NLRP1 is activated by MDP (Faustin et al. 2007). The NLRP1 inflammasome was the first to be characterized. It was described as a complex containing NALP1, ASC, caspase-1 and caspase-5 (Martinon et al. 2002). Unlike NLRP3, NLRP1 has a C-terminal extension containing a CARD domain, which has been reported to interact directly with procaspase-1, obviating a requirement for ASC (Faustin et al. 2007), though ASC was found to augment the interaction. Mouse NLRP1 has no PYD domain and would therefore not be expected to interact directly with procaspase-1. Like the NLRP3 inflammasome, K+ efflux appears to be essential for caspase-1 activation (Wickliffe et al. 2008). Ribonucleoside triphosphates (NTPs) are required for NALP1-mediated caspase-1 activation with ATP being the most efficient, Mg2+ was also required (Faustin et al. 2007). The human NLRP1 gene has 3 paralogues in mouse that are highly polymorphic. Differences between mouse strains underlie susceptibility to anthrax lethal toxin (Boyden & Dietrich 2006).