[Changes in the protease activity in the lungs of mice infected with the influenza A virus]

In uninfected animals, the level of protease and protease-inhibiting activities in the serum are in balance which is broken after influenza A virus infection. Most profound changes occur within the first few hours after infection. In 6 hours postinfection the amount of protease decreases both in the lungs and serum of the infected animals, and the protease-inhibiting activity increases. In the period of the highest accumulation of the infectious virus 2 days after infection, proteolytic activity also decreases, this decrease coinciding with that of the inhibiting activity. The third period of increased protease activity also coincides with amplification of infectious virus progeny and appears to be associated with consequences of virus infection and bacterial superinfection.