Studies on Measles Virus in Tissue Culture (I) Morphological Changes and Development of Virus Antigen Examined by Fluorescent Antibody Technique.

The cytopathogenic effcts of measles virus ( Edomonston strain ) were examined using FL and VERO cells by standard light microscope, phase contrast microscope, acridine orange staining and fluorescent antibody technique. The morphological changes of the infected cells were essentially similar to those observed by several authors in various cell cultures. Enlargement of the nucleoli and formation of syncytial giant cells were outstanding changes at the early stage of infection. Enlarged nucleoli developed brilliant flame red fluorescence in acridine orange stained preparation, suggesting increased RNA activity and possible participation of them in the synthesis of viral nucleic acid. Early localization of virus antigen tended to be perinuclear and specific fluorescence was gradually distributed throughout the cytoplasm as infection progressed. In more advanced stage, inclusion bodies appeared either in the nuclei or in the cytoplasm, or in both of them. Intranuclear inclusion bodies were almost round and eosinophilic with relatively homogeneous inclusion matrix. As they showed negative RNA or DNA staining and did not develop any specific fluorescence by direct fluorescent antibody technique, it would be difficult to assume their participation in viral reproduction. Cytoplasmic inclusion bodies, on the contrary, were remarkably large and irregularly shaped and revealed positive RNA staining, and some of them contained measles virus antigen. So, they are not the secondary degenerative changes due to infection but may have close relation to viral reproduction. At the late stage of infection, small cytoplasmic processes with strong reddish orange fluorescence, characteristic of ribonucleic acid, was observed with acridine orange staining. Virus antigen showed the tendency to be concentrated at the outer surface of the infected cells. From these findings, it may be assumed that viral nucleic acid (RNA) or virus precursor are synthesized chiefly in the cytoplasm and maturation and release of virus particle take place at the cell membrane.