NIBR0213 is an orally bioavailable, potent, and selective antagonist of sphingosine-1-phosphate receptor-1 (S1P1) with IC50 values of 2.5 and 2.0 nM for the hS1P1 in a Ca2+ mobilization assay and GTPγS assay, respectively. It is inactive at S1P2, S1P3, and S1P4 receptors (IC50s = >20, >10, and >10 uM, respectively in a Ca2+ mobilization assay). S1P1 plays a key role in the immune system, regulating lymphocyte egress from lymphoid tissues into the circulation. In rats, NIBR0213 (30 mg/kg) reduces peripheral blood lymphocytes by 75-85% for up to 24 hours. In a mouse model of experimental autoimmune encephalitis (EAE), it significantly reduces disease severity up to 26 days, when administered at 30 mg/kg twice per day for three days, then 60 mg/kg twice per day. However, in a rat model of adjuvant-induced arthritis, chronic administration of 30 mg/kg induces pulmonary damage and chronic lung inflammation.