Electron microscopic study of measles virus infection: unusual antibody-triggered redistribution of antigens on giant cells.

Vero cells infected with measles virus fuse to form multinucleated cells which incorporated virus-specific antigens in their membrane. The distribution of these antigens was analyzed after a brief treatment with human anti-measles immunoglobulin G, using autoradiography and immunoperoxidase labeling combined with transmission and scanning electron microscopy. Virs-specific antigens were distributed over the entire surface of giant cells treated at 4 degrees C with human anti-measles immunoglobulin G and labeled Protein A. When cells were shifted to 37 degrees C, labeled antigen-antibody complexes were redistributed in two stages. Patch formation occurred in 5 to 15 min. Later, antigen-antibody complexes became concentrated in a paracentral "ring" rather than typical caps. Patch formation occurred in the presence of metabolic inhibitors, whereas ring formation was inhibited by metabolic inhibitors. These rings contained membrane folds, villi, and viral buds, whereas the rest of the membrane was smooth. In addition, shedding, endocytosis of antigen-antibody complexes, and reexpression of antigens were observed. Antibodies to nonviral membrane antigens induced the same pattern of redistribution. Infected cells treated with anti-measles Fab' fragments maintained a homogenous distribution of label throughout the experiments. In conclusion, intact immunoglobulins, but not Fab' fragments, were able to induce a dramatic redistribution of viral antigen on the membrane of giant cells infected with measles virus.