Guangwei Liu

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.

MicroRNAs: novel regulators during the immune response.

MicroRNAs (miRNAs), an abundant class of highly conversed, small noncoding RNAs, present an entirely new way of post‐transcriptional gene regulation. miRNAs play a key role in diverse biological processes, such as embryogenesis, differentiation, inflammation, viral infections, and carcinogenesis. Recently, more studies showed the importance of these noncoding small RNAs on immune system development and response, and miRNAs are found to involve in the regulation of immunity, including the development and differentiation of immnue cells, antibody production and the inflammatory mediator release. Here, the latest findings were summarized to explore the function and mechanism of miRNAs in modulating innate and adaptive immune responses. J. Cell. Physiol. 218: 467–472, 2009.

Toll-like receptors and immune regulation: their direct and indirect modulation on regulatory CD4+ CD25+ T cells

Regulatory CD4+ CD25+ T (Treg) cells with the ability to suppress host immune responses against self‐ or non‐self antigens play important roles in the processes of autoimmunity, transplant rejection, infectious diseases and cancers. The proper regulation of CD4+ CD25+ Treg cells is thus critical for optimal immune responses. Toll‐like receptor (TLR)‐mediated recognition of specific structures of invading pathogens initiates innate as well as adaptive immune responses via antigen‐presenting cells (APCs). Interestingly, new evidence suggests that TLR signalling may directly or indirectly regulate the immunosuppressive function of CD4+ CD25+ Treg cells in immune responses. TLR signalling may shift the balance between CD4+ T‐helper cells and Treg cells, and subsequently influence the outcome of the immune response. This immunomodulation pathway may therefore have potential applications in the treatment of graft rejection, autoimmune diseases, infection diseases and cancers.

Changes of CD4+CD25+Foxp3+ regulatory T cells in aged Balb/c mice

A progressive decline in the integrity of the immune system is one of the physiologic changes during aging. The frequency of autoimmune diseases or immune disorders increases in the aging population, but the state of regulatory T (Treg) cells in aged individuals has not been well determined. In the present study, we investigated the levels, phenotypes, and function of CD4+CD25+ Treg cells in Balb/c mice, which were older than 20 months. Significantly enhanced percentages of CD4+CD25+ Treg cells in the periphery (blood, spleen, and lymph nodes) of the aged mice were observed. These Treg cells showed modified Vβ family distribution, reduced levels of CD45 receptor B and CD62 ligand molecules, as well as normal levels of forkhead box p3. However, when the inhibiting function of Treg cells was assayed in the in vitro assays and in a delayed‐type hypersensitivity (DTH) model, CD4+CD25+ Treg cells of aged mice displayed significantly lower inhibiting ability on alloantigen‐induced DTH reaction or cytokine productions (IL‐2 and IFN‐γ) but not cell proliferation of effector T cells, as compared with CD4+CD25+ Treg cells of young mice. In addition, the percentages of CD4+CD8–CD25+ Treg cells in the thymi of aged mice increased significantly, but their total cell numbers decreased markedly in these mice. Our present studies indicated collectively that the percentages, phenotypes, the size of TCR repertoire, and function of CD4+CD25+ Treg cells were altered significantly with aging in mice. The functional defects of CD4+CD25+ Treg cells may shed light on the role of CD4+CD25+ Treg cells in the increased sensitivity to autoimmune diseases of aged populations.

Th17 cell induction and immune regulatory effects.

The T help 1 (Th1) and Th2 cell classification have provided the framework for understanding CD4+ T cell biology and the interplay between innate and adaptive immunity for almost two decades. Recent studies have defined a previously unknown arm of the CD4+ T cell effector response, the Th17 lineage, which promises to change our understanding of immune regulation, immune pathogenesis and host defense. The factors that specify differentiation of IL‐17 producing effector T cells from naïve T cell precursors are being rapidly discovered and are providing insights into mechanisms by which signals from cells of the innate immune system guide alternative pathways of Th1, Th2, or Th17 development. In this review, we will focus on recent studies that have identified new subsets of Th cells, new insights regarding the induced generation and differentiation mechanisms of Th17 cells and immune regulatory effects. J. Cell. Physiol. 211: 273–278, 2007.

