Analysis of mannose receptor regulation by IL-4, IL-10, and proteolytic processing using novel monoclonal antibodies

Myeloid cell-mediated targeting of LIF to dystrophic muscle causes transient increases in muscle fiber lesions by disrupting the recruitment and dispersion of macrophages in muscle

Leukemia inhibitory factor (LIF) can influence development by increasing cell proliferation and inhibiting differentiation. Because of its potency for expanding stem cell populations, delivery of exogenous LIF to diseased tissue could have therapeutic value. However, systemic elevations of LIF can have negative, off-target effects. We tested whether inflammatory cells expressing a LIF transgene under control of a leukocyte-specific, CD11b promoter provide a strategy to target LIF to sites of damage in the mdx mouse model of Duchenne muscular dystrophy, leading to increased numbers of muscle stem cells and improved muscle regeneration. However, transgene expression in inflammatory cells did not increase muscle growth or increase numbers of stem cells required for regeneration. Instead, transgene expression disrupted the normal dispersion of macrophages in dystrophic muscles, leading to transient increases in muscle damage in foci where macrophages were highly concentrated during early stages of pathology. The defect in inflammatory cell dispersion reflected impaired chemotaxis of macrophages to C-C motif chemokine ligand-2 and local increases of LIF production that produced large aggregations of cytolytic macrophages. Transgene expression also induced a shift in macrophage phenotype away from a CD206+, M2-biased phenotype that supports regeneration. However, at later stages of the disease when macrophage numbers declined, they dispersed in the muscle, leading to reductions in muscle fiber damage, compared to non-transgenic mdx mice. Together, the findings show that macrophage-mediated delivery of transgenic LIF exerts differential effects on macrophage dispersion and muscle damage depending on the stage of dystrophic pathology.

Single-molecule imaging of glycan-lectin interactions on cells with Glyco-PAINT

Most lectins bind carbohydrate ligands with relatively low affinity, making the identification of optimal ligands challenging. Here we introduce a point accumulation in nanoscale topography (PAINT) super-resolution microscopy method to capture weak glycan-lectin interactions at the single-molecule level in living cells (Glyco-PAINT). Glyco-PAINT exploits weak and reversible sugar binding to directly achieve single-molecule detection and quantification in cells and is used to establish the relative k_on and k_off rates of a synthesized library of carbohydrate-based probes, as well as the diffusion coefficient of the receptor-sugar complex. Uptake of ligands correlates with their binding affinity and residence time to establish structure-function relations for various synthetic glycans. We reveal how sugar multivalency and presentation geometry can be optimized for binding and internalization. Overall, Glyco-PAINT represents a powerful approach to study weak glycan-lectin interactions on the surface of living cells, one that can be potentially extended to a variety of lectin-sugar interactions.

Mannosylated Cationic Copolymers for Gene Delivery to Macrophages

Macrophages are desirable targets for gene therapy of cancer and other diseases. Cationic diblock copolymers of polyethylene glycol (PEG) and poly-L-lysine (PLL) or poly{N-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (pAsp(DET)) are synthesized and used to form polyplexes with a plasmid DNA (pDNA) that are decorated with mannose moieties, serving as the targeting ligands for the C type lectin receptors displayed at the surface of macrophages. The PEG-b-PLL copolymers are known for its cytotoxicity, so PEG-b-PLL-based polyplexes are cross-linked using reducible reagent dithiobis(succinimidyl propionate) (DSP). The cross-linked polyplexes display low toxicity to both mouse embryonic fibroblasts NIH/3T3 cell line and mouse bone marrow-derived macrophages (BMMΦ). In macrophages mannose-decorated polyplexes demonstrate an ≈8 times higher transfection efficiency. The cross-linking of the polyplexes decrease the toxicity, but the transfection enhancement is moderate. The PEG-b-pAsp(DET) copolymers display low toxicity with respect to the IC-21 murine macrophage cell line and are used for the production of non-cross-linked pDNA-contained polyplexes. The obtained mannose modified polyplexes exhibit ca. 500-times greater transfection activity in IC-21 macrophages compared to the mannose-free polyplexes. This result greatly exceeds the targeting gene transfer effects previously described using mannose receptor targeted non-viral gene delivery systems. These results suggest that Man-PEG-b-pAsp(DET)/pDNA polyplex is a potential vector for immune cells-based gene therapy.

Immunity and Protective Efficacy of Mannose Conjugated Chitosan-Based Influenza Nanovaccine in Maternal Antibody Positive Pigs

Parenteral administration of killed/inactivated swine influenza A virus (SwIAV) vaccine in weaned piglets provides variable levels of immunity due to the presence of preexisting virus specific maternal derived antibodies (MDA). To overcome the effect of MDA on SwIAV vaccine in piglets, we developed an intranasal deliverable killed SwIAV antigen (KAg) encapsulated chitosan nanoparticles called chitosan-based NPs encapsulating KAg (CS NPs-KAg) vaccine. Further, to target the candidate vaccine to dendritic cells and macrophages which express mannose receptor, we conjugated mannose to chitosan (mCS) and formulated KAg encapsulated mCS nanoparticles called mannosylated chitosan-based NPs encapsulating KAg (mCS NPs-KAg) vaccine. In MDA-positive piglets, prime-boost intranasal inoculation of mCS NPs-KAg vaccine elicited enhanced homologous (H1N2-OH10), heterologous (H1N1-OH7), and heterosubtypic (H3N2-OH4) influenza virus-specific secretory IgA (sIgA) antibody response in nasal passage compared to CS NPs-KAg vaccinates. In vaccinated upon challenged with a heterologous SwIAV H1N1, both mCS NPs-KAg and CS NPs-KAg vaccinates augmented H1N2-OH10, H1N1-OH7, and H3N2-OH4 virus-specific sIgA antibody responses in nasal swab, lung lysate, and bronchoalveolar lavage (BAL) fluid; and IgG antibody levels in lung lysate and BAL fluid samples. Whereas, the multivalent commercial inactivated SwIAV vaccine delivered intramuscularly increased serum IgG antibody response. In mCS NPs-KAg and CS NPs-KAg vaccinates increased H1N2-OH10 but not H1N1-OH7 and H3N2-OH4-specific serum hemagglutination inhibition titers were observed. Additionally, mCS NPs-KAg vaccine increased specific recall lymphocyte proliferation and cytokines IL-4, IL-10, and IFNγ gene expression compared to CS NPs-KAg and commercial SwIAV vaccinates in tracheobronchial lymph nodes. Consistent with the immune response both mCS NPs-KAg and CS NPs-KAg vaccinates cleared the challenge H1N1-OH7 virus load in upper and lower respiratory tract more efficiently when compared to commercial vaccine. The virus clearance was associated with reduced gross lung lesions. Overall, mCS NP-KAg vaccine intranasal immunization in MDA-positive pigs induced a robust cross-reactive immunity and offered protection against influenza virus.

