IL1A and infection: Thus, to complement the suite of ‘pattern recognition receptors’ (PRRs) that are trained upon ‘non-self’ molecular structures that indicate the presence of pathogens, IL-1 family cytokine receptors may serve as ‘activity recognition receptors’ (ARRs) for enzymatic activity (in this instance protease activity) that serves as a proxy for the detection of infection or tissue necrosis (reviewed in Ref.