HIV also works from outside"
Researchers at the National Institute of Allergy and Infectious Diseases (NIAID) have discovered a new strategy used by the human immunodeficiency virus (HIV) to weaken the immune system. He is already able to do this from outside the stranger's cell. Drew Weissman and his colleagues at NIAID found that HIV has an effect before it even enters foreign cells. Proteins in the virus' outer coat bind to a molecule called CCR5 on the cell's surface, where it triggers a biochemical reaction: sending a signal inside the cell that could activate the cell and make it more susceptible to HIV infection. If the cell is already infected with HIV, activation can increase production of the virus.
"These new data improve our understanding of the complex ways in which HIV causes the disease," says Dr. Fauci. "This virus is a truly formidable enemy and has many tricks up its sleeve." dr Weissman adds, "Our findings suggest that without infecting a cell, HIV can fundamentally influence the disease process by activating cells and affecting their movement and aggregation."
HIV generally requires two receptors to enter a cell: CD4 and either CCR5 or CXCR4, depending on the strain of the virus. The strains of HIV that are most common in the early stages of HIV disease, called macrophage-tropic (M-tropic) viruses, use CD4 and CCR5 to enter cells. Many strains of the Simian Immunodeficiency Virus (SIV), a relative of HIV that infects non-human primates such as monkeys, also use these receptors.
According to the report in Nature (October 30, 1997 issue), envelope proteins from four different M-tropic HIV strains and one M-tropic SIV strain use the CCR5 receptor to signal the cells in the Culture encouraged movement. In contrast, envelope proteins from other virus strains, the so-called T-cell Tropic (T-tropic) strains, did not trigger any signaling processes.
„HIV disease is characterized by constant immune activation. Signaling stimulated by envelope proteins and triggered by CCR5 may contribute directly or indirectly to this enhanced activation state, with adverse consequences for the HIV-infected individual," says Dr. Fauci.
In activated cells, not only is HIV reproduction and spread enhanced: Chronic immune activation during HIV disease can also lead to massive stimulation of the affected person's B cells. This reduces the ability of these cells to produce antibodies against other pathogens. Furthermore, chronic immune activation can also lead to a type of cell suicide, known as apoptosis, and to increased production of signaling molecules called cytokines, which in turn trigger increased HIV reproduction.
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