Researchers have long known that intravenous drug users are at high risk for HIV infection. Not only does the disease spread through HIV-contaminated needles, but the drugs that are often usedopiates such as heroin and morphinestimulate HIV replication in immune cells. Now new research suggests that methadone, the drug that is widely used to treat heroin addicts, may have the same effect. According to findings announced yesterday at a meeting of the PsychoNeuroImmunology Research Society in Utrecht, the Netherlands, methadone promotes HIV infection in cell culture.

Specifically, Wen-Zhe Ho of the Children's Hospital of Philadelphia and colleagues found that methadone boosted HIV infection of human microglial cells and macrophagescells that serve as reservoirs for the virus in an infected individual. (Apparently, the drug increases the expression of the cell membrane's so-called CCR5 receptors, which enable HIV to enter.) Moreover, methadone converted latent HIV infection to active HIV replication in blood cells taken from HIV infected patients.

"These results support our hypothesis that, like other opiate drugs, methadone may raise the risk of HIV infection," Ho reports. "Further investigations should be done to study whether our laboratory results accurately reflect how HIV infection progresses in patients receiving methadone."