CXCR4 and HIV-1 infection: These findings suggest that an increase in the actin-severing capacity induced by functional gelsolin overexpression provokes defective HIV-1 Env-gp120-mediated CD4-CXCR4 and -CCR5 capping at the cell surface, which may account for the blockade of HIV-1 infection by X4- and R5-tropic viruses, as described previously [6,7,9].