Normal: Histology of the body of the stomach. Acute gastritis: Infiltration of mucosal and submucosal lymphocytes with pockets of polymorphonuclear cells, accompanied by mild mucosal defects and edema. Chronic gastritis: Moderate to severe inflammation with marked epithelial defects including gland dilatation and mineralization. Atrophic gastritis: Chronic inflammation with focal fibrosis and complete loss of oxyntic parietal and chief cells. Intestinal metaplasia: Gastric epithelial metaplasia to an intestinal phenotype characterized by columnar elongation, mucous droplets occasionally forming goblet cells, and production of mixed acidic (blue, intestinal-type) and neutral (red, gastric-type) mucins as shown by pH 2.5 Alcian blue/PAS stain (inset). Dysplasia: High-grade glandular dysplasia characterized by irregular size and shape, infolding, branching and cell piling, and marked cellular and nuclear atypia. Cancer: Gastric intraepithelial neoplasia, here with intramucosal invasion (arrow), develops in H. pylori–infected wild-type B6129 mice, as well as in certain genetically engineered models (124–126). Scale bars: 160 μm (first panel); 400 μm (second through fourth panels); 80 μm (fifth panel; inset, original magnification, ×400); 40 μm (sixth panel); 800 μm (seventh panel). Second panel (acute gastritis): adapted with permission from American Journal of Physiology-Gastrointestinal and Liver Physiology (124). All other panels: adapted from Cancer Research (125, 126).