Check Mate?

AIDS Institute researchers at the University of California, Los Angeles, say they have discovered a potential reason why the body is able to fight off some viruses but others -- like HIV and hepatitis C -- persist chronically. They report in the May 7 online edition of the journal Science that interleukin-21, a key molecule produced by CD4 immune system cells, is needed to fuel the virus-killing activity of another set of immune cells, CD8 lymphocytes. With an IL-21 deficit, which can happen when the CD4 cells that produce it are crippled by HIV, CD8 cells exhaust themselves and die off before they've purged the virus from the body. "These immune cells are running a long-distance race to contain the virus before it spreads. If they don't get fed, they collapse on the track," says lead researcher David Brooks. So the question facing researchers now: How can CD8 cells be fed enough IL-21 so that HIV doesn't become a chronic infection?