Effect of antibody to neuraminidase on the maturation and hemagglutinating activity of an influenza A2 virus.

Antiserum to a recombinant between an A(o) and an A(2) influenza virus had no detectable antibody against an A(2) virus in standard hemagglutination-inhibition tests, and inhibited 95% of viral neuraminidase activity at a 1 to 400 dilution. However, on mixing virus with antiserum, a drop of up to 90% in hemagglutinin titer was observed. The effects of ultrasonication and direct electron microscopic examination indicated that the antiserum caused aggregation of virus particles. When antiserum was added to A(2) virus-infected chick embryo fibroblasts, release of virus appeared markedly inhibited. After ultrasonication to disrupt aggregates, an increase in released hemagglutinin was observed, but the resulting level was considerably lower than that in control cultures containing normal rabbit serum. In thin sections of infected cells, similar numbers of virus profiles were observed in control and antiserum-treated cultures. A marked increase in release of hemagglutinin was noted if receptor-destroying enzyme was added to antiserum-treated cultures. The results indicate that antibody to neuraminidase does not exert a direct effect on viral maturation, but inhibits the detachment of viral progeny from cell surface receptors.