Autoimmune gastritis is an inflammatory reaction in the gastric corpus and fundus due to CD4+ T cells attacking the H+/K+-ATPase proton pump on the luminal side of parietal cells, which results in B cells producing IFA and antiparietal cell antibodies (PCA), in turn contributing to atrophic progression in the gastric corpus and fundus.[4] PCA decreases the secretion of stomach acids from oxyntic glands. This evidence concerns the gene CD4 and autoimmune gastritis.