RIGI and pneumonia: However, transfection experiments have shown that murine bone marrow-derived macrophage production of type I IFN in response to RNA isolated from Legionella pneumophila (a gram-negative bacterium that replicates in host macrophages and causes severe pneumonia) is mediated via RIG-I [61]; while RNA from Helicobacter pylori (a gram positive bacterium that causes gastritis) was also shown to induce type I IFN production via a RIG-I-mediated signalling pathway in mouse dendritic cells [62].