PLACENTAL MONOCYTE FUNCTION

Abstract

Modern technological advances have allowed investigators to learn a great deal about the feto-maternal interface. However, much is still not understood about the immunological basis of a successful pregnancy. Even though a few fetal erythrocytes and leukocytes escape into maternal circulation and minor breaks in the placental barrier allow cells to escape in both directions, cells of the embryo normally do not come into direct contact with maternal blood. Maternal blood flows into the placenta filling the intervillous spaces and circulates around the fetal villous tree. The focus of this study was to investigate maternal monocyte function at the time of labor and delivery, particularly the ability to activate monocytes to phagocytize bacteria. Maternal peripheral blood was collected during labor and again within 24 hours of delivery. Placentas were harvested and maternal blood from the intervillous spaces was collected within 6 hours of delivery. Monocytes were separated from all whole blood test specimens as well as nonpregnant female control subjects by density gradient centrifugation and adhesion of monocytes to plastic. The monocytes were then incubated in culture medium with an equal ratio of Listeria monocytogenes bacilli. Monocytes were treated with recombinant human gamma-interferon as an activation signal. No significant difference in the number of viable phagocytized bacteria between interferon-treated and untreated monocytes was observed in any of the test specimens. There was a small, yet statistically relevant, increase in the interferon-treated control cells after 20 hours incubation. The inability of interferon alone to activate monocytes from the placenta and peripheral circulation of women during delivery may be due to the need of a second cooperative signal, perhaps TNF-a or GM-CSF. An alternative is that due to the nature of the processes of labor and delivery, there were present both locally in the placenta and globally in the general circulation various mediators that have the ability to initiate labor and modulate monocyte activity. Further study is warranted to test the ability to activate these monocytes. The production of reactive nitrogen and oxygen intermediates could be assayed as well as the effect of various uterotonins on the activation process. If the immunological processes preventing the rejection of a genetically dissimilar fetus were understood, progress could be made in transplantation science as well as the treatment of infertility and novel approaches to birth control.