The Functional DNA Methylation Signatures Relevant to Altered Immune Response of Neonatal T Cells with <span style="font-variant: small-caps">l</span>-Arginine Supplementation

<span style="font-variant: small-caps;">l</span>-Arginine is an important nutrient in the infant diet that significantly regulates the maturation of the immune system in neonates, including the maturation of CD4⁺ T cells. The biological activities of CD4⁺ T cells differ substantially between neonates and adults, and these differences may be governed by epigenetic processes. Investigating these differences and the causative processes may help understand neonatal and developmental immunity. In this study, we compared the functional DNA methylation profiles in CD4⁺ T cells of neonates and adults, focusing on the role of <span style="font-variant: small-caps;">l</span>-arginine supplementation. Umbilical cord blood and adult CD4⁺ T cells were cultured with/without <span style="font-variant: small-caps;">l</span>-arginine treatment. By comparing DNA methylation in samples without <span style="font-variant: small-caps;">l</span>-arginine treatment, we found that CD4⁺ T cells of neonatal cord blood generally showed higher DNA methylation than those of adults (average CpG methylation percentage 0.6305 for neonate and 0.6254 for adult, t-test p-value < 0.0001), suggesting gene silencing in neonates. By examining DNA methylation patterns of CpG dinucleotides induced by <span style="font-variant: small-caps;">l</span>-arginine treatment, we found that more CpG dinucleotides were hypomethylated and more genes appeared to be activated in neonatal T-cells as compared with adult. Genes activated by <span style="font-variant: small-caps;">l</span>-arginine stimulation of cord blood samples were more enriched regarding immune-related pathways. CpG dinucleotides at IL-13 promoter regions were hypomethylated after <span style="font-variant: small-caps;">l</span>-arginine stimulation. Hypomethylated CpG dinucleotides corresponded to higher IL-13 gene expression and cytokine production. Thus, DNA methylation partially accounts for the mechanism underlying differential immune function in neonates. Modulatory effects of <span style="font-variant: small-caps;">l</span>-arginine on DNA methylation are gene-specific. Nutritional intervention is a potential strategy to modulate immune function of neonates.