The immunity of splenic and peritoneal F4/80(+) resident macrophages in mouse mixed allogeneic chimeras

Immune effects of glycolysis or oxidative phosphorylation metabolic pathway in protecting against bacterial infection

The metabolism of immune cells reprograms inflammatory responses to protect against infection by pathogenic microorganisms, but the immune effects of glycolysis and the oxidative phosphorylation (OXPHOS) metabolic pathway remain unclear. Herein, the effects of glycolysis or OXPHOS on the neutrophils and T cells were investigated using a pharmacological approach in mice. 2-Deoxy-d-glucose (2-DG), which blocks the key enzyme hexokinase of glycolysis, and dimethyl malonate (DMM), which blocks the key element succinate of OXPHOS, both efficiently expanded the population of neutrophils, but significantly inhibited tumor necrosis factor a secretion and reactive oxygen species (ROS) production. These compounds also effectively inhibited the differentiation of type 1 T helper cells (Th1) but had no effects on the differentiation of type 2 T helper cells (Th2) and regulatory T cells. A study of the underlying mechanism showed that hypoxia-inducible factor 1-alpha (HIF1α) was an upstream signal in the regulation of glycolysis, but not OXPHOS. In thioglycolate broth-induced neutrophil peritonitis, blockade of glycolysis or OXPHOS efficiently expanded the population of neutrophils, but diminished their abilities to secrete proinflammatory factors, produce ROS, and phagocytose bacteria. In Listeria monocytogenes bacteria-infected mice, 2-DG or DMM treatment consistently inhibited antibacterial activity and Th1 function. Thus, our results provide a basis for comprehensively understanding the role of glycolysis and OXPHOS in anti-infectious immunity.

HIF1α-dependent glycolysis promotes macrophage functional activities in protecting against bacterial and fungal infection

Macrophages are important innate immune defense system cells in the fight against bacterial and fungal pathogenic infections. They exhibit significant plasticity, particularly with their ability to undergo functional differentiation. Additionally, HIF1α is critically involved in the functional differentiation of macrophages during inflammation. However, the role of macrophage HIF1α in protecting against different pathogenic infections remains unclear. In this study, we investigated and compared the roles of HIF1α in different macrophage functional effects of bacterial and fungal infections in vitro and in vivo. We found that bacterial and fungal infections produced similar effects on macrophage functional differentiation. HIF1α deficiency inhibited pro-inflammatory macrophage functional activities when cells were stimulated with LPS or curdlan in vitro or when mice were infected with L. monocytogenes or C. albicans in vivo, thus decreasing pro-inflammatory TNFα and IL-6 secretion associated with pathogenic microorganism survival. Alteration of glycolytic pathway activation was required for the functional differentiation of pro-inflammatory macrophages in protecting against bacterial and fungal infections. Thus, the HIF1α-dependent glycolytic pathway is essential for pro-inflammatory macrophage functional differentiation in protecting against bacterial and fungal infections.

The immunotoxicity of dibutyl phthalate on the macrophages in mice

OBJECTIVE

Dibutyl phthalate (DBP), a widely used phthalate chemical, is commonly used as plasticizer. It is well known that DBP causes reproductive and developmental diseases, but the effect of DBP on the immune system remains to be determined. We assessed the effect of DBP on immune functions of murine macrophages, which constitute a key component in the immune response.

MATERIALS AND METHODS

Murine peritoneal exudate macrophages (PEMs) were treated with 0, 1, 5, 10, 50 or 100 μM DBP in vitro for 24 h and then the viability of PEMs were measured by flow cytometry (FCM) and trypan blue count. To investigate the effect of DBP on the functions of PEMs, we treated the PEMs with moderate dose of DBP (0, 1, 5 or 10 μM) in vitro for 24 h. The phenotypes, phagocytosis and cytokine production of PEMs were measured by FCM or real-time PCR. The immunogenicity and antigen presenting capacity of PEMs treated with DBP in vitro were assessed both by the mixed lymphocytereaction (MLR) in vitro assay and through the injection of exposed cells in mice by the delayed-type hypersensitivity (DTH) assay.

