Asthma and pregnancy: emerging evidence of epigenetic interactions in utero

Purpose of review Pregnancy is arguably the most critical period of developmental programming. Here, we particularly focus on the emerging paradigm that disease propensity is epigenetically determined by maternal exposures that have the capacity to activate or silence fetal genes through alterations in DNA and histone methylation, histone acetylation, and chromatin structure. Recent findings The most notable recent candidate to emerge in this role has been dietary folate, a methyl donor clearly associated with changes in gene expression and disease susceptibility through gene hypermethylation. Animal studies also provide the first evidence that the allergy protective effects of microbial exposure in pregnancy may be mediated by changes in methylation of Th1 genes of the offspring. There is also emerging evidence that perinatal differences in immune function of allergy-prone newborns extend beyond previously recognized differences in effector T cell (Th1/Th2) function, to also include differences in neonatal regulatory T cell (Treg) and Th17 function, and moreover, that these pathways are also epigenetically regulated. Summary New studies reinforce the importance of in-utero exposures (including dietary nutrients, microbial products, cigarette smoking, and certain maternal mediations) in fetal immune development and in programming the susceptibility to asthma and allergic disease.