The innate immune system in animals has been forged to detect microbes, coordinate symbiotic responses, and mount immune defenses against pathogens. Recently, innate immunity was shown to detect signals released by damaged cells or tissues such as uric acid or ATP. These danger signals were proposed to be important in promoting and regulating inflammation upon trauma or pathogen insults. The physiological relevance of these signals in the immune response and their mechanisms of action are still unclear. Recent findings suggest that some danger signals activate the NALP3 inflammasome, an innate immune complex that controls inflammatory caspases and IL-1 activation.