New research shows that lentiviruses – the genus of viruses that includes HIV and SIV – have been present in primates in Africa for as long as 16 million years. Scientists from Boston College set out to find out how long lentiviruses have been present as it provides better insights into adaptive mutations and the distant history of host-virus interactions, according to the study published in PLOS Pathogens.
The team focused on an antiviral gene called TRIM5, which is a part of a cluster of antiviral genes or "restriction factors" which have mutated over time to protect cells from viruses. The TRIM5 protein is a product of the protector and interacts with the outer shell of lentivirus particles once they have penetrated the host cell. They then work to stop the lentivirus from multiplying. However, TRIM5 in humans does not work as it does in many monkeys where the protein renders HIV/AIDS virtually harmless.
With that in mind, the researchers theorised that the evolution of TRIM5 in African monkeys may hold the key to revealing selection by lentiviruses closely related to modern SIVs (Simian immunodeficiency virus) which affect non-human primates.
To better understand the TRIM5 gene evolutionary tree, the researchers, led by Welkin Jenkins, analysed its complete protein-coding in DNA sequences from 22 African primate species. They found that in Old World monkeys, which include baboons and macaques, there was a cluster of adaptive changes unique to the TRIM5 protein, suggesting that ancestral lentiviruses closely linked to modern SIVs began forming in ancestral primates in Africa between 11 and 16 million years ago. Previously it had been estimated that they began to form about 30,000 years ago.
The researchers write: "The correlation between lineage-specific adaptations and ability to restrict viruses endemic to the same hosts supports the hypothesis that lentiviruses closely related to modern SIVs were present in Africa and infected the ancestors of cercopithecine primates as far back as 16 million years ago, and provides insight into the evolution of TRIM5 specificity."