JAK2 and ulcerative colitis: For example, tofacitinib is the first pan-JAK inhibitor that targets JAK1, JAK2 and JAK3 for the treatment of moderate or severe active ulcerative colitis (UC), but owing to the simultaneous inhibition of JAK2-mediated erythropoietin and GM-CSF signaling, it has some safety concerns relating to significant adverse reactions including anemia, neutropenia, thrombocytopenia, zoster, and pulmonary embolism [11–13].