Immunofluorescent localization of VPS33B with α-granule, late endosome/lysosome, δ-granule/lysosome, and Golgi complex markers in normal human megakaryocytes. Human cultured megakaryocytes were cytocentrifuged onto glass slides, fixed, permeabilized, and labeled with polyclonal rabbit anti-VPS33B antibodies together with monoclonal antibodies to VWF (A), LAMP-1 (B), CD63 (C), and GM130 (D), followed by labeling with secondary Alexa Fluor 488 goat antirabbit and Cy3 donkey antimouse antibodies. Stained megakaryocytes were visualized by confocal microscopy where multilobed nuclei (unique to megakaryocytes) could be recognized readily using the differential interference contrast mode. Staining was typically granular. Representative images are shown and the white bar corresponds to 10 μm. (A) The merged images revealed significant partial colocalization (yellow) of VPS33B with VWF. (B) Although partial colocalization of VPS33B with LAMP-1 was observed (merged), it was less than with VWF. (C) VPS33B colocalized minimally with CD63 (merged). (D) No colocalization of VPS33B with GM130 was detected (merged).