title: A varying T cell subtype explains apparent tobacco smoking induced single CpG hypomethylation in whole blood.
abstract: BACKGROUND
  Many recent epigenetic studies report that cigarette smoking reduces DNA methylation in whole blood at the single CpG site cg19859270 within the GPR15 gene.
  
  
  RESULTS
  Within two independent cohorts, we confirmed the differentially expression of the GPR15 gene when smokers and non-smokers subjects are compared. By validating the GPR15 protein expression at the cellular level, we found that the observed decreased methylation at this site in white blood cells (WBC) of smokers is mainly caused by the high proportion of CD3+GPR15+ expressing T cells in peripheral blood. In current smokers, the percentage of GPR15+ cells among CD3+ T cells in peripheral blood is significantly higher (15.5 ± 7.2 %, mean ± standard deviation) compared to non-smokers (3.7 ± 1.6 %). Treatment of peripheral blood mononuclear cell (PBMC) cultures with aqueous cigarette smoke extract did not induce a higher proportion of this T cell subtype.
  
  
  CONCLUSIONS
  Our results underline that DNA hypomethylation at cg19859270 site, observed in WBCs of smokers, did not arise by direct effect of tobacco smoking compounds on methylation of DNA but rather by the enrichment of a tobacco-smoking-induced lymphocyte population in the peripheral blood.
authors.affiliation: Department of Environmental Immunology, Helmholtz Centre for Environmental Research-UFZ, Leipzig, 04318 Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Bauer
authors.affiliation: Federal Institute for Occupational Safety and Health, Berlin, 10317 Germany.
authors.forename: Gunter
authors.initials: G
authors.lastname: Linsel
authors.affiliation: Department of Environmental Immunology, Helmholtz Centre for Environmental Research-UFZ, Leipzig, 04318 Germany.
authors.forename: Beate
authors.initials: B
authors.lastname: Fink
authors.affiliation: Department of Environmental Immunology, Helmholtz Centre for Environmental Research-UFZ, Leipzig, 04318 Germany.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Offenberg
authors.affiliation: Nikolaus-Fiebiger-Zentrum for Molecular Medicine, Institute of Genetics, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, 91054 Germany.
authors.forename: Anne Maria
authors.initials: AM
authors.lastname: Hahn
authors.affiliation: Institute of Clinical Immunology, Medical Faculty, University of Leipzig, Leipzig, 04103 Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Sack
authors.affiliation: Institute of Clinical Immunology, Medical Faculty, University of Leipzig, Leipzig, 04103 Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Knaack
authors.affiliation: Division of Endocrinology and Nephrology, University of Leipzig, Leipzig, 04103 Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Eszlinger
authors.affiliation: Department of Environmental Immunology, Helmholtz Centre for Environmental Research-UFZ, Leipzig, 04318 Germany.
authors.forename: Gunda
authors.initials: G
authors.lastname: Herberth
keywords: Blood; CpG; DNA methylation; EWAS cell composition; GPR15; Tobacco smoking