Use of two-colour flow cytometry to assess killing of Giardia muris trophozoites by antibody and complement.

A two-colour flow cytometry technique was used to assess killing of Giardia muris trophozoites by rabbit anti-trophozoite antibodies and complement. Binding of rabbit antibody to trophozoites and killing of trophozoites were documented by flow cytometry, after incubating the organisms with fluorescein-conjugated anti-rabbit IgG and propidium iodide (PI). Percentages of PI+ (dead) trophozoites ranged from greater than 80%, after incubation with rabbit antiserum and complement, to less than 30%, after incubation with complement alone. The assay technique may be applicable to studies aimed at determining whether intestinal antibodies from Giardia-infected mammals can kill Giardia trophozoites.