Involvement of intestinal intraepithelial lymphocytes in turnover of intestinal epithelial cells: Morphological and functional alterations due to daily administration of FK506

► The stimulation of IEL with anti-mouse CD3 mAb induced massive apoptosis of IEC. ► FK506-injection caused a decrease in the cytotoxicity and the number of γδ+ IEL. ► FK506 completely abrogated DNA fragmentation of IEC. ► Incompetent IEC remained on the villus due to inhibition of IEL function by FK506. ► TCR-γδ+ IEL was suggested to take part in the turnover and maintenance of IEC.