Helicobacter pylori expresses a complex surface carbohydrate, Lewis X.

Monoclonal antibodies (MAbs) specific for Lewis X (Lex) reacted with whole cells of Helicobacter pylori NCTC11637, UA799, UA802, UA825, UA861, UA1182, and UA1206 in immunoelectron microscopy and enzyme-linked immunosorbent assay (ELISA) experiments. These MAbs have documented specificity to Lex, whereas MAbs for Lea and Leb were negative in both immunoelectron microscopy and ELISA. H. pylori coccoid forms also reacted with the MAbs, whereas the flagellum lacking the sheath showed no reactivity. The Lex structures were associated with membrane fractions in the ELISA experiments, and silver-stained sodium dodecyl sulfate-polyacrylamide gels confirmed the presence of lipopolysaccharides which reacted with the MAbs in immunoblots. Serum from an H. pylori-infected individual contained immunoglobulins which blocked the binding of the Lex MAbs, indicating that part of the host immune response to H. pylori is to the Lex structure. The ability of this gastric pathogen to mimic an oncofetal antigen (self) could explain the down regulation of anti-H. pylori T-cell response seen in H. pylori-infected individuals.