An electron microscopic study of moderate and virulent virus-cell interactions of the parainfluenza virus SV5

Abstract

The multiplication of the parainfluenza virus SV5 was studied in primary rhesus monkey kidney (MK) cells and in a line of baby hamster kidney (BHK21-F) cells. Virus adsorbs to the cell surface and appears to penetrate by phagocytosis. Virus morphogenesis is similar in the two cells; the helical nucleocapsid forms in the cytoplasmic matrix and aligns under regions of cell membrane which acquire viral surface projections. Assembly and release of virus particles at the cell surface occurs by a budding process involving the incorporation into the viral envelope of a unit membrane which is continuous with and morphologically identical to that of the host cell. Both spherical and filamentous virus particles are formed; filaments frequently contain regularly coiled nucleocapsid throughout their length. In MK cells, which yield high titers of infective virus for many days but show little cytopathic effect, a balance appears to exist between synthesis of nucleocapsid and its continuous release within mature virus particles. In contrast, in BHK21-F cells, which produce little virus and disintegrate after extensive cell fusion, large aggregates of nucleocapsid accumulate in the cytoplasm, suggesting a block in maturation at the cell membrane. The present electron microscopic observations support previous studies which suggested that the virulence and yield of SV5 may depend, at least in part, on the response of the cell membrane to the virus.