The effects of monoclonal antibodies against the hemagglutinin-neuraminidase and fusion protein on the release of Sendai virus from infected cells.

Vero cell cultures in Leighton tubes were infected with egg-grown Sendai virus at high multiplicity of infection. Four hours after infection, the cultures were labelled with 35S-methionine, after which various concentrations of fourteen and five mouse monoclonal antibodies directed against different antigenic determinants of the hemagglutinin-neuraminidase (HN) and fusion (F) protein, respectively, were added to the medium. Fourty-eight hours after infection radiolabelled virions released into the medium were collected and purified by discontinuous sucrose gradient centrifugations. The amount of virus-bound radioactivity obtained in the various extracellular materials allowed an estimation of the capacity of the different monoclonal antibodies to inhibit the release of Sendai virus. In addition, the release of virions from infected cells was studied ultrastructurally. Based on their serological reactivity the fourteen anti-HN monoclonal antibodies could be divided into four groups. The first group of clones could not inhibit any biological activity of the virus. These clones were binding proximally, near the base of the HN glycoprotein and could not inhibit the release of the virus. The second group blocked hemolysis, but did not block hemagglutination (HA) or neuraminidase (NA) activity. The third group of clones blocked all biological activities of the HN glycoprotein. The fourth group could only block NA activity. With the exception of one of five monoclonal antibodies belonging to the second group, antibodies of the second, third and fourth group were found to bind more distally on the HN glycoprotein. Except for two monoclonal antibodies of the second group they could all effectively inhibit release of the virus from infected cells. Ultrastructurally, these antibodies caused aggregation of virions in contact with the plasma membrane. The five monoclonal antibodies directed against the F protein reacted with four different antigenic sites. These antibodies could not prevent the release of Sendai virus.