MBTPS1 and chronic obstructive pulmonary disease: To further establish the key role of S1P in regulating CFTR activity and related COPD development, we blocked the S1P signaling by pretreating the WT mice with FTY720 (10 mg/kg/day), which belongs to a new class of immunosuppressants that inhibit S1P signaling by competitively binding with S1P receptors.