Chronic gastritis is histologically characterized by the presence of lymphocytes and plasma cells. It is impoant to realize that the presence of neutrophils within the glandular epithelium indicates active inflammation and may be the main type of inflammation present (acute gastritis), or may be combined with more numerous chronic inflammations (active chronic gastritis). Chronic gastritis is divided into subgroups based either on etiology (immunologic or infectious), location (antrum or body), histopathology, or clinical features. H. pylori gastritis is associated with infection by H. pylori, a small, curved, gram-negative rod that is found in approximately 20% of the general population. The organisms are found in the mucus overlying the surface/foveolar epithelium. These changes tend to affect primarily the antral or antral-body-fundic mucosa. This is the type of gastritis normally associated with active chronic gastritis. The therapy for Helicobacter is either triple therapy (metronidazole, bismuth salicylate, and either amoxicillin or tetracycline) or double therapy (omeprazole and clarithromycin). In contrast, autoimmune gastritis, also known as diffuse corporal atrophic gastritis or type A atrophic gastritis, is characterized by the presence of autoimmune antibodies including parietal cell antibodies and intrinsic factor antibodies. This type of gastritis is associated with pernicious anemia and achlorhydria. Pernicious anemia is the result of decreased intrinsic factor, which in turn produces a vitamin B12 deficiency. This vitamin deficiency causes megaloblastic anemia and subacute combined disease of the spinal cord. Histologically there is diffuse atrophy (reduced mucosal thickness), gland loss, widespread intestinal metaplasia, and variable chronic and acute inflammation. These changes are found predominately in the body-fundus mucosa (usually absent in the antrum). There is an increased risk for gastric cancer, but these patients do not develop peptic ulcers. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition