S1PR1 and Sjogren syndrome: Cellular studies have shown the expression of S1P1/2/3/4 receptors, as well as SPHK1 and SPHK2, in human submandibular gland cells, and further evidence suggests that S1P triggers the Ca2+ signaling pathway and apoptotic pathway in normal submandibular cells, thus affecting the progression of Sjogren’s syndrome by interfering with S1P1/2/3/4.