Wednesday June 30 2:05 PM ET
By Patricia Reaney
LONDON (Reuters) - British scientists have discovered how malaria, which kills up to 3 million people a year worldwide, disarms the body's immune system.
The mosquito-borne malaria parasite invades red blood cells and adheres to special "dendritic" cells that normally activate the immune system. Malaria-infected red blood cells disable the dendritic cells and prevent them from launching an effective attack against the infection.
"It's a significant finding in a major disease," said Dr David Roberts, of the Institute of Molecular Medicine and the National Blood Service in Britain.
"The dendritic cells can't mature and perform their normal function which is to activate T-cells in the immune system to make antibodies to fight off the parasite," he said in a telephone interview.
Until now scientists had assumed that the malaria parasite evaded the immune cells by clinging to blood vessel walls, not by disabling the immune system.
Dr. Britta Urban, the first author of the research paper published in the science journal Nature, said the finding offers new insights into how the immune system works, as well as the possibility of novel ways of developing a vaccine for one of the world's most infectious diseases.
"If the parasite does indeed affect immune regulation then for a vaccination program to be effective, anyone that has malaria may need to be treated for the malaria first," she said.
The part of the parasite that disables the immune system could be targeted in a vaccine and may also be useful in treating other diseases.
Malaria affects an estimated 500 million people each year, mostly in tropical countries in sub-Saharan Africa, Asia and Central and South America. More than 90 percent of its victims are children.
Most cases are caused by a parasite called plasmodium falciparum. A female mosquito transmits the disease by sucking blood from an infected person and passing on the parasite to everyone she bites. The parasites travel to the liver where they multiply by the thousands and are released into the bloodstream.
The disease is increasing because the parasite is developing a resistance to antimalarial drugs.
Roberts said the parasites attack the immune system in a way that allows the infection to take hold and then cause serious disease and repeated infections.
"The research makes us think how we will be able to use parts of malaria protein for a vaccine and it suggests we might have to modify them before we use them in a vaccine."
In addition to malaria, knowing how the parasite weakens the immune
system could be helpful in dealing with auto-immune disease, when the body
turns against its own cells, and after bone marrow transplants, Urban said.