Cutting Edge: The NLRP3 Inflammasome Links Complement-Mediated Inflammation and IL-1β Release

The complement system is a potent component of the innate immune response, promoting inflammation and orchestrating defense against pathogens. However, dysregulation of complement is critical to several autoimmune and inflammatory syndromes. Elevated expression of the proinflammatory cytokine IL-1 beta is often linked to such diseases. In this study, we reveal the mechanistic link between complement and IL-1 beta secretion using murine dendritic cells. IL-1 beta secretion occurs following intracellular caspase-1 activation by inflammasomes. We show that complement elicits secretion of both IL-1 beta and IL-18 in vitro and in vivo via the NLRP3 inflammasome. This effect depends on the inflammasome components NLRP3 and ASC, as well as caspase-1 activity. Interestingly, sublethal complement membrane attack complex formation, but not the anaphylatoxins C3a and C5a, activated the NLRP3 inflammasome in vivo. These findings provide insight into the molecular processes underlying complement-mediated inflammation and highlight the possibility of targeting IL-1 beta to control complement-induced disease and pathological inflammation.