HIV toll: over a billion white cells a day.

This week, a pair of independent research teams describes the intense battle that erupts when HIV, the AIDS virus, gets a foothold in the body. Using biochemical and genetic techniques, both groups tracked the rise and fall of HIV and of CD4 T lymphocytes, the white cells targeted by the virus. Their results confirm that HIV eventually overwhelms the immune system.

The new analyses document the "titanic struggle" between HIV and the body's immune system, comments Simon Wain-Hobson of the Pasteur Institute in Paris. Wain-Hobson's editorial and the teams' reports appear in the Jan. 12 Nature. The work provides "the precise quantitative and mathematical confirmation of a phenomenon that was strongly suspected . . . but never nailed down," adds Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md.

Last year, scientists began to realize that HIV is not inactive during the time between infection and the appearance of AIDS. Instead, the virus gradually accumulates in the lymphoid organs (SN: 3/27/93, p.196).

The new studies indicate that HIV replicates like mad. "We believe it is the engine that drives the . . . disease," says David D. Ho of the New York University School of Medicine in New York City. At the same time, CD4 T cells are multiplying at terrific rates, he notes. The result is a relentless race between the infecting virus and the immune system, one eventually won by HIV.

For this work, Ho's team administered the antiviral drug ABT-538 to 20 people, most of whom had advanced HIV infection. Throughout the study, the researchers monitored the concentrations of virus and CD4 T cells in the volunteers' blood. Meanwhile, George M. Shaw of the University of Alabama at Birmingham and his colleagues treated 22 HIV-infected people with ABT-538 or other antiviral drugs. Shaw's team also began tracking virus and white cells.

Before treatment, virus destroyed by the immune system was replaced with new virus on an ongoing basis. To keep up its offensive against HIV, the body gets rid of about a billion virus particles per day. With treatment, the amount of virus halved approximately every 2 days for the first few weeks, both groups note.

These drugs also cause a sharp boost in the production of CD4 T cells, the two teams report. They calculate that without treatment, the body loses -- and must make -- more than a billion of these white cells daily.

The dark side of HIV treatment began to surface after drug therapy, however, when Shaw's group found that the dramatic drop in HIV didn't last. Within 2 to 4 weeks, virus that resisted the drug blast replicated, producing a more dangerous, drug-resistant HIV infection.