Caspase-1/ASC Inflammasome-Mediated Activation of IL-1β–ROS–NF-κB Pathway for Control of <i>Trypanosoma cruzi</i> Replication and Survival Is Dispensable in NLRP3^−/− Macrophages

<div><p>In this study, we have utilized wild-type (WT), ASC^−/−, and NLRP3^−/− macrophages and inhibition approaches to investigate the mechanisms of inflammasome activation and their role in <i>Trypanosoma cruzi</i> infection. We also probed human macrophages and analyzed published microarray datasets from human fibroblasts, and endothelial and smooth muscle cells for <i>T. cruzi-</i>induced changes in the expression genes included in the RT Profiler Human Inflammasome arrays. <i>T. cruzi</i> infection elicited a subdued and delayed activation of inflammasome-related gene expression and IL-1β production in mφs in comparison to LPS-treated controls. When WT and ASC^−/− macrophages were treated with inhibitors of caspase-1, IL-1β, or NADPH oxidase, we found that IL-1β production by caspase-1/ASC inflammasome required reactive oxygen species (ROS) as a secondary signal. Moreover, IL-1β regulated NF-κB signaling of inflammatory cytokine gene expression and, subsequently, intracellular parasite replication in macrophages. NLRP3^−/− macrophages, despite an inability to elicit IL-1β activation and inflammatory cytokine gene expression, exhibited a 4-fold decline in intracellular parasites in comparison to that noted in matched WT controls. NLRP3^−/− macrophages were not refractory to <i>T. cruzi</i>, and instead exhibited a very high basal level of ROS (>100-fold higher than WT controls) that was maintained after infection in an IL-1β-independent manner and contributed to efficient parasite killing. We conclude that caspase-1/ASC inflammasomes play a significant role in the activation of IL-1β/ROS and NF-κB signaling of cytokine gene expression for <i>T. cruzi</i> control in human and mouse macrophages. However, NLRP3-mediated IL-1β/NFκB activation is dispensable and compensated for by ROS-mediated control of <i>T. cruzi</i> replication and survival in macrophages.</p>