Stimulation, inhibition and death of macrophages infected with Trichophyton rubrum

Extracellular Vesicles from Candida haemulonii var. vulnera Modulate Macrophage Oxidative Burst

Members of the Candida haemulonii species complex are multidrug-resistant emergent yeast pathogens able to cause superficial and invasive infections in risk populations. Fungal extracellular vesicles (EVs) play a critical role in the pathogenicity and virulence of several species and may perform essential functions during infections, such as carrying virulence factors that behave in two-way communications with the host, affecting survival and fungal resistance. Our study aimed to describe EV production from Candida haemulonii var. vulnera and evaluate whether murine macrophage RAW 264.7 cells respond to their stimuli by generating an oxidative response after 24 h. For this purpose, reactive oxygen species detection assays demonstrated that high concentrations of yeast and EVs (10¹⁰ particles/mL) of Candida haemulonii did not change macrophage viability. However, the macrophages recognized these EVs and triggered an oxidative response through the classical NOX-2 pathway, increasing O₂^•- and H₂O₂ levels. However, this stress did not cause lipid peroxidation in the RAW 264.7 cells and neither lead to the activation of the COX-2-PGE₂ pathway. Thus, our data suggest that low concentrations of C. haemulonii EVs are not recognized by the classical pathway of the oxidative burst generated by macrophages, which might be an advantage allowing the transport of virulence factors via EVs, not identified by the host immune system that could work as fine tube regulators during infections caused by C. haemulonii. In contrast, C. haemulonii var. vulnera and high EV concentrations activated microbicidal actions in macrophages. Therefore, we propose that EVs could participate in the virulence of the species and that these particles could be a source of antigens to be exploited as new therapeutic targets.

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.

Potential Treatment of Dermatophyte Trichophyton rubrum in Rat Model Using Topical Green Biosynthesized Silver Nanoparticles with Achillea santolina Extract

Trichophyton rubrum is the most common dermatophyte, and can cause cutaneous infections in humans and animals (dermatophytosis). In this study, we investigated the anti-dermatophytic potential of green synthesized silver nanoparticles using Achillea santolina extract (AS-AgNPs) in an in vitro and in vivo rat model of dermal T. rubrum dermatophytosis (TRD). The green synthesis of AS-AgNPs was performed using A. santolina extract and characterized by UV-VIS spectroscopy, zeta potential, imaging (transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Energy dispersive X-ray analysis (EDX). The antifungal activity of AS-AgNPs was determined by the broth microdilution method, conidial germination, and hyphal growth inhibition. TEM and SEM were used to study the mode of the antifungal action of AS-AgNPs. AS-AgNPs inhibited the growth of T. rubrum with an MIC of 128 μg/mL, and suppressed the conidial germination and hyphal growth by 55.3% 84.6%, respectively. AS-AgNPs caused modified mycelial structures, increased cell membrane permeability, and cell wall damage. AS-AgNPs significantly increase the permeability of the fungal membrane, as revealed by reducing ergosterol biosynthesis. An increase in the intracellular ROS and the induction of apoptosis were also observed during AS-AgNP treatment. In addition, AS-AgNPs reduced the cell wall integrity, as shown by the reduction in the β-(1,3)-d-glucan synthase and chitin synthase activities. AS-AgNPs showed very low toxicity on primary human dermal fibroblasts (HDF) at the MIC. The topical treatment of the infected skin in the TRD rat model with AS-AgNPs showed a significant reduction in the fugal burden after 7 days and a complete clearance of fungal conidia, with a high recovery of epidermal and dermal structures after 14 days, compared to control rats. Interestingly, AS-AgNPs significantly attenuated the infiltrated inflammatory cells, in association with reducing the tissue proinflammatory cytokines including TNF-α, IL-1, IL-6, MOP and IL-17. In conclusion, our data prove AS-AgNPs to be a novel green topical therapy for dermatophytosis caused by T. rubrum.

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.

State-of-the-Art Dermatophyte Infections: Epidemiology Aspects, Pathophysiology, and Resistance Mechanisms

The burden of fungal infections is not widely appreciated. Although these infections are responsible for over one million deaths annually, it is estimated that one billion people are affected by severe fungal diseases. Mycoses of nails and skin, primarily caused by fungi known as dermatophytes, are the most common fungal infections. Trichophyton rubrum appears to be the most common causative agent of dermatophytosis, followed by Trichophyton interdigitale. An estimated 25% of the world’s population suffers from dermatomycosis. Although these infections are not lethal, they compromise the quality of life of infected patients. The outcome of antidermatophytic treatments is impaired by various conditions, such as resistance and tolerance of certain dermatophyte strains. The adage “know your enemy” must be the focus of fungal research. There is an urgent need to increase awareness about the significance of these infections with precise epidemiological data and to improve knowledge regarding fungal biology and pathogenesis, with an emphasis on adaptive mechanisms to tackle adverse conditions from host counteractions. This review outlines the current knowledge about dermatophyte infections, with a focus on signaling pathways required for fungal infection establishment and a broad perspective on cellular and molecular factors involved in antifungal resistance and tolerance.

