Macrophage priming is dispensable for NLRP3 inflammasome activation and restriction of Leishmania amazonensis replication.

Abstract

The NLRP3 inflammasome is activated in response to multiple stimuli and triggers activation of caspase-1 (CASP1), IL-1β production, and inflammation. NLRP3 activation requires two signals. The first leads to transcriptional regulation of specific genes related to inflammation, and the second is triggered when pathogens, toxins, or specific compounds damage cellular membranes and/or trigger the production of reactive oxygen species (ROS). Here, we assess the requirement of the first signal (priming) for the activation of the NLRP3 inflammasome in bone marrow-derived macrophages (BMDMs) infected with Leishmania amazonensis. We found that BMDMs express the inflammasome components NLRP3, ASC, and CASP1 at sufficient levels to enable the assembly and activation of NLRP3 inflammasome in response to infection. Therefore, priming was not required for the formation of ASC specks, CASP1 activation (measured by fluorescent dye FAM-YVAD), and restriction of L. amazonensis replication via the NLRP3 inflammasome. By contrast, BMDM priming was required for CASP1 cleavage (p20) and IL-1β secretion, because priming triggers robust up-regulation of pro-IL-1β and CASP11 that are important for efficient processing of CASP1 and IL-1β. Taken together, our data shed light into the cellular and molecular processes involved in activation of the NLRP3 in macrophages by Leishmania, a process that is important for the outcome of Leishmaniasis.