ULTRASTRUCTURAL AUTORADIOGRAPHIC DETECTION OF INTRACELLULAR IMMUNOGLOBULINS WITH IODINATED Fab FRAGMENTS OF ANTIBODY THE COMBINED USE OF ULTRASTRUCTURAL AUTORADIOGRAPHY AND PEROXIDASE CYTOCHEMISTRY FOR THE DETECTION OF TWO ANTIGENS (DOUBLE LABELING)

Intracellular immunoglobulins of paraformaldehyde-fixed rat lymph node cells were identified with ultrastructural autoradiography of ¹²⁵I Fab of sheep antirat Ig antibody. We observed excellent intracellular penetration and specific localization of the iodinated Fab fragments of the antirat Ig antibody. In contrast, ¹²⁵I sheep antirat IgG or conjugates of peroxidase and Fab-antibody fragments did not show satisfactory intracellular penetration. Simultaneous detection of plasma membrane and intracellular immunoglobulins has been achieved with the use of iodinated Fab of sheep antirat Ig and peroxidase-labeled Fab of sheep antirat Ig and subsequent processing of the cells for cytochemical (peroxidase) and autoradiographic study. The simultaneous demonstration of specific (antiperoxidase) antibody and Ig molecules is also feasible.