Sequence of Morphological Changes in Epithelial Cell Cultures Infected with Poliovirus

A sequential study is reported of the cytological changes induced in cultures of monkey kidney epithelial cells by poliovirus. The pattern of cytological changes was followed through a single cycle of virus multiplication. Morphological alterations were correlated with the appearance of new infective virus within the cells and in the culture fluid. Alteration of the chromatin pattern of the nucleus, and Type B acidophilic intranuclear inclusions, were seen as early as 4 hours after virus inoculation. Later wrinkling and shrivelling of the nucleus occurred, and eosinophilic cytoplasmic masses appeared. The rounded, pycnotic cell, customarily used as an index of the cytopathic response, was found only during the last stages of the infective process. On the basis of these changes, infected cells could be classified into six different types. Differential cell counts were made on the stained cultures, and the stage of cytopathic degeneration was correlated with the appearance of virus in the cells and in the culture fluid. Newly formed virus could be detected within the infected cells at about the same time that the first nuclear alterations and intranuclear inclusions were seen. The virus-induced morphological changes exhibited a specificity distinct from the classical pycnosis of autolytic degeneration.