Abstract
Multiplication of Cal 10 strain of meningopneumonitis virus (MPV) in vitro was studied using strain L cells as host cells. Relationships could be established among the developmental cycle of virus determined by infectivity titrations, the viral alterations within the cells tinctorially with light microscope, and the submicroscopical structures of various developmental forms and intracellular components, containing matrix, associated with virus under the electron microscopy.
It was found that a sharp decrease in infectivity titer of cell-associated virus during the first 18-20 hours was followed by an increase in titer 22-23 hours after infection, and then a few hours leter, free virus began to increase.
The yield of MPV in a L cell, estimated from the maximum titer of free virus to the number of infected cells, was about 600 mouse LD50 per cell.
It was showed with Macchiavello's stain that hundreds of red stained particles (identified the elementary bodies at the terminal stage of development) were adsorbed on the cells soaked in a suspension of MPV for 2 hours, and a few hours later, most of these particles invaded to form a group in the central region of cytoplasm, where one or more blue stained large particles (initial bodies began to develop 8 hours after infection.
Some particles with elementary body-like structures attached to the cell membrane soaked for 2 hours and several similar particles in the cytoplasm (5 hours after infection) were photographed using ultra-thin sectioning. Single large body enclosed by a intracytoplasmic vacuolar structure (tinctorially invisible matrix) were the first appearance of developmental form of MPV, observed with the electron microscope.
Large bodies in the inclusion (20 hours) often presented a morula-like appearance showing their increase in number by segmentation. A number of elementary bodies (intermingled with various developmental forms) were observed in the inclusion at the initial stage of increase in titer (24 hours after infection).
And it was found that the titration of MPV in strain L cell based on the cyto pathogenic effect was not only sensitive and reliable but also available with ease.
