Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.

Reuters NewMedia, Inc.; Thursday April 16, 10:34 pm EST
Maggie Fox, Health and Science Correspondent

Tests on monkeys show that SIV, their version of HIV, destroys immune cells in the intestines first, before it goes on to the blood and the lymph glands, Andrew Lackner, Ronald Desrosiers and colleagues at Harvard Medical School said. Their finding could solve one of the big mysteries of HIV, which researchers have long suspected hides out somewhere in the body, gathering strength, before launching an all-out assault on the immune system.

"The intestine appears to be a major target for SIV (Simian Immunodeficiency Virus) replication," the researchers wrote in a report in the journal Science. They said most studies regarding HIV (Human Immunodeficiency Virus) may have been looking in the wrong place. The virus attacks immune cells, especially CD4 "helper" T-cells, which are important for activating the body's defenses against invaders.

Consequently, most studies have looked at ways to stop HIV from attacking T-cells in the blood and the lymph glands.

"Although it is clear that HIV targets lymphoid tissue, nearly all studies in this area have focused on peripheral blood and lymph nodes," Lackner's team wrote.

"These studies overlook the fact that the gastrointestinal tract contains most of the lymphoid tissue in the body."

Not only that, but the virus probably behaved differently in the intestines, they said.

While it was hard to study the intestines of humans just days after infection -- people usually do not know they have been infected for some time -- it was easy to study SIV in monkeys. The Harvard group, which has been testing an HIV vaccine in monkeys for years, did just that.

They injected macaques with SIV and checked for signs of infection. Within a week, the virus had depleted the CD4 cells in the intestines, they found. They stayed down for months.

"In marked contrast, there were minimal changes in the percentage of CD4 lymphocytes in the blood, spleen and lymph nodes from these same animals at the same time points," they wrote. "Also, there were more virus-infected cells in the intestine than in the peripheral lymphoid tissues."

A good vaccine should target the intestines, they said, adding their live virus vaccine would do that.

The Harvard team's live vaccine has been the center of controversy. They want to test it in people -- and have many volunteers -- but the National Institutes of Health will not let them, saying it is too dangerous.

A "live" vaccine uses the actual virus, but in a genetically-modified form that is believed to be too weak to replicate inside the body.

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