Immunosuppressive agents, also known as immunosuppressants and antirejection medications, can inhibit or prevent activity of the immune system. Immunosuppression is a reduction of the activation or efficacy of the immune system. Immunosuppressants have many uses, such as preventing rejection of transplanted organs and tissues, treating autoimmune diseases or other non-autoimmune inflammatory diseases. Immunosuppressants and FK506 bind to distinct families of intracellular proteins (immunophilins) termed cyclophilins and FK506-binding proteins (FKBPs). Calcineurin is expressed in T cells, and its activity can be measured in cell lysates.

Cyclosporin A (also known as Cyclosporine A, Ciclosporin A or CsA) is an immunosuppressant which binds to the cyclophilin and inhibits phosphatase activity of calcineurin. And Cyclosporin A is used in allografting, especially in organ transplantation. In vitro, the complexes of Cyclosporin A-cyclophilin and FK506-FKBP-12 bind to and inhibit the activity of calcineurin, a calcium-dependent serine/threonine phosphatase. In addition, this compound is a valuable probe for studying T-cell signal transduction, and Cyclosporin A also inhibits Ca²⁺-dependent activation pathways that lead to transcription of lymphokine genes. Furthermore, in mouse model of pleurisy induced by carrageenan, Cyclosporin A downregulates CD11a/CD18 adhesion molecule in the lungs, as well as TNF-α and IL-1β in the fluid leakage of the pleural cavity.

In summary, Cyclosporin A, an immunosuppressant, binds to the cyclophilin and inhibits calcineurin phosphatase activity.

References:

[1] D A Fruman, et al. Proc Natl Acad Sci U S A. 1992 May 1;89(9):3686-90.

[2] Eduardo Monguilhott Dalmarco, et al. Cell Adh Migr. Oct-Dec 2008;2(4):231-5.