Phenotypical and morphological analyses of intraepithelial and lamina propria lymphocytes in normal and regenerating gastric mucosa of rats in comparison with those in intestinal mucosa.

While the intestine has abundant intraepithelial lymphocytes (IELs) including extrathymically differentiated T-cell populations and natural killer (NK) cells, the stomach contains only a few IELs. To elucidate whether the gastric epithelium is capable of inducing predominant lymphocyte lodging and subsequent differentiation within, we counted the number of IELs and lamina propria lymphocytes (LPLs) and calculated the percentage of IELs to total lymphocytes for each alpha-beta T cell, gamma-delta T cell, CD4+ cell, CD8+ cell and NK cell in normal and regenerating gastric mucosa as well as the intestinal mucosa of the rat. In the normal rat pylorus, a few alpha-beta T cells but no gamma-delta T cells were found in the epithelium and lamina propria. In regenerating gastric mucosa, all subsets of LPLs increased in number to a degree comparable to those in intestinal mucosa, whereas every IEL subset, though slightly increased, was much smaller in number than in the intestinal mucosa, consequently giving lower percentages of IELs. Electron microscopic observations revealed that all IELs in regenerating gastric mucosa were agranular, while 55% of intestinal IELs were large granular lymphocytes positively stained for an NK-cell, alpha-beta-cell or gamma-delta T-cell marker. The present results indicate that, unlike the intestinal epithelium, the gastric epithelium does not induce the preferential localization of T cells/NK cells and T-cell differentiation into granular lymphocytes in the epithelium even under conditions of prominent LPL infiltration.