Host immune responses in dermatophytes infection

Dermatophytosis is a skin infection caused by keratinophilic, filamentous fungi. These are highly prevalent, common mycoses, affecting approximately 20% of the population. These fungi invade the stratum corneum, and other keratinised tissues, like nails and hair, where they grow by secreting enzymes and degrading keratin to obtain nutrients. Clinical presentation is variable and may depend on many factors, such as the infection site, the host's immunity and the dermatophyte's virulence. Generally, patients with acute superficial dermatophytosis mount cell-mediated immune responses. However, those suffering from chronic or recurrent infections are unable to develop this response, for reasons yet unknown. Several reports have described severe and occasionally life-threatening invasive diseases (deep dermatophytosis) associated with genetic mutations in the innate immunity-associated molecule CARD9, displaying the need to better understand its immune response. These dermatoses have substantial clinical consequences, producing chronic and difficult to treat skin lesions. They also lead to a decline in the patient's quality of life and impact their self-esteem. This review summarises findings on the immune response against dermatophytes.

Inherited ichthyosis and fungal infection: an update on pathogenesis and treatment strategies

Inherited ichthyoses are a group of genodermatoses classified as either nonsyndromic or syndromic. Nonsyndromic ichthyoses and keratitis, ichthyosis and deafness (KID) syndrome predispose to fungal infection. The diagnosis and treatment of fungal infections underlying ichthyoses are challenging. In this review, we summarize reported cases of ichthyosis with fungal infection over the past 50 years. Atypical manifestations such as alopecia, papules and brittle nails occurred in patients with ichthyosis combined with fungal infection. Various pathogenic mechanisms have been implicated, including mutations of ichthyosis-related genes leading to disruption of the skin barrier via multiple pathways. Host immune disorders, including atopy and abnormal innate immunity also contribute to susceptibility. Specific fungi may escape the immune response. Extensive and recurrent fungal infections are not uncommon in patients with ichthyosis, making a cure more difficult and increasing the need for systemic antifungal therapy. Traditional and new ichthyosis treatments aiming to improve skin barrier function could help prevent fungal infection. In conclusion, the close relationship between ichthyosis and fungal infection is of vital importance in clinical practice and requires more attention from physicians. More studies are required to investigate the mechanisms and explore useful treatment strategies.

Acanthamoeba castellanii as an alternative interaction model for the dermatophyte Trichophyton rubrum

BACKGROUND

Trichophyton rubrum (Tr) is the main aetiological agent of human dermatophytosis, being isolated from the environment and keratinised tissues. In the environment, Tr can interact with other organisms, such as free-living amoebas (FLA), which can act as an alternative host system to study the interaction between microbes and phagocytic cells.

OBJECTIVES

To characterise the Acanthamoeba castellanii (ALX)-Tr interaction.

METHODS

Interaction was characterised in three conditions: trophozoites (PYG), late (PYG/NES) and early (NES) encystation stimulus, evaluating encystation kinetics, phagocytosis, exocytosis and fungicidal activity dynamics.

RESULTS

Tr was able to induce ALX encystation and be internalised by ALX. The number of internalised conidia was high at 1 hour, and ALX presented fungicidal activity with increased intracellular ROS production and exocytosis. In PYG/NES, phagocytosis and ROS production were reduced, with decreased ALX's fungicidal activity. However, in NES there was an increased fungal engulfment, and a reduced ROS production and higher fungal burden. Furthermore, exogenous mannose decreased phagocytosis of Tr conidia, and divalent cations induced ROS production and increased ALX's fungicidal activity. Interestingly, phagocytosis was reduced in the presence of cytoskeleton inhibitor, but exocytosis was increased, suggesting that Tr conidia may have alternative pathways to escape ALX's cells.

CONCLUSION

A castellanii is a proper model for studying Tr-FLA interaction, since ALX can engulf, produce ROS and kill Tr, and all these parameters are influenced by an encystation stimulus and divalent cations. Moreover, this interaction is likely to occur in the environment implicating in the adaptation to environmental stressful conditions in both organisms.

