Immature CD4−CD103+ Rat Dendritic Cells Induce Rapid Caspase-Independent Apoptosis-Like Cell Death in Various Tumor and Nontumor Cells and Phagocytose Their Victims

We previously reported the characterization of a MHC class II low CD4 − CD103 + (CD4 − ) subset of dendritic cells (DC) in rat spleen that exhibit a Ca 2+ -, Fas ligand-, TRAIL- and TNF-α-independent cytotoxic activity against specific targets in vitro. In this study, we demonstrate that this DC subset was also found in lymph nodes. Freshly extracted and, therefore, immature CD4 − DC exhibited a potent cytotoxic activity against a large panel of tumor cell lines as well as primary endothelial cells. The cytotoxic activity of immature CD4 − DC required cell-to-cell contact and de novo protein expression. CD4 − DC-mediated cell death resembled apoptosis, as evidenced by outer membrane phosphatidylserine exposure and nuclear fragmentation in target cells, but was caspase as well as Fas-associated death domain and receptor-interacting protein independent. Bcl-2 overexpression in target cells did not protect them against DC-mediated cell death. Immature CD4 − DC phagocytosed efficiently apoptotic cells in vitro and, therefore, rapidly and specifically engulfed their victims following death induction. Maturation induced a dramatic down-regulation of the killing and phagocytic activities of CD4 − DC. In contrast, CD4 + DC were both unable to kill target cells and to phagocytose apoptotic cells in vitro. Taken together, these data indicate that rat immature CD4 − CD103 + DC mediate an unusual cytotoxic activity and can use this function to efficiently acquire Ag from live cells.