CYP1A1 and rheumatoid arthritis: Clinical samples have also demonstrated that AHR expression is about two-fold higher in RA patients than in controls [9] and that CYP1A1 and AHRR expression are increased in the synovia of RA patients who smoke cigarettes, but not in the synovia of patients who do not smoke, which indicates that there is a potential interaction between cigarette smoke and AHR activation in RA patients [53].