Our previous ultrastructural study showed that, in the small intestine of the guinea pig, large granular lymphocytes (LGLs) are closely associated with effete epithelial cells at the villus tip, suggesting their involvement in the apoptosis of enterocytes. However, morphological signs of such lymphocyte-mediated apoptosis were not recognizable in the rat intestine. In the present study, perforin, a cytolytic substance of LGLs, was immunohistochemically examined in the small intestine of guinea pigs and rats. Perforin-immunoreactive lymphocytes predominated within the epithelium in guinea pigs. In rats, the epithelium lacked perforinimmunoreactive cells, although they were scattered in the lamina propria. Electron microscopic observation demonstrated the rich existence of LGLs in the intestinal epithelium of both species. Only guinea pigs revealed an intimate relationship of LGLs with apoptotic enterocytes, the former inserting cytoplasmic processes into the latter to erode and separate them into cell fragments. The cytochemical and ultrastructu ral findings of the intraepithelial LGLs seem to account for the species difference between the guinea pig and rat in their mechanisms for disposing of effete enterocytes.
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Iwanaga et al. (1994) studied this question.