Trichophyton rubrum Elicits Phagocytic and Pro-inflammatory Responses in Human Monocytes Through Toll-Like Receptor 2

Dermatophytosis is a superficial fungal infection mostly restricted to keratinized tissues such as skin, hair, and nails but with potential to cause invasive or even systemic disease in immunocompromised patients. Trichophyton rubrum is the main etiologic agent, accounting for approximately 80% of the cases. Mononuclear phagocytes respond to pathogens through phagocytosis followed by production of several antimicrobial molecules, such as reactive oxygen and nitrogen species, and failure in doing so may contribute to development of chronic fungal infections. Toll-like receptors (TLRs) located on the surface of phagocytic cells bind either directly to target particles or through opsonizing ligands and trigger an actin-mediated ingestion. Even though the mechanisms involved in TLR-mediated cytokine responses are well established, the contribution of TLR in the recognition of T. rubrum by adherent monocytes remains unclear. Here, we report that phagocytosis of T. rubrum conidia by adherent monocytes is mediated by TLR2. Blockade of TLR2 by neutralizing antibodies impaired the fungicidal activity of monocytes as well their secretion of tumor necrosis factor (TNF)-α, but neither nitric oxide (NO) production nor interleukin (IL)-10 secretion was disturbed. So far, our data suggest that TLR2 is required for efficient conidial phagocytosis, and the absence of TLR2 signaling in human monocytes may impair the subsequent inflammatory response. These findings expand our understanding of phagocyte modulation by this important fungal pathogen and may represent a potential target for interventions aiming at enhancing antifungal immune responses.

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.

Dichotomous response of Malassezia-infected macrophages to Malassezia pachydermatis and Malassezia furfur

Malassezia pachydermatis and Malassezia furfur are lipophilic yeasts of the cutaneous microbiome, although these organisms are occasionally responsible for serious invasive infections in neonates. Since phagocytosis is an important mechanism mediating the adaptive immune response, here we evaluated the phagocytosis capacity and production of nitric oxide and cytokine by macrophages after challenged with M. furfur CBS-1878 and M. pachydermatis CBS-1696. The phagocytic indexes was determined using RAW 264.7 cultivated or not with M. furfur or M. pachydermatis in the concentrations of 5:1 or 2:1 (yeasts:macrophages ratio) for 6 h, 24 h, and 48 h following the challenges. Evaluation of nitric oxide and pro- and anti-inflammatory cytokines (interleukin [IL]-2, IL-4, IL-6, IL-10, IL-17A, interferon (IFN)-γ and tumor necrosis factor [TNF]-α) by Griess method and flow cytometry, respectively, were performed in the different intervals by collecting the cell culture supernatant. Results showed a higher phagocytic index in the 5:1 ratio in 24 h for both species. Malassezia pachydermatis-infected macrophages had superior phagocytic indexes than M. furfur-infected macrophages. Phagocytosis evaluation at 48 h showed significant microorganisms proliferation and macrophages death, particularly in macrophages infected with M. pachydermatis, suggesting yeast evasion mechanism. Significant variations in the nitric oxide production were observed in macrophages infected with both species. Levels of TNF-α and IL-4 cytokines have increased in M. furfur and M. pachydermatis macrophage-infected cultures, respectively. The low microbicidal activity and the presence of pro- and anti-inflammatory cytokines reinforce the dichotomous character of the relation of these yeasts with the host, acting as a commensal in the cutaneous microbiome or causing infection.

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.

An invertebrate infection model for evaluating anti-fungal agents against dermatophytosis

Animal models of pathogenic infection are needed to evaluate candidate compounds for the development of anti-infectious drugs. Dermatophytes are pathogenic fungi that cause several infectious diseases. We established a silkworm dermatophyte infection model to evaluate anti-fungal drugs. Injection of conidia of the dermatophyte Arthroderma vanbreuseghemii into silkworms was lethal. A. vanbreuseghemii conidia germinated in liquid culture were more potent against silkworms than non-germinated conidia. Germinated conidia of other dermatophytes, Arthroderma benhamiae, Trichophyton rubrum, and Microsporum canis, also killed silkworms. Injection of heat-treated germinated A. vanbreuseghemii conidia did not kill silkworms, suggesting that only viable fungi are virulent. Injecting terbinafine or itraconazole, oral drugs used clinically to treat dermatophytosis, into the silkworm midgut had therapeutic effects against infection with germinated A. vanbreuseghemii conidia. When silkworms were injected with A. vanbreuseghemii expressing enhanced green fluorescent protein (eGFP), mycelial growth of the fungus was observed in the fat body and midgut. Injection of terbinafine into the silkworm midgut, which corresponds to oral administration in humans, inhibited the growth of A. vanbreuseghemii expressing eGFP in the fat body. These findings suggest that the silkworm infection model with eGFP-expressing dermatophytes is useful for evaluating the therapeutic activity of orally administered anti-fungal agents against dermatophytes.

