[Anti-cyclic citrullinated peptide antibodies as a diagnostic test for rheumatoid arthritis]

Early diagnosis of rheumatoid arthritis (RA) is important since aggressive therapy should begin at an early stage. Diagnosis is made on a clinical basis, supported by the determination of rheumatoid factor (RF). However, RF is also positive in healthy subjects, as well as in other autoimmune and infectious diseases. Two other diagnostic markers with a high specificity for RA, antiperinuclear factor (APF) and antikeratin antibodies (AKA), are not in general use because of technical difficulties. APF and AKA are antifilaggrin antibodies (AFA) that bind to determinants rich in the unusual amino acid citrulline, generated by posttranscriptional modification of arginine residues by the enzyme peptidylarginine deiminase (PAD). Enzymatic determination of recombinant filaggrin fragments produces linear peptides, which are recognized by RA-specific autoantibodies. After substitution of serine by cysteine, a cyclic peptide is formed. The conformational change mimics the original structure of the filaggrin and enhances the affinity of the antibodies. Recently, an anti-cyclic citrullinated peptide (anti-CCP) ELISA was developed. The sensitivity of this test is usually 51%-68%, with a specificity of about 96%-98% (significantly higher than that of RF). Together with RF, anti-CCP increases the ability to diagnose patients with early RA. The test might help to predict which patients will develop persistent disease with evidence of radiologic lesions. Implementation of the highly specific anti-CCP test in conjunction with RF would enable reliable early diagnosis in some cases and allow the initiation of aggressive therapy with disease modifying anti-rheumatic drugs (DMARDs).