Steric hindrance of antibody binding to surface proteins of Coxiella burnetti by phase I lipopolysaccharide.
The exposure of surface protein antigens on virulent phase I Coxiella burnetti was compared with that on avirulent phase II cells. Although anti-phase II antibodies did not bind to the surfaces of native intact phase I cells, they bound to phase I proteins if the proteins were solubilized for sodium dodecyl sulfate-polyacrylamide gel electrophoresis and analyzed by immunoblotting. In addition, removal of the phase I lipopolysaccharide (LPS) by trichloroacetic acid exposed surface proteins for reactivity with anti-phase II antibodies, as shown by immunofluorescence assays, direct antibody binding, and immunoelectron microscopy using protein A-colloidal gold conjugates. Based on these observations, a simple model of phase variation is proposed to explain the apparently conflicting notions of the identity of the phase II antigen(s). The model suggests that the phase I LPS sterically hinders access of anti-phase II antibodies to a multitude of shared protein antigens, any one of which may confer phase II specificity. Exposure of these shared protein antigens through the appearance of a more truncated LPS (phase II) or extraction of the smooth-type phase I LPS allows antibody accessibility and therefore confers apparent phase II serospecificity.
Hackstadt
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Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840.
D000907:Antibodies, Bacterial / Q000276:immunology*; D000918:Antibody Specificity; D000937:Antigen-Antibody Reactions; D000942:Antigens, Bacterial / Q000276:immunology*; D000954:Antigens, Surface / Q000276:immunology*; D003381:Coxiella / Q000276:immunology*; D006001:Glycoconjugates / Q000276:immunology; D008070:Lipopolysaccharides / Q000276:immunology*; D008854:Microscopy, Electron; D013329:Structure-Activity Relationship
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D000954:Antigens, Surface; D006001:Glycoconjugates; D008070:Lipopolysaccharides