR-2, and TLR-4 played a role in recognizing M. gypseum cells. Numerous inflammatory cells, mainly macrophages, dendritic cells, polymorphonuclear neutrophils, and inflammatory cytokines (TGF-β, TNF-α, IL-1β, IL-6, IL-10, IL-12, and IL-23), were activated in the early stages of infection. With the high expression of IL-22, IL-17A, and IL-17F, the Th17 pathway exerted an adaptive immune response to M. gypseum infection. These results can potentially aid in the diagnosis and treatment of diseases caused by M. gypseum in giant pandas.

Innate and mild Th17 cutaneous immune responses elicited by subcutaneous infection of immunocompetent mice with Cladosporium cladosporioides

Cladosporium cladosporioides is a dematiaceous hyphomycete that is pathogenic in the superficial and deep tissues of both immunodeficient and immunocompetent humans and animals. Our aim was to evaluate the antifungal immune responses elicited by C. cladosporioides in immunocompetent mice. Hence, we subcutaneously injected suspensions of C. cladosporioides spores into immunocompetent mice to investigate the anti-fungal immune responses in the skin. We collected skin tissue samples for histopathological examination, immunofluorescence staining, and quantitative real-time polymerase chain reaction analysis. We observed subcutaneous abscesses in mice after subcutaneous injection of C. cladosporioides. A large number of inflammatory cells, including dendritic cells, macrophages, and neutrophils, infiltrated the focal abscess, with comparatively few infiltrating inflammatory cells in the epidermal and dermal layers of the skin. We detected the expression of CD54 in the abscesses and the skin. Gene expression of the pattern recognition receptors Dectin-1 and TLR-2 was higher in infected mice than in controls. Gene expression of the cytokines IL-6, IL-1β, and IL-17A also increased after infection, suggesting that the Th17 signaling pathway may be involved in the anti-fungal response. Although the pathogenicity of C. cladosporioides in healthy mice was weak after subcutaneous infection, resulting in few serious pathological phenomena, it appears that innate and Th17 immune responses play important roles in the cutaneous host response to C. cladosporioides. These findings lay a foundation for further study of the pathogenic mechanism and treatment of C. cladosporioides infection.

Towards a Standardized Procedure for the Production of Infective Spores to Study the Pathogenesis of Dermatophytosis

Dermatophytoses are superficial infections of human and animal keratinized tissues caused by filamentous fungi named dermatophytes. Because of a high and increasing incidence, as well as the emergence of antifungal resistance, a better understanding of mechanisms involved in adhesion and invasion by dermatophytes is required for the further development of new therapeutic strategies. In the last years, several in vitro and in vivo models have emerged to study dermatophytosis pathogenesis. However, the procedures used for the growth of fungi are quite different, leading to a highly variable composition of inoculum for these models (microconidia, arthroconidia, hyphae), thus rendering difficult the global interpretation of observations. We hereby optimized growth conditions, including medium, temperature, atmosphere, and duration of culture, to improve the sporulation and viability and to favour the production of arthroconidia of several dermatophyte species, including Trichophyton rubrum and Trichophyton benhamiae. The resulting suspensions were then used as inoculum to infect reconstructed human epidermis in order to validate their ability to adhere to and to invade host tissues. By this way, this paper provides recommendations for dermatophytes culture and paves the way towards a standardized procedure for the production of infective spores usable in in vitro and in vivo experimental models.

Immunopathogenesis of Dermatophytoses and Factors Leading to Recalcitrant Infections

The pathogenesis of dermatophytic infections involves the interplay of three major factors: the dermatophyte, the inherent host defense, and the adaptive host immune response. The fungal virulence factors determine the adhesion and invasion of the skin while the immune response depends on an interaction of the pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMP) with pattern recognition receptors (PRRs) of the host, which lead to a differential Th (T helper) 1, Th2, Th17, and Treg response. While anthropophilic dermatophytes Trichophyton rubrum and now increasingly by T. interdigitale subvert the immune response via mannans, zoophilic species are eliminated due to a brisk immune response. Notably, delayed-type hypersensitivity (Th1) response of T lymphocytes causes the elimination of fungal infection, while chronic disease caused by anthropophilic species corresponds to toll-like receptor 2 mediated IL (interleukin)-10 release and generation of T-regulatory cells with immunosuppressive potential. Major steps that determine the ultimate clinical course and chronicity include genetic susceptibility factors, impaired epidermal and immunological barriers, variations in the composition of sebum and sweat, carbon dioxide tension, skin pH, and topical steroid abuse. It is important to understand these multifarious aspects to surmount the problem of recalcitrant dermatophytosis when the disorder fails conventional therapeutic agents.

