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HMS Faculty Isolate Secondary Strain of HIV

Strain Linked Directly to Onset of Full-Blown AIDS; Could Lead to New Treatments for the Disease

By Ayanna A. Lonian

A team of Harvard Medical School (HMS) researchers, led by Professor Timothy A. Springer and Research Fellow Conrad Bleul, announced yesterday that they have discovered and isolated a secondary strain of HIV, called the T-tropic strain.

The T-tropic strain has been linked directly to the onset of full-blown AIDS.

"All people know that you can be infected with HIV for years before your immune system collapses," said Misia Landau, senior science writer for the HMS Focus.

Springer, the Latham Professor of Pathology, and Bleul, a fellow in pathology at the Center for Blood Research, found that the T-tropic strain attacks a different portion of the immune system than does an earlier strain of HIV, called M-tropic strain.

"The research located the point at which this increase in mutant T-tropic virus, prior to this point M-tropic, occurs," Landau said.

Both strains initiate their entrance and corruption of the immune system via the same entrance--CD4 receptors. CD4 is a protein located on the cellular membrane of T cells (disease fighting white blood cells which identify invaders).

But Springer and Bleul discovered that once partially ingested into the immune system, the two strains complete their invasion through the use of two different chemokine co-receptors. Chemokines are chemicals which signal immune cells to an infection.

Matured T cells have been taught to locate invaders which express the receptor for the M-tropic strain. Those that are not able to spot invaders--native T cells--express the receptor for the T-tropic strain.

"Springer and Bleul discovered that there are separate co-receptors for the strains; M-tropic goes through a [different] set of doors than T-tropic. The critical point of the research is that there are two different doors," Landau said.

"T-tropic HIV can eat native T cells-cells that were originally off limits to M-tropic HIV," Landau said.

This consumption of naive T cells results in the destruction and collapse of the immune system which initiates the development of full-blown AIDS.

"Before this was all really phenomenology. Nobody really had any way of relating this to a basic mechanism, a molecule, a co-receptor," Springer said in a press release.

"Now, we can frame all of the really big questions about what happens in the disease process in terms of what happens to specific molecules," he said.

Springer and Bleul are still investigating the methods by which the receptors of the M-tropic strain of HIV might be blocked, which could lead to a possible new treatment for AIDS.

"Therapy aimed at T-tropic HIV may be difficult because the receptors involved are very important," Springer said. "The M-tropic strain is not as essential."

"There have been people identified because they are resistant to HIV, who have a mutation in the M-tropic receptor," he said. "That antibody could be therapeutic."

AIDS is considered to be one of the most threatening diseases in society today.

Thus far, no cure has been found for the disease. However, there are several treatments for the various symptoms resulting from AIDS.

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