CELL RESEARCH SHEDS LIGHT ON HIV-AIDS LINK.

Byline: Angela La Voie Medical Tribune News Service

Dutch researchers may have gained a new understanding of how HIV impairs the body's immune system, which gradually leads to AIDS.

The current theory is that HIV exhausts the immune system, making the body more susceptible to other infections that lead to AIDS, by constantly killing off its supply of certain disease-fighting cells known as CD4 cells.

But in a new study, researchers have concluded that HIV may cause disease progression by slowing down the production of new CD4 cells, rather than killing them once produced.

This new insight into the mechanism of HIV infection may help scientists develop new ways to fight AIDS, according to the researchers, led by Katja C. Wolthers, a researcher in the department of clinical viro-immunology at the University of Amsterdam in the Netherlands, whose findings are published in the journal Science.

The researchers arrived at their conclusions by measuring certain components of CD4 cells and other immune-system cells known as CD8 cells.

The extremities or arms of a chromosome, called telomeres, naturally shorten each time a cell replicates. By measuring how the lengths of CD4 telomeres changed over a nine-year period, in comparison to how CD8 telomeres changed, the researchers were able to tell how fast both types of cells replicated.

Overall, they found that the telomere length of CD8 cells was significantly shorter than CD4 telomere length in a group of 14 HIV-infected men, suggesting the new CD8 cells were being produced much faster than CD4 cells.

By contrast, the researchers found no difference in CD4 and CD8 telomere length in nine healthy patients.

These findings undermine the current belief that, with HIV infection, both CD8 cells and CD4 cells die and undergo a rapid turnover in the body, according to the researchers.

The researchers speculated that the observed CD8 turnover may result from the CD8 cells exhausting themselves in the face of the AIDS virus, then vigorously renewing their ranks, in an effort to make up for the diminishing ranks of their disease-fighting partners, the CD4 cells.

``We suggest that HIV is slowing down the flow at the tap - that is, the generation of new cells from an as-yet-undefined source,'' the researchers wrote.

``This is an important basic science study,'' said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md.

``It shows that HIV may not have a high rate of destroying CD4 cells, but may cause difficulty in these cells repopulating or reconstituting,'' he said.

He added that while it is difficult to predict the implications of basic science research, the new findings could lead researchers to explore ways ``to induce the expansion of CD4 cells over and above how they're now replicating.''