Assessment of the pulmonary adaptive immune response to Cladosporium cladosporioides infection using an experimental mouse model

Cladosporium cladosporioides causes asthma and superficial and deep infections, mostly in immunodeficient individuals and animals. This study aimed to investigate whether C. cladosporioides spores can enter the lungs through pulmonary circulation and influence pulmonary immune response. We intravenously injected mice with C. cladosporioides spore suspension and conducted several assays on the lungs. Pulmonary hemorrhage symptoms and congestion were most severe on days 1, 2, and 3 post-inoculation (PI). Extensive inflammatory cell infiltration occurred throughout the period of infection. More spores and hyphae colonizing the lungs were detected on days 1, 2, and 3 PI, and fewer spores and hyphae were observed within 21 d of infection. Numerous macrophages, dendritic cells, and neutrophils were observed on day 5 PI, along with upregulation of CD54, an intercellular adhesion molecule. Th1 and Th2 cells increased after infection; specifically, Th2 cells increased considerably on day 5 PI. These results suggest that days 2 and 5 PI represent the inflammatory peak in the lungs and that the Th2 and Th1 signaling pathways are potentially involved in pulmonary immune responses. In conclusion, the further adaptive immune responses played important roles in establishing effective pulmonary immunity against C. cladosporioides systemic infections based on innate immune responses.

Skin Immunity to Dermatophytes: From Experimental Infection Models to Human Disease

Dermatophytoses (ringworms) are among the most frequent skin infections and are a highly prevalent cause of human disease worldwide. Despite the incidence of these superficial mycoses in healthy people and the compelling evidence on chronic and deep infections in immunocompromised individuals, the mechanisms controlling dermatophyte invasion in the skin are scarcely known. In the last years, the association between certain primary immunodeficiencies and the susceptibility to severe dermatophytosis as well as the evidence provided by novel experimental models mimicking human disease have significantly contributed to deciphering the basic immunological mechanisms against dermatophytes. In this review, we outline the current knowledge on fungal virulence factors involved in the pathogenesis of dermatophytoses and recent evidence from human infections and experimental models that shed light on the cells and molecules involved in the antifungal cutaneous immune response. The latest highlights emphasize the contribution of C-type lectin receptors signaling and the cellular immune response mediated by IL-17 and IFN-γ in the anti-dermatophytic defense and skin inflammation control.

Human skin models: From healthy to disease-mimetic systems; characteristics and applications

Skin drug delivery is an emerging route in drug development, leading to an urgent need to understand the behaviour of active pharmaceutical ingredients within the skin. Given, As one of the body's first natural defences, the barrier properties of skin provide an obstacle to the successful outcome of any skin drug therapy. To elucidate the mechanisms underlying this barrier, reductionist strategies have designed several models with different levels of complexity, using non-biological and biological components. Besides the detail of information and resemblance to human skin in vivo, offered by each in vitro model, the technical and economic efforts involved must also be considered when selecting the most suitable model. This review provides an outline of the commonly used skin models, including healthy and diseased conditions, in-house developed and commercialized models, their advantages and limitations, and an overview of the new trends in skin-engineered models.

β-Glucan augments IL-1β production by activating the JAK2/STAT3 pathway in cultured rabbit keratinocytes

Trichophyton mentagrophytes (T. mentagrophytes) is the main cause of rabbit dermatophytosis. As the main pathogen-associated molecular pattern of T. mentagrophytes, the role of β-glucan in the pathogenesis of rabbit dermatophytosis remains elusive. Keratinocytes (KC) are the main cellular component and the first defensive line against fungal pathogens in the skin. Therefore, the present study investigated the effects of β-glucan on rabbit KC from dorsal skin. β-glucan was found to inhibit KC proliferation by 10% at 20 ug/ml and this concentration was thus considered as optimal. Next, 20 ug/ml β-glucan stimulation for 24 h significantly increased CXCL8, CXCL11, and IL-1β secretions in KC. Furthermore, β-glucan exposure induced the expressions of JAK2 mRNA, STAT3 mRNA, and p-STAT3 protein. Silencing JAK2 expression inhibited p-STAT3 protein expression and β-glucan-induced IL-1β secretion. And overexpression of JAK2 further promoted β-glucan-mediated p-STAT3 protein and IL-1β productions. These results suggested that β-glucan-induced CXCL8, CXCL11, and IL-1β secretions in rabbit KC might be involved in the inflammatory response of T. mentagrophytes infected rabbit dorsal skin. However, only IL-1β secretion was promoted by the JAK2/STAT3 signaling pathway. In conclusion, this study is a necessary step toward elucidating the mechanisms that underlie skin immune system injury stimulated by β-glucan.

