Immunobiological activities of chemically defined lipid A from Helicobacter pylori LPS in comparison with Porphyromonas gingivalis lipid A and Escherichia coli-type synthetic lipid A (compound 506).

Helicobacter pylori lipid A, characterised by a glucosamine beta (1-6) disaccharide 1-(2-aminoethyl)phosphate acylated by (R)-3-hydroxyoctadecanoic acid and (R)-3-(octadecanoyloxy)octadecanoic acid at the 2- and 2'-positions, respectively, exhibited no or very low endotoxic activities, i.e. lethal toxicity in galactosamine-loaded mice, pyrogenicity for rabbits and the activity of the Limulus test compared with Escherichia coli-type synthetic lipid A (compound 506), which possesses beta-(1-6)-linked glucosamine disaccharide 1,4'-bisphosphate, with two acyloxyacyl groups at the 2'- and 3'-positions and two 3-hydroxytetradecanoyl groups at the 2- and 3-positions. The endotoxic properties of H. pylori lipid A were also a little weaker than those of the low endotoxic lipid A of P. gingivalis, which has 1-phospho beta-(1-6)-linked glucosamine disaccharide with 3-hydroxy-15-methylhexadecanoyl and 3-hexadecanoyloxy-15-methylhexadecanoyl groups at the 2- and 2'-positions, respectively. Further, the mitogenic activity of H. pylori lipid A in murine splenic mononuclear cells was also less than those of P. gingivalis lipid A and compound 506. However, H. pylori lipid A induced comparable production of interleukin-6 (IL-6) by human peripheral blood mononuclear cells (PBMC) compared with P. gingivalis lipid A and compound 506. H. pylori lipid A also increased human natural killer cell activity, and strongly agglutinated rabbit erythrocytes. However, the lipid As of H. pylori and P. gingivalis showed lower activities in inducing tumour necrosis factor alpha (TNF-alpha) production by human PBMC and IL-8 production by human gingival fibroblasts than that of compound 506. The structural feature of H. pylori lipid A may be associated with low endotoxic properties and potent immunobiological activities.