The macrophage heterogeneity: difference between mouse peritoneal exudate and splenic F4/80+ macrophages.

Macrophages isolated from various tissues manifest differences in cell shape, the expression of surface markers, as well as metabolic and functional activities. However, the heterogeneity of macrophages expressing the same marker in different tissues has not been fully addressed. In the present study, mouse F4/80+ peritoneal exudate macrophages (PEMs) and splenic macrophages (SPMs) appeared similar in most respects. But the percentages of cells expressing CD80, CD40, MHC‐II, TLR2, or TLR4, but not CD11c, CD54, or CD23, in freshly isolated F4/80+ SPMs were significantly higher than those in PEMs, whereas the levels of CD86+ cells in F4/80+ SPMs were markedly lower than those in PEMs. After lipopolysaccharide (LPS) stimulation, F4/80+ SPMs expressed significantly higher levels of CD86, CD40, or MHC‐II than F4/80+ PEMs, but not CD11c, CD80, CD54, or CD23. F4/80+ SPMs had remarkably lower non‐opsonic phagocytotic capacity against chicken RBCs or allo‐T cells than PEMs as determined by two‐photon microscopes and flow cytometry. SPMs produced markedly more NO than PEMs when cultured with LPS or allo‐T cells. Furthermore, SPMs exhibited stronger immunogenicity than PEMs, as determined by the ability to stimulate T cell proliferation, delayed type hypersensitivity, and IFN‐γ production. The data showed the differences between SPMs and PEMs with regard to the phenotypes, phagocytosis, and immunogenicity, which may offer important information for us to better understand the distinguished immune responses of macrophages in spleens and the peritoneal cavity. J. Cell. Physiol. 209: 341–352, 2006.

Phosphatase Wip1 negatively regulates neutrophil development through p38 MAPK-STAT1

Neutrophils are critically involved in host defense and tissue damage. Intrinsic molecular mechanisms controlling neutrophil differentiation and activities are poorly defined. Herein we found that p53-induced phosphatase 1(Wip1) is preferentially expressed in neutrophils among immune cells. The Wip1 expression is gradually up-regulated during the differentiation of myeloid precursors into mature neutrophils. Wip1-deficient mice and chimera mice with Wip1(-/-) hematopoietic cells had an expanded pool of neutrophils with hypermature phenotypes in the periphery. The in vivo and in vitro studies showed that Wip1 deficiency mainly impaired the developing process of myeloid progenitors to neutrophils in an intrinsic manner. Mechanism studies showed that the enhanced development and maturation of neutrophils caused by Wip1 deficiency were mediated by p38 MAPK-STAT1 but not p53-dependent pathways. Thus, our findings identify a previously unrecognized p53-independent function of Wip1 as a cell type-specific negative regulator of neutrophil generation and homeostasis through limiting the p38 MAPK-STAT1 pathway.

The phenotype and functional alterations of macrophages in mice with hyperglycemia for long term