The interplay among Th17 and T regulatory cells in the immune dysregulation of chronic dermatophytic infection

The delineation of the pathogenic interaction between the host skin immune responses and dermatophytes has remained indigent. The obscure enigma in host-dermatophyte immunopathogenic interactions is the T regulatory (Treg) and T-helper (Th) 17  cell role in maintaining immune homeostasis. We attempted to understand the regulation and recognition of lineage-specific response in chronic dermatophytic skin infection patients. The percentages of Th17 (CD4⁺CD161⁺IL23R⁺) and Treg (CD4⁺CD25⁺FoxP3⁺) cell subpopulations in the peripheral circulation of thirty chronic dermatophytic skin infection patients and twenty healthy individuals was determined. The serum cytokine levels were estimated for disease correlation. The mean duration of the disease was 10.68 ± 8.72 months, with Trichophyton mentagrophytes complex as the major pathogen. Total serum IgE level of patients was significantly higher compared to healthy controls (305 ± 117 vs 98.53 ± 54.55 IU/ml; p < 0.01). Expression of Th17 and Treg cell markers on CD4⁺ T cells was significantly elevated in patients than controls (p < 0.05). Comparatively, serum interleukin (IL)-4 and interferon (IFN)-γ levels were increased, with low IL-10 levels in patients. Our data envisages a complex immune dysfunction in chronic dermatophytosis, arising either as a result of dermatophyte exposure or paradoxical precedence of disease establishment. Designing new treatment strategies and preventing recurrences are challenges for future research.

Differential gene expression in HaCaT cells may account for the various clinical presentation caused by anthropophilic and geophilic dermatophytes infections

BACKGROUND

Despite the worldwide prevalence of dermatophyte infections, only a few genes are reported to be related to dermatophyte infections. In addition, the mechanism by which different ecological dermatophytes infection leads to varying intensity of inflammation remains unclear.

OBJECTIVES

To investigate the mechanism of varying intensity of skin inflammation caused by different ecological dermatophytes infection.

METHODS

We infected HaCaT cells with anthropophilic and geophilic dermatophytes to mimic various ecological dermatophyte infections. RNA-sequencing (RNA-seq) was employed to identify the change in the gene expression of HaCaT cells. To verify the expression of differentially expressed genes (DEGs), we selected 18 HaCaT cells genes to conduct qPCR experiments. In addition, immunoblotting was conducted to validate key genes from the MAPK signalling pathway.

RESULTS

After HaCaT cells were infected with the anthropophilic Trichophyton rubrum (T rubrum) and the geophilic Microsporum gypseum (M gypseum), 118 and 619 differentially expressed genes were identified in HaCaT cells, respectively. These genes may provide a clue as to how keratinocytes respond to anthropophilic and geophilic dermatophytes. We also found that JUN may play a critical role in keratinocytes infected with M gypseum.

CONCLUSIONS

Differential gene expression in HaCaT cells may account for the various clinical presentation caused by anthropophilic and geophilic dermatophytes infections. In addition, the intense inflammatory reaction of M gypseum infection may be triggered by activating the JNK-JUN signalling pathway.

In vitro models of dermatophyte infection to investigate epidermal barrier alterations

Fungal infections of the skin, known as dermatophytoses, are initiated at the epidermal barrier and lead to dysfunctions of the stratum corneum and cornified skin appendages. Dermatophytosis affects a significant part of the human population and, despite the availability of effective treatments, its prevalence is still increasing. Numerous dermatophyte species are able to induce lesions in both animals and humans, with different clinical pictures and host inflammatory responses. The understanding of the infectious process and of tissue responses has been impeded by discrepancies between observations in vivo or in research models. Indeed, cells cultured as monolayers do not undergo the keratinization process required to study the adherence and invasion of dermatophytes. Animal models lack relevance to study human dermatophytosis because of species-specific differences in the development of lesions and inflammatory responses. This review focuses on the recent development of cultured human skin equivalents, which partly overcomes those limitations and allows improved understanding of the pathogenesis of dermatophytosis in human being, especially the impacts of infection on epidermal barrier integrity.

