PRTN3 and rheumatoid arthritis: Higher levels of ACPA-IgA prior to disease onset may be a reflection of epitope spreading and isotype expansion, a phenomenon well described in RA13 In addition, when comparing RA tobacco users with RA non-tobacco users, a statistically significant, positive association between smoking, SE genotype and serum concentrations of ACPA-IgA was also evident14–16.