Absence of internalized CXCR4-gp120 complex in late endosomes. CD4⁻/CXCR4⁺ CHO-K1 cells were incubated in the presence of either 10 μg/mL of gp120 wt (A and D), 10 μg/mL of gp120 ▵HX1 (B and E), or medium alone (C and F) for 1 hour at 37°C. After fixation and permeabilization, the intracellular presence of CXCR4 (red; A, B, and C), gp120 (red; D, E, and F), and LAMP1 (green) was analyzed by confocal microscopy. Cells were stained with either the biotin-conjugated anti-CXCR4 12G5 MoAb followed by staining with Texas Red-conjugated streptavidin (A, B, and C) or a rabbit anti-g120 antiserum followed by staining with a Texas Red-conjugated antirabbit IgG (D, E, and F). Coexpression of LAMP1 was assessed after staining of the cells with 10 μL of the anti-CD107 FITC-conjugated MoAb.