Identifying epigenetic associations with cell type and gestational age in the neonatal immune system

Neonates have a uniquely structured immune system characterized by immunotolerance, an unprimed adaptive immune system, and a heavy reliance on innate immune responses. Although this prevents excessive hyperinflammatory responses during gestation and postnatal microbial colonization of the neonate, it also confers vulnerability to infection. This risk is heightened in those born preterm (prior to 37 weeks gestation), as development of their immune system is interrupted by early birth. Throughout gestation, the predominant hematopoietic organ shifts in a defined temporal pattern. Each hematopoietic source produces different types of immune cells in different proportions, to accommodate the needs of the developing fetus. One of the greatest differences between these organs is the release of nucleated red blood cells (nRBCs) into circulation – ranging from the yolk sac, which exclusively releases primitive nRBCs, to the bone marrow, in which erythroid cells are enucleated before entering circulation. Although generally regarded as a consequence of high erythropoietic demand in the fetus, recent functional studies have indicated an immunosuppressive role for fetal nRBCs as well. DNA methylation (DNAm) is the addition of a methyl group to a cytosine base, a modification which does not change the underlying genetic sequence. DNAm mediates hematopoietic lineage commitment and can be a useful marker for cell composition and immune function in blood. Using the Illumina Infinium HumanMethylation450 BeadChip microarray, this thesis establishes DNAm profiles for major cord blood hematopoietic cells in both term and preterm births. In-depth examination of DNAm in term nRBCs revealed that epigenetic marks in this enigmatic cell population are likely highly regulated. Comparisons between cord blood hematopoietic cells collected from term versus preterm births allowed for the identification of both cell-specific and systemic prematurity-associated differential methylation. These findings contribute to current understanding of the molecular mechanisms behind preterm birth and highlight candidate genes for follow-up gene expression or functional analysis of preterm hematopoietic cell populations, including CDC42EP1, CLIP2, FBXO31, the oncogene WWTR1, and tumour suppressor genes STK10 and RARRES3.Medicine, Faculty ofMedical Genetics, Department ofGraduat