Mothers infected with malaria during pregnancy can pass more of their own cells to their baby and change the infant’s risk of later infection, a new study shows.
The study, from researchers at Fred Hutchinson Cancer Research Center and their colleagues, suggests that a mother’s cells could directly act as part of her child’s immune system, even after birth.
The placenta blocks some infectious agents, but 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. It was led by Dr. Whitney Harrington, University of Washington and Seattle Children’s Hospital pediatric infectious disease specialist, and Fred Hutch microchimerism researcher Dr. J. Lee Nelson.
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, but 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 one percent, with a few cases even higher than 10 percent.
The level of increase of mother’s cells present in baby’s blood was a surprise to the researchers. Harrington hypothesizes that the infection led to alterations in placental proteins that control cell trafficking, which allowed more maternal cells to enter the fetuses.
Even more surprising was the lasting effect of this change. When the researchers 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 — but 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.