Topical nitric oxide releasing nanoparticles are effective in a murine model of dermal Trichophyton rubrum dermatophytosis

Systemic therapies are preferred for treating dermal dermatophytosis due to inadequate penetration of topical agents. However, systemic antifungals are associated with off-target effects and limited tissue penetration, and antimicrobial resistance is a growing concern. To address this, we investigated topical nitric oxide-releasing nanoparticles (NO-np), which have been used against superficial fungal infections and bacterial abscesses. In addition to enhanced penetration and permeation conferred by nanoparticles, nitric oxide, a broad-spectrum multi-mechanistic antimicrobial agent, offers decreased likelihood of resistance development. In the current study, NO-np inhibited Trichophyton rubrum in vitro, as well as in a murine model of dermal dermatophytosis. In mice, NO-np reduced fungal burden after three days, with complete clearance after seven. Furthermore, NO-np decreased tissue IL-2, 6, 10 and TNFα, indicating earlier attenuation of the host inflammatory response and decreased tissue morbidity. Thus, topical NO-np represent an attractive alternative to systemic therapy against dermal T. rubrum infection.

The Immunomodulatory Effect of Trichophyton Rubrum Exoantigens in the Treatment of Experimental Septic Arthritis

Background:

Understanding the nature and function of fungal exoantigens might lead to novel approaches in the treatment and prophylaxis of some infectious diseases. Septic arthritis represents a serious problem for medicine due to the high incidence rate and severe complications.

Objective:

The present study aimed at assessing the immunomodulatory effects of Trichophyton rubrum culture filtrate as a novel compound in experimental septic arthritis.

Method:

The septic arthritis was haematogenously induced in Sprague-Dawley rats by a single intravenous injection of 10⁹ colony forming units of the human clinical isolate Staphylococcus aureus producing toxic shock syndrome toxin-1. Trichophyton rubrum culture filtrate at two different doses 20 and 40 mg/kg was administered intraperituneally two days after bacterial inoculation in the treatment groups and concurrently with the appearance of clinical signs in the patient groups. The administration of Trichophyton rubrum solution was continued every other day for 10 injections.

Results:

The clinical evaluation showed that Trichophyton rubrum-treated rats were significantly protected from disease development compared with untreated controls. This finding was correlated with results of radiological evaluation of the involved joints. Although, the inflammatory cell infiltration, cartilage/bone destruction and synovial hypertrophy had been decreased in the treatment groups in comparison with arthritic controls however, the histological changes were not significant in these two groups.

Conclusion:

It is possible that Trichophyton rubrum antigens may play a role in modulating the immune responses and would be efficient in septic arthritis treatment.

TLR2-/- Mice Display Increased Clearance of Dermatophyte Trichophyton mentagrophytes in the Setting of Hyperglycemia

Dermatophytosis is one of the most common human infections affecting both immunocompetent individuals and immunocompromised patients, in whom the disease is more aggressive and can reach deep tissues. Over the last decades, cases of deep dermatophytosis have increased and the dermatophyte-host interplay remains poorly investigated. Pattern recognition molecules, such as Toll-like receptors (TLR), play a crucial role against infectious diseases. However, there has been very little research reported on dermatophytosis. In the present study, we investigated the role of TLR2 during the development of experimental deep dermatophytosis in normal mice and mice with alloxan-induced diabetes mellitus, an experimental model of diabetes that exhibits a delay in the clearance of the dermatophyte, Trichophyton mentagrophytes (Tm). Our results demonstrated that inoculation of Tm into the footpads of normal mice increases the expression of TLR2 in CD115⁺Ly6C^high blood monocytes and, in hypoinsulinemic-hyperglycemic (HH) mice infected with Tm, the increased expression of TLR2 was exacerbated. To understand the role of TLR2 during the development of murine experimental deep dermatophytosis, we employed TLR2 knockout mice. Tm-infected TLR2^-/- and TLR2^+/+ wild-type mice exhibited similar control of deep dermatophytic infection and macrophage activity; however, TLR2^-/- mice showed a noteworthy increase in production of IFN-γ, IL-10, and IL-17, and an increased percentage of splenic CD25⁺Foxp3⁺ Treg cells. Interestingly, TLR2^-/- HH-Tm mice exhibited a lower fungal load and superior organization of tissue inflammatory responses, with high levels of production of hydrogen peroxide by macrophages, alongside low TNF-α and IL-10; high production of IL-10 by spleen cells; and increased expansion of Tregs. In conclusion, we demonstrate that TLR2 diminishes the development of adaptive immune responses during experimental deep dermatophytosis and, in a diabetic scenario, acts to intensify a non-protective inflammatory response.

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.

Severe Dermatophytosis and Acquired or Innate Immunodeficiency: A Review

Dermatophytes are keratinophilic fungi responsible for benign and common forms of infection worldwide. However, they can lead to rare and severe diseases in immunocompromised patients. Severe forms include extensive and/or invasive dermatophytosis, i.e., deep dermatophytosis and Majocchi’s granuloma. They are reported in immunocompromised hosts with primary (autosomal recessive CARD9 deficiency) or acquired (solid organ transplantation, autoimmune diseases requiring immunosuppressive treatments, HIV infection) immunodeficiencies. The clinical manifestations of the infection are not specific. Lymph node and organ involvement may also occur. Diagnosis requires both mycological and histological findings. There is no consensus on treatment. Systemic antifungal agents such as terbinafine and azoles (itraconazole or posaconazole) are effective. However, long-term outcome and treatment management depend on the site and extent of the infection and the nature of the underlying immunodeficiency.

