Potential for involvement of Fas antigen/Fas ligand interaction in apoptosis of epithelial cells by intraepithelial lymphocytes in murine small intestine

Intestinal epithelial cells (I-EC), which move to the villus tips from the crypts, rapidly die by apoptosis at the villus tips and are perpetually renewed at the crypts. To determine whether the Fas antigen (Fas)/Fas ligand (FasL) system is involved in the mechanism leading to apoptosis of i-EC, we examined the expression of Fas and FasL on the i-EC and intestinal intraepithelial lymphocytes (i-IEL) in normal mice. A high level of Fas was expressed on both the i-EC and i-IEL, whereas FasL was expressed in the i- IEL, especially in high-density fraction upon separation (high-density I- IEL), but not in the i-EC. The high-density i-IEL exhibited cytotoxicity against not only Fas transfectant but also the i-EC, and the cytotoxicity was inhibited by addition of Fas-Fragment c chimeric fusion protein. Thus, a significant fraction of i-IEL, such as high-density i-IEL, may partly contribute to induction of apoptosis in the effete i-EC via Fas/FasL interaction.