TEMPERATURE AND VIRAL INFECTION 



METCALF: All I can say is, while we haven't performed pre- 

 cise kinetic studies, we have examined the reaction over a period 

 extending from zero hours through 24 hours. We find that there 

 is a linear release of neuraminic acid for twenty to thirty minutes, 

 after which the rate of release slows down greatly, but does con- 

 tinue for eighteen to twenty- four hours. The initial effect of 

 virus dilution upon the release of neuraminic acid is overcome 

 at the end of twenty- four hours. The effect of temperature seems 

 to consist of a retardation of the reaction with less neuraminic 

 acid split off. 



CAMPBELL: That will be an interesting system to study thermo- 

 dynamically. 



WALKER: I have been trying to relate this to some work that 

 Dr. Billie Padgett and I have done. Dr. Padgett approached the 

 question of the role of the enzyme of influenza a little differently, 

 and actually aimed at selecting a strain of influenza B virus 

 that was different in its enzymatic characteristics. She was 

 able to get a line of virus that is quite different in its enzymatic 

 characteristics from the parent strain in that its peak zone of 

 activity is at about 35 C, whereas the parent strain has its 

 peak activity at about 37° C. The enzymatic activity of this virus 

 is markedly inhibited at temperatures above 35° C, particularly 

 if calcium ion is removed from the medium. She has made an 

 effort to use temperature as a means of cutting the multipli- 

 cation cycle and seeing where the effect of this enzyme may 

 be. The parent and variant viruses appear to be very similar 

 in all other respects, antigenic make-up, general character- 

 istics, and so on, except for their temperature optimum for 

 enzymatic activity. She finds that the time at which elevation 

 of temperature will affect the multiplication cycle of the variant 

 virus is only toward the end of the cycle, suggesting again that 

 the enzyme is not particularly important in penetration. Ele- 

 vation of temperature with this variant virus early in the cycle 

 doesn't have much effect, but late in the cycle it does. 



We also have followed the appearance of enzyme and virus in 

 the cell, but we have interpreted the results a little differently. 

 I am a little reluctant to think that the enzyme necessarily has an 



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