Figure 4.

S1P and S1P-S1PR pathways of mast cells. Recognition of antigens via IgE-FcεRI, the plasma membrane of mast cells, activates SPHK, thereby promoting the generation of S1P. The generated S1P stimulates degranulation and cytokine production intracellularly. On the other hand, S1P released into the extracellular space also acts in an autocrine manner via S1P receptors expressed on mast cells. Mast cells express three S1P receptors, S1PR1, S1PR2, and S1PR4, but not S1PR3 and S1PR5. S1PR1 activates mast cell chemotaxis; meanwhile, S1PR2 suppresses it. S1PR2 and S1PR3 promote mast cell degranulation and cytokine production.