SPONTANEOUS CYTOTOXICITY OF INTESTINAL INTRAEPITHELIAL LYMPHOCYTES - CLUES TO THE MECHANISM

Human intestinal intraepithelial lymphocytes (IEL) demonstrate target cell-restricted spontaneous cytotoxic (SC) activity that is due to CD2 (+)CD3(+)CD8(+)CD16(-)CD56(-) effector cells; they kill epithelial cel l (EC) tumours (such as DLD-1 colon cancer cells), but not natural kil ler (NK)-sensitive K-562 cells. The present study shows that the measu red levels of SC activities by IEL correlated with those of autologous lamina propria lymphocytes (LPL), but not with those of peripheral bl ood lymphocytes (PBL). Also, the susceptibilities of DLD-1 cell clones to lysis by IEL and PBL effector cells did not correlate, suggesting different mechanisms of lysis. Antibody blocking experiments showed th at the main surface molecules involved in lysis depended on the effect or cell type: alpha(E) beta(7) (HML-1) on IEL and CD16 on PBL. No anti body-dependent cell-mediated cytotoxicity (ADCC) was demonstrated by I EL, even after stimulation with interferon-gamma (IFN-gamma). Few IEL expressed Fc receptors for IgG. This study describes further differenc es between the SC activities of IEL and PBL.