Internalization of a monoclonal antibody against human breast cancer by immunoelectron microscopy

Using an avidin-gold conjugate, the binding and internalization of the biotinylated anti-breast cancer monoclonal antibody MBr1 in MCF-7 cells were examined. After labelling MCF-7 cells at 0°C, MBr1 was found to specifically bind to the entire cell surface. MBr1 distribution was diffused in cells fixed before labelling, but appeared in patches of different sizes in cells immediately fixed after labelling. On warming prelabelled cells at 37°C for 2 min, MBr1 was internalized through non-coated small invaginations and vesicles an also through smooth invaginations with coated regions at the bottom. After warming for 15 and 30 min to 37°C, the MBr1 internalization sites were observed as large membrane invaginations, large vesicular structures and lysosomes. The early steps of MBr1 internalization which consists of non-coated micro-invaginations seem to be correlated to the glycolipidic nature of the MBr1 recognized molecule. The MBr1 ability to enter MCF-7 cells suggests that this anti-tumour monoclonal antibody may be used as a toxin carrier agent.