A study of 1,200 HIV-infected U.S. Air Force servicemen has turned up a new genetic risk for HIV infection among people of African descent. A mutation already well known for conferring protection against a type of malaria appears, paradoxically, to dramatically increase the risk of HIV infection.
A team of virologists, geneticists, and immunologists took a close look at the Duffy antigen receptor for chemokines, more commonly known by its acronym, DARC. The gene codes for an immune receptor on red blood cells; lack of that receptor prevents infection by Plasmodium vivax, a species of the malaria parasite.
The vast majority of Africans, including 90 percent of West Africans, lack the DARC receptor. Absence of the receptor may render them more vulnerable to HIV because the DARC receptor binds immune system responders—molecules called chemokines, which crowd out HIV—and may boost chemokine levels in the blood. In the study of U.S. servicemen, the absence of the DARC receptor was associated with a 40 percent increase in the risk of HIV infection.
The study estimates that the absence of DARC could account for about 11 percent of all HIV cases in Africa. The finding coincides with a report by the Black AIDS Institute, which noted that more than 500,000 African-Americans are living with HIV, and a report by the Centers for Disease Control and Prevention showing a rate of infection for African-Americans seven times higher than the rate for Caucasians.
The DARC mutation very “likely plays an important role in increasing the risk of infection for African-Americans,” says coauthor Matthew Dolan, a senior research physician at the San Antonio Military Medical Center in Texas.
“It’s one of those cruel stories of nature, because the African population over thousands of years adapted to the terrible scourge of malaria,” Dolan continues. “But when HIV appeared on the scene, that previous adaptation caused an increased risk of infection with a new disease.”