Antiparasite activity of sea-anemone cytolysins onGiardia duodenalis and specific targeting withanti-Giardia antibodies

The killing activity of sea-anemone cytolysins on Giardia duodenalis wasinvestigated. Three different toxins, sticholysin I and II from Stichodactyla helianthus (St I and St II) and equinatoxin II from Actinia equina (EqtII) were all found to beactive in an acute test, with a C 50 in the nanomolar range (St I, 0.5 nM; St II, 1.6 nM; and EqtII, 0.8 nM). A method to target the cytolysin activity more specifically towards theparasite cells by using anti- Giardia antibodies was then investigated. Parasite cells weresensitised with a primary murine monoclonal or polyclonal antibody followed by a biotinylatedsecondary anti-mouse-IgG monoclonal antibody. Subsequently, avidin and a biotinylated EqtIImutant were added, either in two separate steps or as a pre-formed conjugate. When themonoclonal antibody was used, the C 50 of biotinylated EqtII was 1.3 nM withsensitised cells and 5 nM with non-sensitised cells, indicating a four-fold enhancement of activitywith the cell treatment. Treatment with the polyclonal antibody was somehow more effective thanwith the monoclonal antibody in an acute test. This indicates that sea-anemone cytolysins canefficiently kill Giardia cells, and that it is possible to improve, to a certain extent, theanti-parasite specificity of these toxins with anti- Giardia antibodies. However, thefeasibility of this approach in vivo remains to be demonstrated. © 1999 Australian Society forParasitology