Dysregulation of Leukocyte Trafficking in Type 2 Diabetes: Mechanisms and Potential Therapeutic Avenues

Type 2 Diabetes Mellitus (T2DM) is a chronic inflammatory disorder that is characterized by chronic hyperglycemia and impaired insulin signaling which in addition to be caused by common metabolic dysregulations, have also been associated to changes in various immune cell number, function and activation phenotype. Obesity plays a central role in the development of T2DM. The inflammation originating from obese adipose tissue develops systemically and contributes to insulin resistance, beta cell dysfunction and hyperglycemia. Hyperglycemia can also contribute to chronic, low-grade inflammation resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under inflammatory condition is dysregulated in T2DM. We particularly highlight the obesity-related accumulation of leukocytes in the adipose tissue leading to insulin resistance and beta-cell dysfunction and resulting in hyperglycemia and consequent changes of adhesion and migratory behavior of leukocytes in different vascular beds. Thus, here we discuss how potential therapeutic targeting of leukocyte trafficking could be an efficient way to control inflammation as well as diabetes and its vascular complications.

Modulation of Macrophages M1/M2 Polarization Using Carbohydrate-Functionalized Polymeric Nanoparticles

Exploiting surface endocytosis receptors using carbohydrate-conjugated nanocarriers brings outstanding approaches to an efficient delivery towards a specific target. Macrophages are cells of innate immunity found throughout the body. Plasticity of macrophages is evidenced by alterations in phenotypic polarization in response to stimuli, and is associated with changes in effector molecules, receptor expression, and cytokine profile. M1-polarized macrophages are involved in pro-inflammatory responses while M2 macrophages are capable of anti-inflammatory response and tissue repair. Modulation of macrophages’ activation state is an effective approach for several disease therapies, mediated by carbohydrate-coated nanocarriers. In this review, polymeric nanocarriers targeting macrophages are described in terms of production methods and conjugation strategies, highlighting the role of mannose receptor in the polarization of macrophages, and targeting approaches for infectious diseases, cancer immunotherapy, and prevention. Translation of this nanomedicine approach still requires further elucidation of the interaction mechanism between nanocarriers and macrophages towards clinical applications.

Aging of the immune system and impaired muscle regeneration: A failure of immunomodulation of adult myogenesis

Skeletal muscle regeneration that follows acute injury is strongly influenced by interactions with immune cells that invade and proliferate in the damaged tissue. Discoveries over the past 20 years have identified many of the key mechanisms through which myeloid cells, especially macrophages, regulate muscle regeneration. In addition, lymphoid cells that include CD8+ T-cells and regulatory T-cells also significantly affect the course of muscle regeneration. During aging, the regenerative capacity of skeletal muscle declines, which can contribute to progressive loss of muscle mass and function. Those age-related reductions in muscle regeneration are accompanied by systemic, age-related changes in the immune system, that affect many of the myeloid and lymphoid cell populations that can influence muscle regeneration. In this review, we present recent discoveries that indicate that aging of the immune system contributes to the diminished regenerative capacity of aging muscle. Intrinsic, age-related changes in immune cells modify their expression of factors that affect the function of a population of muscle stem cells, called satellite cells, that are necessary for normal muscle regeneration. For example, age-related reductions in the expression of growth differentiation factor-3 (GDF3) or CXCL10 by macrophages negatively affect adult myogenesis, by disrupting regulatory interactions between macrophages and satellite cells. Those changes contribute to a reduction in the numbers and myogenic capacity of satellite cells in old muscle, which reduces their ability to restore damaged muscle. In addition, aging produces changes in the expression of molecules that regulate the inflammatory response to injured muscle, which also contributes to age-related defects in muscle regeneration. For example, age-related increases in the production of osteopontin by macrophages disrupts the normal inflammatory response to muscle injury, resulting in regenerative defects. These nascent findings represent the beginning of a newly-developing field of investigation into mechanisms through which aging of the immune system affects muscle regeneration.

Transient Multivalent Nanobody Targeting to CD206-Expressing Cells via PH-Degradable Nanogels

To target nanomedicines to specific cells, especially of the immune system, nanobodies can be considered as an attractive tool, as they lack the Fc part as compared to traditional antibodies and, thus, prevent unfavorable Fc-receptor mediated mistargeting. For that purpose, we have site-specifically conjugated CD206/MMR-targeting nanobodies to three types of dye-labeled nanogel derivatives: non-degradable nanogels, acid-degradable nanogels (with ketal crosslinks), and single polymer chains (also obtained after nanogel degradation). All of them can be obtained from the same reactive ester precursor block copolymer. After incubation with naïve or MMR-expressing Chinese hamster ovary (CHO) cells, a nanobody mediated targeting and uptake could be confirmed for the nanobody-modified nanocarriers. Thereby, the intact nanogels that display nanobodies on their surface in a multivalent way showed a much stronger binding and uptake compared to the soluble polymers. Based on their acidic pH-responsive degradation potential, ketal crosslinked nanogels are capable of mediating a transient targeting that gets diminished upon unfolding into single polymer chains after endosomal acidification. Such control over particle integrity and targeting performance can be considered as highly attractive for safe and controllable immunodrug delivery purposes.

Fatty acid oxidation of alternatively activated macrophages prevents foam cell formation, but Mycobacterium tuberculosis counteracts this process via HIF-1α activation

The ability of Mycobacterium tuberculosis (Mtb) to persist inside host cells relies on metabolic adaptation, like the accumulation of lipid bodies (LBs) in the so-called foamy macrophages (FM), which are favorable to Mtb. The activation state of macrophages is tightly associated to different metabolic pathways, such as lipid metabolism, but whether differentiation towards FM differs between the macrophage activation profiles remains unclear. Here, we aimed to elucidate whether distinct macrophage activation states exposed to a tuberculosis-associated microenvironment or directly infected with Mtb can form FM. We showed that the triggering of signal transducer and activator of transcription 6 (STAT6) in interleukin (IL)-4-activated human macrophages (M(IL-4)) prevents FM formation induced by pleural effusion from patients with tuberculosis. In these cells, LBs are disrupted by lipolysis, and the released fatty acids enter the β-oxidation (FAO) pathway fueling the generation of ATP in mitochondria. Accordingly, murine alveolar macrophages, which exhibit a predominant FAO metabolism, are less prone to become FM than bone marrow derived-macrophages. Interestingly, direct infection of M(IL-4) macrophages with Mtb results in the establishment of aerobic glycolytic pathway and FM formation, which could be prevented by FAO activation or inhibition of the hypoxia-inducible factor 1-alpha (HIF-1α)-induced glycolytic pathway. In conclusion, our results demonstrate that Mtb has a remarkable capacity to induce FM formation through the rewiring of metabolic pathways in human macrophages, including the STAT6-driven alternatively activated program. This study provides key insights into macrophage metabolism and pathogen subversion strategies.

Interactions between macrophages and helminths

Macrophages, the major population of tissue-resident mononuclear phagocytes, contribute significantly to the immune response during helminth infection. Alternatively activated macrophages (AAM) are induced early in the anti-helminth response following tissue insult and parasite recognition, amplifying the early type 2 immune cascade initiated by epithelial cells and ILC2s, and subsequently driving parasite expulsion. AAM also contribute to functional alterations in tissues infiltrated with helminth larvae, mediating both tissue repair and inflammation. Their activation is amplified and occurs more rapidly following reinfection, where they can play a dual role in trapping tissue migratory larvae and preventing or resolving the associated inflammation and damage. In this review, we will address both the known and emerging roles of tissue macrophages during helminth infection, in addition to considering both outstanding research questions and new therapeutic strategies.