Abnormal immunity and its related complications are the major causes of mortality and morbidity in diabetes patients. Macrophages, as one of the important innate cells, play pivotal roles in controlling immune homeostasis, immunity, and tolerance. The effects of hyperglycemia on the function of macrophages in hosts remain to be determined. Here we used mice with streptozotocin (STZ)‐induced diabetes for long term to study the changes of macrophages. We found that F4/80+ peritoneal exudate macrophages (PEMs) from mice with diabetes for 4 months displayed significantly reduced CD86 and CD54 expression and tumor necrosis factor (TNF)‐α and IL‐6 production but enhanced nitric oxide (NO) secretion compared with control mice when treated with interferon (IFN)‐γ and lipopolysaccharide (LPS), while the activity of arginase in PEMs from diabetic mice was significantly higher than control mice when stimulating with IL‐4. These dysfunctions of macrophages could be efficiently reversed by insulin treatment. Importantly, in vitro bone marrow‐derived macrophages showed similar functional changes, indicating the epigenetic alteration of macrophage precursors in these mice. In an in vitro culture system, high glucose and insulin significantly altered TNF‐α, IL‐6, and NO production and arginase activity of macrophages, which was reversed by the treatment with AKT and ERK inhibitors. Therefore, hyperglycemia and insulin deficiency can modify macrophage function through AKT‐mTOR and ERK pathways and through epigenetic effects on macrophage precursors. To further identify different components of diabetes on the dysfunction of macrophages is important for efficient prevention of diabetic complications. J. Cell. Physiol. 227: 1670–1679, 2012.

Effect of Low-Level Radiation on the Death of Male Germ Cells

Abstract Liu, G. W., Gong, P. S., Zhao, H. G., Wang, Z. C., Gong, S. L. and Cai, L. Effect of Low-Level Radiation on the Death of Male Germ Cells. Radiat. Res. 165, 379–389 (2006). Hormetic and adaptive responses induced by low-level radiation in hematopoietic and immune systems have been observed, as shown by stimulatory effects on cell growth and resistance to subsequent radiation-induced cytogenetic damage. However, in terms of cell death by apoptosis, the effects of low-level radiation are controversial: Some studies showed decreased apoptosis in response to low-level radiation while others showed increased apoptosis. This controversy may be related to the radiation doses or dose rates and also, more importantly, to the cell types. Testes are one of the most radiosensitive organs. The loss of male germ cells after exposure to ionizing radiation has been attributed to apoptosis. In the present study, the effects of low-level radiation at doses up to 200 mGy on mouse male germ cells in terms of apoptosis and the expression of apoptosis-related proteins were examined at different times after whole-body exposure of mice to low-level radiation. In addition, the effect of pre-exposure to low-level radiation on subsequent cell death induced by high doses of radiation was examined to explore the possibility of low-level radiation-induced adaptive response. The results showed that low-level radiation in the dose range of 25–200 mGy induced significant increases in apoptosis in both spermatogonia and spermatocytes, with the maximal effect at 75 mGy. The increased apoptosis is most likely associated with Trp53 protein expression. Furthermore, 75 mGy low-level radiation given pre-irradiation led to an adaptive response of seminiferous germ cells to subsequent high-level radiation-induced apoptosis. These results suggest that low-level radiation induces increased apoptosis in male germ cells but also induces a significant adaptive response that decreases cell death after a subsequent high-dose irradiation.

Phosphatase Wip1 Negatively Regulates Neutrophil Migration and Inflammation

Neutrophils are critically involved in host defense and tissue damage. Intrinsic signal mechanisms controlling neutrophil activities are poorly defined. We found that the expression of wild-type p53-induced phosphatase 1 (Wip1) in mouse and human neutrophils was downregulated quickly after neutrophil activation through JNK-microRNA-16 pathway. Importantly, the Wip1 expression level was negatively correlated with inflammatory cytokine productions of neutrophils in sepsis patients. Wip1-deficient mice displayed increased bactericidal activities to Staphylococcus aureus and were hypersensitive to LPS-induced acute lung damage with increased neutrophil infiltration and inflammation. Mechanism studies showed that the enhanced inflammatory activity of neutrophils caused by Wip1 deficiency was mediated by p38 MAPK-STAT1 and NF-κB pathways. The increased migration ability of Wip1KO neutrophils was mediated by the decreased CXCR2 internalization and desensitization, which was directly regulated by p38 MAPK activity. Thus, our findings identify a previously unrecognized function of Wip1 as an intrinsic negative regulator for neutrophil proinflammatory cytokine production and migration through multiple signal pathways.