VWFpp alone does not induce Weibel-Palade body formation. The VWFpp and the fusion protein VWFpp*C3α were independently expressed in canine VWD aortic endothelial cells. Transfected cells were processed and examined as described in “Materials and methods.” Cells were immunostained with a rabbit anti-VWFpp (A, D), a mix of several monoclonal anti-VWFpp antibodies (G, J, M), mouse anti-PECAM (B, E), rabbit–anti-P-selectin (H, N), or polyclonal anti-C3 antibody (K). In cells expressing either human VWFpp (A-C) or canine VWFpp (D-F), the distribution of VWFpp was diffuse, although small VWFpp-containing granules were occasionally observed (D). Cells expressing human VWFpp were dual stained for VWFpp (G) and P-selectin (H): P-selectin distribution was unchanged compared with untransfected VWD endothelial cells and very little colocalization of VWFpp and P-selectin was observed (I). Cells expressing the VWFpp*C3α fusion protein showed both diffuse staining as well as granular storage of both VWFpp (J) and C3α (K). Dual-staining for VWFpp (M) and P-selectin (N) revealed very little colocalization of the VWFpp*C3α protein with P-selectin (O). While the VWFpp*C3α protein may induce granule formation in the canine VWD aortic endothelial cells, P-selectin is not recruited to the newly formed granule.