RESULTS

High dose of DBP (50-100 μM) showed cytotoxicity on PEMs, whereas after the treatment with moderate dose of DBP (1-10 μM) in vitro, PEMs expressed low level of CD36, CD80 and MHC-II molecules, and showed significantly decreased phagocytosis on apoptotic cells and Escherichia coli. In addition, DBP treatment exhibited a decrease in the cytokine production, immunogenicity and antigen-presenting capacity of PEMs.

CONCLUSIONS

The present study shows the effects of DBP on macrophages, demonstrating immunogenicity and decreased antigen presentation in vitro.

SIRT1 limits the function and fate of myeloid-derived suppressor cells in tumors by orchestrating HIF-1α-dependent glycolysis

Myeloid-derived suppressor cells (MDSC) display an immature phenotype that may assume a classically activated (M1) or alternatively activated phenotype (M2) in tumors. In this study, we investigated metabolic mechanisms underlying the differentiation of MDSCs into M1 or M2 myeloid lineage and their effect on cancer pathophysiology. We found that SIRT1 deficiency in MDSCs directs a specific switch to M1 lineage when cells enter the periphery from bone marrow, decreasing the suppressive function in favor of a proinflammatory M1 phenotype associated with tumor cell attack. Glycolytic activation through the mTOR-hypoxia-inducible factor-1α (HIF-1α) pathway was required for differentiation to the M1 phenotype, which conferred protection against tumors. Our results define the essential nature of a SIRT1-mTOR/HIF-1α glycolytic pathway in determining MDSC differentiation, with implications for metabolic reprogramming as a cancer therapeutic approach.

IL-17A produced by neutrophils protects against pneumonic plague through orchestrating IFN-γ-activated macrophage programming

Innate immune cells, including neutrophils and macrophages, are critically involved in host antimicrobial defense responses. Intrinsic regulatory mechanisms controlling neutrophil and macrophage activities are poorly defined. In this study, we found that IL-17A, a natural signal factor, could provide protection against early pneumonic plague inflammation by coordinating the functions of neutrophils and programming of macrophages. The IL-17A level is promptly increased during the initial infection. Importantly, abrogation of IL-17A or IL-17AR significantly aggravated the infection, but mIL-17A treatment could significantly alleviate inflammatory injury, revealing that IL-17A is a critical requirement for early protection of infection. We also demonstrated that IL-17A was predominantly produced by CD11b(+)Ly6G(+) neutrophils. Although IL-17A could not significantly affect the antimicrobial responses of neutrophils, it could target the proinflammatory macrophage (M1) programming and potentiate the M1's defense against pneumonic plague. Mechanistically, IFN-γ treatment or IFN-γ-activated M1 macrophage transfer could significantly mitigate the aggravated infection of IL-17A(-/-) mice. Finally, we showed that IL-17A and IFN-γ could synergistically promote macrophage anti-infection immunity. Thus, our findings identify a previously unrecognized function of IL-17A as an intrinsic regulator in coordinating neutrophil and macrophage antimicrobial activity to provide protection against acute pneumonic plague.

Kinase AKT controls innate immune cell development and function

The critical roles of kinase AKT in tumour cell proliferation, apoptosis and protein synthesis have been widely recognized. But AKT also plays an important role in immune modulation. Recent studies have confirmed that kinase AKT can regulate the development and functions of innate immune cells (neutrophil, macrophage and dendritic cell). Studies have shown that different isoforms of kinase AKT have different effects in regulating immunity-related diseases, mainly through the mammalian target of rapamycin-dependent or -independent pathways. The purpose of this review is to illustrate the immune modulating effects of kinase AKT on innate immune cell development, survival and function.

