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September 22, 2008
Scientists find why some primates with HIV-like viruses don’t get AIDS

By Holly Korschun

Scientists at Yerkes National Primate Research Center and the Emory Vaccine Center have discovered important clues from the immune system that explain why sooty mangabey monkeys and other primates stay healthy despite infection with simian immunodeficiency virus (SIV). Understanding how these natural hosts resist illness has been a key unsolved mystery in understanding AIDS.

The Emory scientists have found that the immune systems of sooty mangabeys become much less activated during SIV infection than the immune systems of rhesus macaques, which develop an AIDS-like illness. The scientists believe the less vigorous immune response in mangabeys may explain why SIV and HIV infection leads to AIDS in some primate species but not others.

The reasons are found in major differences in immune signaling in a type of dendritic cells, which play a key role in alerting the body to the presence of invading viruses or bacteria and in initiating immune responses.
In sooty mangabeys, dendritic cells are not activated during the initial or chronic stages of SIV infection so mangabeys don’t mount a significant immune response to the virus. On the other hand, in humans and macaques infected by HIV and SIV, dendritic cells are readily activated.

Unfortunately, rather than helping clear the immunodeficiency virus infection, chronic dendritic cell stimulation may result in chronic immune activation and unintended damage to the immune system. Scientists believe that chronic immune activation in response to HIV infection is a major driving force in the development of AIDS.

The fact that mangabey dendritic cells are less susceptible to activation by SIV may explain why mangabeys don’t have abnormal immune activation and don’t develop AIDS.

The researchers believe new treatment strategies could steer the immune system away from over-activation and complement the use of antiretroviral drugs that focus on inhibiting replication of the virus.