Part of a gene that protects against the progression of HIV in humans has been identified in Tanzanian chimps.
Some people infected with HIV are known to carry a variant of the gene HLA-B that protects them against the virus. They are able to maintain low levels of HIV in their bodies without antiviral therapy. A study of published in PLOS Biology now suggests that chimps have a similar gene variant, PATR-B, that also offers protection.
'Only a part of the chimp gene variant's sequence looks a lot like the human one. That immediately tells us this is the important part of the gene,' said Peter Parham, professor of immunology at Stanford University, USA, who is a senior author of the study.
Understanding the similarities between the protective human and chimp genes may aid in the development of therapeutic approaches to slow or halt the development of AIDS in humans, say the researchers.
They investigated wild chimps from Gombe Stream National Park, where they have been closely monitored over the past 50 years. Gombe chimps naturally have a high rate of SIVcpz infection - the simian equivalent of HIV-1, the virus responsible for AIDS. Close human contact with the Gombe chimps is prohibited, so it is not possible to directly assess viral load in their blood. Instead they looked at stool samples dating back 15 years - stool counts of simian immunodeficiency virus, SIV give a rough estimate of the actual infection levels.
From these samples they were able to sequence a gene of the major histocompatibility complex (MHC) from 125 chimps. The MHC helps the immune system to identify foreign proteins, such as those produced by a virus or those that have been altered, as in a cancerous cell.
'When humans and chimps were part of the same population, there may have been a retrovirus that used a couple of tricks still effective against HIV and SIVcpz today. This super-old genetic variant may be shared between humans and chimps because the pathogens can’t adapt to it,' Dr Pascal Gagneux, an evolutionary biologist at the University of California, San Diego, told Science.