Kinase AKT1 negatively controls neutrophil recruitment and function in mice

Neutrophils are critically involved in host defense and inflammatory injury. However, intrinsic signaling mechanisms controlling neutrophil recruitment and activities are poorly defined. In this article, we showed that protein kinase AKT1 (also known as PKBα) is the dominant isoform expressed in neutrophils and is downregulated upon bacterial infection and neutrophil activation. AKT1 deficiency resulted in severe disease progression accompanied by recruitment of neutrophils and enhanced bactericidal activity in the acute inflammatory lung injury (ALI) and the Staphylococcus aureus infection mouse models. Moreover, the depletion of neutrophils efficiently reversed the aggravated inflammatory response, but adoptive transfer of AKT1(-/-) neutrophils could potentiate the inflammatory immunity, indicating an intrinsic effect of the neutrophil in modulating inflammation in AKT1(-/-) mice. In the ALI model, the infiltration of neutrophils into the inflammatory site was associated with enhanced migration capacity, whereas inflammatory stimuli could promote neutrophil apoptosis. In accordance with these findings, neutralization of CXCR2 attenuated neutrophil infiltration and delayed the occurrence of inflammation. Finally, the enhanced bactericidal activity and inflammatory immunity of AKT-deficient neutrophils were mediated by a STAT1-dependent, but not a mammalian target of rapamycin-dependent, pathway. Thus, our findings indicated that the AKT1-STAT1 signaling axis negatively regulates neutrophil recruitment and activation in ALI and S. aureus infection in mice.

Induction of M2-like macrophages in recipient NOD-scid mice by allogeneic donor CD4(+)CD25(+) regulatory T cells

CD4(+)CD25(+) regulatory T cells (Tregs) play an important role in maintaining host immune tolerance via regulation of the phenotype and function of the innate and adaptive immune cells. Whether allogeneic CD4(+)CD25(+) Tregs can regulate recipient mouse macrophages is unknown. The effect of allogeneic donor CD4(+)CD25(+) Tregs on recipient mouse resident F4/80(+)macrophages was investigated using a mouse model in which allogeneic donor CD4(+)CD25(+) Tregs were adoptively transferred into the peritoneal cavity of host NOD-scid mice. The phenotype and function of the recipient macrophages were then assayed. The peritoneal F4/80(+) macrophages in the recipient mice that received the allogeneic CD4(+)CD25(+) Tregs expressed significantly higher levels of CD23 and programmed cell death-ligand 1(PD-L1) and lower levels of CD80, CD86, CD40 and MHC II molecules compared to the mice that received either allogeneic CD4(+)CD25(-) T cells (Teffs) or no cells. The resident F4/80(+) macrophages of the recipient mice injected with the allogeneic donor CD4(+)CD25(+) Tregs displayed significantly increased phagocytosis of chicken red blood cells (cRBCs) and arginase activity together with increased IL-10 production, whereas these macrophages also showed decreased immunogenicity and nitric oxide (NO) production. Blocking arginase partially but significantly reversed the effects of CD4(+)CD25(+) Tregs with regard to the induction of the M2 macrophages in vivo. Therefore, the allogeneic donor CD4(+)CD25(+) Tregs can induce the M2 macrophages in recipient mice at least in part via an arginase pathway. We have provided in vivo evidence to support the unknown pathways by which allogeneic donor CD4(+)CD25(+) Tregs regulate innate immunity in recipient mice by promoting the differentiation of M2 macrophages.

An instructive role of donor macrophages in mixed chimeras in the induction of recipient CD4(+)Foxp3(+) Treg cells

The immune regulatory function of macrophages (Møs) in mixed chimeras has not been determined. In the present study, with a multi-lineage B6-to-BALB/c mixed chimeric model, we examined the ability of donor-derived splenic Møs in the induction of regulatory T cells (Treg). B6 splenic Møs from mixed chimeras induced significantly less cell proliferation, more IL-10 and TGF-β, and less IL-2 and IFN-γ productions of CD4(+) T cells from BALB/c mice than naive B6 Møs did, whereas they showed similar stimulatory activity to the third part C3H CD4(+) T cells. Importantly, highly purified donor F4/80(+)CD11c(-) Møs efficiently induced recipient CD4(+)Foxp3(+) Treg cells from CD4(+)CD25(-)Foxp3(-) T cells. Furthermore, donor Møs of mixed chimeras produced more IL-10 and less IFN-γ than those of naive mice when cultured with BALB/c but not the third party C3H CD4(+) T cells. Induction of recipient CD4(+) Treg cells by donor Møs was significantly blocked by anti-IL-10, but not by anti-TGF-β mAb. Therefore, donor Møs have the ability to induce recipient CD4(+)Foxp3(+) Treg cells in a donor antigen-specific manner, at least partially, via an IL-10-dependent pathway. This study for the first time showed that, in mixed allogeneic chimeras, donor Møs could be specifically tolerant to recipients and gained the ability to induce recipient but not the third party Foxp3(+) Treg cells. Whether this approach is involved in transplant immune tolerance needs to be determined.

