There are the natural ligands, immunophilin, for the drugs in cells.Immunosuppression is induced only by the drug in form of drug-immunophilin complex.

• 发现了生物体内存在其天然配基----亲免素，并通过形成药物亲免素复合物发挥免疫抑制作用，故又称为亲免素结合类免疫抑制剂。