Cyclophilin A, also known as peptidylprolyl isomerase A (PPIA), is an 18 kDa protein that catalyzes cis-trans isomerization at proline imidic peptide bonds, thereby promoting protein folding/trafficking and regulating protein activity. Cyclophilin A has multiple known functions in inflammation. Intracellularly, cyclophilin A interacts with interleukin (IL)-2 inducible T cell kinase (ITK) to tune T cell receptor signaling. Extracellularly, cyclophilin A is known to function as a leukocyte chemotactic factor. Cells secrete cyclophilin A by a vesicular secretory pathway in response to lipopolysaccharide and oxidative stress, or cyclophilin A may be released during cell death. Cyclophilin A influences inflammatory responses through its actions on immune activation and/or leukocyte trafficking.

> 95% as determined by SDS-PAGE