title: Binding to complement factors and activation of the alternative pathway by Acanthamoeba.
abstract: Acanthamoeba can cause severe ocular and cerebral diseases in healthy and immunocompromised individuals, respectively. Activation of complement appears to play an important role in host defence against infection. The exact mechanism, however, is still unclear. The aim of the present study was to investigate the effect of normal human serum (NHS) and normal mouse serum (NMS) on Acanthamoeba trophozoites, the binding of different complement factors to Acanthamoeba and the activation of the complement system. Moreover, we aimed to work out any possible differences between different strains of Acanthamoeba. A virulent T4 strain, a non-virulent T4 strain and a virulent T6 strain were included in the study. It was shown that NHS, but not NMS clearly has amoebicidal properties. After 5min of incubation with NHS, amoebae showed plasma membrane disruption and extrusion of intracellular components. Cells were completely destroyed within 60min of incubation in NHS but stayed intact after incubation in heat-inactivated serum. The binding of human C3 and C9 to amoebae was established by immunoblotting. Although incubation with mouse serum did not result in lysis of Acanthamoeba trophozoites an immunofluorescence assay (IFA) demonstrated a strong deposition of mouse complement factor C3 activation products, moderate binding of C1q, but no binding of MBL-A and MBL-C. EDTA inhibited the binding of C3 to acanthamoebae. Binding of amoebae to C3b was observed with sera from C1qa-/- and MBL-A/C-/- mice, but not with serum from Bf/C2-/- mice demonstrating an activation of complement via the alternative pathway. There were no significant differences between the three Acanthamoeba strains investigated. Altogether, our results prove that NHS is amoebolytic and that Acanthamoeba binds to C3 and C9 and activates the complement system via the alternative pathway.
authors.affiliation: Department of Medical Parasitology, Institute of Specific Prophylaxis and Tropical Medicine, Medical University of Vienna, Vienna, Austria.
authors.forename: Wilawan
authors.initials: W
authors.lastname: Pumidonming
authors.forename: Julia
authors.initials: J
authors.lastname: Walochnik
authors.forename: Elke
authors.initials: E
authors.lastname: Dauber
authors.forename: Franz
authors.initials: F
authors.lastname: Petry
mesh_terms: D000048:Acanthamoeba / Q000276:immunology* / Q000472:pathogenicity; D000562:Amebiasis / Q000276:immunology*; D000818:Animals; D000936:Antigen-Antibody Complex / Q000276:immunology / Q000378:metabolism*; D001422:Bacterial Adhesion / Q000187:drug effects / Q000235:genetics; D015922:Complement C1q / Q000235:genetics; D003176:Complement C3 / Q000276:immunology / Q000378:metabolism*; D003186:Complement C9 / Q000276:immunology / Q000378:metabolism; D003170:Complement Pathway, Alternative / Q000187:drug effects / Q000235:genetics; D004492:Edetic Acid / Q000494:pharmacology; D006801:Humans; D037601:Mannose-Binding Lectin / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D013045:Species Specificity; D053058:Trophozoites / Q000187:drug effects / Q000473:pathology; D014774:Virulence
chemical_list: D000936:Antigen-Antibody Complex; D003176:Complement C3; D003186:Complement C9; D037601:Mannose-Binding Lectin; D015922:Complement C1q; D004492:Edetic Acid