Viral weakening of the placenta
Immunologists have found out how the Zika virus penetrates to the embryo through the placenta
Specially provoked inflammations help him in this
Brazilian immunologists have found out exactly how the Zika virus manages to penetrate through the placenta of a pregnant woman into the tissues of the embryo. To do this, he "learned" to provoke prolonged inflammation in the placenta area, so that its protection is weakened and virus particles can reach the fetus. The results of the study were published by Frontiers in Immunology (Rabelo et al., Zika Induces Human Placental Damage and Inflammation).
"We have seen with our own eyes how the Zika virus is spreading across Brazil and how its infection affected the condition of pregnant women. Since we have already worked with arboviruses, which include the Zika virus, we decided to study in detail how the fever caused by it affects the body," she said Kissila Rabelo, an immunologist from the University of Rio de Janeiro, one of the authors of the study.
Zika fever was first detected in 1947 in Uganda. The mosquito carries the disease Aedes aegypti. Subsequently, outbreaks of Zika fever were recorded in Asia, Africa, South and North America, as well as in the Pacific region. The last major outbreak of this disease occurred in 2015-2016 in Latin America. There, scientists discovered a dangerous side effect of Zika virus infection – it turned out that children whose mothers contracted this fever during pregnancy develop microcephaly.
According to estimates of the Brazilian Ministry of Health, between April 2015 and October 2016, about 3.2 thousand babies were born in the country with microcephaly and other developmental defects caused by the Zika virus. Because of this, scientists urgently began working on a vaccine against this disease, although it does not cause severe symptoms in most patients.
Scientists do not yet know exactly how the virus enters the body of an unborn child. As a rule, the placenta of the mother does not pass through anything except nutrients, oxygen, hormones and various waste products. It is thanks to this that viruses and microbes cannot penetrate into the fetus.
However, the Zika virus somehow learned to bypass this barrier, penetrate into the embryo and destroy those cells that are responsible for the formation of brain tissue. Brazilian scientists have found out why this is so by studying placenta samples from 15 women who gave birth in 2015 and 2016.
Five of them did not suffer from Zika fever, five more contracted the virus, but gave birth to healthy children, and the offspring of the remaining five participants in the experiment developed microcephaly. Comparing the structure, cellular composition and other properties of their placenta, scientists tried to understand how its work is changing due to the Zika virus.
Their analysis showed that this pathogen is able to penetrate into the cells of the placenta and infect them, which is why chronic foci of infection appear inside it. Their appearance, in turn, attracts the attention of certain types of immune cells, such as macrophages and CD8 cells. They begin to secrete various signaling molecules and enzymes, because of which excessively severe inflammation develops.
Due to the fact that such substances accumulate inside the placenta, it swells, and its protein framework begins to change and collapse under the action of certain enzymes that secrete these immune cells – matrix metalloproteinases. Because of this, the permeability of the placenta increases and viral particles can penetrate into the fetus.
The main problem, as noted by Rabelo and her colleagues, is that the placenta can be in a similar state for several months. This significantly increases the likelihood that the Zika virus will enter the tissues of the growing embryo. This should be taken into account when caring for patients during subsequent outbreaks of this viral fever, as well as when developing drugs that could protect future children from microcephaly.
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