The immune factors driving DNA methylation variation in human blood.

Epigenetic changes are required for normal development, yet the nature and respective contribution of factors that drive epigenetic variation in humans remain to be fully characterized. Here, we assessed how the blood DNA methylome of 884 adults is affected by DNA sequence variation, age, sex and 139 factors relating to life habits and immunity. Furthermore, we investigated whether these effects are mediated or not by changes in cellular composition, measured by deep immunophenotyping. We show that DNA methylation differs substantially between naïve and memory T cells, supporting the need for adjustment on these cell-types. By doing so, we find that latent cytomegalovirus infection drives DNA methylation variation and provide further support that the increased dispersion of DNA methylation with aging is due to epigenetic drift. Finally, our results indicate that cellular composition and DNA sequence variation are the strongest predictors of DNA methylation, highlighting critical factors for medical epigenomics studies.

Regional surveillance of social and geographic inequalities in smoking: the case of Montréal, Canada.

Surveillance of social inequalities in health is a platform for action. We examined the trends in smoking behaviours (current and ever smoking, quit ratios) according to education and place of residence and we quantified the observed inequalities. Data were from repeated cross-sectional surveys (2003-2009) of Montreal (Canada) residents ≥15 years (n=12,053). Trends in smoking behaviours according to education were measured with logistic and log-binomial regressions. Spatial distribution of smoking behaviours across local areas was assessed with Morans' Index. Observed inequalities were quantified with prevalence ratio and difference, population attributable risk, and slope index of inequality. Results showed that ever smoking rose among low-educated individuals. Among their high-educated fellow-citizens, current smoking decreased and quit ratios increased. Adverse smoking behaviours (current and ever smoking) were clustered in south-central areas. We conclude that smoking inequalities in Montreal are growing. We thus encourage a closer monitoring of smoking social differentials.