Department of Medicine, Division of Gastroenterology; Department of Medicine, Division of Digestive Diseases and Nutrition
Animals; Cell Line; Cytokines; Helicobacter felis; Helicobacter hepaticus; Helicobacter pylori; Humans; *Immunity, Natural; Lipopolysaccharides; Macrophages, Peritoneal; Membrane Glycoproteins; Mice; Mice, Inbred C57BL; Mice, Knockout; Receptors, Cell Surface; Signal Transduction; Toll-Like Receptor 2; Toll-Like Receptor 4; Toll-Like Receptors
Gastroenterology | Immunology and Infectious Disease | Life Sciences | Medicine and Health Sciences | Microbiology
Molecular and genetic studies have demonstrated that members of the Toll-like receptor (TLR) family are critical innate immune receptors. TLRs are recognition receptors for a diverse group of microbial ligands including bacteria, fungi, and viruses. This study demonstrates that distinct TLRs are responsible for the recognition of Helicobacter lipopolysaccharide (LPS) versus intact Helicobacter bacteria. We show that the cytokine-inducing activity of Helicobacter LPS was mediated by TLR4; i.e., TLR4-deficient macrophages were unresponsive to Helicobacter pylori LPS. Surprisingly, the cytokine response to whole Helicobacter bacteria (H. pylori, H. hepaticus, and H. felis) was mediated not by TLR4 but rather by TLR2. Studies of HEK293 transfectants revealed that expression of human TLR2 was sufficient to confer responsiveness to intact Helicobacter bacteria, but TLR4 transfection was not sufficient. Our studies further suggest that cag pathogenicity island genes may modulate the TLR2 agonist activity of H. pylori as cagA+ bacteria were more active on a per-cell basis compared to cagA mutant bacteria for interleukin-8 (IL-8) cytokine secretion. Consistent with the transfection studies, analysis of knockout mice demonstrated that TLR2 was required for the cytokine response to intact Helicobacter bacteria. Macrophages from both wild-type and TLR4-deficient mice produced a robust cytokine secretion response (IL-6 and MCP-1) when stimulated with intact Helicobacter bacteria. In contrast, macrophages from TLR2-deficient mice were profoundly unresponsive to intact Helicobacter stimulation, failing to secrete cytokines even at high (100:1) bacterium-to-macrophage ratios. Our studies suggest that TLR2 may be the dominant innate immune receptor for recognition of gastrointestinal Helicobacter species.
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Citation: Infect Immun. 2004 Nov;72(11):6446-54. Link to article on publisher's site