Pathogens are sensed by innate immune receptors that initiate an efficient adaptive immune response upon activation. The elements of the innate immune recognition process for Paracoccidioides brasiliensis include TLR-2, TLR-4, and
dectin-1. However, there are additional receptors necessary for the host immune responses to P. brasiliensis. The
nucleotide-binding oligomerization domain-like receptor (NLRs), which activate
inflammasomes, are candidate receptors that deserve renewed investigation. After pathogen
infection, the NLRs form large signaling platforms called
inflammasomes, which lead to caspase-1 activation and maturation of proinflammatory
cytokines (IL-18 and IL-1β). In this study, we showed that NLR family pyrin domain-containing 3 (Nlrp3) is required to induce caspase-1 activation and further secretion of IL-1β and
IL-18 by P. brasiliensis-infected macrophages. Additionally,
potassium efflux and lysosomal acidification induced by the fungus were important steps in the caspase-1 activation mechanism. Notably, Nlrp3 and caspase-1 knockout mice were more susceptible to
infection than were the wild-type animals, suggesting that the Nlrp3-dependent
inflammasomes contribute to host protection against P. brasiliensis. This protective effect occurred owing to the inflammatory response mediated by
IL-18, as shown by an augmented fungus burden in
IL-18 knockout mice. Taken together, our results show that the Nlrp3
inflammasome is essential for resistance against P. brasiliensis because it orchestrates robust caspase-1 activation and triggers an IL-18-dependent proinflammatory response.