Presentation of peptides and proteins by intestinal epithelial cells

Murine intestinal epithelial cells (IEC) constitutively express major histocompatibility complex (MHC) class II molecules, which enable them to present foreign antigens to T cells in vitro. In this study we have compared the ability of freshly isolated IEC and spleen adherent cells to present both protein and peptide antigens to T cells in vitro. Consistently IEC were unable to present protein but could readily present immunogenic peptides in an MHC-dependent fashion to stimulate lymphokine release from T cells. Consistent with their inability to process protein antigens, IEC were also unable to present a synthetic peptide which requires intracellular processing, whereas spleen antigen-presenting cells (APC) could readily present the same peptide. These findings indicate that IEC may lack the necessary intracellular machinery to process exogenous antigens but they raise the possibility that IEC may play an important immunological role in vivo by presenting processed peptides to T cells.