Plasmodium falciparium is particularly dangerous for pregnant women, as it infects the placenta and is usually fatal for the mother and the fetus. This, combined with the often feeble medical resources of malaria-stricken countries, can lead to such serious complications that the mother dies during delivery.
“For some reason, women in their first pregnancy lose the semi-immunity that is normally found in adults,” explained a Karolinska Institutet graduate student who has been working with the study. “The placenta seems to be an anatomically favorable environment for a subpopulation of the parasites.”
The research group from Karolinska Institutet, under the leadership of Professor Mats Wahlgren, has been working with Karolinksa Institutet’s partner university in Uganda to study in detail how the parasite infects the placenta. Their results, which are published in the American scientific journal PNAS, can enable the development of vaccines and therapies to combat severe malarial infections.
During one particular phase of its lifecycle, the parasite enters human red blood cells, where it produces proteins that attach themselves to receptors in the wall of the blood vessels. This causes the red blood cells to accumulate in organ capillaries, and gives rise to life-threatening symptoms. Adults who have been infected several times can become partly immune as their defense system gradually starts to recognize the parasite’s proteins. When the placenta is formed, however, a new environment is introduced with a different set of receptors. This means that a new growth niche is made available to a subpopulation of the parasites.
Earlier studies have suggested that each protein from the parasite attaches to only one specific protein, a receptor, in the placenta. This study shows, however, that the natural mechanisms are more complex than laboratory studies have shown.
“Most of the parasites we studied could bind to three different receptors in the placenta,” said Professor Wahlgren. “This would mean that a future vaccine cannot be based on the principle of one protein-one receptor, as was previously believed.”
The Karolinska Institutet commented that now that scientists know that several placental receptors are involved in the binding mechanism, attention will be shifted to the parasite itself, and whether it produces many different surface proteins or if one and the same protein is able to bind to many host receptors.