Relationship among Short and Long Term of Hypoinsulinemia-Hyperglycemia, Dermatophytosis, and Immunobiology of Mononuclear Phagocytes

Dermatophytes are fungi responsible for causing superficial infections. In patients with diabetes mellitus (DM), dermatophytosis is usually more severe and recurrent. In the present study, we aimed to investigate the influence of short and long term hypoinsulinemia-hyperglycemia (HH) during experimental infection by Trichophyton mentagrophytes as well as alterations in the mononuclear phagocytes. Our results showed two distinct profiles of fungal outcome and immune response. Short term HH induced a discrete impaired proinflammatory response by peritoneal adherent cells (PAC) and a delayed fungal clearance. Moreover, long term HH mice showed low and persistent fungal load and a marked reduction in the production of TNF-α by PAC. Furthermore, while the inoculation of TM in non-HH mice triggered high influx of Gr1⁺ monocytes into the peripheral blood, long term HH mice showed low percentage of these cells. Thus, our results demonstrate that the time of exposure of HH interferes with the TM infection outcome as well as the immunobiology of mononuclear phagocytes, including fresh monocyte recruitment from bone marrow and PAC activity.

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.

IL-1 signaling inhibits Trichophyton rubrum conidia development and modulates the IL-17 response in vivo

Dermatophytosis are one of the most common fungal infections in the world. They compromise keratinized tissues and the main etiological agent is Trichophyton rubrum. Macrophages are key cells in innate immunity and prominent sources of IL-1β, a potent inflammatory cytokine whose main production pathway is by the activation of inflammasomes and caspase-1. However, the role of inflammasomes and IL-1 signaling against T.rubrum has not been reported. In this work, we observed that bone marrow-derived macrophages produce IL-1β in response to T.rubrum conidia in a NLRP3-, ASC- and caspase-1-dependent fashion. Curiously, lack of IL-1 signaling promoted hyphae development, uncovering a protective role for IL-1β in macrophages. In addition, mice lacking IL-1R showed reduced IL-17 production, a key cytokine in the antifungal defense, in response to T.rubrum. Our findings point to a prominent role of IL-1 signaling in the immune response to T.rubrum, opening the venue for the study of this pathway in other fungal infections.

Low DEFB4 copy number and high systemic hBD-2 and IL-22 levels are associated with dermatophytosis

Dermatophytes initiate dermatophytosis, but susceptibility to infection is dictated by host genetic factors, although the role of some of these-such as human beta-defensin 2 (hBD-2) genomic (DEFB4) copy number (CN) variation and its induction by IL-22-remains unclear. This was investigated in this cross-sectional study in 442 unrelated Caucasian subjects, including 195 healthy controls and 247 dermatophytosis patients who were divided into five subgroups according to clinical presentation. DNA samples were evaluated for DEFB4 CN variation by relative quantification using the comparative CT method, and serum hBD-2 and IL-22 levels were determined by ELISA. DEFB4 CN in patients was significantly lower and, except in the tinea cruris subgroup, serum hBD-2 levels were higher than in controls. The positive correlation between hBD-2 levels and DEFB4 CN observed in controls was not detected in patients, who also had higher serum IL-22 levels that were positively correlated with hBD-2 levels. Moreover, unlike in control subjects, the serum IL-22 level was negatively correlated with DEFB4 CN in patients. Taken together, these findings suggest an association between decreased DEFB4 CN, elevated serum hBD-2 and IL-22 levels, and dermatophytosis, underscoring a gene/cytokine interaction in the occurrence of this infection.

Dermatomycoses and inflammation: The adaptive balance between growth, damage, and survival

Dermatomycosis is characterized by both superficial and subcutaneous infections of keratinous tissues and mucous membranes caused by a variety of fungal agents, the two most common classes being dermatophytes and yeasts. Overall, the stepwise process of host infection is similar among the main dermatomycotic species; however, the species-specific ability to elicit a host reaction upon infection is distinct. Yeasts such as Candida albicans elicit a relatively low level of host tissue damage and inflammation during pathogenic infection, while dermatophytes may induce a higher level of tissue damage and inflammatory reaction. Both pathogens can, however, manipulate the host's immune response, ensuring survival and prolonging chronic infection. One common element of most dermatomycotic infections is the disease burden caused by inflammation and associated signs and symptoms, such as erythema, burning and pruritus. There is a strong clinical rationale for the addition of a topical corticosteroid agent to an effective antimycotic therapy, especially in patients who present with inflammatory dermatomycoses (e.g., tinea inguinalis). In this review, we aim to compare the pathogenesis of common dermatomycotic species, including Candida yeasts (Candida albicans), dermatophytes (Trichophyton, Epidermophyton or Microsporum species), and other pathogenic yeasts (Malassezia), with a special focus on unique species-specific aspects of the respective infection processes, the interaction between essential aspects of pathogenic infection, the different roles of the host inflammatory response, and the clinical consequences of the infection-related tissue damage and inflammation. We hope that a broader understanding of the various mechanisms of dermatomycoses may contribute to more effective management of affected patients.

