A, U937 cells were either singly transfected or cotransfected for expression of hemagglutinin epitope (HAp) alone or F2-Nef-HAp and WT Rab5 or DN Rab5 in combinations as indicated. Cells were stained for cell surface MHCI or MHCII 24 h later and analyzed by flow cytometry. Single-color histograms show surface MHCI or MHCII levels on HAp-gated cells. Isotype controls are shown as gray-shaded curves. B, U937 cells were either singly transfected or cotransfected for expression of HAp alone or F2-Nef-HAp and WT Rab5, CA Rab5, or DN Rab5 in combinations as indicated. Cells were stained with anti-MHCII-biotin 12 h later and cultured for various times as shown before detection of the residual cell surface label. Mean fluorescence intensities were calculated for HAp-gated cells and the data were normalized to the starting intensities as a percentage of the residue of surface-labeled MHCII as shown. C, BMDMs derived from WT C57BL/6 or bg/bg (Bg) mice were transfected to express either eGFP alone (yellow curves) or Nef and GFP (black lines) and stained for cell surface MHCI or MHCII 24 h later for analysis by flow cytometry. Single-color histograms show surface MHCI or MHCII levels on eGFP-gated cells. Isotype controls are shown as gray-shaded curves.