Influenza virus neuraminidase.

Antiserum specific for influenza A2 neuraminidase was produced by immunization of rabbits with the purified enzyme which had been isolated by electrophoresis from the proteins of a detergent-disrupted AoA2 influenza virus recombinant [X-7 (Fl)]. This recombinant contained hemagglutinin of the Ao subtype and A2 neuraminidase. Antiserum to the isolated A2 neuraminidase did not react in any of four serological tests with Ao or A2 subtype viruses that lacked the A2 enzyme. In contrast, the antiserum inhibited the neuraminidase activity only of wild-type and recombinant viruses containing the A2 enzyme, regardless of the nature of their hemagglutinin proteins. The antiserum caused hemagglutination-inhibition of some, but not all, viruses bearing the A2 enzyme, and it reduced the plaque size or plaque number of all viruses tested that contained A2 neuraminidase. In the chick embryo and in cell culture, low dilutions of antiserum reduced the yield of virus. True neutralization of virus in the chick embryo did not occur. We conclude that an antiserum specific for A2 neuraminidase influenced the yield and release of virus from influ-