Monday, June 25, 2007

Human immunity to ancient retrovirus linked to HIV susceptibility

Washington, June 22 (ANI): A new study has found that human resistance to a retrovirus that infected chimpanzees and other nonhuman primates 4 million years ago might be partially responsible for the susceptibility of humans to HIV infection today.

The study was conducted by a team of researchers including Michael Emerman, Harmit Singh Malik and Shari Kaiser at Fred Hutchinson Cancer Research Center.

Researchers believed that inborn protection against Pan troglodytes endogenous retrovirus, or PtERV1 in humans could be credited to the presence of an ancient, rapidly evolving antiviral defence gene called TRIM5a, which produces a protein that binds to and destroys the virus before it can replicate within the body.

As part of the research, scientists tested the hypothesis by using DNA sequences from the chimp genome to reconstruct a small part of the PtERV1 virus.

Scientists reassembled about one-fifth of the virus by taking dozens of PtERV1 sequences and aligning them to create an 'ancestral' sequence, teasing out areas of commonality between them. They then used this information to make a partial viral genome.

During reconstruction the viral segment was debilitated, enabling only one round of infection in cells.

Researchers found that the human antiviral protein TRIM5a effectively neutralized this extinct retrovirus, which never successfully fixed into the human genome.

The study noted that changes in TRIM5a that made it better at fighting HIV actually inhibited its ability to stop PtERV1 and vice versa, which indicated that this antiviral gene might only be good at fighting off one virus at a time.

"However, while TRIM5a may have served humans well millions of years ago, the antiviral protein does not seem to be good at defending against any of the retroviruses that currently infect humans, such as HIV-1," Emerman said.

The findings of the study were published in the June issue of Science. (ANI)

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