Cytokine production by M-CSF- and GM-CSF-induced mouse bone marrow-derived macrophages upon coculturing with late apoptotic cells

MRP8/14 mediates macrophage efferocytosis through RAGE and Gas6/MFG-E8, and induces polarization via TLR4-dependent pathway

Myeloid-related protein 8/14 (MRP8/14) participates in various inflammatory responses, however, its effect on macrophage efferocytosis remains unclear. Here, we demonstrate that MRP8/14 significantly inhibits the efferocytosis of apoptotic thymocytes by mouse bone marrow-derived macrophages (BMDMs), which later proves to be associated with the receptor for advanced glycation end products (RAGE) or for reducing the expression of growth arrest-specific protein 6 and milk fat globule epidermal growth factor 8, independent of RAGE. Furthermore, MRP8/14 promotes polarization of BMDMs from the M₂ - to M₁ -like phenotype by upregulating expression of M₁ -related surface receptor proteins and signature M₁ -marker genes and by downregulating signature M₂ -marker gene expression, which depends on Toll-like receptor 4 and p38 mitogen-activated protein kinase/nuclear factor κB pathways. Thus, we report a significant inhibitory effect of MRP8/14 on macrophage efferocytosis and MRP8/14-mediated phenotypic polarization, which may be helpful in developing novel therapeutic strategies leading to inflammation resolution.

Pruritus in ordinary scabies: IL-31 from macrophages induced by overexpression of thymic stromal lymphopoietin and periostin

BACKGROUND

Scabies is a common contagious skin disease caused by an infestation of the skin by Sarcoptes scabiei var. hominis. A hallmark symptom of scabies is severe itch.

METHODS

We sought to determine the generation of a pruritogenic cytokine, interleukin (IL)-31, together with immune profiles in skin lesions of ordinary scabies through immunohistochemical and immunofluorescent studies. To elucidate the pathological mechanisms of IL-31 generation, murine peritoneal macrophages were stimulated with various T helper 2 (Th2) cytokines and proteins ex vivo.

RESULTS

A large number of CCR4(+) Th2 cells, eosinophils, and basophils infiltrated in scabies lesions. Increased generation of IL-31, thymic stromal lymphopoietin (TSLP), and periostin was also observed. A major population of IL-31(+) cells were Arginase-1(+)/CD163(+) M2 macrophages. Murine peritoneal macrophages showed an M2 phenotype and generated IL-31 when stimulated with TSLP and periostin.

CONCLUSION

IL-31 appeared to be largely generated by M2 macrophages in ordinary scabies lesions. This IL-31 induction was mediated by TSLP and periostin.

Kinetics of cytokine mRNA and protein expression by plastic adherent cells in the thymus after split-dose irradiation

Whole body irradiation causes significant apoptosis in various tissues such as the thymus. If apoptotic cells outnumber the phagocytic capacity of macrophages, apoptosis becomes secondary necrosis, inducing inflammatory cytokine expression in macrophages. Radiation also induces thymic lymphomas in C57BL/6 mice after four consecutive irradiations with 1.6 Gy X-rays with nearly 100% incidence. Since cancer development is modulated by a microenvironment involving macrophages, we examined the kinetics of thymocyte number and plastic adherent cell number in the thymus as well as cytokine mRNA expression by plastic adherent cells in the thymus after split-dose irradiation. Upon split-dose irradiation, thymocyte number changed dramatically, whereas plastic adherent cell number did not. Among cytokine mRNAs tested, IL-1β, IL-11 and IL-12p40 mRNAs were up regulated 2 days after the 1st and 2nd, 3rd and 4th, and 2nd and 3rd irradiations, respectively. On the other hand, TNF-α mRNA was up regulated 2 days after the 3rd irradiation and 2 weeks after the 4th irradiation. The level of IL-11 protein was also increased 2 days after 3rd and 4th irradiations. These results suggest that, upon split-dose irradiation, macrophages in the thymus produce various cytokines in a time-dependent manner, thereby contributing to induction of thymic lymphomas.

