CD4 and gastric cancer: To further study the association of L57–69 and L83–95-specific CD4+ T cell responses with gastric diseases induced by H. pylori, HLA-DRB1*1501 and DRB1-1602*-expressing subjects with different gastric diseases, including atrophic gastritis, non-atrophic gastritis, antral gastritis pangastritis, peptic ulcer, duodenal ulcer, gastric cancer, will be assessed for L57–69 and L83–95-specific CD4+ T cell responses.