Splenic Stroma-Educated Regulatory Dendritic Cells Induce Apoptosis of Activated CD4 T Cells via Fas Ligand-Enhanced IFN-γ and Nitric Oxide

Abstract

Stromal microenvironments of bone marrow, lymph nodes, and spleen have been shown to be able to regulate immune cell differentiation and function. Our previous studies demonstrate that splenic stroma could drive mature dendritic cells (DC) to further proliferate and differentiate into regulatory DC subset that could inhibit T cell response via NO. However, how splenic stroma-educated regulatory DC release NO and whether other molecules are involved in the suppression of T cell response remain unclear. In this study, we show that splenic stroma educates regulatory DC to express high level of Fas ligand (FasL) by TGF-β via ERK activation. The findings, that inhibition of CD4 T cell proliferation by regulatory DC required cell-to-cell contact and FasL deficiency impaired inhibitory effect of regulatory DC, indicate that regulatory DC inhibit CD4 T cell proliferation via FasL. Then, regulatory DC have been found to be able to induce apoptosis of activated CD4 T cells via FasL in caspase 8- and caspase 3-dependent manner. Interestingly, FasL on regulatory DC enhanced IFN-γ production from activated CD4 T cells, and in turn T cell-derived IFN-γ induced NO production from regulatory DC, working jointly to induce apoptosis of activated CD4 T cells. Blockade of IFN-γ and NO could reduce the apoptosis induction. Therefore, our results demonstrated that splenic stroma-educated regulatory DC induced T cell apoptosis via FasL-enhanced T cell IFN-γ and DC NO production, thus outlining a new way for negative regulation of T cell responses and maintenance of immune homeostasis by regulatory DC and splenic stromal microenvironment.

Immunosuppressive Mechanisms of Regulatory Dendritic Cells in Cancer

“…The stromal microenvironment of the spleen, lung and liver can induce appearance of regDCs with different phenotypes [11,12]. For instance, murine lung cancer could "educate" cDCs to differentiate into CD11c low CD11b high Ia low regDCs that inhibit T cell response, as was reported by Liu et al using the freshly isolated tumor cells to mimic the tumor microenvironment in DC co-culture studies [13].…”

“…Stroma-derived TGF-β might be responsible for the induction of high-level FasL expression on regulatory DCs via ERK activation. Interestingly, FasL-enhanced IFN-γ from activated CD4 T cells could in turn induce highlevel NO production from regulatory DCs, being involved in apoptosis induction of activated CD4 T cells [11]. In turn, DCs co-cultured with apoptotic cells up-regulate iNOS generation and STAT3 phosphorylation and can induce regulatory T cells after engulfing apoptotic cells.…”

Heligmosomoides polygyrus bakeri Induces Tolerogenic Dendritic Cells that Block Colitis and Prevent Antigen-Specific Gut T Cell Responses

“…It is likely that helminths function through several independent regulatory pathways to protect mice from IBD. Tolerogenic DC can limit T cell responses via Treg independent mechanisms including induction of effector T cell anergy (32)(33) or apoptosis through upregulation of Fas ligand expression (34). Thus, there is precedence for our observation.…”

Stromal Cell Induction of Regulatory Dendritic Cells

“…To date, stromal cell-induced rDCs have been reported in murine spleen (Svensson et al, 2004; Zhang et al, 2004; Tang et al, 2006; Nguyen Hoang et al, 2010; Xu et al, 2012), liver (Xia et al, 2008), kidney (Huang et al, 2009), lung (Li et al, 2008), and tumor tissue (Liu et al, 2009). Despite their divergent tissue localization, the majority of studies reporting stromal cell-induced rDCs have characterized them as populations of CD11c lo MHCII lo/int CD11b + cells, based on surface protein expression assessed by flow cytometry.…”

“…In contrast, splenic stroma-induced rDCs specifically recruit CXCR3 + Th1 cells to more efficiently suppress their proliferation, via the IFNα/β-dependent production of IP-10 after TLR triggering (Qian et al, 2007). More recent evidence has suggested that splenic rDCs are also able to directly induce apoptosis of activated CD4 + T cells by a process involving NO, Fas-Ligand, and IFNγ (Xu et al, 2012), a mechanism also reported to occur in the liver (Xia et al, 2008). This capacity for direct suppression of CD4 + T cell proliferation, even after TLR induced “maturation,” is a cardinal feature of rDCs that allows for them to be distinguished from cDCs.…”