Changes in the function and phenotype of resident peritoneal macrophages after housing in an enriched environment

Exposure to an enriched environment (EE) affects not only brain functions but also immune responses upon viral or bacterial infections. In this study, we examined changes in the phagocytic response and chemokine production of resident peritoneal macrophages after mice had been housed under EE conditions for 6 or 8 weeks, and then explored the possibility that EE could cause a change in the macrophage phenotype by means of flow cytometry as well as quantitative RT-PCR. The percentages of EE macrophages phagocytosing S. aureus and apoptotic neutrophils were significantly larger than those of standard environment (SE) macrophages. After coculturing with S. aureus, EE macrophages tended to produce greater amounts of chemokines such as MIP-2, KC and MCP-1 than SE ones, although the increases for MIP-2 and KC were not statistically significant. As compared with SE macrophages, EE macrophages included more CD40-positive cells (M1 marker), and expressed more mRNAs of IL-6 (M1 marker) and IRF4 (M2 marker), and less mRNA of CD38 (M1 marker), suggesting either the possibility that EE macrophages are a mixed population of M1 and M2 macrophages or the possibility that they are a unique population with a mixed M1 and M2 macrophage phenotype.

Skewing of peritoneal resident macrophages toward M1-like is involved in enhancement of inflammatory responses induced by secondary necrotic neutrophils in aged mice

Secondary necrotic cells, which are generated if apoptotic cells are incompletely cleared, induce severe inflammatory responses involving MIP-2 production and subsequent neutrophil infiltration. Recently, we showed that the phagocytic capacity of peritoneal resident macrophages from wild type (WT) aged mice as well as SMP30(-/-) mice fed a VC-limited diet as to secondary necrotic cells was reduced as compared with that in young mice, and that the inflammatory responses induced were stronger than those in young mice, presumably because of the delay in removal of secondary necrotic cells in aged mice. In this study, we investigated why MIP-2 production was increased in aged mice upon injection of secondary necrotic cells and why the phagocytic capacity of peritoneal resident macrophages from aged mice was reduced. When cocultured with secondary necrotic cells, the peritoneal resident macrophages from both types of aged mice significantly produced MIP-2 even in the absence of IFN-γ, whereas MIP-2 production by macrophages from WT young mice required IFN-γ. The peritoneal resident macrophages from both types of aged mice expressed CD40, a M1 macrophage marker, as in the case of M1 macrophages, which were obtained by treatment of macrophages from WT young mice with IFN-γ and LPS. Furthermore, M1 macrophages exhibited less phagocytic capacity as to secondary necrotic cells than non-treated macrophages. These results suggest that the phenotype of peritoneal resident macrophages is skewed toward M1-like in aged mice and that such skewing toward M1-like is involved in enhancement of inflammatory responses induced by secondary necrotic neutrophils in aged mice.

Attenuated phagocytosis of secondary necrotic neutrophils by macrophages in aged and SMP30 knockout mice

AIM

Secondary necrotic cells generated in vivo induce inflammatory responses; for example, the production of macrophage inflammatory protein-2 (MIP-2) and subsequent infiltration of neutrophils. The aim of the present study was to elucidate the effect of aging on the phagocytosis of secondary necrotic cells and the inflammatory responses by using either wild-type (WT) young mice, WT aged mice or senescence-accelerated mice (SMP30(-/-) mice).

METHODS

The phagocytosis of secondary necrotic neutrophils with resident macrophage from either WT young mice, WT aged mice or SMP30(-/-) mice was examined by coculturing macrophages with secondary necrotic neutrophils in vitro. To investigate the inflammatory response induced by secondary necrotic cells, time-dependent infiltration of neutrophils and production of MIP-2 were determined in the peritoneal cavity on the injection of secondary necrotic cells.

RESULTS

The phagocytosis of secondary necrotic cells by macrophages from WT aged and SMP30(-/-) mice was significantly reduced as compared with that by macrophages from WT young mice. On peritoneal injection of secondary necrotic cells, the peak time of neutrophil infiltration was earlier in SMP30(-/-) mice than in WT young mice. The number of neutrophils in SMP30(-/-) mice at the peak time was also greater than that in WT young mice.

