Introduction

Epigenetics is a rapidly emerging field investigating the interface between our genomes and our environments. Epigenetic mechanisms are responsible for the structural organization of DNA and its packaging proteins; one major function of which is to regulate gene expression by controlling DNA accessibility. While the genetic sequence is unaltered, these structural changes act as a regulatory stratum on the genome, instructing cellular identity and driving important cellular processes. Current characterized epigenetic marks include post-translational modifications to histone proteins, such as acetylation and methylation, histone variants, non-coding RNAs, and chemical modifications covalently bound directly to DNA. The latter include DNA methylation, the most commonly studied epigenetic mark, especially in human populations, which refers to the covalent attachment of a methyl group primarily to the 5'carbon of cytosine bases [1]. This chapter will briefly review DNA methylation, then examine the role of DNA methylation in three important areas: cell type specification, environmental embedding, and disease; using examples from the immune system. We will then discuss the interesting connections between DNA methylation and ageing, and conclude with emerging hypotheses on how this might influence ageing of the immune system.

 
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