Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.

Antibodies to CCP Versus the Unmodified Arginine-Containing Peptide (CAP) as a Serological Marker To Differentiate SLE from RA.

Chan2,  Jason, Burlingame1,  Rufus, Ceribelli2,  Angela, Sobel3,  Eric S., Li3,  Yi, Reeves3,  Westley H., Chan3,  Edward K. L.

INOVA Diagnostics, Inc.
University of Florida
University of Florida, Gainesville, FL


Anti-cyclic citrullinated peptide (CCP) ELISA has been established as a serological marker of RA and used extensively in clinical practice. Early studies on anti-CCP emphasized the selective reactivity of sera from patients with RA for CCP but not with the corresponding unmodified peptide containing arginine (CAP); however, reactivity against CAP is not generally considered in clinical practice or in most studies using commercial anti-CCP ELISA. Recent studies reported that anti-CCP reactivity in non-RA patients is often not specific for CCP but also reactive with CAP, indicating the importance of comparing reactivity with CCP vs CAP. In the present study, reactivity against CCP was compared with that to corresponding unmodified peptide containing arginine (CAP3) in RA, SLE, scleroderma (SSc), polymyositis/dermatomyositis (PM/DM), and controls.


An ELISA kit using a peptide corresponding to CCP3 but containing unmodified arginine (CAP3) was developed. Anti-CCP3 and CAP3 in sera from SLE (n = 201), SSc (n = 105), PM/DM (n = 44), RA (n = 84), and healthy individual (n = 34) were tested by ELISA. Reactivity of each serum was calculated as units following the manufacturer's protocol. Patients were classified into 4 groups based on their serum reactivity against CCP vs CAP. Clinical information was from a database.


Anti-CCP was positive in 70% of RA (69% were specific for CCP) vs 12% in SLE (7% specific for CCP), 6% in SSc, and 4% PM/DM, similar to previous studies. All except one anti-CCP positive RA showed CCP selective reactivity but 42% (10/24) of anti-CCP positive SLE sera also reacted strongly with CAP, indicating lack of specificity for citrullinated peptide in SLE. Surprisingly, anti-CAP reactivity without anti-CCP was frequently seen in SLE (45%) but uncommon in other systemic rheumatic diseases or NHS (P < 0.0001).

RA (84)SLE (201)SSc (105)PM/DM (44)NHS (34) 
CCP(+) CAP(-)69%7%5%4%0%
CCP(+) CAP(+)1%5%1%0%0%
CCP(-) CAP (+)1%45%5%0%3%
CCP(-) CAP(-)29%43%89%96%97%


Anti-CAP without CCP was in high prevalence and relatively specific for SLE among systemic rheumatic diseases. When patients with early undiagnosed arthritis are seen at clinic, positive anti-CAP and negative anti-CCP can serve as a useful serological marker to differentiate SLE from RA. RA sera specifically reacted with CCP but not with CAP as previously described. In contrast to CCP specific reactivity in RA, CAP positivity was common in anti-CCP positive SLE sera.

To cite this abstract, please use the following information:
Chan, Jason, Burlingame, Rufus, Ceribelli, Angela, Sobel, Eric S., Li, Yi, Reeves, Westley H., et al; Antibodies to CCP Versus the Unmodified Arginine-Containing Peptide (CAP) as a Serological Marker To Differentiate SLE from RA. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :735
DOI: 10.1002/art.28503

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