Sphingosine-1-phosphate receptors (S1PRs) are a group of proteins located on the surface of cells that play a crucial role in various biological processes. They are activated by sphingosine-1-phosphate (S1P), a lipid signaling molecule involved in regulating immune responses, cell growth, and vascular development. There are five known subtypes of S1PRs, labeled S1P1 through S1P5, each with distinct functions and tissue distributions. These receptors are important in maintaining the balance of immune cell movement and are also targets for certain therapeutic drugs used in treating autoimmune diseases and other conditions.