title: Complement S-protein (vitronectin) is associated with cytolytic membrane-bound C5b-9 complexes.
abstract: It has been assumed that S-protein (vitronectin) associates with terminal C5b-9 complement complexes only when the latter fail to attach to target lipid bilayers, thereby forming inactive fluid-phase SC5b-9 complexes. Using monoclonal anti-S-protein antibodies, we show here that a minor portion of C5b-9 complexes associated with both homologous and heterologous cells contain S-protein. This conclusion derives from Western blot analyses, from the sedimentation behaviour of solubilized S-protein, and from the fact that the protein co-immunoprecipitates with C5b-9(m). Association of S-protein with C5b-9(m) takes place primarily at the stage of C9-binding. An average of less than or equal to 0.4 moles of S-protein are estimated to be present per mole C5b-9(m). Hence, only a fraction of C5b-9 complexes contain S-protein. The function of cell-bound S-protein is unknown. Haemolytic titrations with purified components failed to demonstrate any protective effect of S-protein on the lysis of sheep or human erythrocytes by C5b-9. S-protein bound to complement-lysed homologous or heterologous cells is readily detectable by conventional immunocytochemical staining. We conclude that differentiation between tissue-deposited fluid-phase C5b-9 and membrane C5b-9 complexes cannot be made on the basis of immunohistological stainings for S-protein alone.
authors: Institute of Medical Microbiology, Max-Planck-Gesellschaft, University of Giessen, FRG.
authors: S
authors: S
authors: Bhakdi
authors: R
authors: R
authors: Käflein
authors: T S
authors: TS
authors: Halstensen
authors: F
authors: F
authors: Hugo
authors: K T
authors: KT
authors: Preissner
authors: T E
authors: TE
authors: Mollnes
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000276:immunology*; D015153:Blotting, Western; D003186:Complement C9 / Q000276:immunology; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D004910:Erythrocyte Membrane / Q000276:immunology; D006023:Glycoproteins / Q000032:analysis / Q000276:immunology*; D006461:Hemolysis; D006801:Humans; D011233:Precipitin Tests; D011817:Rabbits; D012756:Sheep; D019096:Vitronectin
chemical_list: D001798:Blood Proteins; D003186:Complement C9; D015938:Complement Membrane Attack Complex; D006023:Glycoproteins; D019096:Vitronectin; D003165:Complement System Proteins