Complement activation directly induced by Helicobacter pylori.
OBJECTIVE
Helicobacter pylori is a frequent gram-negative colonizer of the human stomach. Its interaction with complement may be involved in the pathogenesis of chronic gastritis, and was mechanistically studied in vitro.


METHODS
Four H. pylori strains, 2 cytotoxin-associated genes (cag)A+ and 2 cagA-, were isolated from infected patients. Bacteria or purified H. pylori lipopolysaccharides (LPSs) were incubated with nonimmune serum at 37 degrees C; the activation products C3b/iC3b/C3c (C3bc) and terminal complement complex (TCC) were then quantified by immunoassays. The serum sensitivity of 1 strain (L01, cagA+) was tested by counting the numbers of colony-forming units.


RESULTS
All strains and LPSs generated large amounts of C3bc and TCC. Blocking of the classic complement pathway by the calcium chelator ethylene glycol tetraacetic acid (EGTA) markedly reduced the complement products, suggesting that H. pylori and its LPSs directly engage the classic activation pathway. H. pylori was shown to be serum sensitive, but 30% or more nonimmune serum was necessary to induce marked killing. After 5 minutes, swelled bacteria coated with C3bc and TCC were shown.


CONCLUSIONS
H. pylori is complement sensitive and activates the classic pathway even in the absence of specific antibodies. Released cell wall constituents such as LPSs can activate complement and may explain why this bacterium induces gastric pathology without invading the mucosa.
Berstad
A E
AE
Laboratory for Immunohistochemistry and Immunopathology (LIIPAT), Rikshospitalet, Institute of Pathology, N-0027 Oslo, Norway. audun.berstad@rh.uio.no
Høgåsen
K
K
Bukholm
G
G
Moran
A P
AP
Brandtzaeg
P
P
D000907:Antibodies, Bacterial / Q000276:immunology; D000942:Antigens, Bacterial; D001426:Bacterial Proteins / Q000235:genetics; D001798:Blood Proteins / Q000494:pharmacology; D003167:Complement Activation / Q000187:drug effects / Q000276:immunology*; D003179:Complement C3b / Q000276:immunology; D015932:Complement C3c / Q000276:immunology; D004269:DNA, Bacterial / Q000032:analysis; D005455:Fluorescent Antibody Technique; D016481:Helicobacter Infections / Q000276:immunology*; D016480:Helicobacter pylori / Q000235:genetics / Q000276:immunology*; D006801:Humans; D066298:In Vitro Techniques; D008070:Lipopolysaccharides / Q000494:pharmacology
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001798:Blood Proteins; D004269:DNA, Bacterial; D008070:Lipopolysaccharides; C080866:cagA protein, Helicobacter pylori; D003179:Complement C3b; D015932:Complement C3c