The GI tract is also referred to as the digestive tract and constitutes the organ system that connects the mouth to the anus. The GI tract contains the mouth, esophagus, stomach, small intestine, large intestine, and anus. Due to the characteristics of the digestive system, many external stimuli, such as food antigens and bacteria, may affect cellular activities in this region. In particular, the gut of human adults contains over ten times more bacterial cells than human cells. These bacteria build their ecosystem in the gut and maintain homeostasis with epithelial cells and immune cells via mutual interaction. Recently, increased interest in the microbiota has revealed that dysbiosis correlates with various human diseases4. In addition, the study of the functional roles of PRRs such as FPRs in the GI tract has attracted interest because many ligands of FPRs, including formylated peptides and lipid metabolites, exist in the GI track.