Inhibition of Microglial TGFβ Signaling Increases Expression of Mrc1

Microglia are constantly surveying their microenvironment and rapidly react to impairments by changing their morphology, migrating toward stimuli and adopting gene expression profiles characterizing their activated state. The increased expression of the M2-like marker Mannose receptor 1 (Mrc1), which is also referred to as CD206, in microglia has been reported after M2-like activation in vitro and in vivo. Mrc1 is a 175-kDa transmembrane pattern recognition receptor which binds a variety of carbohydrates and is involved in the pinocytosis and the phagocytosis of immune cells, including microglia, and thought to contribute to a neuroprotective microglial phenotype. Here we analyzed the effects of TGFβ signaling on Mrc1 expression in microglia in vivo and in vitro. Using C57BL/6 wild type and Cx3cr1^CreERT2:R26-YFP:Tgfbr2^fl/fl mice-derived microglia, we show that the silencing of TGFβ signaling results in the upregulation of Mrc1, whereas recombinant TGFβ1 induced the delayed downregulation of Mrc1. Furthermore, chromatin immunoprecipitation experiments provided evidence that Mrc1 is not a direct Smad2/Smad4 target gene in microglia. Altogether our data indicate that the changes in Mrc1 expression after the activation or the silencing of microglial TGFβ signaling are likely to be mediated by modifications of the secondary intracellular signaling events influenced by TGFβ signaling.

Poly(triazolyl methacrylate) glycopolymers as potential targeted unimolecular nanocarriers

Synthetic glycopolymers are increasingly investigated as multivalent ligands for a range of biological and biomedical applications. This study indicates that glycopolymers with a fine-tuned balance between hydrophilic sugar pendant units and relatively hydrophobic polymer backbones can act as single-chain targeted nanocarriers for low molecular weight hydrophobic molecules. Non-covalent complexes formed from poly(triazolyl methacrylate) glycopolymers and low molecular weight hydrophobic guest molecules were characterised through a range of analytical techniques - DLS, SLS, TDA, fluorescence spectroscopy, surface tension analysis - and molecular dynamics (MD) modelling simulations provided further information on the macromolecular characteristics of these single chain complexes. Finally, we show that these nanocarriers can be utilised to deliver a hydrophobic guest molecule, Nile red, to both soluble and surface-immobilised concanavalin A (Con A) and peanut agglutinin (PNA) model lectins with high specificity, showing the potential of non-covalent complexation with specific glycopolymers in targeted guest-molecule delivery.

Mannose-Modified Serum Exosomes for the Elevated Uptake to Murine Dendritic Cells and Lymphatic Accumulation

The surface of bovine serum-derived exosomes (EXOs) are modified with α-d-mannose for facile interaction with mannose receptors on dendritic cells (DCs) and for efficient delivery of immune stimulators to the DCs. The surface of the EXOs is modified with polyethylene glycol (PEG) without particle aggregation (≈50 nm) via the incorporation of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) into the lipid layer of the EXO, compared to chemical conjugation by N-hydroxysuccinimide activated PEG (NHS-PEG). PEG modification onto the exosomal surface significantly decreases the non-specific cellular uptake of the EXOs into the DCs. However, the EXOs with mannose-conjugated PEG-DSPE (EXO-PEG-man) exhibit excellent intracellular uptake into the DCs and boost the immune response by the incorporation of adjuvant, monophosphoryl lipid A (MPLA) within the EXO. After an intradermal injection, a higher retention of EXO-PEG-man is observed in the lymph nodes, which could be used for the efficient delivery of immune stimulators and antigens to the lymph nodes in vivo.

The Cross-Talk between miR-511-3p and C-Type Lectin Receptors on Dendritic Cells Affects Dendritic Cell Function

MicroRNAs are small, noncoding RNAs that function as posttranscriptional modulators of gene expression by binding target mRNAs and inhibiting translation. They are therefore crucial regulators of several biological as well as immunological events. Recently, miR-511-3p has been implicated in the development and differentiation of APCs, such as dendritic cells (DCs), and regulating several human diseases. Interestingly, miR-511-3p is embedded within the human MRC1 gene that encodes the mannose receptor. In this study, we sought to examine the impact of miR-511-3p up- or downregulation on human DC surface phenotype, cytokine profile, immunogenicity (using IDO activity as a surrogate), and downstream T cell polarization. Using gene silencing and a selection of microRNA mimics, we could successfully suppress or induce the expression of miR-511-3p in DCs. Consequently, we show for the first time, to our knowledge, that inhibition and/or overexpression of miR-511-3p has opposing effects on the expression levels of two key C-type lectin receptors, namely the mannose receptor and DC-specific ICAM 3 nonintegrin at protein and mRNA levels, thereby affecting C-type lectin receptor-induced modulation of IDO activity in DCs. Furthermore, we show that downregulation of miR-511-3p drives an anti-inflammatory DC response characterized by IL-10 production. Interestingly, the miR-511-3p^low DCs also promoted IL-4 secretion and suppressed IL-17 in cocultures with autologous T cells. Together, our data highlight the potential role of miR-511 in regulating DC function and downstream events leading to Th polarization and immune modulation.

Mannosylated Polyrotaxanes for Increasing Cellular Uptake Efficiency in Macrophages through Receptor-Mediated Endocytosis

Macrophages play an important role in the regulation of inflammation and immune response as well as the pathogenesis of chronic inflammatory diseases and cancer. Therefore, targeted delivery of therapeutic reagents to macrophages is an effective method for treatment and diagnosis. We previously examined the therapeutic applications of polyrotaxanes (PRXs) comprised of multiple cyclodextrins (CDs) threaded on a polymer chain and capped with bulky stopper molecules. In the present study, we designed an α-d-mannose-modified α-CD/poly(ethylene glycol)-based PRX (Man-PRX). The intracellular uptake of Man-PRX through the interaction with macrophage mannose receptor (MMR) in macrophage-like RAW264.7 cells was examined. Intracellular Man-PRX uptake was observed in MMR-positive RAW264.7 cells but was negligible in MMR-negative NIH/3T3 cells. In addition, the intracellular Man-PRX uptake in RAW264.7 cells was significantly inhibited in the presence of free α-d-mannose and an anti-MMR antibody, which suggests that MMR is involved in the intracellular uptake of Man-PRX. Moreover, the polarization of RAW264.7 cells affected the Man-PRX internalization efficiency. These results indicate that Man-PRX is an effective candidate for selective targeting of macrophages through a specific interaction with the MMR.

Macrophage Activation and Functions during Helminth Infection: Recent Advances from the Laboratory Mouse

Macrophages are highly plastic innate immune cells that adopt an important diversity of phenotypes in response to environmental cues. Helminth infections induce strong type 2 cell-mediated immune responses, characterized among other things by production of high levels of interleukin- (IL-) 4 and IL-13. Alternative activation of macrophages by IL-4 in vitro was described as an opposite phenotype of classically activated macrophages, but the in vivo reality is much more complex. Their exact activation state as well as the role of these cells and associated molecules in type 2 immune responses remains to be fully understood. We can take advantage of a variety of helminth models available, each of which have their own feature including life cycle, site of infection, or pathological mechanisms influencing macrophage biology. Here, we reviewed the recent advances from the laboratory mouse about macrophage origin, polarization, activation, and effector functions during parasitic helminth infection.

