The interaction of monoclonal antibodies directed against envelope glycoprotein E1 of Sindbis virus with virus-infected cells.

Two monoclonal antibodies specific for the Sindbis virus envelope glycoprotein E1 were evaluated for their ability to maintain long-term infection when present in the medium of virus-infected cells. One of them, previously shown to have neutralizing activity and to inhibit haemagglutination, caused suppression of both virus expression at the cell surface and prolonged intracellular virus presence. The other monoclonal antibody which lacked neutralizing activity but inhibited virus-specific haemolysis caused redistribution of viral antigens on the cell surface but only slightly prolonged cell survival. Both epitopes were located on the surface of the virus. By electron microscopy it was demonstrated that the determinant associated with haemolytic activity resided near the virus membrane while the haemagglutination inhibition antibody attached near the apex of the virus spikes.