Important note: Information in this article was accurate in 1996. The state of the art may have changed since the publication date.
Important note: Information in this article was accurate in 1996. The state of the art may have changed since the publication date.
Reuters NewMedia, Inc. - Thursday, 14 November 1996.
It uses one receptor on the cell as a sort of handle to attach itself. This then reveals a second handle that lets it take a firm hold on its victim, the two separate reports in the science journal Nature said.
The HIV virus infects cells by first hooking up to them, then injecting genetic material that forces the cell to make copies of the virus.
Scientists know where HIV attaches. Two receptors are involved -- the CD4 receptor and the CCR-5 receptor.
The CD4 receptor is meant for CD4 T-cells, the "helper" cells of the immune system, while the CCR-5 receptor is designed for chemokines -- chemicals used by cells to signal when they are in distress. But HIV circumvents the immune system by attaching to these receptors itself.
What scientists did not know was which was more important to HIV -- CD4 or CCR-5.
The two studies, published in the science journal Nature, show that CD4 makes it easier for a protein on the surface of the virus, gp-120, to hook up with the CCR-5 receptor.
"The virus is trying to get through the cell membrane," said Joseph Sodroski of the Dana-Farber Cancer Institute in Boston, Mass., who helped write one of the reports.
"It first has to attach to the cell and it then has to bring its envelope proteins closer to the cell membrane. CD4 sticks out like a stalk. CCR-5 is actually embedded in the membrane."
The CD4 receptor, he said, is "probably this rather flexible thing that binds the virus and then bends over and brings the virus down to CCR-5."
Their findings, they said, should help in designing drugs to battle HIV, and perhaps aid efforts to find a vaccine.
John Moore and colleagues at New York's Rockefeller University made a similar discovery.
Moore said the two-step process helped HIV protect itself from immune system attack.
"The virus wants to preserve its vulnerable sites from immune reaction, so it hides them as long as possible. They are exposed only transiently, until the virus hooks up to CCR-5."
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