FOXP3 and asthma: Interestingly, T regulatory cells, suppressor of allergic immune responses, were shown to be impaired by ambient air pollution (i.e., PAH) exposure and associated with increased Foxp3 promoter methylation and worsened asthma severity scores of 71 children who participated in the Fresno Asthmatic Children’s Environment Study (Nadeau et al. 2010).