PrP^c colocalizes with tetraspanins CD81 and CD82 at the plasma membrane. (Ai) Fixed and permeabilized day-6 erythroblasts were dual stained with PrP^c mAb (red) and CD81 mAb (green). Overlays were prepared and the highlighted area magnified to show (Aii) an internal colocalized vesicle (arrow) and the plasma membrane. (Aiii) ROIs were drawn through a cell (ROI1) and along the cell surface (ROI2), and profiles of green and red fluorescence along these ROIs were constructed using Leica quantiation software. Scale bars equal 10μm. (Bi) Fixed and permeabilized day-6 erythroblasts were dual stained with PrP^c mAb (red) and CD82 mAb (green). Overlays were prepared and highlighted areas magnified to show (Bii) plasma membrane at cell-cell contact site and (Biii) internal PrP-containing vesicle (arrow). Scale bars equal 10 μm.