Particle agglutination assay for detection of albumin and IgG binding cell surface components of Helicobacter pylori.
Human serum albumin (HSA), bovine serum albumin (BSA) and human IgG were immobilized on latex beads to detect cell surface components of Helicobacter pylori binding to BSA, HSA, and IgG by a particle agglutination assay (PAA). In a total of 32 H. pylori strains tested, 16 strains interacted with BSA and 12 strains with HSA; 24 strains expressed binding of human IgG. The specificity of the agglutination reaction was studied by a particle agglutination inhibition assay performed by pre-incubating bacterial cell suspensions in buffers containing homologous proteins, unrelated glycoproteins and a number of common monosaccharides. Treatment of H. pylori cells with heat and proteolytic enzymes abolished binding to microbeads with immobilized IgG and albumin. IgG-binding surface components from cells of H. pylori strain CCUG 17875 were effectively extracted by incubating a cell suspension with 10 mM EDTA, 0.015 M sodium phosphate buffer (pH 7.2), and by washing H. pylori cells with distilled water. However, attempts to extract a fraction rich in albumin-binding components were unsuccessful. We conclude that cells of various H. pylori strains express commonly IgG-binding proteins, and that albumin-binding is probably mediated by non-specific hydrophobic interactions.