HIV in the brain and spinal cord.

HIV in the brain and spinal cord 

When HIV crosses the blood-brain barrier, it can trigger a host of neuropsychological problems. At least two-thirds of AIDS patients suffer from memory impairment, limb weakness and poor concentration -- symptoms collectively known as AIDS dementia. However, despite AIDS' widespread damage to nerve cells, autopsy studies have revealed these cells do not appear to harbor the virus. Instead, scientists have accumulated evidence that HIV in the central nervous system mainly replicates inside two types of related cells: macrophages (scavenger cells that have migrated from the blood) and microglial cells (the resident immune cells of the brain and spinal cord).

Researchers, however, had not directly linked microglial cell death to HIV infection and were uncertain whether the virus could infect other glial cells. To settle these questions, Brynmor A. Watkins and his colleagues at the National Institutes of Health added several HIV strains to a culture of microglial cells and astrocytes -- star-shaped glial cells that surround and support nerve cells. In the Aug. 3 SCIENCE, they report that an HIV strain with a preference for macrophages infected only the microglial cells, causing them to fuse and die.

Enzymes and other chemicals released by dying microglial cells may degrade nerve tissue, Watkins now suspects, triggering symptoms related to AIDS dementia. He adds that his team's microglial cell culture may help test drugs targeted at halting HIV infection in the central nervous system.