140 ALICK ISAACS 



RDE was given with each hourly washing in order to restrict virus liberation 

 to a single cycle, a finding which they demonstrated experimentally. It was 

 found that virus liberation occurred at a constant rate for 36 hours, so that 

 the virus must leave the cells by a process which does not destroy the 

 cells. 



Cairns and Mason (1953) measured the amount of influenza hemagglutinin 

 in chorioallantoic membrane and allantoic fluid at hourly intervals after 

 infection with very large doses of virus and found that between the 4th and 

 8th hours the membrane titers were consistent with a constant release period 

 of about one hour. The experiments were then repeated but with large doses 

 of RDE given 2| hours after the virus. No hemagglutinin was detectable in 

 the membrane until 7 hours after infection and thereafter the titer was about 

 one-tenth of that in the fluid. The effect of the RDE was therefore to elute 

 newly released virus from the surface of the cells, and Cairns and Mason 

 calculated that the liberation time, excluding the time during which virus 

 can be released by the action of RDE, is less than 2 minutes. The most 

 obvious explanation of these findings is that once it is formed the viral 

 hemagglutinin is rapidly liberated from the cells, but that it remains adsorbed 

 to the cell surface, from which it is released within about one hour, presumably 

 by its own enzymatic action. Support for this theory comes from the work of 

 Ackermann and Maassab (1954). They found that the release of influenza 

 virus from chick chorioallantoic membrane in vitro was inhibited by a-amino- 

 jo-methoxyphenylmethane sulfonic acid (AMPS), and that this effect was 

 reversible by RDE given after the virus. When concurrent titrations of virus 

 in fluid and membrane were carried out, it could be shown that the effect of 

 the AMPS was to delay by many hours the liberation of virus from the cells. 

 Ackermann and Maassab interpret these results as indicating that normally 

 the viral enzyme functions in liberating virus from the cells and that AMPS 

 inhibits the enzymatic activity of the virus, the action of AMPS being in 

 turn reversible by RDE. 



Rubin et al. (1957) calculated the release time for Newcastle disease virus 

 grown in chick embryo lung epithelium, using the same assumptions and 

 formula as these workers had adopted in their work on western equine 

 encephalitis virus. The average release time for NDV was found to be 80 

 minutes. However, by treating the cells with NDV antiserum before disrupt- 

 ing them, it was found that a great deal of cell-associated virus could be 

 neutralized during the period of exponential rise, although antiserum treat- 

 ment had little effect when carried out during the lag period. This suggests 

 that during the period of exponential rise in virus titer most of the cell- 

 associated virus is superficially adsorbed to the cell surface; when the release 

 period was recalculated to take this into account, it was found that only a few 

 minutes were required for newly matured virus particles to reach the cell 



