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Reply to J. Gao's commentary on: Aromatic hydrocarbon receptor provides a link between smoking and rheumatoid arthritis in peripheral blood mononuclear cells.

Sirs, We thank Dr Lingyan Zhou et al. for their interest in our publication “Aromatic hydrocarbon receptor provides a link between smoking and rheumatoid arthritis in peripheral blood mononuclear cells” (1) . It was generally known that cytochrome P4501A1 (CYPlAl) and AHR repressor (AHRR) were characteristic factors responsive to AHR activiation (2, 3), the mRNA expression levels of AHR downstream gene (AHRR and CYP1A1) by RT-PCR could reflect the activation of AHR although the western blot and flow cytometry were not used in our experiment. In fact, in our previous studies, we used flow cytometry to detect the ratio of ARH positive cells for different research purposes (4). The issue regarding the association of ESR, CRP, DAS28 score, anti-CCP antibodies and AHR had been discussed and the results had been previously published (4, 5), and no correlation was found between the indicators above and AHR expression. As Zhou et al. noted that multiple inflammatory factors like IL-6, TNF-α, IL-17 might play crucial roles in RA. However, the patients of RA included in our study were in stable condition, so it made little sense to analyse the associations of inflammatory factor and AHR in the study. Maybe further studies are needed to include the patients of different disease activities to certify the relationship.