In, IL-1α, IL-6 and IL-4 LCRs our study delineated regions with lower methylation in T cells in CPA individuals who also show lower levels of these cytokines in plasma (Figure 1A, 1B and 2A bottom, highlighted in blue). These results might be consistent with the hypothesis that lower methylation in these regions permits more frequent binding of a putative repressor leading to the decreased IL-4, IL-6 and IL-1α expression. Indeed, there is evidence that increased DNA methylation of certain regions is associated with increased gene expression. For example, DNA methylation in a repressor-binding site of the multidrug-resistance gene (MDR-1) enhancer was shown to increase its expression [83]. Another example is the H19/IGF2R imprinted control regions (ICR). Methylation of the ICR on the paternal allele prevents H19 activity but allows IGF2 activity whereas hypomethylation on the maternal allele allows H19 activity but prevents IGF2 activity [84]. These hypotheses on the effect of DNA methylation on cytokine genes expression need to be tested in vitro as well as in vivo as the data presented here only reveal associations but do not provide causal relationships between the differentially methylated regions and expression.
