The SPR measurements and ligand immobilization procedures were conducted at 760 nm in a fully automatic Biacore 2000 instrument (GE-Healthcare GmbH, Uppsala, Sweden) equipped with four flow cells, and the temperature was 25 °C in all experiments. The running buffer was HBS-EP (0.01 M HEPES, 0.15 M NaCl, 3 mM EDTA, 0.005 % surfactant P20, pH 7.4) (GE-Healthcare GmbH). Ligands were coupled to carboxymethylated dextran CM5 chips (GE Healthcare GmbH) by conventional carbodiimide chemistry using 200 mM N-ethyl-N-(3 diethylaminopropyl) carbodiimide (EDC) and 50 mM N-hydroxysuccinimide (NHS). The activation time was 7 min, followed by a 7 min ligand injection. Deactivation of the remaining active esters was performed by a 7 min injection of ethanolamine/hydrochloride, pH 8.5. A flow rate of 5 μl/min was used during the immobilization and measurement procedures. Antibodies developed against bacteria were diluted 1:10 in 10 mM acetate buffer, pH 4.5, below the isoelectric point of the protein, thus enhancing the electrostatic interactions between the dextran matrix and the ligands. Anti-guinea pig IgG and anti-human IgG (Sigma Aldrich) and heat-killed ATCC bacterial strains (CCUG, Gothenburg, Sweden) were used as controls. The contact time was 7 min, which resulted in immobilization levels between 15000 and 40000 response units (RU). Ulcer secretions were diluted 1:1 in PBS (Apoteket AB, Umeå, Sweden). Injection of equal mixture of 1 M NaCl and 10 mM glycine, pH 2, followed by one injection of borate pH 8.5, were used for regeneration (1 min).