Host- and pathogen-dependent susceptibility and predisposition to dermatophytosis

Dermatophytes are a highly specialized group of keratinophilic and keratinolytic filamentous fungi causing a ringworm disease called dermatophytosis or superficial mycoses. Although dermatophyte infections do not threaten the host's life, they lower its quality in humans by causing discomfort related to cosmetic problems and through their epidemiological significance, whereas in farm animals they are responsible for economic losses and constitute a source of the spread of spores. Evidence from countless observational studies that have been conducted over the last 90 years indicates that dermatophytes infect humans of every age, race, gender and socioeconomic status with strikingly high rates, as well as both farmed and wild animals in various health conditions and with various epidemiological statuses. However, the prevalence of superficial fungal infections is highly variable, since it depends on several parameters associated with the infected individual and the dermatophyte, their mutual interactions, and epidemiological and geographical factors. The curious disparity in dermatophyte infection patterns has prompted many investigators to search for a link between the host, the host's predispositions and susceptibility to the disease, and the dermatophyte species and virulence. Thus, the question arises as to whether, in addition to the generally recognized factors predisposing hosts to diseases, there are some other predispositions to dermatophyte infections in a species-specific host. In this review, we describe recent findings about the mechanism of dermatophyte infections, focusing on the adaptation of the fungi to the host and conditions predisposing each side to the disease.

Responses of Reconstructed Human Epidermis to Trichophyton rubrum Infection and Impairment of Infection by the Inhibitor PD169316

Despite the threatening incidence of dermatophytosis, information is still lacking about the consequences of infection on epidermal barrier functions and about the keratinocyte responses that alert immune components. To identify the mechanisms involved, arthroconidia of the anthropophilic dermatophyte Trichophyton rubrum were prepared to infect reconstructed human epidermis (RHE) in vitro. Integrity of the barrier was monitored during infection by measurements of transepithelial electrical resistance and dye-permeation through the RHE. Expression and release of pro-inflammatory cytokines and antimicrobial peptides by keratinocytes inserted into the RHE were assessed, respectively, by quantitative reverse transcriptase-PCR (to analyze mRNA content in tissue extracts) and by ELISA (to detect proteins in culture media). Results reveal that infection by T. rubrum is responsible for disruption of the epidermal barrier, including loss of functional tight junctions. It additionally causes simultaneous expression and release of cytokines and antimicrobial peptides by keratinocytes. Potential involvement of the p38 mitogen-activated protein kinase signaling pathway was evaluated during infection by targeted inhibition of its activity. Intriguingly, among several p38 mitogen-activated protein kinase inhibitors, PD169316 alone was able to inhibit growth of T. rubrum on Sabouraud agar and to suppress the process of infection on RHE. This suggests that PD169316 acts on a specific target in dermatophytes themselves.

IL-17-Mediated Immunity Controls Skin Infection and T Helper 1 Response during Experimental Microsporum canis Dermatophytosis

Despite worldwide prevalence of superficial mycoses, the immune response in dermatophytosis has scarcely been investigated. In this study, we developed a model of superficial skin infection in C57BL/6 mice with Microsporum canis, a highly prevalent human pathogen. This model mimics mild inflammatory human dermatophytosis, characterized by neutrophil recruitment and fungal invasion limited to the epidermis and exhibits the establishment of a specific T helper type 17 immune response during infection. By using IL-17RA- or IL-17A/F-deficient mice we showed that, in the absence of a functional IL-17 pathway, M. canis extensively colonizes the epidermis and promotes an exaggerated skin inflammation and a shift to an IFN-γ-mediated (T helper type 1) response. IL-17 signaling was not involved in neutrophil influx to skin or fungal invasion to deeper tissues. Finally, this study shows that skin langerin-expressing cells contribute to the antifungal T helper type 17 response in vivo. In conclusion, these data directly show a dual function of IL-17 cytokines in dermatophytosis by controlling superficial infection and down-modulating a T helper type 1 antifungal response.

