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* Department of Medicine, University of Pennsylvania School of Medicine; and
Department of Animal Biology, University of Pennsylvania School of Veterinary Medicine, Philadelphia
Correspondence: Ronald Collman, 807 Abramson Bldg., 34th & Civic Center Blvd., Philadelphia, PA 19104-4399. E-mail: collmanr{at}mail.med.upenn.edu
To better understand CXCR4 function on macrophages and the relationship
between coreceptor use and macrophage tropism among diverse HIV-1
isolates, we analyzed macrophage pathways involved in Env-mediated
fusion, productive HIV-1 infection, and chemokine-elicited signaling.
We found that both CXCR4 and CCR5 transduced intracellular signals in
monocyte-derived macrophages, activating K+ and
Cl- ion channels and elevating intracellular calcium in
response to their chemokine ligands stromal cell-derived factor-1
and macrophage inflammatory protein-1ß, respectively. The prototype
T-tropic X4 strain IIIB infected macrophages poorly, and this was
associated with failure of the IIIB Env to fuse efficiently with target
macrophages despite functional CXCR4. In contrast, several primary X4
isolates mediated efficient CXCR4-dependent fusion and productive
macrophage infection. Several R5X4 strains could fuse with and infect
macrophages through both CCR5 and CXCR4. Thus, macrophages express
functional CXCR4 and CCR5 but primary and prototype X4 isolates differ
in their ability to utilize macrophage CXCR4. Isolates classified as X4
based on coreceptor use may be phenotypically either T-tropic or
dual-tropic and, conversely, phenotypically dual-tropic isolates may be
either R5X4 or X4 based on coreceptor use.
Key Words: gp120 gp160 envelope chemokine receptor ion channel calcium
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