Cyclophilin A (CyPA, 18 kDa) is a ubiquitously distributed protein belonging to the immunophilin family. Cyclophilin A (CyPA) is a peptidyl-prolyl cis-trans isomerase that exists in the intracellular and secretory forms and has multiple functions. Intracellular CypA takes part in folding, transport, and assembly of proteins; regulates cell proliferation; is a ligand for cyclosporine A (CsA), mediating its immune-suppressive activity; mediates signal transduction from a T cell receptor, and controls the balance of T helpers 1 and 2, inhibiting activity of T helpers 2.