CONCLUSIONS

Our findings showed that the phagocytosis of secondary necrotic cells was attenuated in aged mice and SMP30(-/-) mice, and that the MIP-2 production was enhanced and subsequently neutrophil infiltration was exaggerated on peritoneal injection of secondary necrotic cells into those mice.

SIGN-R1, a C-type lectin, enhances apoptotic cell clearance through the complement deposition pathway by interacting with C1q in the spleen

Complements, such as C1q and C3, and macrophages in the splenic marginal zone (MZMs) play pivotal roles in the efficient uptake and processing of circulating apoptotic cells. SIGN-R1, a C-type lectin that is highly expressed in a subpopulation of MZMs, regulates the complement fixation pathway by interacting with C1q, to fight blood-borne Streptococcus pneumoniae. Therefore, we examined whether the SIGN-R1-mediated classical complement pathway plays a role in apoptotic cell clearance and immune tolerance. SIGN-R1 first-bound apoptotic cells and this binding was significantly enhanced in the presence of C1q. SIGN-R1-C1q complex then immediately mediated C3 deposition on circulating apoptotic cells in the MZ, leading to the efficient clearance of them. SIGN-R1-mediated C3 deposition was completely abolished in the spleen of SIGN-R1 knockout (KO) mice. Given that SIGN-R1 is not expressed in the liver, we were struck by the finding that C3-deposited apoptotic cells were still found in the liver of wild-type mice, and dramatically reduced in the SIGN-R1 KO liver. In particular, SIGN-R1 deficiency caused delayed clearance of apoptotic cells and aberrant secretion of cytokines, such as TNF-α, IL-6, and TGF-β in the spleen as well as in the liver. In addition, anti-double- and single-stranded DNA antibody level was significantly increased in SIGN-R1-depleted mice compared with control mice. These findings suggest a novel mechanism of apoptotic cell clearance which is initiated by SIGN-R1 in the MZ and identify an integrated role of SIGN-R1 in the systemic clearance of apoptotic cells, linking the recognition of apoptotic cells, the opsonization of complements, and the induction of immune tolerance.

PET imaging of tumor associated macrophages using mannose coated 64Cu liposomes

Macrophages within the tumor microenvironment (TAMs) have been shown to play a major role in the growth and spread of many types of cancer. Cancer cells produce cytokines that cause macrophages to express scavenger receptors (e.g. the mannose receptor) and factors that facilitate tissue and blood vessel growth, suppress T cell mediated anti-tumor activity, and express enzymes that can break down the extracellular matrix, thereby promoting metastasis. We have designed a mannosylated liposome (MAN-LIPs) and show that it accumulates in TAMs in a mouse model of pulmonary adenocarcinoma. These liposomes are loaded with (64)Cu to allow tracking by PET imaging, and contain a fluorescent dye in the lipid bilayer permitting subsequent fluorescence microscopy. We injected these liposomes into a mouse model of lung cancer. In vivo PET images were acquired 6 h after injection followed by the imaging of select excised organs. MAN-LIPs accumulated in TAMs and exhibited little accumulation in remote lung areas. MAN-LIPs are a promising new vehicle for the delivery of imaging agents to lung TAMs. In addition to imaging, MAN-LIPs hold the potential for delivery of therapeutic agents to the tumor microenvironment.

Different antigen presentation tendencies of granulocyte-macrophage colony-stimulating factor-induced bone marrow-derived macrophages and peritoneal macrophages

Granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced bone marrow-derived cells (BMCs) and primary peritoneal exudate cells (PECs) are usually used for antigen presentation in in vitro experiments. In order to expound their tendency for uptake and antigen presentation, we compared differences in the degree of phagocytosis, the expression of co-stimulatory molecules, and the activation of T lymphocytes between these two cell types. These assays used the F4/80 marker expression, as it is the general marker for macrophages. The BMC population was found to contain both F4/80(bright) and F4/80(dim) subtypes, while PECs were mainly composed of the F4/80(bright) subtype. Expression levels of cell surface co-stimulatory molecules, CD80, CD86, CD54, and CD40, were significantly higher for F4/80(+)BMCs than F4/80(+)PECs. Their expressions were further upregulated for F4/80(+)BMCs than for F4/80(+)PECs after stimulation with flagellin. F4/80(+)BMCs had a weaker ability to phagocytize microbeads than F4/80(+)PECs (P < 0.05), and we determined no relationship between F4/80 expression and phagocytosis. T lymphocytes were activated more efficiently after incubation with BMCs pulsed with flagellin than with pulsed PECs. In this study, F4/80(+)BMCs and F4/80(+)PECs represent the bone marrow-derived macrophages (BMMs) and peritoneal macrophages (PMs), respectively. These results indicate that PMs showed greater potential for phagocytosis, whereas GM-CSF-induced BMMs showed a tendency toward antigen presentation.

Marginal zone macrophages suppress innate and adaptive immunity to apoptotic cells in the spleen

Marginal zone macrophages (MZMs) are a small subset of specialized splenic macrophages known to interact with apoptotic material entering the spleen from circulation. To evaluate whether MZMs regulate immunity to apoptotic material we depleted MZMs and assessed innate and adaptive immune responses to apoptotic cells administered systemically. MZM depletion altered the spatial localization of apoptotic cells, which accumulated in T-cell areas of the lymphoid follicles. MZM depletion also enhanced phagocytosis of apoptotic cells by red pulp (CD68(+)F4/80(+)) macrophages, which expressed increased CD86, MHCII, and CCR7. MZM depletion led to increased production of proinflammatory cytokines and enhanced lymphocyte responsiveness to apoptotic cell antigens. Furthermore, we found that MZM depletion accelerated autoimmune disease progression in mice genetically prone to systemic lupus erythematosus and caused significant mortality in wild-type mice repeatedly exposed to exogenous apoptotic thymocytes. These findings support the hypothesis that MZMs are central in the clearance of apoptotic cells to minimize the immunogenicity of autoantigens.

Evidence for a DC-specific inhibitory mechanism that depends on MyD88 and SIGIRR

Dendritic cells (DC) are an essential link between the innate and adaptive immune response. To become effective antigen-presenting cells DC need to undergo maturation, during which they up-regulate co-stimulatory molecules and produce cytokines. There is great interest in utilizing DC in vaccination regimes. Over recent years, Toll-like receptor (TLR) signalling has been recognized to be one of the major inducers of DC maturation. This study describes a mutant version of the TLR adaptor molecule MyD88 (termed MyD88lpr) as a novel adjuvant for vaccination regimes. MyD88lpr specifically activates DC by disrupting a DC intrinsic inhibitory mechanism, which is dependent on single immunoglobulin IL-1R-related. Moreover, MyD88lpr was able to induce an IgG2a-dominated response to a co-expressed antigen, suggesting Th1 immunity. However, when used as a vaccine adjuvant for Influenza nucleoprotein there was no significant difference in the lung viral titres during the infection. This study describes MyD88lpr as a potential adjuvant for vaccinations, which would be able to target DC specifically.

Cross, but not direct, presentation of cell-associated virus antigens by spleen macrophages is influenced by their differentiation state

The initiation of T-cell immune responses requires professional antigen-presenting cells. Emerging data point towards an important role for macrophages (Mphi) in the priming of naïve T cells. In this study we analyzed the efficiency and the mechanisms by which Mphi derived from spleen (Sp-Mphi) or bone marrow (BM-Mphi) present Lymphocytic choriomeningitis virus (LCMV) antigens to epitope-specific T cells. We demonstrate that because of phagosomal maturation, Sp-Mphi downregulate their ability to cross-present cell-associated, but not soluble, antigens, as they are further differentiated in culture without altering their capacity to directly present virus antigens after infection. We propose that Sp-Mphi are extremely efficient at direct and cross-presentation. However, if these cells undergo further M-CSF-dependent maturation, they will adapt to be more scavenger and phagocytic and concurrently reduce their cross-presenting capacity. Accordingly, Sp-Mphi can have an important role in regulating T-cell responses through cross-presentation depending on their differentiation state.