the known antigen, is fixed to a microscope slide. If
there are antibodies against Treponema pallidum in the patient's serum,
they will bind to the spirochete. All other antibodies are washed from the slide.
Fluorescent anti-human gamma
globulin (anti-HGG) is added to the well. (Anti-HGG is an antibody made by another
animal against human IgG antibodies. A fluorescent dye is then attached to the
antibody.) The anti-HGG will with any human IgG antibodies bound to the Treponema
pallidum on the slide. All unbound anti-HGG is then washed from the slide.
When viewed with a flourescent microscope, the spirochetes will fluoresce.