Nature Immunology pp 1166 - 1174

Almost half the world's population is infected with the stomach-residing bacteria Helicobacter pylori. Although many people suffer few or no symptoms, others develop severe inflammation of the stomach and can develop gastric cancer. In the November issue of Nature Immunology, scientists have discovered how this pathogen can cause gastric inflammation in some people.

Richard Ferrero and colleagues found that a component of the bacterial surface, peptidoglycan, triggers stomach cells to undergo an inflammatory response. Nod1, a molecule found inside stomach cells, is responsible for recognizing the peptidoglycan and switching on signals that lead to inflammation. However, H. pylori do not normally invade cells, raising the question of how the bacterial peptidoglycan gets inside the cell. The researchers found that the bacteria required a syringe-like apparatus that essentially injects the peptidoglycan into the stomach cells. Because only certain strains of H. pylori carry this syringe-like apparatus, this explains why some people are less affected by H. pylori infection.