Exogenous Local Hyperthermia at 41℃ Is Effective to Eliminate Mouse Model of Sporotrichosis, Independent of Neutrophil Extracellular Traps Formation

Background: Local hyperthermia is recommended for the treatment of patients with fixed cutaneous sporotrichosis, though the effectiveness and mechanisms of action remain elusive. While neutrophils represent the main inflammatory cells associated with sporotrichosis lesions, the issue of whether hyperthermia is involved with interactions between neutrophils and Sporothrix globosa remains unclear.

Objective: To evaluate the effect of local hyperthermia on sporotrichosis and determine whether local hyperthermia involves effects of neutrophils against Sporothrix.

Methods: For the in vivo study, mice were infected with yeast cells of S. globosa followed by treatment with local hyperthermia. In vitro, an isolated Sporothrix strain was co-cultured with or without neutrophils and subjected under different temperatures. Immunofluorescence was used to assess the formation of neutrophil extracellular trap (NETs) were formed under these different culture conditions and the number of fungi colony forming units were compared.

Results: Hyperthermia was significantly more effective in clearing the lesions in the mouse model, as compared to sham treatment. Neutrophils failed to exert any fungicidal effects against S. globosa in response to hyperthermia. Moreover, NETs were formed after interaction with S. globosa, and the percentage of NETs formed was not significantly different at 41℃ or 37℃.

Conclusion: While hyperthermia could serve as an effective therapy for fixed cutaneous sporotrichosis, this ability does not involve the formation of NETs.