Maternal and cord blood miR-223 expression associates with prenatal tobacco smoke exposure and low regulatory T-cell numbers.

Background: There is evidence that microRNAs (miRNAs) are sensitive to environmental stressors, including tobacco smoke. On the other hand, miRNAs are involved in immune regulation, such as regulatory T (Treg) cell differentiation. The aim of the present study was to investigate the association between prenatal tobacco smoke exposure, miRNAs, and Treg cell numbers.

Methods: Within a prospective mother-child study (Lifestyle and Environmental Factors and Their Influence on Newborns Allergy Risk), we analyzed the expression of miR-155 and miR-223 together with Treg cell numbers in maternal blood during pregnancy, as well as in cord blood (n = 441). Tobacco smoke exposure was assessed based on questionnaire answers and maternal urine cotinine levels. Additionally, the concentration of smoking-related volatile organic compounds was measured in dwellings of study participants.

Results: Both maternal and cord blood miR-223 expressions were positively correlated with maternal urine cotinine levels. An association was also found between maternal miR-223 expression and indoor concentrations of benzene and toluene. High miR-223 expression was associated with lower Treg cell numbers in maternal and cord blood. Furthermore, children with lower Treg cell numbers at birth had a higher risk of atopic dermatitis during the first 3 years of life. The concentration of the toluene metabolite S-benzylmercapturic acid in maternal urine was associated with decreased cord blood, but not maternal blood, miR-155 expression. A relationship between miR-155 expression and Treg cell numbers was not found.

Conclusions: For the first time, we show that maternal tobacco smoke exposure during pregnancy correlates with the level of miRNA-223 expression in blood, with an effect on children's cord blood Treg cell numbers and subsequent allergy risk.