Lovinsky-Desir et al. found a negative correlation between the DNA methylation rate of the IFN-γ promoter in CD4 + T lymphocytes and the relative IFN-γ gene expression in a cohort of children and adults with allergic asthma [23]; a similar negative correlation between IFN-γ DNA methylation and gene expression of T effector cells was reported by Kohli et al. in children exposed to secondhand smoke and air pollution [24]. Here, CD4 is linked to allergic asthma.