Genetics and Kinetics of Fetal Cell Microchimerism.
each pregnancy, cells from the fetus travel into the maternal circulation and organs,
resulting in the development of life-long microchimerism. It is currently uncertain
whether persistent fetal cells have beneficial or harmful effects on maternal health, or
whether they have any effect at all. Evidence from multiple laboratories suggests that
microchimeric fetal cells contri... read morebute to maternal tissue repair after injury. A deeper
understanding of their phenotype and postpartum trafficking patterns of fetal cells
would permit better understanding of possible mechanisms by which they affect maternal
health. The research presented here aimed to close these knowledge gaps. Using a mouse
model in which a wild type female is mated to a male homozygous for the Egfp transgene,
fetal cells in the maternal organs were easily identified by their green fluorescence
using high-speed flow cytometery. Small numbers of fetal cells were flow-sorted from the
maternal lung in both syngeneic and allogeneic matings, facilitating discovery-driven
gene expression analysis. Multidimensional gene expression microarray analysis of these
fetal cells suggests that fetal cells in the murine maternal lung are a mixed population
during pregnancy, consisting of trophoblasts, mesenchymal stem cells (MSCs) and cells of
the immune system. Further characterization of fetal MSCs and immune cells in the
maternal organs was limited by the small number of cells present. These results
underscore the challenges of working with these rare cells. Functional significance of
these cell types was further explored in two different injury models, contact
hypersensitivity and unilateral pneumonectomy. Previous work has shown that the maternal
lungs contain the greatest number of fetal cells, and that their levels increase
throughout gestation. These findings were augmented through analysis in this
dissertation of the natural history of fetal cells in the postpartum maternal lungs and
bone marrow. The results showed that fetal cells persist in these organs until at least
three months postpartum in healthy female mice. A two-stage decline was observed, with
an initial two and a half-week rapid clearance followed by a trend of gradual decrease.
Additionally, an increase in the ratio of live to dead cells within the lung over time
suggests that these cells may replicate in vivo. In conclusion, in this work we
demonstrate that low numbers of fetal cells can be flow-sorted from the maternal organs
and reproducible gene expression information can be obtained from them. In syngeneic
pregnancy, fetal cells in the maternal lung are primarily trophoblasts, mesenchymal stem
cells, and cells of the immune system. In allogeneic pregnancies, fetal cells appear to
be less differentiated. We recommend that future mouse studies of fetal cell
microchimerism should use allogeneic matings wherever possible, to more closely reflect
the heterogeneity found in human reproduction. We also show that fetal cell clearance in
postpartum maternal organs is a two-stage process. Future murine injury experiments
investigating the potential postpartum effects of fetal cells on maternal tissue repair
should start at a minimum of 17-18 days after delivery to be certain that the initial
clearance stage has been completed.
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Genetics.
Advisor: Diana Bianchi.
Committee: Peter Brodeur, Gordon Huggins, Janis Lem, and Keelin O'Donoghue.
Keywords: Genetics, Medicine, and Developmental biology.read less