During pregnancy, fetal cells can migrate into maternal tissues (fetal microchimerism), or maternal cells can migrate into fetal tissues (maternal tissues). These cells can persist in the bodies of their hosts for up to decades after pregnancy. However, it is not well-established whether these cells are beneficial or detrimental to the health of their hosts. 

The objective of the presentation is to describe the phenomenon of pregnancy-related microchimerism, discuss the animal model used to study this phenomenon, and determine how microchimerism affects short-term and long-term maternal and child health outcomes. 

To demonstrate fetal microchimerism, we crossed a male homozygous transgenic mouse model that expressed the fluorescent protein TdTomato with female nulligravid wild-type female mouse. This produced mouse embryos that expressed TdTomato in all their cells and tissues, allowing their presence to be detected in maternal tissues. At E15, 104 colony-forming units Escherichia coli were administered intravaginally to emulate ascending infection. The presence of fetal cells and DNA was detected using fluorescent microscopy and polymerase chain reaction of the SRY gene, respectively, at E16 and 28 days postpartum. The immunophenotype of chimeric cells was determined using advanced cytometry. Their effects will be assessed using physiologic and histopathologic techniques. Techniques and recent studies on maternal microchimerism will also be discussed. 

At E16 of gestation, fetal cells and DNA were detected in different maternal organs, with lungs having the most amount. These cells were shown to persist for at least 28 days postpartum. The composition of fetal cells in both the maternal heart and lungs was different in normal term pregnancy than in ascending infection-complicated pregnancy, with more antigen-presenting cells and less stem cells present in the latter. Ascending infection-complicated pregnancy resulted in decrease in cardiac ejection fraction after 3 months, and development of airway inflammation when exposed to house dust mice extract. Meanwhile, maternal microchimerism has been shown in recent studies to shape neurodevelopment and behavior in mice.

This shows that pregnancy-related microchimerism can influence host tissue microenvironment by modulation of regenerative capacity and differential immune responses, therefore affecting maternal and child health outcomes. Whether it is beneficial or detrimental depends on the composition of these cells, which can in turn depend on the context of pregnancy.