Tryptanthrin promotes keratinocyte and fibroblast responses in vitro after infection with Trichophyton benhamiae DSM6916

Exceedingly virulent pathogens and growing antimicrobial resistances require new therapeutic approaches. The zoophilic dermatophyte Trichophyton benhamiae causes highly inflammatory, cutaneous fungal infections. Recently, it could be shown that the plant-derived alkaloid tryptanthrin (TRP) exhibits strong anti-microbial activities against yeasts and dermatophytes. The aim of this study was to analyse the bioactivity of TRP under infectious conditions using an in-vitro dermatophytosis model employing fibroblasts and keratinocytes infected with T. benhamiae DSM6916. Analyses comprised determination of cell viability, effects on the innate immune response including expression and secretion of pro-inflammatory cytokines/chemokines as well as expression of various antimicrobial peptides (AMP), toll-like receptor (TLR) 2 and proliferation marker MKI67. T. benhamiae caused severe inflammation in the cutaneous cell models. TRP almost fully prevented T. benhamiae-derived damage of dermal fibroblasts and substantially reduced it in epidermal keratinocytes. A distinct down-regulation of the expression and secretion of pro-inflammatory cytokines was observed. Further, TRP promoted AMP expression, especially of HBD2 and HBD3, in keratinocytes even without fungal presence. This study provides crucial evidence that TRP is not only a strong antifungal agent but also potentially modulates the innate immune response. This makes it interesting as a natural antimycotic drug for adjuvant treatment and prevention of fungal re-infection.

First report of tinea corporis caused by Arthroderma benhamiae in Brazil

Arthroderma benhamiae is a zoophilic dermathophyte that can cause highly inflammatory tinea corporis and tinea capitis in humans. This is the first report of a patient with dermatophytosis caused by A. benhamiae in Brazil. The lesion was an erythematous, annular plaque on the lumbar region that appeared few weeks after playing with a street cat in a 19-month-old girl. Initial presumed diagnosis was tinea corporis caused by Microsporum canis. Topical treatments were ineffective and the patient required systemic treatment with griseofulvin. Mycological diagnosis was inconclusive: morphological differentiation between M. canis and Trichophyton benhamiae may be difficult, especially when the latter present yellow colonies. The etiological agent was identified only by ITS sequencing of the isolates aligned with reference strains to A. benhamiae. This report highlights the importance of ITS sequencing in the identification of isolates from some cases of dermatophytosis, because conventional morphological diagnosis may result in misdiagnosis of the agent and delay proper treatment.

Innate immune response of human epidermal keratinocytes and dermal fibroblasts to in vitro incubation of Trichophyton benhamiae DSM 6916

BACKGROUND

Superficial cutaneous infection caused by the zoophilic dermatophyte Trichophyton benhamiae is often associated with a highly inflammatory immune response. As non-professional immune cells, epidermal keratinocytes and dermal fibroblasts contribute to the first line of defence by producing pro-inflammatory cytokines and antimicrobial peptides (AMP).

OBJECTIVE

Purpose of this study was to gain a deeper understanding of the pathogenesis and the fungal-host interaction as not much is known about the innate immune response of these cutaneous cells against T. benhamiae.

METHODS

Using a dermatophytosis model of fibroblasts and keratinocytes incubated with T. benhamiae DSM 6916, analyses included determination of cell viability and cytotoxicity, effects on the innate immune response including expression and secretion of pro-inflammatory cytokines/chemokines and expression of AMP, as well as alterations of genes involved in cell adhesion.

RESULTS

Trichophyton benhamiae DSM 6916 infection led to severe cell damage and direct induction of a broad spectrum of pro-inflammatory cytokines and chemokines in both cutaneous cells. Only keratinocytes differentially up-regulated AMP genes expression after T. benhamiae DSM 6916 infection. Expression of AMPs in fibroblasts was not inducible by fungal infection, whereas their absences potentially contributed to a continuous increase in the fungal biomass on fibroblasts, which in turn was reduced in keratinocytes possibly due to the antimicrobial actions of induced AMPs. On mRNA level, T. benhamiae DSM 6916 infection altered cell-cell contact proteins in keratinocytes, indicating that targeting specific cell-cell adhesion proteins might be part of dermatophytes' virulence strategy.

CONCLUSION

This study showed that in addition to immune cells, keratinocytes and fibroblasts could participate in antimicrobial defence against an exemplary infection with T. benhamiae DSM 6916.