Smoking is a risk factor for anti-cyclic citrullinated peptide (anti-CCP) antibody-positive rheumatoid arthritis (RA) in patients with HLA-DRB1 shared epitope (SE) alleles. It is unknown whether smoking influences not only the presence of these antibodies, but also other characteristics of the anti-CCP response, such as isotype usage. The aim of this study was to determine the influence of smoking on anti-CCP isotypes in RA patients, and to determine whether this influence is observed in the presence and/or absence of SE alleles.
IgA, IgM, and IgG subclasses of anti-CCP antibodies were measured by enzyme-linked immunosorbent assay in serum obtained at the first visit to the Leiden Early Arthritis Clinic from 216 patients with anti-CCP-positive RA whose smoking habits were also assessed. HLA genotyping data were available for 202 of these patients.
IgA and IgM anti-CCP were more frequent in RA patients who were smokers than in those who were nonsmokers (odds ratio 2.8 and 1.8, respectively). In addition, levels of all isotypes of anti-CCP, except IgG3, were significantly higher (P < 0.05) in smokers. The number of anti-CCP isotypes was higher in smokers compared with nonsmokers, both in SE-negative RA (P = 0.04) and in SE-positive RA (P = 0.07).
Patients with anti-CCP-positive RA who have a current or former tobacco exposure display a more extensive anti-CCP isotype usage in general, and IgA and IgM in particular, compared with patients with anti-CCP-positive RA who have never smoked. In contrast to its influence on the incidence of anti-CCP positivity, the influence of tobacco exposure on the constitution of the anti-CCP response is significant in SE-negative RA. These findings suggest a differential effect of tobacco exposure on the induction as compared with the propagation of the anti-CCP antibody response.