Receptor (immunophilin-binding) assay for immunosuppressive drugs

The major immunophilins that bind cyclosporine (cyclophilin) and FK-506/rapamycin (FK-BP12) have been well characterized. They possess rotamase activity, which is inhibited by the immunosuppressant that binds to them. The immunosuppressive action does not appear to be coupled to rotamase activity. The literature on some possible mechanisms of immunosuppression is reviewed. Minor immunophilins of 14, 37, and 52 kDa have also been isolated and partially characterized. The 14-kDa immunophilin binds FK-506 and rapamycin whereas the 52-kDa immunophilin binds all three drugs. Neither of these proteins have rotamase activity. Receptor assays employing immunophilins have been developed. Preliminary results are encouraging indicating that they may possess some advantages over current immunoassay procedures.