Keratinocyte Response to Infection with Sporothrix schenckii

Inflammation and epigenetics of sporotrichosis disease

Sporotrichosis, a fungal disease, is caused by exposure to soil that harbors Sporothrix schenckii or through inhalation of fungal spores. Skin is the most frequently exposed organ making sporotrichosis a primarily dermal disease. Many described reports in the literature suggest a connection of sporotrichosis with cutaneous squamous cell carcinoma with some connection between initial sporotrichosis diagnosis and treatment followed by development of cutaneous squamous cell carcinoma at the very site. Conversely, there is also evidence for sporotrichosis subsequent to skin cancer diagnosis, even after cancer chemotherapy, which points towards weakening of immune response by cancer chemotherapy leading to attack and infection by Sporothrix schenckii. We also propose and focus on inflammation as the connection between sporotrichosis, cancer and even the metastatic spread of cancer. Inflammation-associated IL-6, IFN-γ, natural killer cells and M2-macrophages possibly mechanistically link sporotrichosis with cancer, particularly cutaneous squamous cell carcinoma. These inflammation related factors/cells are regulated epigenetically raising the possibility of epigenetic regulation of sporotrichosis, which has not been described yet in the available literature. Clinical management of inflammation may thus be effective strategy not just against sporotrichosis but also the related onset of cutaneous squamous cell carcinoma and possibly its metastasis to lymph nodes.

Differential Recognition of Clinically Relevant Sporothrix Species by Human Mononuclear Cells

Sporotrichosis is a human and animal fungal infection distributed worldwide that is caused by the thermodimorphic species of the Sporothrix pathogenic clade, which includes Sporothrix brasiliensis, Sporothrix schenckii, and Sporothrix globosa. The cell wall composition and the immune response against the Sporothrix species have been studied mainly in S. brasiliensis and S. schenckii, whilst little is known about the S. globosa cell wall and the immune response that its components trigger. Therefore, in this study, we aimed to analyze the cell wall composition of S. globosa in three morphologies (germlings, conidia, and yeast-like cells) and the differences in cytokine production when human peripheral blood mononuclear cells (PBMCs) interact with these morphotypes, using S. schenckii and S. brasiliensis as a comparison. We found that S. globosa conidia and yeast-like cells have a higher cell wall chitin content, while all three morphologies have a higher β-1,3-glucan content, which was found most exposed at the cell surface when compared to S. schenckii and S. brasiliensis. In addition, S. globosa has lower levels of mannose- and rhamnose-based glycoconjugates, as well as of N- and O-linked glycans, indicating that this fungal cell wall has species-specific proportions and organization of its components. When interacting with PBMCs, S. brasiliensis and S. globosa showed a similar cytokine stimulation profile, but with a higher stimulation of IL-10 by S. globosa. Additionally, when the inner cell wall components of S. globosa were exposed at the surface or N- and O-glycans were removed, the cytokine production profile of this species in its three morphotypes did not significantly change, contrasting with the S. schenckii and S. brasiliensis species that showed different cytokine profiles depending on the treatment applied to the walls. In addition, it was found that the anti-inflammatory response stimulated by S. globosa was dependent on the activation of dectin-1, mannose receptor, and TLR2, but not TLR4. All of these results indicate that the cell wall composition and structure of the three Sporothrix species in the three morphologies are different, affecting their interaction with human PBMCs and generating species-specific cytokine profiles.

Innate Immune Responses to Sporothrix schenckii: Recognition and Elimination

Sporothrix schenckii (S. schenckii), a ubiquitous thermally dimorphic fungus, is the etiological agent of sporotrichosis, affecting immunocompromised and immunocompetent individuals. Despite current antifungal regimens, sporotrichosis results in prolonged treatment and significant mortality rates in the immunosuppressed population. The innate immune system forms the host's first and primary line of defense against S. schenckii, which has a bi-layered cell wall structure. Many components act as pathogen-associated molecular patterns (PAMPs) in pathogen-host interactions. PAMPs are recognized by pattern recognition receptors (PRRs) such as toll-like receptors, C-type lectin receptors, and complement receptors, triggering innate immune cells such as neutrophils, macrophages, and dendritic cells to phagocytize or produce mediators, contributing to S. schenckii elimination. The ultrastructure of S. schenckii and pathogen-host interactions, including PRRs and innate immune cells, are summarized in this review, promoting a better understanding of the innate immune response to S. schenckii and aiding in the development of protective and therapeutic strategies to combat sporotrichosis.