GastritisParietal Cells, GastricH(+)-K(+)-Exchanging ATPaseGastritis, AtrophicAutoimmune DiseasesThymectomyStomachAnemia, PerniciousGastric MucosaGastrinsAchlorhydriaHelicobacter pyloriHelicobacter InfectionsIntrinsic FactorAutoantibodiesMice, Inbred BALB CAutoantigensStomach NeoplasmsLymphopeniaPyloric AntrumStomach DiseasesGastritis, HypertrophicStomach UlcerGastroscopyMetaplasiaCD4-Positive T-LymphocytesPepsinogen AT-Lymphocytes, RegulatoryImmunoglobulin GBile RefluxDisease Models, AnimalMice, Inbred C57BLPeptic UlcerPepsinogen CGastric JuiceHelicobacter felisDuodenal UlcerHelicobacter heilmanniiDuodenitisChronic DiseaseDyspepsiaPepsinogensHelicobacterUreaseBiopsyGastric FundusPostgastrectomy SyndromesGastric AcidEndoscopy, GastrointestinalPrecancerous ConditionsEndoscopyAnti-Ulcer AgentsGastrectomyCampylobacterAtrophyDuodenum