Propagation of Theiler's GD-VII Mouse Virus in Tissue Culture

Abstract

Theiler''s GD-VII virus of mouse encephalomyelitis was propagated for 20 passages (transfers) in cultures of chopped mouse embryo brain suspended in ox serum ultrafiltrate and Simms'' X7 soln. After an initial series of culture passages, the cell-free culture fluid killed mice in dilutions as high as 1:1,000,000 when 0.03 ml. was injd. intracerebrally. Eventually, the same results were achieved when the ox serum ultrafiltrate was replaced by heated rabbit serum. The virus multiplied more abundantly at 35[degree] than at 37.5[degree] C; and the yield was higher in 125-ml. Erlenmeyer flasks containing 3 ml. of medium than in 50-ml. flasks containing 4 ml. of medium. No increase in virus output was ever obtained by inoculating subcultures with ground material; nor did grinding the culture tissues improve the mouse titrations. Also, no real advantage was gained by subjecting the cultures to continuous gassing with mixtures of O2, CO2 and N2. The conc. of virus in the culture medium was higher after 2 days'' incubation than after 1 day. After 2 days, the yield diminished. Culture virus from 20th passage embryo mouse brain cultures that had been frozen at [long dash]60[degree] C for 49 days was propagated for 13 additional passages in cultures of brain tissue from 1-day-old mice (5 passages), 3-day-old mice (3 passages), 5-day-old mice (4 passages) and 14-day-old mice (1 passage), respectively.