The recent identification of cytosolic pattern recognition receptors (PRRs) with leucine-rich repeats, which recognize pathogen-associated molecular patterns (PAMPs), has been garnering considerable attention. Activated PRRs form molecular complexes called inflammasomes, consisting of related proteins that include procaspase 1[interleukin (IL) 1β converting enzyme (ICE)]. Inflammasomes have been shown to facilitate molecular proximity, stimulate activation of procaspase 1, which consequently produces inflammatory cytokines IL-1β and IL-18 and ultimately lead to the initiation of innate immunity. An adaptor protein, apoptosis-associated speck-like protein containing a CARD (ASC), which recruits PRRs carrying the pyrin homologous domain (PYD) and procaspase 1 through PYD and CARD, respectively, is responsible for the formation of some inflammasomes and also activation of procaspase 1. In this review, our main attention will be directed to PYD region analysis of ASC to understand the interaction between PYD-carrying PRRs and ASC. Taking into consideration the other aspects of the ASC gene in the proapoptotic ability and down-regulation by methylation, the biological function of ASC will be discussed in relation to the epigenetic aspects of infection, inflammation, and cancer.