Assessment of immunogenicity and protective efficacy of Microsporum canis secreted components coupled to monophosphoryl lipid-A adjuvant in a vaccine study using guinea pigs

Microsporum canis is the most common dermatophyte in pets and is of zoonotic importance but currently there is no effective vaccine available to prevent dermatophytosis. The aim of this work was to assess the immunogenicity and protective efficacy of secreted components (SC) from M. canis adjuvanted with the monophosphoryl lipid-A (MPLA), in a vaccine study using the guinea pig as an experimental model. Animals were vaccinated with either the SC adjuvanted with the MPLA, the MPLA adjuvant alone or PBS three times at two-week intervals, until 42 days prior to M. canis infection. A blind evaluation of dermatophytosis symptoms development and fungal persistence in skin was monitored weekly. The antibody response towards the SC and the levels of Interferon (IFN)γ and Interleukin-4 expressed in peripheral blood mononuclear cells were assessed along or at the end of the study period respectively. The animals that received MPLA had a significantly lower clinical score than those inoculated with PBS. However, no significant difference was observed between the guinea pigs vaccinated with the SC adjuvanted with the MPLA and those having received MPLA alone. The results also showed that vaccination induced a strong antibody response towards the SC and an increase in IFNγ mRNA level. Our results show that the MPLA adjuvant used in this vaccine study can induce per se a partial protection against a M. canis infection. Although they induce a delayed-type hypersensitivity reaction in guinea pigs, the SC do not confer a protection under the present experimental conditions.

Monocyte-derived dendritic cells from patients with dermatophytosis restrict the growth of Trichophyton rubrum and induce CD4-T cell activation

Dermatophytes are the most common agents of superficial mycoses that are caused by mold fungi. Trichophyton rubrum is the most common pathogen causing dermatophytosis. The immunology of dermatophytosis is currently poorly understood. Recently, our group investigated the interaction of T. rubrum conidia with peritoneal mouse macrophages. We found that macrophages phagocytose T. rubrum conidia resulted in a down-modulation of class II major histocompatibility complex (MHC) antigens and in the expression of co-stimulatory molecules. Furthermore, it induced the production of IL-10, and T. rubrum conidia differentiated into hyphae that grew and killed the macrophages after 8 hrs of culture. This work demonstrated that dendritic cells (DCs) and macrophages, from patients or normal individuals, avidly interact with pathogenic fungus T. rubrum. The dermatophyte has two major receptors on human monocyte-derived DC: DC-SIGN and mannose receptor. In contrast macrophage has only mannose receptor that participates in the phagocytosis or bound process. Another striking aspect of this study is that unlike macrophages that permit rapid growth of T. rubrum, human DC inhibited the growth and induces Th activation. The ability of DC from patients to interact and kill T. rubrum and to present Ags to T cells suggests that DC may play an important role in the host response to T. rubrum infection by coordinating the development of cellular immune response.

IFN-γ impairs Trichophyton rubrum proliferation in a murine model of dermatophytosis through the production of IL-1β and reactive oxygen species

Trichophyton rubrum is the main etiological agent of dermatophytosis, an infection of the skin that affects millions of people worldwide. In this study, we developed a murine model of the dermatophytosis caused by T. rubrum in which C57BL/6 wild-type, interleukin (IL)-12(-/-), and interferon-gamma (IFN-γ(-/-)) mice were inoculated with 1 × 10(6) conidia/animal. The fungal burden, myeloperoxidase and N-acetylglucosaminidase activities, cytokine and chemokine profiles, and histopathology of the skin were evaluated on the seventh and fourteenth days post infection. Phagocytic indices, intracellular proliferation rates, and oxidative bursts generated by macrophages from WT and IFN-γ(-/-) mice were determined. On day 7 post infection, higher fungal burdens were observed comparison with burdens on day 14 post infection. The IL-12(-/-) and IFN-γ(-/-) mice showed higher fungal burdens on the skin and lower levels of IL-1β. Conversely, the WT mice showed lower fungal burdens with higher production of TNF-α, IL-1β, and chemokine ligand 1/keratinocyte chemoattractant (CXCL1/KC). The macrophages from WT mice proved to be more efficient at engulfing and killing T. rubrum conidia through the production of reactive oxygen species. The results show that our model is a useful tool for understanding the pathogenesis of dermatophytosis caused by T. rubrum and that IL-12 and IFN-γ are pivotal in controlling the infection through the recruitment and activation of neutrophils and macrophages.

