Demonstration of the binding of monoclonal immunoglobulin G to Treponema pallidum, Nichols strain, by electron microscopy

The binding to the surface of Treponema pallidum, Nichols strain, of six mouse-derived monoclonal immunoglobulin G (IgG) preparations was demonstrated by whole mount indirect immunoelectron microscopy. T. pallidum from 10-day old rabbit orchitides was processed fresh and after 4 hours aerobic incubation at 34°C. Monoclonal IgG bound to treponemes was detected with colloidal gold-labeled Fe fragment-specific goat anti-mouse IgG. Treponemes were processed for whole mount immunoelectron microscopy and were negatively stained. Treponemal integrity depended on the length of incubation of the suspension. Each of the six monoclonal antibodies, but not a monoclonal antibody with specificity for Neisserig gonorrhea, was shown to bind to the intact surface of T. pallidum. The gold label was distributed randomly and was not seen on endoflagella or in areas of obvious membrane disruption. Colloidal gold alone did not bind to any combination of treponemes with monoclonal IgG. Binding occur red at low levels both in terms of the number of gold spheres per organisms and the number of labeled organisms per grid. These results indicate that the cognate epitopes of the monoclonal antibodies are domains of surface-exposed outer membrane immunogens.