Anti-citrullinated protein antibody (ACPA) (ACPA)

Anti-citrullinated protein antibodies (ACPAs) are a diverse group of autoantibodies that specifically recognize proteins containing citrulline, a non-coded amino acid produced by the deimination of arginine residues by peptidylarginine deiminase (PAD) enzymes (Malmström et al., 2017). These antibodies are the hallmark of rheumatoid arthritis (RA), where they are found in approximately 60-80% of patients and are highly specific for the disease, often appearing years before clinical symptoms manifest (Schellekens et al., 2000). The interaction between ACPAs and citrullinated antigens, such as vimentin, fibrinogen, and alpha-enolase, leads to the formation of immune complexes that activate the complement system and stimulate macrophages to release pro-inflammatory cytokines like TNF-alpha (Klareskog et al., 2008). Furthermore, ACPAs have been shown to directly promote osteoclastogenesis, contributing to the characteristic bone erosions seen in RA (Harre et al., 2012). Therapeutic interventions targeting this axis include B-cell depleting agents like rituximab, which reduce ACPA production, and emerging small-molecule inhibitors of PAD enzymes that aim to prevent the generation of citrullinated neoantigens (Mondal & Thompson, 2019). Additionally, T-cell modulators like abatacept interfere with the costimulatory signals necessary for the B-cell response against these antigens (Smolen et al., 2017). ACPAs serve as critical biomarkers for diagnosis, prognosis, and treatment stratification in clinical practice, as their presence typically correlates with a more aggressive disease course and increased joint destruction (Smolen et al., 2017).

Other names

Anti-cyclic citrullinated peptide antibodyAnti-CCPCitrullinated protein antigenDeiminated protein antigenAnti-citrullinated peptide antibody

Therapeutic strategies focus on depleting the B-cell populations responsible for ACPA production, blocking T-cell costimulation required for B-cell activation, or inhibiting peptidylarginine deiminase (PAD) enzymes to prevent the post-translational citrullination of proteins that creates these neoantigens.