Formyl peptide receptors in the mucosal immune system

Formyl peptide receptors: Receptors in the mucosal immune system Key receptors in defense against bacteria may also be attractive targets for diseases of the mucosa, the tissue that lines and protects areas such as the airways and gastrointestinal tract. Formyl peptide receptors (FPRs) detect substances produced by bacteria and host cells triggering immune or wound-healing responsesYoe-Sik Bae and Yu Sun Jeong at Sungkyunkwan University, Suwon, South Korea, have reviewed how FPRs in the mucosa mediate the immune response. They report that FPRs play many roles, promoting wound closure, enhancing fibrosis of tissues, and promoting or suppressing inflammation in various tissues. FPRs may also be involved in conditions such as Crohn's disease and asthma. Further study may reveal opportunities for development of FPRs as therapeutic targets in mucosal diseases. Formyl peptide receptors (FPRs) belong to the G protein-coupled receptor (GPCR) family and are well known as chemotactic receptors and pattern recognition receptors (PRRs) that recognize bacterial and mitochondria-derived formylated peptides. FPRs are also known to detect a wide range of ligands, including host-derived peptides and lipids. FPRs are highly expressed not only in phagocytes such as neutrophils, monocytes, and macrophages but also in nonhematopoietic cells such as epithelial cells and endothelial cells. Mucosal surfaces, including the gastrointestinal tract, the respiratory tract, the oral cavity, the eye, and the reproductive tract, separate the external environment from the host system. In mucosal surfaces, the interaction between the microbiota and host cells needs to be strictly regulated to maintain homeostasis. By sharing the same FPRs, immune cells and epithelial cells may coordinate pathophysiological responses to various stimuli, including microbial molecules derived from the normal flora. Accumulating evidence shows that FPRs play important roles in maintaining mucosal homeostasis. In this review, we summarize the roles of FPRs at mucosal surfaces.