BACKGROUND & AIMS: The extensive infiltration of CD8(+) T cells in the intestinal mucosa of celiac disease (CD) patients is a hallmark of the disease. We identified a gliadin peptide (pA2) that is selectively recognized by CD8(+) T cells infiltrating intestinal mucosa of HLA-A2(+) CD patients. Herein, we investigated the phenotype, the tissue localization, and the effector mechanism of cells responsive to pA2 by using the organ culture of CD intestinal mucosa. The target of pA2-mediated cytotoxicity was also investigated by using the intestinal epithelial cell lines Caco2 and HT29, A2(+) and A2(-), respectively, as target cells. METHODS: Jejunal biopsy specimens from CD patients were cultured in vitro with pA2, and cellular activation was evaluated by immunohistochemistry and cytofluorimetric analysis. Cytotoxicity of pA2-specific, intestinal CD8(+) T cells was assayed by granzyme-B and interferon-gamma release and by apoptosis of target cells. RESULTS: pA2 challenge of A2(+) CD mucosa increased the percentage of CD8(+)CD25(+) and of CD80(+) cells in the lamina propria, the former mainly localized beneath the epithelium, as well as the number of terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling-positive cells (TUNEL(+)) in the epithelium. Intraepithelial CD3(+) cells and enterocyte expression of Fas were also increased. CD8(+)CD25(+) and CD8(+)FASL(+) T cells were significantly increased in cell preparations from biopsy specimens cultured with pA2. CD8(+) T-cell lines released both granzyme-B and interferon-gamma following recognition of pA2 when presented by Caco2 and not by HT29. CONCLUSIONS: These data indicate that gliadins contain peptides able to activate, through a TCR/HLA class I interaction, CD8-mediated response in intestinal CD mucosa and to induce the enterocyte apoptosis.