Effects of influenza virus replication on neutral proteolytic activities in embryonated egg fluids

The levels of neutral protease activity associated with allantoic and amniotic fluids of embryonated eggs during the replication of influenza strains A/PR/8/34 (H1N1) and A/turkey/Ontario/7732/66 (H5N9) were investigated. A sensitive fluorometric technique proved useful for characterization and monitoring changes of protease activities in egg fluids. The predominant type of protease in allantoic and amniotic fluids had trypsin-like specificities. Variation in protease levels of both fluids occurred throughout the course of virus replication irrespective of the virus strain or the route of inoculation used. Concomitant with the production of high levels of infectious virus there was a marked decrease in neutral protease activity in the fluid from the cavity initially infected. Translocation of virus also occurred especially with amniotically infected eggs, as evidenced by high infectious virus titers and decreased protease activities in allantoic fluids.