NALP is a type of NOD-like receptor. NALP proteins are part of the innate immunity and detect conserved pathogen characteristics such as peptidoglycan. It is thought that NALP proteins sense inherent danger, and link this with microbial products, creating a response under the concept of the inflammasome including K+ efflux and caspase 1 activation. NALP has been linked to autoimmune diseases, but is currently poorly understood.
References
NALP Wikipedia(Text) CC BY-SA