ACPAs

Anti–citrullinated protein antibodies (ACPAs) are autoantibodies (antibodies directed against an individual's own proteins) that are directed against peptides and proteins that are citrullinated. They are present in the majority of patients with rheumatoid arthritis. Clinically, cyclic citrullinated peptides (CCP) are frequently used to detect these antibodies with high sensitivity in patient serum or plasma (then referred to as anti–citrullinated peptide antibodies). One of the first identified antigens for these antibodies is citrullinated filaggrin. Historically, the same antibody specificity has been described as anti-keratin antibodies (AKA) and anti-perinuclear factor (APF).