[The trypsin cleavage of hemagglutinin enhances the infectivity of the influenza virus in mice].

Mouse-pathogenic influenza A/Aichi 2/68 (H3N2) grown in cell culture and having uncleaved hemagglutinin HA after treatment with trypsin underwent proteolytic shearing of HA (m.w. 75 kD) into two fragments: NAL (60 kD) and HA2 (15 kD); its lethal effect on mice inoculated intranasally increased more than 200-fold. The virus treated with chemotrypsin underwent similar shearing of HA into HAL and HA2; however, its lethal effect on mice was weak, analogous to that of intact virus with uncleaved HA.