Evidence is emerging that in addition to its role in regulating gene expression during differentiation, the DNA methylation pattern is responsive to external environmental exposures including the social environment [46] in animals [47]–[54] and in humans [55]–[59]. Importantly, DNA methylation alterations associated with social exposures are not restricted to the brain and are detected in whole blood cell (WBC) DNA [27], [55], [57], [58], [60]–[67]. It is therefore plausible that alteration in DNA methylation of cytokine regulatory regions and the transcription factors that regulate them occur in response to social signals and play a role in human behavior, including aggression.
