The effects of macrophage colony-stimulating factor (M-CSF) on CD4 receptor expression, susceptibility to human immunodeficiency virus type 1 (HIV) infection, and anti-HIV activity of dextran sulfate and soluble-CD4 were studied in cultured, human primary macrophages. M-CSF stimulated macrophage cells to express the CD4 receptor, and this resulted in an increase of both the number of CD4+ cells and the density of the receptor on the cell surface. M-CSF also significantly enhanced the susceptibility of macrophage cells to HIV infection. Interestingly, the anti-HIV activity of dextran sulfate and soluble-CD4 (two compounds that interfere with HIV-CD4 binding with different mechanisms) was reduced 100-fold and fivefold, respectively, in M-CSF- treated macrophages. Human blood concentrations of M-CSF are reported to be similar to those used in this work (1,000 U/mL); thus, it is conceivable that also in vivo this cytokine may modify the susceptibility of macrophages to HIV and the ability of dextran sulfate and soluble CD4 to inhibit HIV replication. These results suggest that the in vitro study in M-CSF-treated macrophages of promising drugs inhibitors of HIV-CD4 binding could provide further insights into the potential efficacy of these compounds in patients.

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