The major immunophilins that bind cyclosporine (cyclophilin) and FK-50
6/rapamycin (FK-BP 12) have been well characterized. They possess rota
mase 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 is reviewed on some possible mechan
isms of immunosuppression. Minor immunophilins of 14, 36, and 52 kDa h
ave also been isolated and partially characterized. Receptor assays em
ploying immunophilins have been developed.