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publicado em 05/05/2010 às 20h30:00
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Study offers new data on the natural immunity against HIV

Patients with HLA B57 gene produce more white blood cells that help defend the body from infectious invaders

 
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Foto: Divulgação/MIT
Amplification of samples of the AIDS virus attacks healthy cells of the human body
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Amplification of samples of the AIDS virus attacks healthy cells of the human body

When people become infected by HIV, it' s usually only a matter of time, barring drug intervention, until they develop full-blown AIDS. However, a small number of people exposed to the virus progress very slowly to AIDS and some never develop the disease at all.

In the late 1990s, researchers showed that a very high percentage of those naturally HIV-immune people, who represent about one in 200 infected individuals, carry a gene called HLA B57. Now a team of researchers from the Ragon Institute of Massachusetts General Hospital, MIT and Harvard has revealed a new effect that contributes to this gene' s ability to confer immunity.

The research team, led by MIT Professor Arup Chakraborty and Harvard Professor Bruce Walker at MGH, found that the HLA B57 gene causes the body to make more potent killer T cells white blood cells that help defend the body from infectious invaders. Patients with the gene have a larger number of T cells that bind strongly to more pieces of HIV protein than people who do not have the gene. This makes the T cells more likely to recognize cells that express HIV proteins, including mutated versions that arise during infection. This effect contributes to superior control of HIV infection (and any other virus that evolves rapidly), but it also makes those people more susceptible to autoimmune diseases, in which T cells attack the body' s own cells.

This new knowledge, published online in Nature on May 5, could help researchers develop vaccines that provoke the same response to HIV that individuals with HLA B57 muster on their own, says Walker, who is director of the Ragon Institute and a professor at Harvard Medical School.

" HIV is slowly revealing itself," says Walker. " This is another point in our favor in the fight against the virus, but we have a long way to go."

Most killer T cells are genetically unique and recognize different pieces of foreign proteins, known as epitopes, attached to the surface of cells that have been infected by viruses or bacteria. After a killer T cell grabs hold of such a protein, it becomes activated and starts sweeping the body for more cells that express the same protein, so it can kill them. It also clones itself to produce an army of T cells targeting the invader.

The new Ragon Institute study shows that individuals with the HLA B57 gene produce larger numbers of killer T cells that are cross-reactive, meaning they can attack more than one epitope associated with HIV, including mutants that arise to escape activated killer T cells.

The finding offers hope that researchers could design a vaccine to help draw out cross-reactive T cells in people who don' t have the HLA B57 gene. " It' s not that they don' t have cross-reactive T cells," says Chakraborty. " They do have them, but they' re much rarer, and we think they might be coaxed into action with the right vaccine."

Source: Isaude.net
   Palavras-chave:   HIV    HLA B57    Natural immunity    Massachusetts General Hospital    Arup Chakraborty   
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