As debate continues on whether to destroy the world's last two vials of smallpox virus, scientists have discovered that a virus related to smallpox uses the same route of entry as HIV to invade its host. This is the first virus other than HIV known to exploit structures called chemokine receptors on the surface of immune cells. Its discovery strengthens a new theory on the origins of a rare, life-saving immunity to the AIDS virus.
Like HIV, the myxoma poxvirus -- a pathogen that causes a rapid AIDS-like immune deficiency in rabbits -- hones in on chemokine receptors called CCR5 and CXCR4, reports a research team led by a UC San Francisco scientist. The research is published in the December 3 issue of Science.
Both viruses can dock with CCR5 or CXCR4 for successful invasion, although the scientists don't yet know if the poxvirus exploits another portal known as the CD4 receptor, as HIV does.
Linking CCR5 to an aggressive relative of smallpox strengthens an intriguing theory about the origins of a rare immunity to the HIV virus, so far found only in a small percentage of Caucasians. A mutation in one of the genes for the CCR5 receptor has recently been identified as the strongest source of this protective trait in HIV-resistant people.
Genetic analysis has traced the likely emergence of the mutation to a major epidemic about 700 years ago - possibly the European smallpox plague.
"The protective mutation in the CCR5 chemokine receptor gene almost certainly emerged well before HIV began to infect humans - just about 50 years," said Alshad Lalani, PhD, a post-doctoral researcher at UC San Francisco and lead author of the report on the poxvirus/CCR5 finding. Senior author is Grant McFadden, PhD, professor of microbiology and immunology at the University of Western Ontario and a scientist of the Robarts Research Institute.
"HIV researchers have deduced that the CCR5 mutation probably evolved at least
Contact: Wallace Raven
University of California - San Francisco