Apoptosis-Associated Speck-like Protein Containing a Caspase Recruitment Domain Inflammasomes Mediate IL-1β Response and Host Resistance to Trypanosoma cruzi Infection

The innate immune response to Trypanosoma cruzi infection comprises several pattern recognition receptors (PRRs), including TLR-2, -4, -7, and -9, as well as the cytosolic receptor Nod1. However, there are additional PRRs that account for the host immune responses to T. cruzi. In this context, the nucleotide-binding oligomerization domain-like receptors (NLRs) that activate the inflammasomes are candidate receptors that deserve renewed investigation. Following pathogen infection, NLRs form large molecular platforms, termed inflammasomes, which activate caspase-1 and induce the production of active IL-1 beta and IL-18. In this study, we evaluated the involvement of inflammasomes in T. cruzi infection and demonstrated that apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) inflammasomes, including NLR family, pyrin domain-containing 3 (NLRP3), but not NLR family, caspase recruitment domain-containing 4 or NLR family, pyrin domain-containing 6, are required for triggering the activation of caspase-1 and the secretion of IL-1 beta. The mechanism by which T. cruzi mediates the activation of the ASC/NLRP3 pathway involves K+ efflux, lysosomal acidification, reactive oxygen species generation, and lysosomal damage. We also demonstrate that despite normal IFN-gamma production in the heart, ASC(-)/(-) and caspase-1(-)/(-) infected mice exhibit a higher incidence of mortality, cardiac parasitism, and heart inflammation. These data suggest that ASC inflammasomes are critical determinants of host resistance to infection with T. cruzi.