Tissue-resident macrophages as replicative niches for intracellular pathogens

Macrophages are considered a critical component of innate immunity against intracellular pathogens. Although macrophages have historically been viewed as monocyte-derived and terminally differentiated cells, recent progress has revealed that many tissue-resident macrophages are embryonically seeded, self-renewed, and perform homeostatic functions associated with M2-like activation programs. There is evidence that tissue-resident macrophages (TRMs) maintain their M2-like phenotype even in an infection-driven pro-inflammatory environment. In this regard, several intracellular pathogens are shown to exploit M2-like TRMs as replicative niches to evade pathogen-specific immunity. This knowledge provides a new perspective to understand the chronicity of infections and develop therapeutic strategies which can selectively target TRMs.

Mannose receptor high, M2 dermal macrophages mediate nonhealing Leishmania major infection in a Th1 immune environment

The origin and functional specialization of dermal macrophages in cutaneous infections have been little studied. In this paper, we show that a strain of Leishmania major (L. major Seidman [LmSd]) that produces nonhealing cutaneous lesions in conventionally resistant C57BL/6 mice was more efficiently taken up by M2-polarized bone marrow (BM)-derived macrophages (BMDMs) in vitro and by mannose receptor (MR)^hi dermal macrophages in vivo compared with a healing strain (L. major Friedlin V1). Both in steady and in T helper type 1 (Th1) cell-driven inflammatory states, the MR^hi dermal macrophages showed M2 characteristics. The dermal macrophages were radio resistant and not replaced by monocytes or adult BM-derived cells during infection, but were locally maintained by IL-4 and IL-10. Notably, the favored infection of M2 BMDMs by LmSd in vitro was MR dependent, and genetic deletion of MR or selective depletion of MR^hi dermal macrophages by anti-CSF-1 receptor antibody reversed the nonhealing phenotype. We conclude that embryonic-derived, MR^hi dermal macrophages are permissive for parasite growth even in a strong Th1-immune environment, and the preferential infection of these cells plays a crucial role in the severity of cutaneous disease.

The soluble mannose receptor (sMR) is elevated in alcoholic liver disease and associated with disease severity, portal hypertension, and mortality in cirrhosis patients

Background and aims

Hepatic macrophages (Kupffer cells) are involved in the immunopathology of alcoholic liver disease (ALD). The mannose receptor (MR, CD206), expressed primarily by macrophages, mediates endocytosis, antigen presentation and T-cell activation. A soluble form, sMR, has recently been identified in humans.

We aimed to study plasma sMR levels and its correlation with disease severity and survival in ALD patients.

Methods

We included 50 patients with alcoholic hepatitis (AH), 68 alcoholic cirrhosis (AC) patients (Child-Pugh A (23), B (24), C (21)), and 21 healthy controls (HC). Liver status was described by the Glasgow Alcoholic Hepatitis Score (GAHS), Child-Pugh (CP) and MELD-scores, and in AC patients the hepatic venous pressure gradient (HVPG) was measured by liver vein catheterisation. We used Kaplan-Meier statistics for short-term survival (84-days) in AH patients and long-term (4 years) in AC patients. We measured plasma sMR by ELISA.

Results

Median sMR concentrations were significantly elevated in AH 1.32(IQR:0.69) and AC 0.46(0.5) compared to HC 0.2(0.06) mg/L; p<0.001 and increased in a stepwise manner with the CP-score (p<0.001). In AC sMR predicted portal hypertension (HVPG ≥10 mmHg) with an area under the Receiver Operator Characteristics curve of 0.86 and a high sMR cut-off (>0.43 mg/l) was associated with increased mortality (p = 0.005).

Conclusion

The soluble mannose receptor is elevated in alcoholic liver disease, especially in patients with AH. Its blood level predicts portal hypertension and long-term mortality in AC patients.

The Mannose Receptor in Regulation of Helminth-Mediated Host Immunity

Infection with parasitic helminths affects humanity and animal welfare. Parasitic helminths have the capacity to modulate host immune responses to promote their survival in infected hosts, often for a long time leading to chronic infections. In contrast to many infectious microbes, however, the helminths are able to induce immune responses that show positive bystander effects such as the protection to several immune disorders, including multiple sclerosis, inflammatory bowel disease, and allergies. They generally promote the generation of a tolerogenic immune microenvironment including the induction of type 2 (Th2) responses and a sub-population of alternatively activated macrophages. It is proposed that this anti-inflammatory response enables helminths to survive in their hosts and protects the host from excessive pathology arising from infection with these large pathogens. In any case, there is an urgent need to enhance understanding of how helminths beneficially modulate inflammatory reactions, to identify the molecules involved and to promote approaches to exploit this knowledge for future therapeutic interventions. Evidence is increasing that C-type lectins play an important role in driving helminth-mediated immune responses. C-type lectins belong to a large family of calcium-dependent receptors with broad glycan specificity. They are abundantly present on immune cells, such as dendritic cells and macrophages, which are essential in shaping host immune responses. Here, we will focus on the role of the C-type lectin macrophage mannose receptor (MR) in helminth-host interactions, which is a critically understudied area in the field of helminth immunobiology. We give an overview of the structural aspects of the MR including its glycan specificity, and the functional implications of the MR in helminth-host interactions focusing on a few selected helminth species.

Mannosylated liposomes improve therapeutic effects of paclitaxel in colon cancer models

Mannose receptor (MR) is a highly effective endocytic receptor. It is closely related to tumour immune escape and metastasis. We found that MR was highly expressed in some colon cancer cell lines such as CT26 and HCT116 cells. Therefore, MR might be a potential target in colon cancer therapy. In this study, we aimed to develop mannosylated liposomes containing anticancer drug paclitaxel and investigate the potential effects on targeted therapy for colon cancer. Mannosylated liposomes were prepared by film dispersion method. Characterisation, drug release behaviour, cytotoxicity, cellular uptake, anti-tumour efficacy and safety profiles of liposomes were investigated. The results showed that mannosylated liposomes had a higher CT26 cells uptake efficiency and tumour inhibition rate, which might be due to the target effect to MR. And no notable toxicity was observed. Taken together, these data demonstrated that mannosylated liposomes could target colon cancer and improve the efficacy of chemotherapy.

F4/80+ Macrophages Contribute to Clearance of Senescent Cells in the Mouse Postpartum Uterus

Cellular senescence, defined as an irreversible cell cycle arrest, exacerbates the tissue microenvironment. Our previous study demonstrated that mouse uterine senescent cells were physiologically increased according to gestational days and that their abnormal accumulation was linked to the onset of preterm delivery. We hypothesized that there is a mechanism for removal of senescent cells after parturition to maintain uterine function. In the current study, we noted abundant uterine senescent cells and their gradual disappearance in wild-type postpartum mice. F4/80+ macrophages were present specifically around the area rich in senescent cells. Depletion of macrophages in the postpartum mice using anti-F4/80 antibody enlarged the area of senescent cells in the uterus. We also found excessive uterine senescent cells and decreased second pregnancy success rate in a preterm birth model using uterine p53-deleted mice. Furthermore, a decrease in F4/80+ cells and an increase in CD11b+ cells with a senescence-associated inflammatory microenvironment were observed in the p53-deleted uterus, suggesting that uterine p53 deficiency affects distribution of the macrophage subpopulation, interferes with senescence clearance, and promotes senescence-induced inflammation. These findings indicate that the macrophage is a key player in the clearance of uterine senescent cells to maintain postpartum uterine function.

