Dendritic cells (DCs), as potent phagocytes engulf dead cells and present peptide fragments of tumor antigens or pathogens derived from infected cells to naïve CD8⁺ T-lymphocytes. Dendritic cells can also induce apoptosis in target cells, thus getting an opportunity to sample their microenvironment. Here, we present that the supernatants of LPS- or CL075-activated DCs induced cell death in different cell lines, but during the differentiation to mature DCs, they lost their cytotoxic potential. Dexamethasone-pre-treated tolerogenic DCs induced less intensive death indicating that the tissue microenvironment can downregulate DC-mediated killing. Exploring the signaling of DC-induced cell death, we observed that the supernatant of activated DCs induced TNF-dependent cell death, since TNF antagonist blocked the cytotoxic activity of DCs, contrary to inhibitors of Fas and TRAIL receptors. We identified that the DC-induced killing is at least partially a RIPK1-dependent process, as RIPK1 positive target cells were more susceptible to DC-induced cell death than their RIPK1 deficient counterparts. Moreover, both the elevated phosphorylation of RIPK1 and the increase in RIPK1-caspase-8 interaction in target cells suggest that RIPK1-mediated signals contribute to DC supernatant-induced cell death. We also proved that the cytotoxic activity of DC-derived supernatant induced apoptosis in the target cells and not necroptosis, as it was completely abrogated with the pan caspase inhibitor (Z-VAD), while the necroptosis inhibitor (Nec-1) had no effect.

Our work revealed that the supernatant of activated DCs induces the apoptosis of target cells in a RIPK1-dependent manner. This phenomenon could be relevant for the initiation of cross-presentation and may broaden the plethora of cytotoxic mechanisms acting against tumor cells.

树突状细胞 (DC)，作为强大的吞噬细胞吞噬死细胞，并将肿瘤抗原或源自感染细胞的病原体的肽片段呈递给幼稚 CD8 ⁺T淋巴细胞。树突状细胞还可以诱导靶细胞凋亡，从而有机会对其微环境进行采样。在这里，我们提出 LPS 或 CL075 激活的 DCs 的上清液在不同的细胞系中诱导细胞死亡，但在分化为成熟 DCs 的过程中，它们失去了细胞毒性潜力。地塞米松预处理的耐受性 DC 诱导的死亡强度较低，表明组织微环境可以下调 DC 介导的杀伤。探索 DC 诱导的细胞死亡的信号传导，我们观察到活化的 DCs 的上清液诱导 TNF 依赖性细胞死亡，因为 TNF 拮抗剂阻断了 DCs 的细胞毒活性，这与 Fas 和 TRAIL 受体的抑制剂相反。我们发现 DC 诱导的杀伤至少部分是依赖于 RIPK1 的过程，因为 RIPK1 阳性靶细胞比缺乏 RIPK1 的对应物更容易受到 DC 诱导的细胞死亡。此外，RIPK1 磷酸化的升高和靶细胞中 RIPK1-caspase-8 相互作用的增加都表明 RIPK1 介导的信号有助于 DC 上清液诱导的细胞死亡。我们还证明了 DC 衍生上清液的细胞毒活性诱导靶细胞凋亡而不是坏死性凋亡，因为它被泛半胱天冬酶抑制剂 (Z-VAD) 完全消除，而坏死性凋亡抑制剂 (Nec-1) 没有效果.

我们的工作表明，活化的 DCs 的上清液以 RIPK1 依赖性方式诱导靶细胞凋亡。这种现象可能与交叉呈递的开始有关，并可能拓宽对肿瘤细胞起作用的过多细胞毒性机制。