Cytotoxic potential of intraepithelial lymphocytes (IELs). Presence of TIA-1, the cytolytic granule-associated protein, in human IELs in normal and diseased intestine.

Human intestinal intraepithelial lymphocytes (IELs) have phenotypic characteristics of cytotoxic T cells, yet a cytotoxic function has not been demonstrated in redirected lysis assays. A monoclonal antibody that reacts with a cytotoxic granule-associated protein, TIA-1, was used in this study to identify this protein in many, but not all, IELs of normal human proximal small intestine. Furthermore, in active celiac disease, in which the number of IELs is significantly increased, a corresponding increase in the number of TIA-1 cells was found. These results indicate that whereas cytotoxicity of human IELs has been difficult to demonstrate, they contain at least one of the proteins associated with cytotoxicity, and a failure to demonstrate this function may be related to the in vitro assay system used.