Certain human immune cells known as macrophages are composed of hybrid HIV strains that elude treatment and antiretroviral drugs, according to a new study by researchers from the University of Florida and other institutions, the Gainesville Sun reports.

For the study, researchers examined tissue from HIV-positive people and discovered that as much as half of the macrophages present were hybrids, made from genetic material from several HIV viruses that when combined formed new HIV strains. Marco Salemi -- assistant professor of pathology, immunology and laboratory medicine at the University of Florida's College of Medicine -- said that macrophages likely make HIV more aggressive over time, adding, "If we want to eradicate HIV, we need to find a way to actually target the virus specifically infecting the macrophages."

According to the Sun, current research and treatment target T-cells, and although antiretrovirals are effective at blocking infection from new cells and lowering viral loads, they are unable to reduce the viral level in an HIV-positive person to zero. The Sun notes that macrophages can be targeted by HIV multiple times, and once they are infected, they can live for months, unlike T-cells. The team of researchers, led by Michael McGrath of the University of California - San Francisco, is developing macrophage-targeting drugs through a grant from the National Institute of Mental Health, the Sun reports (Chun, Gainesville Sun, 5/28).