Inactivation of the hemagglutinins of type A influenza viruses by physical and chemical means: an aid to classification.

The effects of temperature and treatment with sodium dodecyl sulfate, Tween 20, dithiothreitol, trypsin, or guanidine on the hemagglutinating capacity of six strains of type A influenza virus (A(0)/PR8/34, A(1)/CAME/46, A(2)/J305/57, A(2)/Bethesda/63, A(2)/HK/Aichi/68, and A(2)/HK/80/68), one strain of swine virus (A/Swine/76/?), and one equine strain (A/Equi-2/63) were determined. The two Hong Kong strains could be readily distinguished from the earlier A(2) strains by the resistance of their hemagglutinins to trypsin treatment and their inability to recover hemagglutinating capacity after removal of dithiothreitol from treated virus preparations. In these respects, the equine strain most closely resembled the Hong Kong variants. The pattern of hemagglutination inactivation also set the swine, PR8, and CAME strains apart from each other as well as from the other five strains. The results suggest that separation of type A viruses into groups by the pattern of inactivation of their hemagglutinins may be a valuable adjunct to standard serology for a more definite classification of these viruses.