This is an endothelial cell, the cell type that lines your blood vessels. This cell is neat because we grew it from a routine blood sample of a person with a common bleeding disorder, von Willebrand disease (VWD), and used it to figure out how their genetic mutation lead to a deficiency of von Willebrand factor (VWF), a vital clotting protein. VWF (green) is supposed to be stored in rod-shaped packets, but we found that proper storage was eliminated in this cell. Likely, the VWF is trapped, and cannot escape the cell to help with clotting.