Objective: The PD-1/PD-L1 pathway plays a key role in the immune evasion of tumor cells from the host immune system. This study aimed to examine PD-L1 expression and prevalence of infiltrating T cellin gastric diseases , and elucidate the relevance of PD-L1 and prevalence of infiltrating T cell in the pathogenesis of gastric car-cinoma. Methods: Immunohistochemistry and HE staining were used to investigate the in situ expression of PD-L1, CD4 and CD8 in paraffin-embedded gastric tissues from

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... ients with gastric ulcer (n=21), intestinal metaplasia/ atrophic gastritis (n=26) and gastric carcinoma tissues (n=38). Results: The expression of PD-L1 was found to be most prevalent in gastric carcinoma and, by comparison, decreased in gastric tissues from patients with gastric ulcer or intestinal metaplasia/atrophic gastritis. The overexpression of PD-L1 was notably more prevalent in cancer tissues and tissues from cases of intestinal metaplasia/atrophic gastritis, with the highest prevalence observed in intestinal metaplasia/atrophic gastritis. Meanwhile, decreasing prevalence was observed for CD4 and CD8 expression in gastric carcinoma. Therefore, PD-L1 expression in gastric carcinoma appeared to be inversely correlated with prevalence of infiltrating T cell. Conclusion: PD-L1 expression was more prevalent while CD4 and CD8 expression were decreased in gastric carcinoma compared with gastric ulcer and intestinal metaplasia/atrophic gastritis. As the activated immunological status in gastric ulcerappears to switch to one of immunological suppression in intestinal metaplasia/atrophic gastritis and gastric carcinoma, this may suggest that the immune evasion associated with the PD-L1 pathway may be triggered in the pathogenesis of human gastric carcinoma.