title: Leishmania amazonensis promastigotes evade complement killing by interfering with the late steps of the cascade.
abstract: During their growth in vitro, promastigotes of Leishmania amazonensis undergo differentiation from complement-susceptible to complement-resistant forms. Here, we demonstrate that both forms bind comparable amounts of C3 on their surfaces, with the predominant molecule species being the haemolytically active C3b. Likewise, equivalent amounts of C9 are deposited on both forms of promastigotes. However, while C9-bearing complexes are exposed on the cell surface of resistant promastigotes, they are cryptic in the susceptible stage of the parasites. The membrane fraction of complement-resistant promastigote lysates has the ability to inhibit complement-mediated haemolysis, blocking C9, but not C3 deposition to complement-activating complexes. Moreover, the membrane fraction of complement-resistant promastigote lysates can inhibit the late steps of guinea-pig erythrocyte lysis much more efficiently than complement-susceptible ones. Our results indicate that L. amazonensis promastigotes evade complement killing by inhibiting the cytolytic pathway of the complement cascade.
authors.affiliation: Departamento de Bioquímica-Immunologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
authors.forename: A C
authors.initials: AC
authors.lastname: Nunes
authors.forename: F R
authors.initials: FR
authors.lastname: Almeida-Campos
authors.forename: M F
authors.initials: MF
authors.lastname: Horta
authors.forename: F J
authors.initials: FJ
authors.lastname: Ramalho-Pinto
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002462:Cell Membrane / Q000276:immunology; D003176:Complement C3 / Q000276:immunology / Q000378:metabolism; D003179:Complement C3b / Q000276:immunology / Q000378:metabolism; D003186:Complement C9 / Q000276:immunology / Q000378:metabolism; D015941:Complement Hemolytic Activity Assay; D003169:Complement Inactivator Proteins; D003170:Complement Pathway, Alternative; D003165:Complement System Proteins / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D006168:Guinea Pigs; D006790:Host-Parasite Interactions; D006801:Humans; D007894:Leishmania mexicana / Q000254:growth & development / Q000276:immunology* / Q000472:pathogenicity*
chemical_list: D003176:Complement C3; D003186:Complement C9; D003169:Complement Inactivator Proteins; D003179:Complement C3b; D003165:Complement System Proteins