PRTN3 and rheumatoid arthritis: Recently it has been shown that ACPA of the IgA2 subclass increase the proinflammatory cytokine response of macrophages to TLR1/2 co-stimulation by eliciting metabolic changes [118], which may explain the observed association between IgA2:IgA1-ACPA ratios and RA disease severity and flares [30,100].