Kupffer cells are fixed macrophages found in the walls of hepatic sinusoids.
This animal was injected with trypan blue. For most cells, trypan blue is a vital dye. It is excluded from living cells and enters into and stains dead cells. However, trypan blue is also taken up by living cells actively engaged in phagocytosis.
In this liver, trypan blue demonstrates the presence of phagocytosis in Kupffer cells.
These macrophages readily phagocytize and retain the foreign molecule, trypan blue.
(The other tissue section is from the kidney with uptake of the dye by the proximal convoluted tubules.)