Monocyte differentiation and macrophage priming are regulated differentially by pentraxins and their ligands

Background

Circulating bone marrow-derived monocytes can leave the blood, enter a tissue, and differentiate into M1 inflammatory, M2a remodeling/fibrotic, or M2c/Mreg resolving/immune-regulatory macrophages. Macrophages can also convert from one of the above types to another. Pentraxins are secreted proteins that bind to, and promote efficient clearance of, microbial pathogens and cellular debris during infection, inflammation, and tissue damage. The pentraxins C-reactive protein (CRP), serum amyloid P (SAP), and pentraxin-3 (PTX3) can also bind a variety of endogenous ligands. As monocytes and macrophages are exposed to differing concentrations of pentraxins and their ligands during infection, inflammation, and tissue damage, we assessed what effect pentraxins and their ligands have on these cells.

Results

We found that many polarization markers do not discriminate between the effects of pentraxins and their ligands on macrophages. However, pentraxins, their ligands, and cytokines differentially regulate the expression of the hemoglobin-haptoglobin complex receptor CD163, the sialic acid-binding lectin CD169, and the macrophage mannose receptor CD206. CRP, a pentraxin generally thought of as being pro-inflammatory, increases the extracellular accumulation of the anti-inflammatory cytokine IL-10, and this effect is attenuated by GM-CSF, mannose-binding lectin, and factor H.

Conclusions

These results suggest that the presence of pentraxins and their ligands regulate macrophage differentiation in the blood and tissues, and that CRP may be a potent inducer of the anti-inflammatory cytokine IL-10.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-017-0214-z) contains supplementary material, which is available to authorized users.

miR-511-3p, embedded in the macrophage mannose receptor gene, contributes to intestinal inflammation

MiR-511-3p is embedded in intron 5 of the CD206/MRC1 gene Mrc1, expressed by macrophage and dendritic cell populations. CD206 and miR-511-3p expression are co-regulated, and their contribution to intestinal inflammation is unclear. We investigated their roles in intestinal inflammation in both mouse and human systems. Colons of CD206-deficient mice displayed normal numbers of monocytes, macrophage, and dendritic cells. In experimental colitis, CD206-deficient mice had attenuated inflammation compared with wild-type (WT) mice. However, neither a CD206 antagonist nor a blocking antibody reproduced this phenotype, suggesting that CD206 was not involved in this response. Macrophages isolated from CD206-deficient mice had reduced levels of miR-511-3p and Tlr4 compared with WT, which was associated with reduced pro-inflammatory cytokine production upon lipopolysaccharides (LPS) and fecal supernatant stimulation. Macrophages overexpressing miR-511-3p showed 50% increase of Tlr4 mRNA, whereas knockdown of miR-511-3p reduced Tlr4 mRNA levels by 60%, compared with scrambled microRNA (miRNA)-transduced cells. Response to anti-tumor necrosis factor (TNF) treatment has been associated with elevated macrophage CD206 expression in the mucosa. However, in colon biopsies no statistically significant change in miR-511-3p was detected. Taken together, our data show that miR-511-3p controls macrophage-mediated microbial responses and is involved in the regulation of intestinal inflammation.

Tumor-associated macrophages and anti-tumor therapies: complex links

Myeloid cells infiltrating the tumor microenvironment, especially tumor-associated macrophages (TAMs), are essential providers of cancer-related inflammation, a condition known to accelerate tumor progression and limit the response to anti-tumor therapies. As a matter of fact, TAMs may have a dual role while interfering with cancer treatments, as they can either promote or impair their functionality. Here we review the connection between macrophages and anticancer therapies; moreover, we provide an overview of the different strategies to target or re-program TAMs for therapeutic purposes.

TonEBP suppresses IL-10-mediated immunomodulation

TonEBP is a key transcriptional activator of M1 phenotype in macrophage, and its high expression is associated with many inflammatory diseases. During the progression of the inflammatory responses, the M1 to M2 phenotypic switch enables the dual role of macrophages in controlling the initiation and resolution of inflammation. Here we report that in human and mouse M1 macrophages TonEBP suppresses IL-10 expression and M2 phenotype. TonEBP knockdown promoted the transcription of the IL-10 gene by enhancing chromatin accessibility and Sp1 recruitment to its promoter. The enhanced expression of M2 genes by TonEBP knockdown was abrogated by antagonism of IL-10 by either neutralizing antibodies or siRNA-mediated silencing. In addition, pharmacological suppression of TonEBP leads to similar upregulation of IL-10 and M2 genes. Thus, TonEBP suppresses M2 phenotype via downregulation of the IL-10 in M1 macrophages.

Fasciola hepatica Surface Coat Glycoproteins Contain Mannosylated and Phosphorylated N-glycans and Exhibit Immune Modulatory Properties Independent of the Mannose Receptor

Fascioliasis, caused by the liver fluke Fasciola hepatica, is a neglected tropical disease infecting over 1 million individuals annually with 17 million people at risk of infection. Like other helminths, F. hepatica employs mechanisms of immune suppression in order to evade its host immune system. In this study the N-glycosylation of F. hepatica’s tegumental coat (FhTeg) and its carbohydrate-dependent interactions with bone marrow derived dendritic cells (BMDCs) were investigated. Mass spectrometric analysis demonstrated that FhTeg N-glycans comprised mainly of oligomannose and to a lesser extent truncated and complex type glycans, including a phosphorylated subset. The interaction of FhTeg with the mannose receptor (MR) was investigated. Binding of FhTeg to MR-transfected CHO cells and BMDCs was blocked when pre-incubated with mannan. We further elucidated the role played by MR in the immunomodulatory mechanism of FhTeg and demonstrated that while FhTeg’s binding was significantly reduced in BMDCs generated from MR knockout mice, the absence of MR did not alter FhTeg’s ability to induce SOCS3 or suppress cytokine secretion from LPS activated BMDCs. A panel of negatively charged monosaccharides (i.e. GlcNAc-4P, Man-6P and GalNAc-4S) were used in an attempt to inhibit the immunoregulatory properties of phosphorylated oligosaccharides. Notably, GalNAc-4S, a known inhibitor of the Cys-domain of MR, efficiently suppressed FhTeg binding to BMDCs and inhibited the expression of suppressor of cytokine signalling (SOCS) 3, a negative regulator the TLR and STAT3 pathway. We conclude that F. hepatica contains high levels of mannose residues and phosphorylated glycoproteins that are crucial in modulating its host’s immune system, however the role played by MR appears to be limited to the initial binding event suggesting that other C-type lectin receptors are involved in the immunomodulatory mechanism of FhTeg.

