title: Membrane vesiculation of Naegleria fowleri amoebae as a mechanism for resisting complement damage.
abstract: Pathogenic and nonpathogenic Naegleria amoebae activate the alternative C pathway; however, only pathogenic amoebae are resistant to C-mediated damage. The present study was undertaken to determine the mechanism by which highly pathogenic N. fowleri amoebae resist C-mediated damage. Nomarski optics microscopy and electron microscopy of Naegleria amoebae revealed membrane blebbing on the surface of C-resistant N. fowleri, but not on C-sensitive N. gruberi, in response to incubation in normal human serum diluted 1:4 to 1:16. Immunofluorescent staining of pathogenic amoebae, by using antiserum to human C proteins comprising the membrane attack complex, C5b through C9, and FITC-labeled goat anti-rabbit IgG, confirmed that the membrane attack complex was concentrated on the membrane blebs. Binding studies with the use of radioiodinated C9 demonstrated a decrease in the 125I-labeled C9 cpm associated with N. fowleri amoebae and an increase in the 125I-labeled C9 cpm associated with the released membrane vesicles after increasing incubation periods in normal human serum. Treatment of pathogenic, C-resistant N. fowleri with cytochalasin D or cytochalasin B to inhibit actin-dependent exocytic processes increased the susceptibility of the amoebae to C damage. In contrast, incubation of nonpathogenic, C-sensitive amoebae with cytochalasins did not alter their susceptibility to C lysis. These data indicate that pathogenic N. fowleri use membrane vesiculation to remove membrane-deposited C proteins, specifically the membrane attack complex (C5b-C9). The ability to remove surface-associated membrane attack complexes serves as one mechanism by which pathogenic N. fowleri resist C lysis.
authors.affiliation: Virginia Commonwealth University, Medical College of Virginia, Department of Microbiology and Immunology, Richmond 23298.
authors.forename: D M
authors.initials: DM
authors.lastname: Toney
authors.forename: F
authors.initials: F
authors.lastname: Marciano-Cabral
mesh_terms: D000818:Animals; D001790:Blood Physiological Phenomena; D002462:Cell Membrane / Q000502:physiology; D015938:Complement Membrane Attack Complex / Q000502:physiology; D003165:Complement System Proteins / Q000502:physiology*; D006801:Humans; D008854:Microscopy, Electron; D016848:Naegleria fowleri / Q000276:immunology* / Q000648:ultrastructure
chemical_list: D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins