One of the biggest reasons that Zika virus is such a public health concern is the danger that it poses for women who are pregnant and their unborn fetuses. Women who become infected with the Zika virus when pregnant are known to have “prolonged viremia” and a higher risk of passing the virus on to the fetus, a transmission that can result in a number of serious birth defects
, such as microcephaly.
In a presentation on February 24, 2017 at The First International Zika Conference in Washington, DC, Lenore Pereira, PhD, professor of Cell and Tissue Biology at the University of California, San Francisco, highlighted her research, which is dedicated to answering the question of how the Zika virus is able to spread from maternal blood to the placenta to reach the fetus.
Dr. Pereira opened up her talk with an image illustrating the surface of the placenta in the maternal blood space, that depicted how maternal blood infuses around the villi in the placenta. Dr. Pereira explained how the branching structure of chorionic villi, “increases [the] exchange of nutrients, gages, and IgG for passive immunity.” She continued, “If you look closer, you can see the surface of the villi branch creating a huge surface area for this exchange between maternal blood and the villi themselves.”
Underneath the surface of the villi are the cytotrophoblasts, which are “the building blocks of the placenta.” These are the cells that will proliferate at the tips of the villi and then invade the decidua of the mother. Dr. Pereira explained, “they create a new vasculature, so they move the maternal blood vessel components and they create a low-resistance blood vessel, so that by mid-gestation, a liter a minute of maternal blood is pouring on the surface of the placenta.” She added that this is the time when the baby starts to grow and all “that material and nutrients” are needed in order to do that.
Dr. Pereira stressed that the biggest takeaway from her presentation involves a model that her and her colleagues have developed. In the laboratory, the team used dissected pieces from first trimester placentas placed in matrigel and found that “at the tips of the villi, the cytotrophoblasts proliferated and then they began to invade the matrigel.”
Dr. Pereira explained, “We [took] the villus and we [fixed] it and we put it in a matrix, an embedding medium, and then as an intact tissue, it [was] sectioned.” She continued, “We [could] see at different levels the various cells. So, at any one section you won’t see everything, but you will see some portion of what the villus is doing as it grows, what the functional differences are.” The model allows you to see the mitotic cells that form a cell column as well as the invasive cytotrophoblasts and researchers are then able to measure the distance that the cells invade. Dr. Pereira explained, “So, we [were able to] see how far they go in 3 days, cell-by-cell.”