Aryl hydrocarbon receptor ( AHR ) expression and activation in inflamed rheumatoid tissues. (A) Overall AHR expression in synovial tissues (closed circles, n = 20) and nodule tissues (closed squares, n = 18). (B) AHR, (C) CYP1A1 and (D) AHR receptor (AHRR) expression in synovial tissues from rheumatoid arthritis (RA) patients who smoked (closed circles, n = 7) and non-smokers (open circles, n = 13), and nodule tissues of RA patients who smoked (closed squares, n = 4) and non-smokers (open squares, n = 14). (E) AHR and CYP1A1 expression in synovia from two separate patients with osteoarthritis (OA), labelled P1 and P2. n.d., not detected. Data are mean ± standard error of the mean (SEM). All mRNA levels are expressed relative to glyceraldehede-3-phosphate dehydrogenase (GAPDH). ***P < 0.001; **P < 0.01; *P < 0.05, Mann-Whitney U-test.