G protein-coupled receptor 35 (GPR35), originally an orphan receptor, was discovered in 1998. At that time, the lack of pharmacological tools and convincingly defined endogenous ligands of GPR35 hindered the understanding of its functions and therapy. De Giovanni et al. recently discovered that 5- hydroxyindoleacetic acid (5-HIAA) is a new ligand of GPR35. Notably, 5-HIAA can promote neutrophil recruitment to inflammatory sites to clear pathogenic bacteria by activating GPR35. Interestingly, this new ligand is derived from platelets and mast cells. Based on this, we briefly commented that plat...
