Chronic gastritis is classified as type A (immune/fundal), or type B (nonimmune/antral). When both types occur, it is known as type AB, or pangastritis. Type C is associated with reflux of bile and pancreatic secretions into the stomach, causing chemical injury (Huether & McCance, 2017, p. 914).
Chronic immune/fundal gastritis is associated with loss of T-cell tolerance and development of autoantibodies to gastric H+-K+ ATPase. The gastric mucosa degenerates extensively in the body and fundus of the stomach, leading to gastric atrophy. Loss of parietal cells diminishes acid and intrinsic factor secretion (Huether & McCance, 2017, p. 914).
Chronic nonimmune/antral gastritis is caused by H. pylori bacteria and it also is associated with use of alcohol, tobacco, and NSAIDs. There are high levels of hydrochloric acid secretion with an increased risk of duodenal ulcers (Huether & McCance, 2017, p. 915).