Refractory Trichophyton rubrum infection in lamellar ichthyosis

A 10-month-old boy with congenital lamellar ichthyosis presented with a chronic Trichophyton rubrum infection. There was no history of atopy or immunosuppression, and examination revealed high total immunoglobulin E (IgE) with a positive specific IgE for T. rubrum. Multiple treatments with fluconazole were necessary to control the infection. T. rubrum is present worldwide and is responsible for the vast majority of chronic dermatophytosis. Lamellar ichthyosis is a risk factor for chronic dermatophytosis because of excessive keratin and the barrier defect. A delayed-type hypersensitivity reaction to T. rubrum is associated with cure, whereas immediate hypersensitivity and IgE are not protective and may lead to chronic infection. Atopy and the Th2 profile therefore seem to be associated with chronic dermatophytosis. The association between ichthyosis and atopy is well documented. T. rubrum also has an interesting ability to evade immunity, which helps explain the chronic infection. Finally, in ichthyosis, it is likely that fluconazole has difficulty penetrating the acanthotic stratum corneum, which explains treatment failure. We report this case to alert clinicians to the possible association between lamellar ichthyosis and chronic dermatophytosis and to report the difficulties of management.

Dermatophyte-host relationship of a murine model of experimental invasive dermatophytosis

Recognizing the invasive potential of the dermatophytes and understanding the mechanisms involved in this process will help with disease diagnosis and with developing an appropriate treatment plan. In this report, we present the histopathological, microbiological and immunological features of a model of invasive dermatophytosis that is induced by subcutaneous infection of Trichophyton mentagrophytes in healthy adult Swiss mice. Using this model, we observed that the fungus rapidly spreads to the popliteal lymph nodes, spleen, liver and kidneys. Similar to the human disease, the lymph nodes were the most severely affected sites. The fungal infection evoked acute inflammation followed by a granulomatous reaction in the mice, which is similar to what is observed in patients. The mice were able to mount a Th1-polarized immune response and displayed IL-10-mediated immune regulation. We believe that the model described here will provide valuable information regarding the dermatophyte-host relationship and will yield new perspective for a better understanding of the immunological and pathological aspects of invasive dermatophytosis.

Trichophyton rubrum manipulates the innate immune functions of human keratinocytes

Evasion or subversion of host immune responses have been shown for a variety of microorganisms, and this might be the case for Trichophyton rubrum, the most common pathogenic fungus causing chronic dermatophytosis in humans. Keratinocytes, the main epidermal cells, have important roles as a first defense against microbial challenges in local immune reactions. Epidermal keratinocytes express several Toll-like receptors and produce host defense peptides, cytokines and chemokines in response to various stimuli. We analyzed the expression of Toll-Like receptor TLR2, TLR4, TLR6, and Human Beta Defensin (HBD)-1, HBD-2, Interleukin IL-1b and IL-8 production, when exposing primary keratinocyte cultures to T. rubrum. We observed changes in size and granularity of keratinocytes stimulated with either whole conidia or conidial homogenates compared to other treatments. Intact conidia decreased keratinocytes’ TLR2 and TLR6 expression without affecting that of TLR4, while conidial homogenates increased the expression of these three receptors. Interestingly, whole conidia decreased HBD-1 and HBD-2 production, whereas conidial homogenate increased it. No changes were observed in IL-1b and IL-8 production after stimulation with conidia or conidial homogenate. CONCLUSIONS. Our results suggest that: 1) Keratinocytes can recognize and respond to cell wall components of T. rubrum; 2) Viable intact conidia inhibit TLR-2 and TLR6 expression and decrease HBD-1 and HBD-2 production; 3) Conidial homogenate from T. rubrum increases the expression of TLR2, TLR4 and TLR6 and induces HBD-1 and HBD-2 production; 4) Therefore, innate immune functions of keratinocytes as the first level of local skin immunity are apparently manipulated by T. rubrum, likely to ensure its establishment, persistence and survival.

Dermatophyte virulence factors: identifying and analyzing genes that may contribute to chronic or acute skin infections

Dermatophytes are prevalent causes of cutaneous mycoses and, unlike many other fungal pathogens, are able to cause disease in immunocompetent individuals. They infect keratinized tissue such as skin, hair, and nails, resulting in tinea infections, including ringworm. Little is known about the molecular mechanisms that underlie the ability of these organisms to establish and maintain infection. The recent availability of genome sequence information and improved genetic manipulation have enabled researchers to begin to identify and study the role of virulence factors of dermatophytes. This paper will summarize our current understanding of dermatophyte virulence factors and discuss future directions for identifying and testing virulence factors.

