An enzyme that binds the immunosuppressant compound cyclosporin, thereby blocking its activity as a peptidylprolyl cis¿trans isomerase. Cyclophilin A is present in the cytosol and when bound to cyclosporin it inhibits the phosphatase calcineurin and this underlies the immunosuppressant activity of cyclosporin. Cyclophilin D is found in the mitochondrial matrix and its activity is required for the mitochondrial permeability transition, which can thereby be inhibited by cyclosporin.