The Molecules of HIV

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CXCR4

CXCR4 (aka "fusin") and R5">CCR5 are both chemokine receptors. That is, they are proteins normally embedded in the membrane of a cell, and responds to the presence of chemokines">chemokines outside the cell to trigger some kind of response within the cell.

HIV-1 is able to use either CXCR4 or R5">CCR5 as a co-receptor (CD4 being the main receptor) to facilitate binding and entry into T cells. There are other possible co-receptors, but these are most commonly used.

CXCR4 was the first HIV coreceptor to be discovered, and it's one of the most important ones.

In HIV-positive individuals, the level of expression of CXCR4 is downregulated (i.e. less is produced) in T cells, and studies have found that CXCR4 expression remains low even after HAART treatment.

More information:

• Naming: These receptors are so called because they are receptors of CXC chemokines">chemokines. CXC chemokines">chemokines (such as CXCR4) are distinct from CC chemokines">chemokines (such as R5">CCR5) in that they have one amino acid imbetween the first two cysteine residues, instead of them being adjacent.
• HIV strains which use CXCR4 are called "X4";HIV strains which use R5">CCR5 are called "R5"

Written by
Dan Stowell
(©2002-2006)