Expression of HLA-DR and secretory component antigens and lymphocyte infiltration in human gastric nonmalignant and malignant tissues: an immunohistochemical study. The relation between HLA-DR and secretory component (SC) expression and the degree of lymphocyte infiltration was immunohistochemically examined in human gastric mucosa with or without intestinal metaplasia and gastric carcinoma tissues. Gastric mucosa without obvious inflammation showed neither expression of HLA-DR or SC nor remarkable lymphoid infiltration. In contrast, gastric mucosa with chronic inflammation, tissues with incomplete type of intestinal metaplasia, and carcinoma demonstrated both HLA-DR and SC in almost the same area and also prominent lymphoid infiltration in the surrounding stroma. This simultaneous expression of HLA-DR and SC was not observed in complete type of intestinal metaplasia. The results indicate a close relationship between expression of HLA-DR and SC and the presence of lymphocyte infiltration in gastric mucosa, areas of incomplete type of intestinal metaplasia and in gastric carcinomas. 