LONDON, Dec. 16 (Xinhua) -- HIV deals a body blow to the immunesystem almost immediately after infection by destroying key cells in the gut lining, new research findings show.
HIV attacks CD4 cells, known as "helper" T-cells, which help coordinate immune responses. In the blood of infected people, there is a steady fight between viral replication and the production of new CD4 cells to replace those that are lost to the virus. If left untreated, HIV eventually wins this battle, and the immune system collapses.
New research have shown that only about 2 percent of CD4 cells circulate in the blood, and the vast majority of CD4 cells, some 98 percent, are in mucosal tissues, such as those lining the vagina, airways and especially the gut - possibly because pathogens typically enter the body through such tissues, according to the latest issue of the New Scientist published on Saturday.
The number of CD4 cells in the gut lining plummets by up to 60 percent within the first few weeks of infection.
Researchers led by Martin Markowitz of the Aaron Diamond AIDS Research Center in New York are picking apart the mechanisms by which HIV wreaks havoc in the gut, the report said.
The virus not only kills gut CD4 cells directly but also gets the immune system to turn on itself: some CD4 cells self-destruct and others seem to be killed by other T-cells, which the researchers believe is linked to the way HIV activates the immune system abnormally.
This may explain why highly active anti-retroviral therapy (HAART), most successful treatment for HIV now, does not fix all the damage that HIV causes, even in people who are treated very early after being infected.
The virus hits immune cells in mucosal tissues hard and fast, usually before treatment with HAART even starts. Despite being put on drugs within about three weeks, 70 percent of Markowitz's patients lost more than half of the CD4 cells in their lower gut, the report said.
The damage may also trigger further harmful immune activation throughout the body, said Daniel Douek at the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, whose work suggests that damage to the gut enables molecules including lipopolysaccharides which are a component of bacterial cell walls and stimulate the immune system, from microbes in the gut to enter the bloodstream, the New Scientist said.
However, one big unknown is what these findings mean for people with HIV who are on HAART which uses cocktails of drugs that can tip the balance in the blood in the immune system's favor: people with HIV who have now been on the therapy for years seem to remain healthy, according to the researchers.