EMBARGOED FOR RELEASE
Thursday, August 23, 2001
2:00 p.m. EST
NIMH Scientists Discover New Details of HIV Infectious Process
Scientists at the National Institute of Mental Health (NIMH)
Laboratory of Molecular Biology, reporting in the August 24, 2001, issue of
Science Magazine, have discovered an unexpected step in the process
that the human immunodeficiency virus (HIV) uses to get around natural barriers,
infect human cells, and eventually cause AIDS.
HIV replicates predominantly in the subset of blood cells
called CD4 T cells, and the loss of these cells results in immunodeficiency.
Most T cells are in a resting state, a condition that resists HIV infection.
The researchers found that HIV has evolved a way around this natural barrier.
NIMH Director Steven E. Hyman, M.D., said, " This work
further demonstrates the subtle ways in which HIV avoids the body's natural
resistance to infection. Our understanding of these evolved mechanisms better
prepares us to attack this deadly virus."
HIV belongs to a class of viruses called retroviruses whose
genetic structure, or genome, is composed of RNA, differing, for example,
from the human genome, which is composed of DNA. After entering a human
cell, the HIV RNA manufactures a DNA copy of its RNA, which then gets integrated
into the human cell's DNA. After this integration, the viral DNA acts very
much like a normal human gene, but rather than making proteins that are
essential for human life, it makes new virus particles. Retroviruses such
as HIV must integrate into the human cell's DNA in order to replicate.
The new study shows that after the viral RNA's manufacture
of the DNA copy, but prior to the viral DNA's integration into the cellular
DNA, the HIV DNA serves as a template to make viral proteins called Nef
and Tat, which bring the CD4 T cells out of their resting state, allowing
the virus to integrate into the cellular DNA and replicate.
Scientists have previously shown that persons infected with HIV have many
cells in the brain and elsewhere that contain non-integrated HIV DNA. Although
non-integrated DNA cannot produce new virus, these new findings show that
it does contribute to disease progression.
NIMH is one of 26 components that make up the National Institutes
of Health, part of the U.S. Department of Health and Human Services.