Cyclosporin A - 13 C 2 ,d 4 (Cyclosporine A- 13 C 2 ,d 4 ; Ciclosporin A- 13 C 2 ,d 4 ) is a 13 C labeled Cyclosporin A. Cyclosporin A (Cyclosporine A) is an immunosuppressant which binds to the cyclophilin and inhibits phosphatase activity of protein phosphatase 2B (PP2B/calcineurin) with an IC 50 of 5 nM. Cyclosporin A also inhibits CD11a/CD18 adhesion.