Preparation of an immunotoxin for Acanthamoeba castellanii

Acanthamoeba castellanii (Neff) is a small free-living amoeba which is closely related to pathogenic organisms that produce almost invariably fatal human infections (1). The f(ab)' fragment of a monoclonal antibody (designated A9) specifically reactive to the A. castellanii cell surface, was covalently linked to the A chain of diphtheria toxin. This immunotoxin inhibited cell division completely, whereas nonspecific mouse IgG or nonspecific f(ab)' derivatized with diphtheria toxin A chain (DTA), A chain alone, or unlinked A chain and A9-f(ab)' in combination, had no effect on cell division.