Mechanism discovered that allows malaria to hide from pregnant mothers' immune systems

Researchers from the University of Copenhagen in Denmark have discovered a camouflage mechanism used by malaria parasites to hide from the immune defenses of expectant mothers.

By hiding from the mothers’ immune systems, the parasites are able to attack the placenta. According to the research, one human being in 12 is infected with malaria.

"We have found one likely explanation for the length of time it takes for the expectant mother's immune defenses to discover the infection in the placenta," Lea Barfod, said. "The parasites are able to assume a camouflage that prevents their recognition by the immune system antibodies which would otherwise combat them. So although the immune system has all the weapons it needs to fight the infection of the placenta, these weapons are ineffectual simply because the enemy is hard to spot. Ironically the camouflage also consists of antibodies, but of a type that does not help to fight infection."

When the parasite enters the human body, it begins by hiding in the red blood cells, which the immune system does not typically dispose of because the spleen usually filters defective blood cells. The parasites avoid this filter by ejecting a protein hook to attach to the inner wall of the blood vessel. Even if the immune system antibodies destroy one such hook, the parasite has over 60 hooks at its disposal. While the immune system attempts to stop the parasite, it propagates and infects more and more red blood cells that are usually used for transporting oxygen and nutrients around the body.

"In an advanced version of hide-and-seek the parasites keep looking for new ways of preventing the antibodies from recognizing them. It is a kind of urban guerrilla war in which the fighting is conducted from house to house," Professor Lars Hviid of the Center for Medical Parasitology at the University of Copenhagen said. "One example is the ability of the parasites to hide in the placenta. The first time an African woman conceives her placenta provides a new opportunity for the parasite to hide: a new house, so to speak, and in a way that prevents discovery by the immune system. It takes time for the immune defenses to react to the new threat, and meanwhile the camouflaged parasite harms the woman and her unborn child."

The researchers will now study if the malaria parasite also uses its camouflage at other stages of infection.

"Perhaps it is not only the parasites in the placenta that are capable of hiding like this," Hviid said. "It takes the body a surprisingly long time to develop protection from Malaria, and perhaps the trick we have just discovered is part of the explanation. It is important for us to find out if this is the case in order to help us to understand malaria in general, but also to help us in our efforts to develop a vaccination. We have plenty of work to be going on with."