Demonstration of binding of specific polyclonal immunoglobulin G to Treponema pallidum, Nichols strain, by electron microscopy

The binding of specific polyclonal antitreponemal rabbit immunoglobulin G (IgG) to Treponema pallidum, Nichols strain, was demonstrated by whole mount indirect immunoelectron microscopy. T. pallidum from 7- and 10-day old rabbit orchitides was processed both fresh and after 3-5 h anaerobic incubation at 34 C. Polyclonal IgG with demonstrated treponemicidal activity was isolated from immune rabbit serum, as was IgG from nonimmune serum. IgG bound to treponemes was detected with ferritin-labeled Fe fragment-specific goat anti-rabbit IgG. Treponemes were processed for whole mount immune-electron microscopy and negatively stained. Treponemal integrity depended upon duration of orchitis and length of incubation of the suspension. Specific antitreponemal but not nonimmune IgG was shown to bind to T. pallidum. The amount and distribution of immune IgG bound to treponemes increased with the degree of their disruption; IgG attached to the protoplasmic cylinder, cytoplasmic components, and endoflagella. (See more in text.)