LETTER Sevil Kamali Æ Nuray Gurel Polat Æ Esen Kasapoglu Ahmet Gul Æ Lale Ocal Æ Orhan Aral Æ Meral Konice Selim Badur Æ Murat Inanc Anti-CCP and antikeratin antibodies in rheumatoid arthritis, primary Sjo ¨ gren’s syndrome, and Wegener’s granulomatosis Received: 22 October 2004 / Revised: 3 February 2005 / Accepted: 3 February 2005 / Published online: 31 May 2005 Ó Clinical Rheumatology 2005 Abstract The objective of this study was to investigate the frequency of antibodies against cyclic citrullinated peptides (anti-CCP) and keratin (AKA) in patients with rheumatoid arthritis (RA) as well as in patients with primary Sjo¨gren’s syndrome (pSS) and Wegener’s granulomatosis (WG), who may present with rheuma- toid factor (RF)-positive arthritis. The study group consisted of 46 patients with RA (26 patients were negative for RF), 32 with pSS, 22 with WG, and 40 healthy controls. The RF, anti-CCP, and AKA were detected in serum using the latex agglutination test, en- zyme-linked immunosorbent assay, and indirect immu- nofluorescence, respectively. The agreement between those tests was evaluated by kappa test. No positive result for AKA was detected in pSS and WG patients, and anti-CCP was found in only one patient with pSS. The results of kappa tests were low, varying between 0.25 (RF-anti-CCP) and 0.02 (RF-AKA). The sensitivity and specificity values were 43 and 44% for RF, 65 and 98% for anti-CCP, and 58 and 100% for AKA, respectively, in RA patients. In the RF-negative RA group, AKA was found to have a high frequency (55%) in comparison to anti-CCP (38%). Seropositivity was found to be 87% for any one of the three autoantibodies tested in RA patients. With a higher specificity, values for RA, anti-CCP, and AKA seem to be helpful for the differential diagnosis of patients with RF-positive arthritis, which may include patients with WG and pSS, and screening of all three antibodies may increase the diagnostic performance. Introduction Several autoantibodies have been utilized as predictive, diagnostic, and prognostic markers in rheumatoid arthritis (RA) [1]. Among these autoantibodies, rheu- matoid factor (RF) has been the one most widely used for the diagnosis of RA, having 40–75% sensitivity and 74–90% specificity [2–6]. Antikeratin antibodies (AKA), reactive towards filaggrin extracted from human epi- dermis, have been identified as another diagnostic autoantibody with a higher specificity (83–100%) for RA [2, 4, 6–8]. After citrulline had been discovered as an essential constituent of antigenic determinants of the filaggrin-related autoantibodies, Schellekens et al. [3] showed that AKA reacted with the synthetic peptides containing citrulline using an enzyme-linked immuno- sorbent assay (ELISA). The ELISA method for detect- ing autoantibodies against cyclic citrullinated peptides (CCP) was reported to have a moderate sensitivity (41– 68%) and high specificity (96–98%) for the diagnosis of RA [3–6, 9]. Although the presence of RF has long been consid- ered a specific test for RA, RF positivity is frequently demonstrated in other connective tissue diseases, including systemic lupus erythematosus (SLE), Sjo¨ gren’s syndrome (SS), progressive systemic sclerosis, and mixed connective tissue disease [10]. Development of erosive arthritis is an important feature of RA, which helps in the differential diagnosis of patients with RF-positive joint disease. However, erosive changes cannot be de- tected frequently in the evaluation of patients with early arthritis [11]. In primary SS (pSS), a chronic inflammatory disease associated with lymphocytic infiltration of exocrine glands, arthralgia or nonerosive arthritis may be the presenting clinical features [12]. Not infrequently, SS may coexist with or even precede RA, and RF positivity S. Kamali (&) Æ E. Kasapoglu Æ A. Gul Æ L. Ocal Æ O. Aral M. Konice Æ M. Inanc Division of Rheumatology, Department of Internal Medicine, Istanbul Medical Faculty, Istanbul University, Capa, Istanbul, 34390, Turkey E-mail: sevilkamali@hotmail.com N. G. Polat Æ S. Badur Department of Virology and Basic Immunology, Istanbul Medical Faculty, Istanbul University, Capa, Istanbul, 34390, Turkey Clin Rheumatol (2005) 24: 673–676 DOI 10.1007/s10067-005-1104-y