Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
CCR5 is the chemokine receptor which HIV uses as a coreceptor to gain entry into macrophages. Certain strains of HIV target macrophages rather than T cells, because their envelope protein is configured such that it works best with CCR5 as a coreceptor - these strains are called macrophage-tropic. (Interestingly, macrophage-tropic strains tend not to be able to induce syncytia.)
The level of CCR5 expression is upregulated in chronic HIV infection - that is, HIV infection causes more CCR5 to be produced than would otherwise occur. Measuring the expression of CCR5 is therefore one indicator of an individual's disease progression. Studies have found that CCR5 expression decreases after a person receives HAART treatment - but not as far as returning it to "normal" levels.
There has been some recent media coverage about a group of individuals with high resistance to HIV infection. These people have a mutation in their CCR5 gene which seems to confer resistance - for more information read my delta32 page.