Measurements of the neuraminidase content of two recombinant influenza viruses [X-7 and X-7 (F1)] possessing A0 (nws) haemagglutinin and A2 (r1/5+) neuraminidase showed that particles of X-7 (F1) virus had more than twice as much A2 neuraminidase as those of X-7 virus.
Antibody to A0 haemagglutinin reacted to high titre in antihaemagglutinin, neutralization and complement-fixation tests with both viruses. Antibody to A2 neuraminidase (at the same concentration) did not inhibit haemagglutination by either virus and did not prevent X-7 virus from infecting cells. It did, however, reduce the size of X-7 virus plaques. Antineuraminidase neutralized, but only to a low titre, the infectivity of X-7 (F1) virus for cells of the chick allantonic membrane and completely inhibited plaque formation by this virus in tissue cultures. Antineuraminidase and antihaemagglutinin antibodies reacted with both viruses in complement-fixation tests to similar titres.
The biological ineffectiveness of antineuraminidase antibodies on the haemagglutinin activity or on the infectivity of these viruses was not due to lack of combination of antibody with the virus. The average avidity of the antineuraminidase antibody was high and not different from the antihaemagglutinin antibody (K≃2 × 1011 c.g.s. units). X-7 virus has approximately one quarter and X-7 (F1) virus one half of the number of enzyme antigenic sites as haemagglutinin sites.
ChoppinP. W.,
TammI.1960; Studies of two kinds of virus particles which comprise influenza A2 virus strains. I. Characterization of stable homogeneous substrains in reaction with specific antibody, mucoprotein inhibitors, and erythrocytes. J. exp. Med 112:895
Fazekas de St GrothS.1961b; Methods in immunochemistry of viruses. 2. Evaluation of parameters from equilibrium measurements. Aust. J. exp. Biol. med. Sci 39:563
Fazekas de St GrothS.,
GrahamD. M.,
JackI.1958; The serology of mumps infection. 1. A new source of antigen and a simplified complement fixation test. J. Lab. clin. Med 51:883
Fazekas de St GrothS.,
WithellJ.,
LaefertyK. J.1958; An improved assay method for neutralizing antibodies against influenza viruses. J. Hyg. Camb 56:415
JahielR. I.,
KilbourneE. D.1966; Reduction in plaque size and reduction in plaque number as differing indices of influenza virus-antibody reactions. J. Bact 92:1521
KilbourneE. D.,
LaverW. G.,
SchulmanJ. L.,
WebsterR. G.1968; Anti-viral activity of antiserum specific for an influenza virus neuraminidase. J. Virol 2:281
KilbourneE. D.,
LiefF. S.,
SchulmanJ. L.,
JahielR. I.,
LaverW. G.1967; Antigenic hybrids of influenza viruses and their implications. Persped. Virol 5:87