Introduction H pylori recognition by the host is poorly understood, although there is evidence that lipid A recognition occurs via Toll-like receptor 4. H pylori produces two lipid A species, a minor E coli-like hexa-acylated species and a major tetra-acylated species. The latter is thought to be important for immune evasion, with many laboratory strains thought to lack the minor more immunogenic species which is present in clinical strains.
Aim To assess whether changes in lipid A alter H pylori's ability to induce an inflammatory response.
Methods H pylori strains were repeatedly subcultured on blood agar and structural changes in the lipopolysaccharide were analysed using Deoxycholate Polyacrylamide Gel Electrophoresis (DOC-PAGE) and Gas Chromatography Mass Spectrometry (GC-MS). Additional ultracentrifugation removed contaminating lipoproteins and capsular polysaccharides. A monocyte/LPS challenge system was used to assess pro-inflammatory cytokine production by the different H pylori LPS preparations. Prediction of the orientations adopted by H pylori LPS structures within TLR4 receptor complex interactions were generated using the automated docking program AutoDock v4.
Results H pylori LPS was not altered by subculturing, although purified laboratory and clinical strains were shown to have compositional differences. Fatty acids of carbon length 14 and 16 (indicative of hexa-acylated lipid A) were absent from laboratory strain H pylori lipid A following purification, but remained in the lipid A purified from clinical strains. Unpurified laboratory strain LPS induced greatest levels of cytokine production in monocyte/LPS challenge experiments followed by purified clinical strain LPS, with purified laboratory strain LPS inducing the lowest levels (Abstract 053). Modelling analysis confirmed that the tetra-acylated species was less effective than the hexa-acylated species at interacting with the TLR4 signalling complex.
Conclusion Purification of H pylori LPS had a dramatic effect on inflammatory cytokine production indicating that contaminating lipoprotein and or capsular polysaccharide can impact the immune response. However, LPS derived from clinical isolates is significantly more immunogenic than laboratory strains. This further strengthens the evidence that TLR4-mediated immune responses are important in H pylori infections.