Methods: Blood samples were collected in first (weeks 8-21) and second (weeks 22-38) halves of pregnancy from the Isle of Wight birth cohort to measure DNA-M using Illumina Infinium HumanMethylation450 beadchip. DNA-M was obtained in first (13 mothers) and second (8 mothers) halves for two consecutive pregnancies. First, mixed linear models were used to compare DNA-M across two consecutive pregnancies, separately for first and second halves, to detect cytosine-phosphate-guanine (CpG) sites with significant changes (p≤0.05) in TH1 (155 CpGs, 19 genes), TH2 (77 CpGs, 12 genes), TH17 (106 CpGs, 15 genes) and Treg (10 CpGs, 2 genes). Then we compared the proportion of significant CpGs to determine whether T cell pathway CpGs were more often different than 20 random samples each containing 348 CpGs.
Results: Only Th17 CpGs in the second half of pregnancy were differentially methylated in two consecutive pregnancies. Among the 28 significantly differentially methylated Th17 CpGs, 24 belong to IL17-family and four to IL21-family. Compared to changes in random samples (14.1-17.8%), the methylation of more CpGs in TH17 (26.4%) were significantly more often changed in the second half of pregnancy.
Conclusions: Significant more methylation changes in TH17 genes in the second half of gestation comparing consecutive pregnancies may suggest changes in methylation with parity.