Association of the shared epitope, smoking and the interaction between the two with the presence of autoantibodies (anti-CCP and RF) in patients with rheumatoid arthritis in a hospital in Seville, Spain

Objectives To evaluate the association of shared epitope, smoking and their interaction on the presence of autoantibodies (anti-cyclic citrullinated peptide [CCP] antibodies and rheumatoid factor) in patients with rheumatoid arthritis in our geographical area. Methods A descriptive and cross-sectional study was carried out in a cohort of 106 patients diagnosed with RA. Odds ratios (OR) for antibody development were calculated for shared epitope, tobacco exposure and smoking dose. Statistical analysis was performed with univariate and multivariate statistics using ordinal logistic regression. Odds ratios were calculated with 95% confidence interval (95% C I) and a value of P Results In univariate analysis, shared epitope (OR = 2.68; 95% CI: 1.11–6.46), tobacco exposure (OR = 2.79; 95% CI: 1.12–6.97) and heavy smoker (>20 packs/year) (OR = 8.93; 95% CI: 1.95–40.82) were associated with the presence of anti-CCP antibodies. For rheumatoid factor, the association was only significant for tobacco exposure (OR = 3.89; 95% CI: 1.06–14.28) and smoking dose (OR = 8.33; 95% CI: 1.05–66.22). By ordinal logistic regression analysis, an association with high titres of anti-CCP (>200 U/mL) was identified with South American mestizos, patients with homozygous shared epitope, positive FR and heavy smokers. Conclusions Being a South American mestizo, having a shared epitope, rheumatoid factor positivity and a smoking dose >20 packs/year are independent risk factors for the development of rheumatoid arthritis with a high titre of anti-CCP (>200 U/mL). In shared epitope-positive rheumatoid arthritis patients, the intensity of smoking is more strongly associated than tobacco exposure with an increased risk of positive anti-CCP.