Obesity-associated increases in adipose tissue (AT) CD11c+ cells suggest that dendritic cells (DC), which are involved in the tissue recruitment and activation of macrophages, may play a role in determining AT and liver immunophenotype in obesity. This study addressed this hypothesis. With the use of flow cytometry, electron microscopy, and loss-and-gain of function approaches, the contribution of DC to the pattern of immune cell alterations and recruitment in obesity was assessed. In AT and liver there was a substantial, high-fat diet (HFD)–induced increase in DC. In AT, these increases were associated with crown-like structures, whereas in liver the increase in DC constituted an early and reversible response to diet. Notably, mice lacking DC had reduced AT and liver macrophages, whereas DC replacement in DC-null mice increased liver and AT macrophage populations. Furthermore, delivery of bone marrow–derived DC to lean wild-type mice increased AT and liver macrophage infiltration. Finally, mice lacking DC were resistant to the weight gain and metabolic abnormalities of an HFD. Together, these data demonstrate that DC are elevated in obesity, promote macrophage infiltration of AT and liver, contribute to the determination of tissue immunophenotype, and play a role in systemic metabolic responses to an HFD.

Prolonged inhibition of the kinase, mammalian target of rapamycin (mTOR), during myeloid dendritic cell (DC) generation confers resistance to maturation. Recently, however, mTOR inhibition immediately before Toll-like receptor ligation has been found to exert proinflammatory effects on myeloid cells, notably enhanced IL-12p40/p70 production. We show, for the first time, that mouse or human DCs generated under mTOR inhibition exhibit markedly enhanced IL-12p70 production after lipopolysaccharide (LPS) stimulation, despite impaired costimulatory molecule expression and poor T-cell stimulatory ability. Consistent with this finding, we reveal that increased IL-12p40 production occurs predominantly in CD86 lo immature DCs. High IL-12p40/p70 production by CD86 lo DC resulted from failed down-regulation of glycogen synthase kinase-3 (GSK-3) activity and could not be ascribed to enhanced Akt function. Despite high IL-12p70 secretion, rapamycinconditioned, LPS-stimulated DCs remained poor T-cell stimulators, failing to enhance allogeneic Th1 cell responses. We also report that inhibition of GSK-3 impedes the ability of LPS-stimulated DCs to induce forkhead box p3 in CD4 ؉ CD25 ؊ T cells, as does the absence of IL-12p40/ p70. Thus, GSK-3 activity in DC is regulated via signaling linked to mTOR and modulates their capacity both to produce IL-12p40/p70 and induce forkhead box p3 in CD4 ؉ IntroductionMammalian target of rapamycin (mTOR) is an integrative kinase that coordinates environmental signals, especially those activating phosphoinositide 3-kinase (PI3K) and its effector, the Akt kinase. 1,2 The relationship between the 2 identified mTOR-containing complexes (mTORC1 and mTORC2) and PI3K/Akt is under intensive investigation, but it is understood that mTORC1 is located downstream of PI3K and activated by Akt. 1 Akt, however, lies both upstream and downstream of mTOR and must be phosphorylated on S473 by mTORC2 to be fully activated. 1 Although the immunosuppressant rapamycin (RAPA) potently targets mTORC1 activity to limit cell growth and proliferation, mTORC2 is RAPA-resistant, although prolonged RAPA exposure can limit its activity in some cells and tissues. 3 Consistent with ubiquitous leukocyte mTOR expression, RAPA exerts significant immunomodulatory effects. 4 At clinically relevant concentrations, it inhibits cytokine-induced proliferation of effector T cells while sparing the proliferation and function of regulatory T cells (Treg). [4][5][6] Both in vitro and in vivo, continued exposure to RAPA suppresses myeloid (m) dendritic cell (DC) generation, maturation, and T-cell stimulatory function. [7][8][9][10][11][12][13] More precisely, propagation of murine bone marrow (BM)-derived mDCs in RAPA (RAPA-conditioned mDCs; RAPA-DCs) generates mDCs with low surface major histocompatibility complex and costimulatory molecules, even after exposure to potent inflammatory stimuli, such as Toll-like receptor (TLR) ligands, and CD40 ligation. 8,[10][11][12] Although in vitro-generated RAPA-DCs are weak stimulators of T cells 8...

Hepatic stellate cells (HSCs) may play an important role in hepatic immune regulation by producing numerous cytokines/chemokines, and expressing Ag-presenting and T cell co-regulatory molecules. Due to disruption of the endothelial barrier during cold-ischemic storage and reperfusion of liver grafts, HSCs can interact directly with cells of the immune system. Endotoxin (LPS), levels of which increase in liver diseases and transplantation, stimulates the synthesis of many mediators by HSCs. We hypothesized that LPS-stimulated HSCs might promote hepatic tolerogenicity by influencing naturally-occurring immunosuppressive CD4+CD25+FoxP3+ regulatory T cells (Tregs). Following their portal venous infusion, allogeneic CD4+ T cells, including Tregs, were found closely associated with HSCs, and this association increased in LPS-treated livers. In vitro, both unstimulated and LPS-stimulated HSCs up-regulated Fas (CD95) expression on conventional CD4+ T cells and induced their apoptosis in a Fas/FasL-dependent manner. By contrast, HSCs induced Treg proliferation, which required cell-cell contact, and was MHC class II-dependent. This effect was augmented when HSCs were pretreated with LPS. LPS increased the expression of MHC class II, CD80 and CD86, and stimulated the production of IL-1α, IL-1β, IL-6, IL-10 and TNFα by HSCs. Interestingly, production of IL-1α, IL-1β, IL-6 and TNFα was strongly inhibited, but that of IL-10 enhanced, in LPS-pretreated HSC/Treg co-cultures. Adoptively transferred allogeneic HSCs migrated to the secondary lymphoid tissues and induced Treg expansion in lymph nodes. These data implicate endotoxins-stimulated HSCs as important immune regulators in liver transplantation by inducing selective expansion of tolerance-promoting Tregs, and reducing inflammation and allo-immunity.

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Phong et al. show that depending on the expression of p-Lyn, mast cell activation by antigen can result in dichotomous effects on mast cell function and signaling that can be accentuated by Tim-3 ligation.