Phenotypic and functional switch of macrophages induced by regulatory CD4+CD25+ T cells in mice

CD4(+)CD25(+) regulatory T cells (Treg cells) are important in maintenance of peripheral tolerance. The direct effect of CD4(+)CD25(+) Treg cells on macrophages was studied using a mouse model in which syngeneic CD4(+)CD25(+) Treg cells were adoptively transferred into the peritoneal cavity of SCID mice. Peritoneal macrophages in mice transferred with CD4(+)CD25(+) Treg cells expressed significantly higher levels of CD23, CD47 and CD206 and less CD80 and major histocompatibility complex class II molecules as compared with those mice that received either CD4(+)CD25(-) T cells or no cells. Macrophages of mice injected with CD4(+)CD25(+) Treg cells displayed a remarkably enhanced phagocytosis of chicken red blood cells, and arginase activity together with an increased interleukin-10 (IL-10) production, whereas they showed a decreased antigen-presenting ability and nitric oxide production. Furthermore, CD4(+)CD25(+) Treg cells and CD4(+)CD25(-) T cells showed strong antagonistic effects on macrophage polarizations in vivo. Blocking arginase, IL-10 and/or transforming growth factor-β (TGF-β) partially but significantly reversed the effects of CD4(+)CD25(+) Treg cells to induce M2 macrophages in vivo suggesting that CD4(+)CD25(+) Treg cells have the ability to induce M2 macrophages at least in part through arginase, IL-10 and TGF-β pathways. Thus, we have provided the in vivo evidence to support the unknown pathways for CD4(+)CD25(+) Treg cells to regulate innate immunity by promoting the differentiation of M2 macrophages as well as by inhibiting M1 macrophage induction by CD4(+)CD25(-) T cells in mice. CD4(+)CD25(+) Treg cells efficiently induced M2 macrophage differentiation in mice, offering the in vivo evidence to support the role of CD4(+)CD25(+) Treg cells in regulating innate immunity.

Gamma-ray resistance of regulatory CD4+CD25+Foxp3+ T cells in mice

Abstract CD4(+)CD25(+) regulatory T cells (Treg cells) are an important subset of T cells for keeping proper immune responses and tolerance. However, the effects of gamma radiation on CD4(+)CD25(high) Foxp3(+) Treg cells have not been examined previously. In the present study, we compared the sensitivity of mouse CD4(+)CD25(high) Foxp3(+) Treg cells and CD4(+)CD25(-) T cells to gamma radiation in vitro and in vivo. After C57BL/6 mice received a whole-body dose of 5 Gy gamma rays, the numbers of lymphocyte subsets in blood, lymph nodes, spleens and thymuses clearly decreased. However, gamma radiation significantly enhanced the ratios of CD4(+)CD25(high) Treg cells and CD4(+)CD25(high) Foxp3(+) Treg cells to CD4(+) T cells in the blood, lymph nodes, spleens and thymuses of mice. More dead cells were observed in CD4(+)CD25(-) T cells than in CD4(+)CD25(high) Treg cells or CD4(+)CD25(high) Foxp3(+) Treg cells when the cells were irradiated in vitro, indicating that CD4(+)CD25(high) Foxp3(+) Treg cells are more resistant to gamma radiation than other T cells. Moreover, a higher expression of Bcl-2 in CD4(+)CD25(high) Treg cells was detected compared with that in CD4(+)CD25(-) T cells. CD4(+)CD25(+) Treg cells from irradiated mice were functional, though their immunosuppressive ability was somewhat impaired compared to those from nonirradiated mice as determined by an in vitro assay. These results indicate that mouse CD4(+)CD25(+) Treg cells and CD4(+)CD25(-) T effector cells have different sensitivities to gamma radiation in mice.