Abstract

Using immunogold double-labeling the intracellular routing of immunotoxin molecules has been studied ín cultured Molt-4 cells by electrón mícroscopy. Molt-4 cells were incubated with anti-T cell immunotoxin consisting of monoclonal antibodies against CD2, CD5, CD8, and CD27 and ricin and colloidal gold-labeled rabbit anti- ricin IgG and goat anti-mouse IgG antibodies. Cells were taken, after various intervals, and processed for electrón microscope observation. The results indícate that immunotoxin conjúgate molecules are internalized via coated pits by receptor-mediated endocytosis and endocytosed from the invaginations of the noncoated areas oí the plasma membrane into target cells. The molecules of ricin do not disassociate from the monoclonal antibodies routing in the cells during a certain period of time. They are delivered synchronously to the endosomes, vacuole/ and tubule-vesícular portions of the endosomal system. The coated pits that contained gold particles or were gold particle-free were seen at the surface oí tbe plasma membrane of Molt-4 cells. The observation may suggest the presence oí múltiple receptor sites at the surface membrane of target cells