Endocytosis in lymphocyte (peripheral blood, rat)

Electron microscopy. Thorotrast is a suspension of thorium dioxide particles and was formerly used as a contrast medium in X-ray diagnostics. These particles were found to accumulate in spleen, lymph nodes and most likely in macrophages and phagocytizing reticular cells. Generally lymphocytes do not phagocytize large complexes of foreign material. However, when small thorotrast particles are presented for a short while to isolated mature lymphocytes the subsequent stages of internalization can be demonstrated. The electron-dense thorotrast particles (→) adhere to the cell surface, become internalized and clustered within endosomes (1). (3) nucleus; (4) autophagic vacuoles.