Researchers familiar with the terrible progression HIV infection to AIDS, but they are less clued into how the virus gets a foothold in the body. The virus - which attacks the immune cells called CD4 T cells - appears very early in the lymph nodes. But a study in Science today suggests that the virus may strike first with a punch sucker to CD4 cells in the gut, it holing while replicates. The discovery could help scientists develop drugs and vaccines for HIV disarm before it spreads.
Usually CD4 T cells act like sentries who roam the lymph and blood from the body in a dormant state until they encounter a foreign antigen, which triggers them to attack the invader . Ironically, these "activated" cells are particularly vulnerable to HIV, which deceives cells activated by letting. Then it slides its genetic material into the DNA of the cell so that it can spread and eventually kill the cell. Because many lymphocytes gather in the intestine, previous work had looked for early signs of HIV infection. But bowel tissue samples were difficult to obtain, and it was difficult to say how long the person has been infected.
For a clearer picture, researchers at the Primate Center Harvard Medical School in Southborough, Massachusetts, worked with SIV - simian analogue of HIV. The researchers inoculated a group of macaque monkeys with SIV, then killed two weekly intervals to study the T CD4 cells in the gut. Although CD4 levels have not fallen in the blood of monkeys for nearly two months, the researchers found that the population of CD4 T cells in the gut was almost divided in the first week. And by the third week, only a small percentage of cells remained. "It was quite surprising," said Andrew Lackner, head of pathology compared to the primate center. "We spent a lot of time convincing us that there was not another explanation."
"It is a very important document," said Marion Neutra, a biologist from the lining to the Children's Hospital Boston. The intestine was largely overlooked as a base to launch HIV, she said, but it is logical that the virus would start there. "Many of the cells in the gut are activated T" because of their exposure to foreign bodies, she said, making the "choices for the infection of target." The idea "seems very plausible" says William Paul, head of immunology at the National Institute of allergy and infectious diseases in Bethesda, Maryland. One consequence is that any vaccine against HIV should enhance immunity in the intestine, said Paul.
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