Fascioliasis, caused by the liver fluke Fasciola hepatica, is a neglected tropical disease infecting over 1 million individuals annually with 17 million people at risk of infection. These worms infect the liver and can survive for many years in its animal or human host because they supress the host’s immune system that is important in clearing worm infection. Worms are similar to humans in that they are made of proteins, fats and sugars, and while there are many studies on worm proteins, few studies have examined the sugars. We are interested in the sugars because we believe that they help the parasite survive for many years within its host. To examine this, we have used a technique called mass spectrometric analysis to characterise the sugars present in F. hepatica. We also have developed systems in the laboratory to test if these sugars can suppress the host’s immune system. We conclude that F. hepatica sugars are crucial in suppressing its host’s immune system; however, the exact way the sugars can do this requires further studies. These studies are important for the development of worm vaccines or therapies.

Murine pattern recognition receptor dectin-1 is essential in the development of experimental autoimmune uveoretinitis

Mycobacteria in complete Freund's adjuvant (CFA) are an essential component of immunization protocols in a number of autoimmune disease animal models including experimental autoimmune encephalomyelitis and uveoretinitis (EAE and EAU, respectively). We determined the role in EAU of two C-type lectin receptors on myeloid cells that recognize and respond to mycobacteria. Using receptor-specific antibodies and knockout mice, we demonstrated for the first time that the macrophage mannose receptor delays disease development but does not affect severity. In contrast, dectin-1 is critically involved in the development of CFA-mediated EAU. Disease severity is reduced in dectin-1 knockout mice and antibody blockade of dectin-1 during the induction, but not the effector phase, prevents EAU development. Significantly, similar blockade of dectin-1 in vivo has no effect in non-CFA-mediated, spontaneously induced or adoptive transfer models of EAU. Thus dectin-1 plays a critical role in the ability of complete Freund's adjuvant to induce EAU in mice.

Macrophage responses to implants: prospects for personalized medicine

Implants, transplants, and implantable biomedical devices are mainstream solutions for a wide variety of human pathologies. One of the persistent problems around nondegradable metallic and polymeric implants is failure of macrophages to resolve the inflammation and their tendency to stay in a state, named "frustrated phagocytosis." During the initial phase, proinflammatory macrophages induce acute reactions to trauma and foreign materials, whereas tolerogenic anti-inflammatory macrophages control resolution of inflammation and induce the subsequent healing stage. However, implanted materials can induce a mixed pro/anti-inflammatory phenotype, supporting chronic inflammatory reactions accompanied by microbial contamination and resulting in implant failure. Several materials based on natural polymers for improved interaction with host tissue or surfaces that release anti-inflammatory drugs/bioactive agents have been developed for implant coating to reduce implant rejection. However, no definitive, long-term solution to avoid adverse immune responses to the implanted materials is available to date. The prevention of implant-associated infections or chronic inflammation by manipulating the macrophage phenotype is a promising strategy to improve implant acceptance. The immunomodulatory properties of currently available implant coatings need to be improved to develop personalized therapeutic solutions. Human primary macrophages exposed to the implantable materials ex vivo can be used to predict the individual's reactions and allow selection of an optimal coating composition. Our review describes current understanding of the mechanisms of macrophage interactions with implantable materials and outlines the prospects for use of human primary macrophages for diagnostic and therapeutic approaches to personalized implant therapy.

Regulation of IL-10 by chondroitinase ABC promotes a distinct immune response following spinal cord injury

Chondroitinase ABC (ChABC) has striking effects on promoting neuronal plasticity after spinal cord injury (SCI), but little is known about its involvement in other pathological mechanisms. Recent work showed that ChABC might also modulate the immune response by promoting M2 macrophage polarization. Here we investigate in detail the immunoregulatory effects of ChABC after SCI in rats. Initially, we examined the expression profile of 16 M1/M2 macrophage polarization markers at 3 h and 7 d postinjury. ChABC treatment had a clear effect on the immune signature after SCI. More specifically, ChABC increased the expression of the anti-inflammatory cytokine IL-10, accompanied by a reduction in the proinflammatory cytokine IL-12B in injured spinal tissue. These effects were associated with a distinct, IL-10-mediated anti-inflammatory response in ChABC-treated spinal cords. Mechanistically, we show that IL-10 expression is driven by tissue injury and macrophage infiltration, while the p38 MAPK is the central regulator of IL-10 expression in vivo. These findings provide novel insights into the effects of ChABC in the injured spinal cord and explain its immunoregulatory activity.

CX3CR1 reduces kidney fibrosis by inhibiting local proliferation of profibrotic macrophages

A dense network of macrophages and dendritic cells (DC) expressing the chemokine receptor CX3CR1 populates most tissues. We recently reported that CX3CR1 regulates the abundance of CD11c(+) DC in the kidney and thereby promotes renal inflammation in glomerulonephritis. Given that chronic inflammation usually causes fibrosis, we hypothesized that CX3CR1 deficiency should attenuate renal fibrosis. However, when we tested this hypothesis using the DC-independent murine fibrosis model of unilateral ureteral obstruction, kidney fibrosis was unexpectedly more severe, despite less intrarenal inflammation. Two-photon imaging and flow cytometry revealed in kidneys of CX3CR1-deficient mice more motile Ly6C/Gr-1(+) macrophages. Flow cytometry verified that renal macrophages were more abundant in the absence of CX3CR1 and produced more of the key profibrotic mediator, TGF-β. Macrophages accumulated because of higher intrarenal proliferation, despite reduced monocyte recruitment and higher signs of apoptosis within the kidney. These findings support the theory that tissue macrophage numbers are regulated through local proliferation and identify CX3CR1 as a regulator of such proliferation. Thus, CX3CR1 inhibition should be avoided in DC-independent inflammatory diseases because it may promote fibrosis.

Human osteoarthritic synovium impacts chondrogenic differentiation of mesenchymal stem cells via macrophage polarisation state

OBJECTIVE

Mesenchymal stem cells (MSCs) are a promising cell type for the repair of damaged cartilage in osteoarthritis (OA). However, OA synovial fluid and factors secreted by synovium impede chondrogenic differentiation of MSCs, and the mechanism responsible for this effect remains unclear. In this study, we sought to investigate whether M1 and M2 synovial macrophages can contribute to the inhibition of MSC chondrogenesis.

DESIGN

The constitution of synovial macrophage subsets was analysed by immunohistochemical staining of human OA synovium sections for CD86 (M1 marker) and CD206 (M2 marker). To assess the effect of synovial macrophages on chondrogenesis, collagen type II (COL2) and aggrecan (ACAN) gene expression were compared between MSCs undergoing chondrogenic differentiation in medium conditioned (CM) by human OA synovial explants, human synovial macrophages and fibroblasts, or peripheral blood derived primary human monocytes differentiated towards an M1 or M2 phenotype.

RESULTS

OA synovium contained both M1 and M2 macrophages. Medium conditioned by synovial macrophages (CD45 + plastic adherent cells) down-regulated chondrogenic gene expression by MSCs. Additionally, CM of M1 polarised monocytes significantly decreased COL2 and ACAN gene expression by MSCs; this effect was not observed for treatment with CM of M2 polarised monocytes.

CONCLUSION

MSC chondrogenesis is inhibited by OA synovium CM through factors secreted by synovial macrophages and our findings suggest that M1 polarised subsets are potential mediators of this anti-chondrogenic effect. Modulation of macrophage phenotype may serve as a beneficial strategy to maximise the potential of MSCs for efficient cartilage repair.

