Human cellubrevin colocalizes with the transferrin receptor in HEK-293 cells and is present in megakaryocytes. HEK-293 cells were fixed with methanol and incubated with (A) anti-Hceb antibody (1/25), FITC-conjugated antirabbit antibody (1/150); (B) antitransferrin receptor antibody (1/25), Texas Red-conjugated antimouse antibody (1/150); (C) overlap of (A) and (B), which was generated with Adobe Photoshop 5.0; (D) differential interference contrast microscopy (DIC) image of the same cells. Original magnification 600×. Megakaryocytes were fixed with 3.7% formaldehyde, permeabilized with 100 μg/mL digitonin and incubated with (E) anti-Hceb antibody (1/25), FITC-conjugated antirabbit antibody (1/150); (F) anti-gpIIβ/III antibody (1/100), Texas Red-conjugated antimouse antibody (1/150). Original magnification 1,000×.