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Sunday, 15 May 2011

Malaria Parasites Protect their Territory in the Body

The malaria parasite can ensure it keeps a host body all to itself by preventing further malarial infections, according to international researchers

The parasite initially reproduces in the liver and moves into the blood. A study on mice, published in Nature Medicine, showed the parasite can trigger iron deficiency in the liver and therefore prevent more infections.
An expert said the research was "very cool and very interesting", and improved understanding of infection.
The researchers were looking at super-infections, when a patient already infected with malaria is infected with another batch of malaria parasites.



Protecting turf

In experiments on mice, researchers showed that parasites in the blood were able to stimulate the production of the hormone hepcidin, which regulates iron levels.
Hepcidin,  the 25-amino acid peptide  is secreted by the liver, which seems to be the "master regulator" of iron metabolism. Hepcidin inhibits iron transport by binding to the iron channel ferroportin, which is located on the basolateral surface of gut enterocytes and the plasma membrane of reticuloendothelial cells. Inhibiting ferroportin shuts off the iron transport out of these cells which store iron. Ferroportin is also present on enterocytes and macrophages. By inhibiting ferroportin, hepcidin prevents enterocytes of the intestines from secreting iron into the hepatic portal system, thereby functionally reducing iron absorption. The iron release from macrophages is also prevented by ferroportin inhibition, therefore the hepcidin maintains iron homeostasis
This reduced the level of iron in the liver, preventing other malaria parasites from reproducing in the organ.
Dr Hal Drakesmith, from the Weatherall Institute at Oxford University, who was part of the research team, said: "Now that we understand how malaria parasites protect their territory in the body from competitor parasites, we may be able to enhance this natural defence mechanism to combat the risk of malaria infections."
Malaria is often accompanied by anaemia, which is treated with iron supplements.
In this study, mice given iron supplements were more susceptible to additional infections.
Dr Drakesmith said: "We may need to look again at the advisability of iron supplementation programmes in malaria-endemic regions, as possible increased risk of infection may need to be weighed against benefits."
Dr Rita Tewari, a malaria researcher at the University of Nottingham, said: "It's very cool and very interesting.
"It tells us a bit more about the mechanism of malaria infection and gives us some sort of tool, this molecule hepcidin, that you can manipulate which can affect infection."