Development of optical probes for in vivo imaging of polarized macrophages during foreign body reactions

Plasticity of macrophage (MΦ) phenotypes exist in a spectrum from classically activated (M1) cells, to alternatively activated (M2) cells, contributing to both the normal healing of tissues and the pathogenesis of implant failure. Here, folate- and mannose-based optical probes were fabricated to simultaneously determine the degree of MΦ polarization. In vitro tests show the ability of these probes to specifically target M1 and M2 cells. In an in vivo murine model, they were able to distinguish between the M1-dominated inflammatory response to infection and the M2-dominated regenerative response to particle implants. Finally, the probes were used to assess the inflammatory/regenerative properties of biomaterial implants. Our results show that these probes can be used to monitor and quantify the dynamic processes of MΦ polarization and their role in cellular responses in real time.

The transcription factor Gata6 links tissue macrophage phenotype and proliferative renewal

Tissue-resident macrophages are heterogeneous as a consequence of anatomical niche-specific functions. Many populations self-renew independently of bone marrow in the adult, but the molecular mechanisms of this are poorly understood. We determined a transcriptional profile for the major self-renewing population of peritoneal macrophages in mice. These cells specifically expressed the transcription factor Gata6. Selective deficiency of Gata6 in myeloid cells caused substantial alterations in the transcriptome of peritoneal macrophages. Gata6 deficiency also resulted in dysregulated peritoneal macrophage proliferative renewal during homeostasis and in response to inflammation, which was associated with delays in the resolution of inflammation. Our investigations reveal that the tissue macrophage phenotype is under discrete tissue-selective transcriptional control and that this is fundamentally linked to the regulation of their proliferation renewal.

Aging enhances classical activation but mitigates alternative activation in the central nervous system

The roles of microglia and macrophages during neuroinflammation and neurodegenerative diseases remain controversial. To date, at least 2 activations states have been suggested, consisting of a classical response (M1) and the alternative response (M2). Identifying selective biomarkers of microglia that representative their functional activation states may help elucidate disease course and enable a better understanding of repair mechanisms. Two cocktails containing either tumor necrosis factor (TNF)-α, interleukin (IL)-12, and IL-1β (referred to as CKT-1) or IL-13 and IL-4 (referred to CKT-2) were injections into the hippocampus of mice aged 6, 12, or 24 months. Microarray analysis was performed on hippocampal tissue 3 days postinjection. Gene transcripts were compared between CKT-1 versus CKT-2 stimulator cocktails. Several selective transcripts expressed for the CKT-1 included CXCL13, haptoglobin, MARCO, and calgranulin B, whereas a smaller subset of genes was selectively induced by the CKT-2 and consisted of FIZZ1, IGF-1, and EAR 11. Importantly, selective transcripts were induced at all ages by CKT-1, whereas selective gene transcripts induced by CKT-2 decreased with age suggesting an age-related reduction in the IL-4/ IL-13 signaling pathway.

Establishing the flow cytometric assessment of myeloid cells in kidney ischemia/reperfusion injury

Polychromatic flow cytometry is a powerful tool for assessing populations of cells in the kidney through times of homeostasis, disease and tissue remodeling. In particular, macrophages have been identified as having central roles in these three settings. However, because of the plasticity of myeloid cells it has been difficult to define a specific immunophenotype for these cells in the kidney. This study developed a gating strategy for identifying and assessing monocyte and macrophage subpopulations, along with neutrophils and epithelial cells in the healthy kidney and following ischemia/reperfusion (IR) injury in mice, using antibodies against CD45, CD11b, CD11c, Ly6C, Ly6G, F4/80, CSF-1R (CD115), MHC class II, mannose receptor (MR or CD206), an alternatively activated macrophage marker, and the epithelial cell adhesion marker (EpCAM or CD326). Backgating analysis and assessment of autofluorescence was used to extend the knowledge of various cell types and the changes that occur in the kidney at various time-points post-IR injury. In addition, the impact of enzymatic digestion of kidneys on cell surface markers and cell viability was assessed. Comparisons of kidney myeloid populations were also made with those in the spleen. These results provide a useful reference for future analyses of therapies aimed at modulating inflammation and enhancing endogenous remodeling following kidney injury.

Small ruminant macrophage polarization may play a pivotal role on lentiviral infection

Small ruminant lentiviruses (SRLV) infect the monocyte/macrophage lineage inducing a long-lasting infection affecting body condition, production and welfare of sheep and goats all over the world. Macrophages play a pivotal role on the host’s innate and adaptative immune responses against parasites by becoming differentially activated. Macrophage heterogeneity can tentatively be classified into classically differentiated macrophages (M1) through stimulation with IFN-γ displaying an inflammatory profile, or can be alternatively differentiated by stimulation with IL-4/IL-13 into M2 macrophages with homeostatic functions. Since infection by SRLV can modulate macrophage functions we explored here whether ovine and caprine macrophages can be segregated into M1 and M2 populations and whether this differential polarization represents differential susceptibility to SRLV infection. We found that like in human and mouse systems, ovine and caprine macrophages can be differentiated with particular stimuli into M1/M2 subpopulations displaying specific markers. In addition, small ruminant macrophages are plastic since M1 differentiated macrophages can express M2 markers when the stimulus changes from IFN-γ to IL-4. SRLV replication was restricted in M1 macrophages and increased in M2 differentiated macrophages respectively according to viral production. Identification of the infection pathways in macrophage populations may provide new targets for eliciting appropriate immune responses against SRLV infection.

Characterization of phenotype markers and neuronotoxic potential of polarised primary microglia in vitro

Microglia mediate multiple facets of neuroinflammation, including cytotoxicity, repair, regeneration, and immunosuppression due to their ability to acquire diverse activation states, or phenotypes. Modulation of microglial phenotype is an appealing neurotherapeutic strategy but a comprehensive study of classical and more novel microglial phenotypic markers in vitro is lacking. The aim of this study was to outline the temporal expression of a battery of phenotype markers from polarised microglia to generate an in vitro tool for screening the immunomodulatory potential of novel compounds. We characterised expression of thirty-one macrophage/microglial phenotype markers in primary microglia over time (4, 12, 36, and 72 h), using RT-qPCR or multiplex protein assay. Firstly, we selected Interleukin-4 (IL-4) and lipopolysaccharide (LPS) as the strongest M1-M2 polarising stimuli, from six stimuli tested. At each time point, markers useful to identify that microglia were M1 included iNOS, Cox-2 and IL-6 and a loss of M2a markers. Markers useful for quantifying M2b-immunomodulatory microglia included, increased IL-1RA and SOCS3 and for M2a-repair and regeneration, included increased arginase-1, and a loss of the M1 and M2b markers were discriminatory. Additional markers were regulated at fewer time points, but are still likely important to monitor when assessing the immunomodulatory potential of novel therapies. Further, to facilitate identification of how novel immunomodulatory treatments alter the functional affects of microglia, we characterised how the soluble products from polarised microglia affected the type and rate of neuronal death; M1/2b induced increasing and M2a-induced decreasing neuronal loss. We also assessed any effects of prior activation state, to provide a way to identify how a novel compound may alter phenotype depending on the stage of injury/insult progression. We identified generally that a prior M1/2b reduced the ability of microglia to switch to M2a. Altogether, we have characterised a profile of phenotype markers and a mechanism of assessing functional outcome that we can use as a reference guide for first-line screening of novel immunomodulatory therapies in vitro in the search for viable neuroprotectants.