Skin Fungi from Colonization to Infection

Humans are exceptional among vertebrates in that their living tissue is directly exposed to the outside world. In the absence of protective scales, feathers, or fur, the skin has to be highly effective in defending the organism against the gamut of opportunistic fungi surrounding us. Most (sub)cutaneous infections enter the body by implantation through the skin barrier. On intact skin, two types of fungal expansion are noted: (A) colonization by commensals, i.e., growth enabled by conditions prevailing on the skin surface without degradation of tissue, and (B) infection by superficial pathogens that assimilate epidermal keratin and interact with the cellular immune system. In a response-damage framework, all fungi are potentially able to cause disease, as a balance between their natural predilection and the immune status of the host. For this reason, we will not attribute a fixed ecological term to each species, but rather describe them as growing in a commensal state (A) or in a pathogenic state (B).

Is Antifungal Resistance a Cause for Treatment Failure in Dermatophytosis: A Study Focused on Tinea Corporis and Cruris from a Tertiary Centre?

Background:

Dermatophytoses are one of the most common skin diseases that have been largely simple to treat. However, in recent years, these infections have become recalcitrant to treatment which can possibly be due to antifungal resistance.

Aim:

To analyze the resistance pattern of patients with recalcitrant dermatophytoses.

Materials and Methods:

A cross-sectional evaluation was undertaken of 40 consecutive patients with recalcitrant tinea corporis/cruris/both who had taken systemic antifungal treatment and did not respond completely to therapy or had recurrent lesion within 1 month of stopping the therapy. Terbinafine, fluconazole, itraconazole, ketoconazole, amphotericin B, and voriconazole were the antifungals tested using broth microdilution assay for antifungal susceptibility testing of dermatophytes, and MIC50, 90 values were recorded.

Results:

KOH mount was positive in 18 (45%) patients, culture was positive in 28 (70%) patients. Trichophyton mentagrophytes (35%) and T. rubrum (27.5%) were the predominant isolates. Overall, activity of terbinafine and itraconazole were significantly higher than the other drugs tested. For terbinafine, both T. mentagrophytes and T. rubrum were inhibited at MIC₉₀ of 0.125 μg/ml. Itraconazole-inhibited T. mentagrophytes and T. rubrum at MIC₉₀ of 0.0625 and 0.25 μg/ml, respectively. All isolates had reduced susceptibility to fluconazole.

Conclusion:

While MIC seen were higher than western data, in-vitro resistance (>1 μg/ml) to antifungals was not seen and probably may not be a cause of treatment failure. Possibly, treatment failure lies in the intricate host fungal interaction and virulence of species which help it to evade host immune response.

Are Th17 Cells Playing a Role in Immunity to Dermatophytosis?

Despite their superficial localization in the skin, pathogenic dermatophytes can induce a complex but still misunderstood immune response in their hosts. The cell-mediated immunity (CMI) is correlated with both clinical recovery and protection against reinfection, and CD4+ T lymphocytes have been recognized as a crucial component of the immune defense against dermatophytes. Before the discovery of the Th17 pathway, CMI was considered to be only dependent of Th1 cells, and thus most studies on the immunology of dermatophytosis have focused on the Th1 pathway. Nevertheless, the fine comparative analysis of available scientific data on immunology of dermatophytosis in one hand and on the Th17 pathway mechanisms involved in opportunistic mucosal fungal infections in the other hand reveals that some key elements of the Th17 pathway can be activated by dermatophytes. Stimulation of the Th17 pathway could occur through the activation of some C-type lectin-like receptors and inflammasome in antigen-presenting cells. The Th17 cells could go back to the affected skin and by the production of signature cytokines could induce the effector mechanisms like the recruitment of polymorphonuclear neutrophils and the synthesis of antimicrobial peptides. In conclusion, besides the Th1 pathway, which is important to the immune response against dermatophytes, there are also growing evidences for the involvement of the Th17 pathway.

