Primates Living with Immunodeficiency Viruses

Humans who acquire HIV can often live for years, even decades with it until it progresses to full-blown AIDS, which it inevitably does. However, recent research has determined that some primates who have acquired an immunodeficiency virus have been able to live with it indefinitely without it ever progressing to any AIDS illnesses. As you may already know, AIDS has its roots from primates like mangabeys and chimpanzees in the wild that became infected with simian immunodeficiency viruses (SIV) that ultimately were transmitted to humans. What is surprising is that these initial primate hosts have remained healthy despite being carriers of SIV. Their body’s resistance to developing the disease is essential in determining how AIDS progresses in the human body.

Researchers from both the Emory Vaccine Center and the Yerkes National Primate Research Center performed studies on both sooty mangabeys and rhesus macaques. The mangabeys have been able to resist SIV, while the macaques, much like humans, inevitably succumb to it. Research determined that the immune systems of primates like mangabeys are not activated to such a high extent as the immune systems of the macaques when SIV infection occurs. This could be very helpful in figuring out why AIDS occurs in some of the primate species and not other ones. According to the senior author of the research, Mark Feinberg, “During both HIV infection in humans and SIV infection in macaques, the host immune system becomes highly activated, experiences increased destruction and decreased production of key immune effector cells and progressively fails as a result. In contrast, natural hosts for SIV infection, like sooty mangabeys, do not exhibit aberrant immune activation and do not develop AIDS despite high levels of ongoing SIV replication. Our studies sought to understand the basis for the very different responses to AIDS virus infections in different species.”

The key difference involves something known as dendritic cells. These cells comprise the immune system and are responsible for making the body aware of viruses or bacteria that are invading it. They also mimic responses by the immune system to help clear the body of the infections. Feinberg and fellow researchers determined that in sooty mangabeys, these dendritic cells do not signal as intense an alarm as they should when SIV attacks; thus, these important cells do not become activated during the initial stages when SIV infects. On the other hand, these dendritic cells in the immune systems of mangabeys are readily activated by SIV/HIV.

Says Feinberg, “Better understanding of the biological basis by which sooty mangabeys and the numerous primate species that represent natural hosts for AIDS virus infections have evolved to resist disease promises to teach us a great deal about the emergence of the AIDS pandemic, and about the mechanisms underlying AIDS progression in humans. In addition, such insights will hopefully help inform new approaches to treat HIV infection most effectively. Also, better understanding how natural hosts for SIV remain healthy may provide clues as to the future evolutionary trajectory of human populations in response to the profound selective pressures now being felt in regions of the world where the tragic consequences of HIV infection are most severe.”