['Epigenetic changes in DNA methylation have recently been demonstrated to be involved in effector T-cell polarization, resulting in differential secretion of T(H)1 and T(H)2 cytokines. However, the contribution to the development of a chronic inflammatory phenotype remains still unclear.', 'We sought to investigate changes in DNA methylation in marker genes of T-cell subsets during allergen sensitization/challenge and their influence on the development of an allergic airway inflammatory response.', 'The relationship between changes in DNA methylation and phenotype development were examined in a well-established model of experimental asthma. DNA methylation was investigated at genomic loci associated with T(H)1 (IFNG promoter) or T(H)2 (conserved noncoding sequence 1 [CNS1]) cytokine production by using bisulfite pyrosequencing.', 'Analysis of CD4(+) T cells revealed a significant increase in DNA methylation at the IFNG promoter after allergen sensitization/challenge, which correlated with decreased IFN-γ cytokine expression, whereas only minor changes were observed at the CNS1 locus. Furthermore, the increase in DNA methylation at the IFNG promoter could be reversed with a DNA methyltransferase (DNMT) inhibitor in\xa0vitro and in\xa0vivo with beneficial effects on sensitization status and allergic phenotype. The specific importance of the DNA methylation status in CD4(+) T cells could be confirmed by using adoptive transfer experiments.'] Does dNA methylation of TH1/TH2 cytokine genes affect sensitization and progress of experimental asthma?