Lysis of retroviruses with monoclonal antibodies against viral envelope proteins

Monoclonal antibodies identifying six independent antigenic determinants (epitopes) on the gp70 and p15(E) envelope proteins of murine leukemia virus were tested for their ability to lyse a panel of serologically different [³H]uridine-labeled retroviruses in the presence of complement. Antibodies against the gp70^a, gp70^b, and gp70^c epitopes were uniformly negative in virolysis assays, whereas antibodies against the p15(E)^a, p15(E)^b, and p15(E)^c epitopes lysed the viruses to high titer. The lytic activities of these p15(E)-specified antibodies paralleled their specific binding characteristics determined in previous assays with viral proteins. The p15(E) protein is known to be embedded directly into the viral membrane while the bulk of the glycoprotein (gp70) projects from the surface of the virion; thus our results indicate that the lytic activity of an antibody is related to the distance of the antibody:epitope complex from the membrane bilayer.