S1PR4 and ulcerative colitis: Additionally S1P1 is upregulated during inflammatory bowel disease [31] and targeting this receptor either by the unspecific S1P agonist FTY720, by the specific S1P1/S1P5 agonist Ozanimod, or by the specific S1P1/S1P4/S1P5 agonist Etrasimod, has been shown to be an effective treatment option in ulcerative colitis patients [32].