Effects of anti-E2 monoclonal antibody on sindbis virus replication in AT3 cells expressing bcl-2

Antibodies directed to Sindbis virus (SV) envelope protein E2 are able to control virus replication in vivo and in persistently infected cultures of neurons in vitro. We investigated the mechanisms by which anti-E2 monoclonal antibody (MAb) alters virus replication by using AT3 rat prostatic carcinoma cells expressing the inhibitor of apoptosis bcl-2. Treatment of SV-infected AT3-bcl-2 cells with anti-E2 MAb G5 for 2 h decreased the rate of virus release for 6 to 8 h after removal of the antibody. Electron microscopic analysis of MAb-treated cells revealed that failure of virus release was linked to a defect in the budding process. The decrease in extracellular virus particles occurred despite continued formation of nucleocapsids and synthesis of envelope glycoproteins. MAb treatment delayed the inhibition of K⁺ influx and shutoff of host cell protein synthesis by SV infection in a dose-dependent manner. Synthesis of host cell factors and of nonstructural polyprotein precursors required for the formation of initial replication complexes was also prolonged, causing a slower shutdown of overall vital RNA synthesis. We conclude that one mechanism by which anti-E2 MAb treatment down-regulates SV replication is by reestablishing certain critical host cell functions in infected cells.