Electron microscopic visualization of receptor internalization induced by a monoclonal antibody recognizing the monocyte specific glycoprotein CD 14.

We produced a monoclonal antibody against human monocytes (ROMO 1) which was identified to be directed against the monocyte specific glycoprotein CD 14. For electron microscopic studies, this antibody was labelled with colloidal gold. By using a preembedding technique, we investigated the binding and internalization of gold labelled ROMO 1. The binding is highly specific. No other cells than monocytes bind it. Suspensions of monocytes, prepared from human blood, were incubated for 15 to 90 min with the marked antibody. The cells were labelled on the whole surface. Already after an incubation period of 15 min, the internalization of the antibody receptor-complex is demonstrable. This process is similar to that of receptor-mediated endocytosis (RME), described for different ligands such as cell nutrients, growth factors, hormones, and others.