Dr. Anil Kumar and colleagues at the Ponce School of Medicine, Puerto Rico, have discovered key ways in which morphine may accelerate the progression of AIDS: The drug increases both viral replication and alterations in a particular part of the virus's coating. Monkeys exposed to long-term morphine administration—20 weeks prior to infection with simian/human immunodeficiency virus (SIV/SHIV) and throughout the 56-week study period—progressed to AIDS faster and showed more signs of compromised immune systems than comparison animals. Of the morphine-exposed animals that developed AIDS, three demonstrated higher viral replication in their blood and cerebrospinal fluid (CSF). When the researchers zeroed in on particular areas of the viral envelope—a lipid-protein covering that helps viruses penetrate cells—they found that morphine-exposed monkeys demonstrated a higher degree of change in the V4 region than control animals. This difference, which may expand the range of cells that HIV can infect, occurred in both CSF and blood. The extent of V4 evolution corresponded with rapid disease progression. Studies such as this aim to open new avenues for intervening against HIV.