Are epithelial cells involved in the generation and/or maintenance of CD8+CD28– T cells?
Cells expressing high levels of MHC-class II molecules, such as dendritic cells, activated monocytes and B cells and tissue macrophages, are considered the classical APC. However, evidence accumulated during the past decade indicates that intestinal epithelial cells (iEC) are also capable of activating T cells.148 Early in vitro studies demonstrated that ex vivo iEC from rats and humans were capable of activating peripheral blood T cells. Paradoxically, the T cells driven into proliferation by iEC were CD8+ T cells.149, 150 It is now known that both ex vivo iEC and iEC tumour cell lines are capable of generating CD8+CD28– T cells in vitro, although using different mechanisms.150, 151 While CD8+CD28– T-cell generation by ex vivo iEC involves activation and proliferation of CD8+ T cells, generation by iEC lines entails death of CD4+CD28+ and CD8+CD28+ T cells, thus strengthening the resistance of CD8+CD28– T cells to apoptosis.151Evidence gathered during the last few years suggests that
