Crotoxin Upregulating NLRP-3 Inflammasome and IL-18 and Activating CD4+ and CD8+ Lymphocytes in Experimental Encephalitozoon cuniculi Infection

<i>Encephalitozoon cuniculi</i> is an atypical, opportunistic, obligate intracellular fungal pathogen that infects vertebrates. It survives within the host by modulating the host immune response. Crotoxin (CTX), a bioactive compound isolated from the venom of <i>Crotalus durissus terrificus</i>, has been reported to modulate immune responses. This study evaluated the effects of CTX on the immune response of mice infected with <i>E. cuniculi</i>. Mice were immunosuppressed with cyclophosphamide (Cy), infected with <i>E. cuniculi</i> spores, and treated with a single dose of CTX on the day of experimental. The animals were euthanized on day 14 post-infection. Levels of T helper (Th1, Th2, and Th17) cytokines were measured in plasma, and macrophage and lymphocyte populations were analyzed in peritoneal lavage fluid and spleen. In addition, histopathological alterations, hepatic fungal burden, and mRNA expression levels of NLRP3 inflammasome-related genes were assessed. CTX upregulated NLRP3 inflammasome expression and increased IL-18 production, while reducing fungal burden in <i>E. cuniculi</i>-infected mice. Moreover, CTX increased the proportions of macrophages and B cells and enhanced IFN-γ expression in CD4⁺ and CD8⁺ T lymphocytes. Collectively, these findings indicate that CTX reduces fungal load in Cy-immunosuppressed mice infected with <i>E. cuniculi</i> by priming the NLRP3 inflammasome complex and upregulating IL-18 production.