Risk of developing rheumatoid arthritis in subjects exposed to different combinations of cigarette smoking status (never or ever smoker), MBL-high genotype, and the PTPN22 *620W risk allele. Subjects were stratified by the presence of rheumatoid factor (a,b) or anti-citrullinated protein antibodies (c,d). Risk is calculated as odds ratios by using logistic regression adjusted for age, sex, and geographic location. *Significant 95% confidence interval. ACPA, anti-citrullinated peptide antibody; MBL, mannan-binding lectin; RF, rheumatoid factor.