Feline polymorphonuclear neutrophils produce pro-inflammatory cytokines following exposure to Microsporum canis

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.

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.

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.

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.

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.

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

BACKGROUND

Dermatophytoses are common but poorly understood skin infections. Most in vivo studies have been performed using the guinea pig as the experimental animal model, which has several limitations.

OBJECTIVES

To develop a mouse model of dermatophytosis suitable for multiple purposes, including the investigation of immunity against dermatophytes.

MATERIALS AND METHODS

Two peculiar fungal species, Arthroderma benhamiae and A. vanbreuseghemii, isolated from tinea in humans having contact with rodents were used for epicutaneous inoculation. During the infection, clinical and histopathological follow-up were performed. The recruitment of immune cells was evaluated by immunofluorescence staining and the levels of cytokine mRNA were quantified by quantitative reverse transcriptase-polymerase chain reaction in the skin of infected mice.

RESULTS

The skin symptoms and microscopic lesions, including the colonization of keratinized epidermal and follicular structures by both dermatophytes, were highly similar to those observed in guinea pig infection models and in natural infections, mimicking acute superficial tinea in humans. The dermal inflammatory cellular infiltrate consisted of macrophages, dendritic cells and especially polymorphonuclear neutrophils, which are one of the histological 'clues' to the diagnosis of dermatophytosis. The in situ cytokine profile was characterized by the overexpression of transforming growth factor-β, interleukin (IL)-1β and IL-6 mRNA during infection, suggesting a role of the T-helper 17 pathway in the establishment of immunity.

CONCLUSIONS

Our new reproducible and validated mouse model of dermatophytosis is a modern in vivo tool that allows a more in-depth understanding of the pathogenesis of human dermatophyte infections.

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.

Autophagy mediates neutrophil responses to bacterial infection

Neutrophils constitute the first line of cellular defense against pathogens and autophagy is a fundamental cellular homeostasis pathway that operates with the intracellular degradation/recycling system. Induction of the autophagic process in neutrophils, in response to invading pathogens, constitutes a crucial mechanism in innate immunity. Exploration of autophagy has greatly progressed and diverse strategies have been reported for studying this molecular process in different biological systems; especially in infectious and inflammatory diseases. Furthermore, the role of autophagy in neutrophils, during pathogenic infection, continues to be of interest, due to the role of the cell in immunity function, its recruitment to the site of infection and its implication in inflammatory diseases. This review focuses on the known role of autophagy in neutrophils defence against pathogenic infections. A more detailed discussion will concern the recent findings highlighting the role of autophagy in inflammation and cell death in infected neutrophils.

Evaluation of trace elements, oxidant/antioxidant status, vitamin C and β-carotene in dogs with dermatophytosis

The aim of the study was to determine zinc, copper and iron levels, erythrocyte oxidant/antioxidant status, vitamin C and β-carotene in dogs with dermatophytosis. A total of 23 dogs with clinically established diagnosis of dermatophytosis by trichogram and positive fungal culture and six dogs as control were included in this study. On cultural examination 52.17% fungal isolates were found to be Microsporum canis, 30.43% were Trichophyton mentagrophytes and 17.39% were M. gypseum. In comparison to healthy control, the dogs with dermatophytosis had significantly lower levels of zinc (P < 0.01), copper (P < 0.05), β-carotene and vitamin C levels (P < 0.05) and activities of superoxide dismutase (SOD) (P < 0.05) and catalase (P < 0.01), whereas the iron (P < 0.05) and malondialdehyde (MDA) (P < 0.01) levels were significantly increased. On correlation analysis, SOD activity was observed to be positively correlated (P < 0.05) with zinc and copper in both healthy and dermatophytosis affected dogs. In dermatophytosis affected dogs the MDA levels were negatively correlated (P < 0.05) with iron, β-carotene levels and the activities of antioxidant enzymes; SOD and catalase. Our results demonstrated that dermatophytosis in dogs is associated with significant alteration in oxidant/antioxidant balance and trace elements. It might be secondary consequence of dermatophytosis infection or contributing factor in its pathogenesis.

Pathogenic fungus Microsporum canis activates the NLRP3 inflammasome

Microsporum canis is a pathogenic fungus with worldwide distribution that causes tinea capitis in animals and humans. M. canis also causes invasive infection in immunocompromised patients. To defy pathogenic fungal infection, the host innate immune system is the first line of defense. As an important arm of innate immunity, the inflammasomes are intracellular multiprotein complexes that control the activation of caspase-1, which cleaves proinflammatory cytokine pro-interleukin-1β (IL-1β) into its mature form. To determine whether the inflammasome is involved in the host defense against M. canis infection, we challenged human monocytic THP-1 cells and mouse dendritic cells with a clinical strain of M. canis isolated from patients with tinea capitis. We found that M. canis infection triggered rapid secretion of IL-1β from both THP-1 cells and mouse dendritic cells. Moreover, by using gene-specific shRNA and competitive inhibitors, we determined that M. canis-induced IL-1β secretion was dependent on NLRP3. The pathways proposed for NLRP3 inflammasome activation, namely, cathepsin B activity, K(+) efflux, and reactive oxygen species production, were all required for the inflammasome activation triggered by M. canis. Meanwhile, Syk, Dectin-1, and Card9 were found to be involved in M. canis-induced IL-1β secretion via regulation of pro-IL-1β transcription. More importantly, our data revealed that M. canis-induced production of IL-1β was dependent on the NLRP3 inflammasome in vivo. Together, this study unveils that the NLRP3 inflammasome exerts a critical role in host innate immune responses against M. canis infection, and our data suggest that diseases that result from M. canis infection might be controlled by regulating the activation of inflammasomes.