Maternal Immune Cells Fend Off Infection by Selectively Killing Bacteria in the Placenta

NIAID Now | September 03, 2020

During pregnancy, the mother’s immune system accepts, or tolerates, the presence of the fetus rather than rejecting it as something foreign in the body. This immune tolerance, which dampens the normal maternal immune response, must be carefully balanced with the need to prevent infections from spreading to the placenta and then to the developing fetus. 

One such infection is caused by the bacterium Listeria monocytogenes. Pregnant women are ten times more likely than other people to get a Listeria infection, which can result in miscarriage, stillbirth, premature birth, or serious illness or even death in newborns.

A NIAID-funded basic research study used animal models and cells grown in the laboratory to show that a protein called granulysin is transferred, via a tiny molecular nanotube, to Listeria-infected placental cells from decidual natural killer cells—a type of immune cell found at the interface between maternal and fetal tissues. Once inside the cell, granulysin selectively kills the bacteria by making holes in the bacterial protective outer membrane without harming the placental cell. This process defends against infection while maintaining tolerance to the developing fetus. These findings may have broader implications and explain how maternal cells may protect the fetus from other disease-causing microbes. 

Reference: Crespo AC et al. Decidual NK Cells Transfer Granulysin to Selectively Kill Bacteria in Trophoblasts. Cell. 2020 Sept 3;182(5):1125-1139.

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