Molecules of pathogens infecting animals are recognized by cellular components of the hosts, such as pattern recognition receptors including Toll-like receptors (TLRs) and NOD-like receptors (NLRs), resulting in induction of inflammation and various immune responses. Some of the NLRs are components of inflammasomes, which are cytoplasmic protein complexes recognizing microbial molecules and molecules indicating endogenous danger signals. NLRC4 inflammasome recognizes flagellin or components of the type III secretion system, and plays an important role in clearance of intracellular bacteria. We cloned pig genomic regions corresponding to the genes encoding two key components of the NLRC4 inflammasome, NLRC4 itself and NAIP. Sequencing of the cloned genomic regions showed that pig has single loci coding NLRC4 and NAIP, respectively. Interestingly, in comparison with the human counterparts, several intermediate exons were not observed in pig NLRC4 and NAIP. In addition, we could not find any valid open reading frames encoding functional NLRC4 or NAIP protein in the genomic sequences. Expression of the NLRC4 or NAIP gene in pigs was not detected in the ESTs and by RT-PCR with leukocytes. Taken together, it was suggested that pig does not have a functional gene of NLRC4 or NAIP on the genome, resulting in loss of the NLRC4 inflammasome.