Abstract
IL-1β is a "master" cytokine regulating a wide variety of physiologic and immunologic processes. The most frequently studied models for NLRP3 inflammasome-mediated IL-1β production are the macrophages; however, depending on their microenvironment, they can develop into functionally different cells. Several protocols have been developed to model the diversity of these cells in vitro. Here, we report for the first time, to our knowledge, a comparative study about the dynamics and molecular mechanisms of NLRP3 inflammasome priming and activation in LPS-stimulated, human, monocyte-derived GM- or M-macrophages, differentiated in the presence of GM-CSF or M-CSF, respectively. Our results show that IL-1β production by LPS-stimulated M-macrophages is a rapid and short event that requires ATP supplementation and is attenuated, in part, by the presence of IL-10, which reduces Akt signaling. However, IL-1β production by GM-macrophages develops gradually, and these cells produce IL-1β, even in the absence of ATP supplementation, because of the constitutively active caspase-1 enzyme. We show that the membrane-bound ectonucleotidases have an important regulatory role on the IL-1β secretion in GM-macrophages. Furthermore, we provide evidence that adenosine treatment enhances LPS-primed IL-1β secretion by GM-macrophages, but not by M-macrophages. These results show that, because of the different activation status and expression levels of the NLRP3 inflammasome components, as well as the signaling activity of the pathways, the two subtypes of macrophages respond very differently to the same stimuli. For this reason, the molecular composition of the microenvironment that shapes macrophage development should be considered when research or therapeutic methods are planned to control IL-1β production.