Immunoresponses in dermatomycoses

Contact with fungal pathogens initiates a series of host responses beginning with innate immunity, which leads to fungal recognition and microbial killing. The innate immune system also modulates the adaptive immune responses, leading to the establishment of immunological memory and protection against pathogens. In the case of dimorphic fungi such as Candida albicans and Malassezia, the immune system plays an important role in tolerance and resistance when managing the organisms either as commensal microbiota or invading pathogens, and disruption of this balance can result in pathological consequences for the host. In addition, Malassezia and dermatophytes have immunomodulatory capabilities that allow them to adapt to their environments and they may exert different effects in healthy and diseased skin. Here, we discuss the host immune responses to dermatomycoses caused by dimorphic fungi such as C. albicans and Malassezia as well as dermatophytes such as Trichophyton spp. and Arthroderma benhamiae to gain a better understanding of the mechanisms of the host-dermatomycosis interaction.

The Role of Phagocytes and NETs in Dermatophytosis

Innate immunity is the host first line of defense against pathogens. However, only in recent years, we are beginning to better understand the ways it operates. A key player is this branch of the immune response that are the phagocytes, as macrophages, dendritic cells and neutrophils. These cells act as sentinels, employing specialized receptors in the sensing of invaders and host injury, and readily responding to them by production of inflammatory mediators. They afford protection not only by ingesting and destroying pathogens, but also by providing a suitable biochemical environment that shapes the adaptive response. In this review, we aim to present a broad perspective about the role of phagocytes in dermatophytosis, focusing on the mechanisms possibly involved in protective and non-protective responses. A full understanding of how phagocytes fit in the pathogenesis of these infections may open the venue for the development of new and more effective therapeutic approaches.

Tinea Capitis: Current Status

Tinea capitis remains a common childhood infection in many parts of the world. Yet knowledge of the underlying pathogenetic mechanisms and the development of effective immunity have shown striking advances, and new methods of diagnosis ranging from dermoscopy to molecular laboratory tests have been developed even though they have not been assimilated into routine practice in many centres. Treatment is effective although it needs to be given for at least 1 month. What is missing, however, is a systematic approach to control through case ascertainment and therapy.

Cutaneous murine model of infection caused by Neoscytalidium dimidiatum: a preliminary study of an emerging human pathogen

Neoscytalidium dimidiatum is an emerging fungus that causes a skin infection similar to dermatophytosis; it affects both immunocompetent and immunosuppressed individuals, and it may invade deeper tissues and organs and cause systemic disease. Little is known about the etiopathogenesis of the infection caused by this fungus, and no standard effective treatment is available. The aim of the present experimental study was to develop an animal model of skin infection with N. dimidiatum. BALB/c mice were inoculated with two fungal strains, and different routes of infection were tested. When challenged intradermally, N. dimidiatum strain HUPE164165 caused skin infection in 67% of the animals whereas strain HUPE115669 did it in 49%. Neoscytalidium dimidiatum was isolated from the skin of 25% of the animals inoculated via epidermal scarification and from 100% of the animals challenged via subcutaneous injection. Mice inoculated intradermally were followed-up during four weeks, and clinical samples were collected on days 3, 8, 15, and 29 after inoculation, corresponding to different stages of infection. The cutaneous infection rate, as measured by the recovery of N. dimidiatum strain HUPE164165 from skin biopsies of animals inoculated intradermally, revealed the presence of infection in 90% of the animals sacrificed at 3 days post-inoculation, 71% at 8, 85% at 15, and 33% at 29. Conidia and hyphae were observed in PAS-stained sections as well as a mild to moderate inflammatory infiltrate in haematoxylin-eosin, although it did not differ from animals inoculated either with T. quinckeanum or PBS. The intradermal route of inoculation was considered to be suitable for the study of skin infection with N. dimidiatum The animal model developed in this preliminary study is the first to allow the study of cutaneous infection with N. dimidiatum and may contribute to further investigations of the aetiology, immunology, pathogenesis and treatment targeting this emerging mycosis.

Overexpression of TLR-2 and TLR-4 mRNA in feline polymorphonuclear neutrophils exposed to Microsporum canis

BACKGROUND

Polymorphonuclear neutrophils (PMNs), along with macrophages, are the first leukocytes recruited to the site of infection in dermatophytoses and are responsible for the in fine elimination of the fungus. It has been demonstrated that feline PMNs produce pro-inflammatory cytokines after stimulation with Microsporum canis. The activation of these cells results from the recognition of specific PAMPs (pathogen associated molecular patterns) from M. canis by PRRs (pattern recognition receptors) of PMNs. The C-type lectin receptors (CLRs) and toll-like receptors (TLRs) are the two main PRRs in phagocytic cells that recognize fungal components.

