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HIV HAS BAG OF TRICKS TO EVADE IMMUNE CELLS

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The virus that causes AIDS can not only disguise itself to trick the body's immune system but can also temporarily inactivate killer immune cells, British scientists reported Wednesday.

The human immunodeficiency virus (HIV) provokes a strong response by the immune system, but the virus always manages to escape the T-cells sent out to destroy invaders.In a report in the science journal Nature, researchers at the Medical Research Council and the Wellcome Trust said they had found the virus changes the proteins on its surface so they become unrecognizable to the T-cells.

They also found the virus can de-activate the T-cells.

"The virus cannot only hide from the killer cells, but can also change these surface proteins in such a way that, while they still provide targets for the T-cells, they do not provoke a lethal immune reaction," they said in a statement.

"This would appear to be yet another defense mechanism through which the virus can escape capture," Andrew McMichael, one of the researchers, said.

"This is a result of the virus's variability," McMichael added in a telephone interview. "The T-cells . . . may actually be inhibited from recognizing the normal virus. The T-cell may actually make contact with the variant bit of the virus. It'll sort of half-recognize it but be turned off, temporarily."

McMichael said researchers were working to find out how the T-cells were turned off.

Another team, in a report in the same issue of Nature, said they had found the hepatitis virus could act in a similar way against T-cells.

"This mechanism could represent a powerful factor for the development of persistent infection by the hepatitis B virus, and perhaps by other viruses that display uncommonly high mutation rates, such as the human immunodeficiency virus and hepatitis C virus," researchers at the University of Parma, Italy and Cytel Corporation in La Jolla, California, wrote.

Paul Allen, a pathologist at Washington University in St. Louis said in an accompanying commentary that the findings were "evidence of a further, more sophisticated strategy - this is antagonism, whereby a virus can combat antiviral effector T-cells directly by blocking their activity."