Micoses superficiais e os elementos da resposta imune

As micoses superficiais são prevalentes em todo o mundo, geralmente ocasionadas por dermatófitos e restritas à camada córnea. A resposta imunológica do hospedeiro às infecções dos fungos dermatófitos depende basicamente das defesas do hospedeiro a metabólitos do fungo, da virulência da cepa ou da espécie infectante e da localização anatômica da infecção. Serão revistos alguns dos fatores da defesa imunológica do hospedeiro que influenciam na eficácia da resposta imune. Em especial, a participação dos receptores de padrão de reconhecimento (PRRs), tais como os receptores toll-like ou os da família lectina (DC-SIGN e dectin-2), que participam da resposta imune inata, conferindo-lhe especificidade e definindo o padrão da resposta imune como um todo. O predomínio celular ou humoral da resposta imune definirá o quadro clínico e o prognóstico da infecção, levando à cura ou cronicidade

Experimental medical mycological research in Latin America - a 2000-2009 overview

An overview of current trends in Latin American Experimental Medical Mycological research since the beginning of the 21(st) century is done (search from January 2000 to December 2009). Using the PubMed and LILACS databases, the authors have chosen publications on medically important fungi which, according to our opinion, are the most relevant because of their novelty, interest, and international impact, based on research made entirely in the Latin American region or as part of collaborative efforts with laboratories elsewhere. In this way, the following areas are discussed: 1) molecular identification of fungal pathogens; 2) molecular and clinical epidemiology on fungal pathogens of prevalence in the region; 3) cell biology; 4) transcriptome, genome, molecular taxonomy and phylogeny; 5) immunology; 6) vaccines; 7) new and experimental antifungals.

Pathogenesis of tinea

Dermatophytes are hyphomycetes that can degrade keratin. This puts them in a position to cause infections of the keratin-containing superficial skin. The resulting clinical picture is called tinea. The pathogenesis and course of tinea is decisively determined by pathogen-related factors and by the defense mechanisms of the host. An infection starts with an adherence of fungal propagules, followed by the formation of hyphae that can spread within the tissue. This process is accompanied by a release of fungal enzymes and other pathogenic factors. Next keratinocytes are activated, the epidermal barrier is destroyed, epidermal proliferation is enhanced and defensins are expressed within the epidermis. In addition, innate and specific immune responses are initiated, involving neutrophilic granulocytes, macrophages, antibodies and T cells. The cellular mechanisms are thought to be crucial for healing. Special conditions apply to nail infections, because within nail plates the fungi are not accessible to effective defense mechanisms, as well as to infections of hair follicles that contain specific concentrations of steroid hormones. Dermatophytes that penetrate into the dermis can cause granulomatous inflammatory reactions and systemic immune reactions are supposed to be a trigger of so-called id reactions.

Pathogenesis of dermatophytosis and tinea versicolor

Dermatophytoses are infections caused by keratinophilic fungi known as dermatophytes. Several steps are required for infection to take place: contact, adherence, and invasion of keratin layers. The severity of the infection depends on the type of agent, environmental factors, and the host immunologic status. Tinea versicolor is caused by the Malassezia spp yeasts, which are microorganisms that belong to normal biota in seborrheic areas, but some contributing factors, such as the application of oily preparations, creams, an increase in ambient humidity, corticosteroid abuse, or genetic predisposition can induce its overgrowth in both filamentous and yeast structures. Exposure to sunlight stimulates the production of azelaic acid, which causes the appearance of hypopigmented spots. Currently, there is no scientific explanation for hyperpigmented lesions.

Immunization and dermatophytes

PURPOSE OF REVIEW

Despite the availability of effective vaccines for certain animal species, vaccination against dermatophytosis requires improvement and further development in both animals and humans. This review provides an update on the current situation and focuses on recent advances in host-dermatophyte relationships that could have implications for future vaccination against the most prevalent of the fungal diseases.

RECENT FINDINGS

Numerous dermatophytic virulence factors have recently been isolated and characterized at the molecular level, notably secreted proteases involved in the invasion of the keratin network. Their precise roles in the different steps of the infectious process and in immunopathogenesis are being studied, while all aspects of the host immune response against dermatophytes, including the innate response, are becoming increasingly documented. In addition, new molecular tools are now available for studying dermatophytes, which will accelerate research on this topic.

SUMMARY

The growth of knowledge concerning all aspects of the host-dermatophyte relationship should contribute towards sound strategies for the development of effective and safe vaccines against dermatophytosis.

Pathogenesis of dermatophytosis

Despite the superficial localization of most dermatophytosis, host-fungus relationship in these infections is complex and still poorly elucidated. Though many efforts have been accomplished to characterize secreted dermatophytic proteases at the molecular level, only punctual insights have been afforded into other aspects of the pathogenesis of dermatophytosis, such as fungal adhesion, regulation of gene expression during the infection process, and immunomodulation by fungal factors. However, new genetic tools were recently developed, allowing a more rapid and high-throughput functional investigation of dermatophyte genes and the identification of new putative virulence factors. In addition, sophisticated in vitro infection models are now used and will open the way to a more comprehensive view of the interactions between these fungi and host epidermal cells, especially keratinocytes.