HYPOTHESIS/OBJECTIVE

The aim of this study was to evaluate the expression of TLR-2, TLR-4 and dectin-1 mRNA in feline PMNs exposed to different components from M. canis.

METHODS

Feline PMNs were stimulated for 2 h or 4 h with either live arthroconidia, heat-killed arthroconidia or secreted components from M. canis. The levels of TLR-2, TLR-4 and dectin-1 mRNA were assessed by RT-qPCR.

RESULTS

Results showed an increase of TLR-2 and TLR-4 mRNA levels in feline PMNs stimulated with live and heat-killed arthroconidia, but not in those stimulated with the secreted components from M. canis. No significant variation in dectin-1 mRNA expression was observed in PMNs stimulated with the different fungal components.

CONCLUSIONS AND CLINICAL IMPORTANCE

The overexpression of TLR-2 and TLR-4 mRNAs in stimulated feline PMNs suggests that these receptors are involved in the host immune response through the recognition of M. canis PAMPs.

Chronic widespread dermatophytosis due to Trichophyton rubrum: a syndrome associated with a Trichophyton-specific functional defect of phagocytes

Dermatophytes are agents of typically benign superficial infections. However, an increasing number of severe infections in immunocompromised hosts has been reported. We aimed to understand the factors underlying the existence of a cohort of patients presenting with chronic widespread dermatophytosis (CWD) due to Trichophyton rubrum, but with no signs of immunodeficiency. Their disease is usually recurrent and difficult to manage. Fourteen patients meeting the following criteria for CWD were studied: T. rubrum culture-proven skin lesions of ≥10 cm in at least one dimension; the involvement of at least three non-contiguous localizations of >1 year's duration; and no predisposing conditions. For comparison, we also studied 13 acute Tinea pedis patients. Macrophages and neutrophils were isolated and tested for T. rubrum conidia phagocytic and killing activity. H2O2, NO, and pro- and anti-inflammatory cytokine release were measured. All experiments were run with age- and sex-matched healthy donors' cells in parallel. CWD patients' macrophages and neutrophils presented with reduced T. rubrum-phagocytic and killing abilities, and reduced H2O2 and NO release when compared with those of healthy donors. CWD patients' macrophages secreted lower levels of the proinflammatory cytokines interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α, but enhanced levels of the anti-inflammatory cytokine IL-10. Neutrophil secretion closely followed this unbalanced pattern. In contrast, responses to the positive controls zymosan, lipopolysaccharide, and phorbol myristate acetate were comparable with those of healthy donors. The same experiments were performed with macrophages and neutrophils from the acute Tinea pedis patients and showed no differences when compared with the matched healthy donors. Patients with CWD have a T. rubrum-related functional deficiency of phagocytes and may represent a distinct clinical entity in the complex spectrum of the Trichophyton-host interaction.

Trichophyton species of Arthroderma benhamiae - a new infectious agent in dermatology

In Germany, infections due to the zoophilic dermatophyte Trichophyton (T.) species of Arthroderma benhamiae are being more frequently diagnosed. The source of infection of this emerging pathogen overlaps with that of the zoophilic species T. interdigitale. The most common source are guinea pigs. T. species of Arthroderma benhamiae causes inflammatory dermatophytosis in children and adolescents. In addition to tinea capitis, it may cause both tinea corporis, tinea manus and frequently tinea faciei. In Germany, T. species of Arthroderma benhamiae is a frequent zoophilic dermatophyte, which in regions is probably more frequent than Microsporum canis. The mycological identification of the isolates with their yellow stained colonies is based on their macroscopic and microscopic features. However, some exhibit colony features consistent with those of T. interdigitale. These strains only can be identified unambiguously by means of molecular techniques. Using detection methods such as PCR-ELISA or real-time PCR, the dermatophyte can be identified directly from clinical material. Sequencing of the internal transcribed spacer region (ITS) of the ribosomal DNA has been approved as culture confirmation test for T. species of Arthroderma benhamiae. In addition, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) is useful. Widespread dermatophytosis due to T. species of Arthroderma benhamiae, in particular of tinea capitis, requires oral antifungal agents. Terbinafine is most effective, alternatives are fluconazole and itraconazole.