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     Gel: 8%SDS-PAGE, Lysate: 40 μg, Lane: Human breast cancer tissue lysate, Primary antibody: P04529(ACR Antibody) at dilution 1/200, Secondary antibody: Goat anti rabbit IgG at 1/5000 dilution, Exposure time: 1 minute    

  
  

Anti-citrullinated protein/peptide antibodies (ACPAs), commonly referred to as ACR antibodies in clinical contexts, are a group of autoantibodies targeting citrullinated epitopes formed by post-translational modification of arginine residues. First identified in the 1960s as "anti-keratin antibodies" in rheumatoid arthritis (RA) patients, their significance became clearer with the discovery of cyclic citrullinated peptides (CCPs) as primary targets in the 1990s. Citrullination, mediated by peptidylarginine deiminases (PADs), occurs in inflammatory environments and alters protein structure, creating neoepitopes recognized as foreign by the immune system.

ACR antibodies are highly specific biomarkers for RA (specificity >95%), detectable years before clinical symptoms emerge. Their presence correlates with severe disease progression, joint erosion, and poor prognosis. The antibody response is strongly associated with HLA-DRB1*04 alleles, suggesting genetic predisposition to citrullinated antigen recognition. Modern diagnostic assays (e.g., anti-CCP2 ELISA) revolutionized RA classification, incorporated into 2010 ACR/EULAR diagnostic criteria. Beyond diagnostics, ACR antibodies may participate in RA pathogenesis through immune complex formation and osteoclast activation. Recent research explores epitope spreading patterns and links to environmental triggers like smoking and periodontal pathogens. Their role in predicting treatment response remains an active investigation area, underscoring their clinical and pathophysiological relevance in autoimmune disorders.