New evidence suggests that mothers infected with malaria during pregnancy, with parasites that have anchored themselves to cells within the placenta—placental malaria—may be a double-edged sword for their newborns. A group of scientists led by investigators at the Fred Hutchinson Cancer Research Center has just published data suggesting that a mother's cells could directly act as part of her child's immune system, even after birth, changing the infant's risk of later infection.
While the placenta blocks some infectious agents, it easily passes oxygen and nutrients to the baby. It also allows a unique exchange of cells between mother and child, known as microchimerism. The research team looked at how malaria can alter the mother–child cell sharing that happens during pregnancy. The findings from the new study were published recently in the Journal of Infectious Diseases in an article entitled “Maternal Microchimerism Predicts Increased Infection but Decreased Disease due to P. falciparum during Early Childhood.”
Malaria is the leading cause of death in children under 5 years of age, thus a better understanding of how the immune system fights the parasite is imperative. “This is fascinating biology and super important to explore,” explained lead study author Whitney Harrington, M.D., Ph.D., a pediatric infectious disease fellow at the University of Washington, Seattle. “We’ve always considered the effect of a vaccine or an infection as being the product of one person’s immune system. What we’re basically proposing is that it’s actually the product of two different immune systems that are interacting.”
Most babies carry a very small number of foreign cells acquired from their mothers, on the order of a few maternal cells in every 100,000. However, the researchers found that babies born to Tanzanian mothers infected with malaria during pregnancy and whose infections had traveled to their placentas had evidence for far more maternal cells on board at the time of their births—on average about 1%, with a few cases even higher than 10%.
The researchers examined 53 umbilical cord blood samples from pregnant women and their babies enrolled in a previous study in Muheza, Tanzania, from 2002 to 2006. About half of the women had placental malaria, and about half of those infected women had what's called inflammatory placental malaria, in which the placenta gets very diseased and can stop functioning properly.
To their surprise, when the research team looked at the health records of the babies, they found that those with higher levels of maternal microchimerism were twice as likely to be infected with malaria during childhood. Yet, amazingly these children were only half as likely to get sick from that infection, suggesting that the cells transferred from the mothers might confer some protection against the disease.
The researchers also looked at levels of maternal DNA in the babies' umbilical cord blood in this study. This is representative of the level of maternal microchimerism the children had at the moment they were born, the researchers noted, although it's not known how long that level may persist after birth. Women with placental malaria gave birth to babies with higher-than-average maternal microchimerism, and babies born to mothers with inflammatory placental malaria had even higher average levels.
The investigators were excited by their findings and are optimistic about future studies, where they plan to explore how the maternal and infant cells interact to affect future malaria risk.