Whole-cell ELISA Standard procedures [6, 7, 45], were adapted for the use of peroxidase conjugated secondary antibody. All antibodies were obtained from Calbiochem. Overnight cultures of bacteria were collected by centrifugation Raf pathway at 3500 × g for 10-15 min, washed in Dulbecco’s phosphate buffered saline, and repelleted at 10,000 × g for 2 min, then resuspended

in 15% glycerol/0.9% NaCl. The cell suspensions were assayed for protein content and stored at -20°C. Cell samples containing known amounts of protein were rapidly diluted into 50 mM sodium bicarbonate/carbonate pH 9.55 and dispensed immediately into wells of an ELISA plate (Costar #9017). Plates were sealed and refrigerated overnight, then blocked for 90 min in 3% bovine serum albumin dissolved in the wash buffer which consisted of 0.1 M sodium phosphate pH 7.4/0.1 M NaCl/0.1% w/v Tween-20. Primary antibody, monoclonal anti-Lewis X (Signet clone P12) or anti-Lewis Y (Signet clone F3),

diluted 1:500 in wash buffer/1% BSA, was added for 2 hours, followed by four changes of wash buffer. The secondary antibody, a 1:2500 dilution of horseradish peroxidase-conjugated goat anti-mouse IgM in wash buffer/1% BSA, was added for 90 min, followed by four changes of wash buffer. The chromogenic substrate was 0.42 mM tetramethylbenzidine and 0.02% H2O2 in 50 mM acetate/citrate pH 5.5 [46]. After 15 minutes at room temperature, reaction was stopped with 1/5th vol 2.5 N H2SO4, and color change was measured in a plate

reader at 450 nm. In negative controls omitting either primary or secondary antibody, or with E. coli strain HB101 click here substituted for H. pylori, color change was negligible (A<0.05). Levels of Lewis Y were negligible (A<0.1) in strain 26695 or 43504, as were Lewis X levels in SS1. Electrophoretic analyses of lipopolysaccharides H. pylori cultures were collected as described above, and washed cell pellets were stored at -70°C. Cells were lysed in 60 mM Tris HCl pH 6.8 containing 2% SDS at 95-98°C for 10 min. Protein content was measured using the bicinchoninic acid assay (Pierce). Samples of cell lysates were adjusted to equal protein content (1 mg/ml), then Non-specific serine/threonine protein kinase proteolyzed in reactions containing (final) 60 mM Tris HCl pH 6.8, 0.67% SDS, and 0.67 mg/ml proteinase K at 60°C for 2 hours [47]. To eliminate electrophoretic artifacts due to the presence of lipid/detergent complexes, proteolyzed samples were extracted with hot phenol [48]. Control experiments verified that all LPS bands were recovered through the following extraction procedure qualitatively and without bias. Proteolyzed samples were mixed with 1 volume of 90% aqueous phenol and incubated at 70°C for 20 min. After cooling to 10°C for 1 min, the samples were centrifuged at 12,000 × g for 20 min at 10°C, and the aqueous phase collected. The phenolic phases were re-extracted with 1 volume of H2O at 70°C for 10 min, and the centrifugation repeated.