Increased levels of IgA antibodies to cytokeratin‐18 and epidermal keratin in rheumatoid arthritis

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Abstract
Objective. To investigate whether levels of antibodies to cytokeratin‐18 (CK‐18) and epidermal keratin (EPK) were raised in patients with rheumatoid arthritis (RA). Methods. We measured antibodies to CK‐18 and EPK in patients with RA and in patients with osteoarthritis (OA), as well as in normal control subjects by means of an enzyme‐linked immunosorbent assay. Results. IgA antibodies to both CK‐18 and EPK were significantly increased in patients with RA compared with the controls and with patients with OA (P < 0.0001). No difference was noted in the levels of IgG or IgM antibodies to CK‐18 or EPK between controls and patients with OA or RA. Conclusion. Raised levels of IgA autoantibody to CK‐18 and EPK may reflect damage to cytokeratin‐containing cells (e.g., in synovial endothelium) and could be a useful disease marker in RA.