AIDS InfoNet www.aidsinfonet.org
Fact Sheet Number 129
WHAT IS VIRAL TROPISM?
When HIV attaches to a CD4 cell it is
going to infect, it uses molecules on the
cell surface. These are called receptors
or chemokine co-receptors. The first
receptor HIV uses is the CD4 molecule.
The virus then uses a "co-receptor."
This is either a CCR5 molecule or a
A Project of the New Mexico AIDS Education and Training Center. Partially funded by the National Library of Medicine
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The virus usually uses one co-receptor
or the other. HIV that uses the CCR5
co-receptor is called "CCR5 tropic" or
"R5 tropic." However, viral tropism can
be CCR5, CXCR4, or "dual/mixed" (or
D/M) if some of the sample of virus
uses each co-receptor.
At the present time, the "best" viral
tropism to have is CCR5. This is
because there is now an antiviral
medication that is active against CCR5-
tropic HIV. This attachment inhibitor is
Maraviroc only works against R5-tropic
SOME PEOPLE "NATURALLY"
BLOCK THE CCR5 RECEPTOR
While scientists were
CCR5 blockers, they discovered that
some people do not have the CCR5
receptor on their T-cells. They have a
genetic mutation called a "delta 32
mutation." Because these people live a
healthy life without a CCR5 receptor,
researchers believe that using a CCR5
blocker may not be dangerous.
HOW IS THE TEST USED?
The tropism test is helpful in deciding
whether maraviroc will be useful in
controlling a patient's HIV.
This situation may change in the future.
For example, if a new drug is developed
that is active against X4 virus, the
tropism test could help choose which
type of drug would be most effective.
IS VIRAL TROPISM
Viral tropism is measure by genetic
testing of a blood sample. The blood
and virus sample is amplified. Then it is