Macrophages Believed to Host ‘Reservoir’ of HIV

Scientists from the National Institute of Allergy and Infectious Diseases have found that macrophages, specialized immune cells known to be susceptible to HIV, "contain and continue to produce large amounts of an HIV-like virus in monkeys even after the virus depletes CD4+ T cells," according to a NIAID news release. The findings, published in the online edition of the Proceedings of the National Academy of Sciences, provide "new insight" into how the virus survives antiretroviral treatment and opens up new avenues for treatments to "eliminat[e]" the virus. According to study author Dr. Malcolm Martin, the macrophage cells become "immediately" infected after HIV exposure and are "relatively resistant to virus killing." They are also able to produce "lots" of new virus, leading to an "underappreciated reservoir." As most treatments currently attack HIV while it is in the T cells, this discovery may require the development of new drug therapies to target HIV in macrophages. Dr. Martin and his team studied SHIV, an engineered hybrid virus, in macaque monkeys. SHIV infection in monkeys is "an extremely rapid and exaggerated model of HIV infection in humans," which allows researchers to study aspects of retroviral biology that are difficult to study in humans because of the slower T cell depletion rate. During the study, SHIV "quickly" destroyed most CD4+ T cells in the monkeys, yet they continued to produce "high levels of virus." Researchers then examined lymphoid organs and found that 95% of the remaining virus-producing cells were macrophages. These findings may explain why the virus "bounces back" when patients on highly active antiretroviral therapy, or HAART, stop taking their medications (NIH release, 1/1).