Altered polarization, morphology, and impaired innate immunity germane to resident peritoneal macrophages in mice with long-term type 2 diabetes

Type 2 diabetes (T2D) is associated with perturbed innate immunity. Macrophages, bridging innate immunity and metabolic disturbances, play important roles in controlling immune homeostasis. However, the effect of long-term diabetic milieu (DM) on the functions and phenotypes of macrophages is still not clear. In this study, we used resident peritoneal macrophages (RPMs) from 5-month-old db/db mice to investigate the changes of macrophages. It was found that RPMs in db/db mice significantly reduced phagocytosis and adhesion capacity. After standardization with body weight, the number of F4/80⁺ RPMs markedly reduced in db/db mice, and, furthermore, the macrophages skewed to M2-polarizated macrophages. The results of morphology found that the RPMs shape of db/db mice was nearly round, but the RPMs shape of control mice was spindle-shaped and irregular. In this study, we found the cell numbers, morphology, and innate immunity functions of RPMs in 5-month-old type 2 diabetic mice (db/db mice) obtained by abdominal cavity lavage were significantly altered. Importantly, we also found the remarkably increased M2-RPMs in diabetic mice for the first time.

Characterization of functional mannose receptor in a continuous hybridoma cell line

Background

The mannose receptor is the best described member of the type I transmembrane C-type lectins; however much remains unanswered about the biology of the receptor. One difficulty has been the inability to consistently express high levels of a functional full length mannose receptor cDNA in mammalian cells. Another difficulty has been the lack of a human macrophage cell line expressing a fully functional receptor. Commonly used human macrophage cell lines such as U937, THP-1, Mono-Mac and HL60 do not express the mannose receptor. We have developed a macrophage hybridoma cell line (43^MR cells) created by fusion of U937 cells with primary human monocyte-derived macrophages, resulting in a non-adherent cell line expressing several properties of primary macrophages. The purpose of this study was to identify and select mannose receptor-expressing cells using fluorescence-activated cell sorting and to characterize the expression and function of the receptor.

Results

In the current study we show that the mannose receptor found on this novel cell has endocytic characteristics consistent with and similar to the mannose receptor found on the surface of monocyte-derived human macrophages and rat bone marrow-derived macrophages. In addition, we demonstrate that these cells engage and internalize pathogen particles such as S. aureus and C. albicans. We further establish the transfectability of these cells via the introduction of a plasmid expressing influenza A hemagglutinin.

Conclusions

The 43^MR cell line represents the first naturally expressed MR-positive cell line derived from a human macrophage background. This cell line provides an important cell model for other researchers for the study of human MR biology and host-pathogen interactions.

The mannose receptor

The MR is a highly effective endocytic receptor with a broad binding specificity encompassing ligands of microbial and endogenous origin and a poorly characterized ability to modulate cellular activation. This review provides an update of the latest developments in the field. It discusses how MR biology might be affected by glycosylation and proteolytic processing, MR involvement in antigen delivery, and the potential contribution of MR to T cell differentiation and cellular activation. Further understanding of these areas will, no doubt, inform the design of novel, therapeutic tools for improved vaccination, control of inflammation, and tumor chemotherapy, which will benefit from exploiting MR-efficient internalization properties and unique pattern of expression.

Peritoneal macrophage from male and female SJL mice differ in IL-10 expression and macrophage maturation

Injection of proteins and particulate antigens into the peritoneal cavity of male SJL mice preferentially activates T cells secreting Th2 cytokines. Identical immunizations of females activate T cells secreting Th1 cytokines. CD11b(+)F4/80(hi) LPM and CD11b(+)F4/80(lo) SPM populations were compared between naive males and females to define their role in supporting differential Th1 versus Th2 T cell activation. No sex-dependent differences in the expression of MHC class II, costimulatory molecules, and MR were detected. Immunization induced influx of CD11b(lo)F4/80(lo) cells in both sexes. CD11b(lo)F4/80(lo) cells consist predominantly of Ly6C(hi) monocytes, which mature into a Ly6C(-) SPM subset. Following immunization, equivalent frequencies of LPM had taken up antigen. However, the CD11b(lo)F4/80(lo) population, which had taken up antigen, was decreased significantly in males compared with females. Similar to naïve macrophages, antigen-positive cells in immunized males and females exhibited no phenotypic differences. However, fewer Ly6C(-)F4/80(+) cells were present in males compared with females, consistent with the reduced number of antigen-positive cells. Furthermore, CD11b(lo)F4/80(lo) cells, which had taken up antigen in males, expressed increased IL-10 and limited IL-12 mRNA compared with the predominant IL-12 mRNA expression in female-derived, antigen-positive CD11b(lo)F4/80(lo) cells. IL-10 blockade increased the frequency of Ly6C(-)F4/80(+) cells in males to the frequency in females, suggesting that preferential activation of Th2 T cells in male SJL mice is associated with increased IL-10 expression and limited antigen presentation as a result of decreased macrophage maturation under the influence of IL-10.

CD169+ macrophages at the crossroads of antigen presentation

CD169(+) macrophages have fascinated immunologists because of their unique distribution in secondary lymphoid organs, redistribution upon immune activation and, lately, because of their contribution to antigen handling. Their association with B cell follicles prompted early studies on their involvement in B cell activation, and recent work has unveiled an unexpected role in facilitating activation of other lymphocyte subsets, such as invariant natural killer T (iNKT) cells. New data also argue that CD169(+) macrophages activate CD8 T cells in response to dead cell-associated antigens in lymph nodes and by transferring antigen to dendritic cells (DCs) in the spleen. Understanding the role of CD169(+) macrophages in the activation of acquired immunity could benefit the design of vaccination strategies, for example those aimed at eliciting cytotoxic T cells.

Selective inhibition and augmentation of alternative macrophage activation by progesterone

Progesterone is the female sex hormone necessary for the maintenance of pregnancy, and is known to modulate macrophage activation. However, studies have concentrated exclusively on the ability of progesterone to negatively regulate the innate and classical pathways of activation, associated with nitric oxide (NO) and interleukin (IL)-12 production. Our aim was to examine the ability of progesterone to modulate alternative macrophage activation. Bone marrow cells were isolated and differentiated from male BALB/c mice, exposed to varying concentrations of progesterone and stimulated with lipopolysaccharide (LPS) (innate activation), IL-4 (alternative activation) or LPS in combination with IL-4. Our present study demonstrates that progesterone not only down-regulates inducible nitric oxide synthase 2 (iNOS) activity in macrophages but also arginase activity, in a dose-dependent manner, independent of the stimuli, whether it is induced by LPS (innate activation), IL-4 (alternative activation) or LPS in combination with IL-4. The ability of progesterone to down-modulate IL-4-induced cell surface expression of the mannose receptor further suggested a negative regulation of alternative macrophage activation by this hormone. Analysis of mRNA expression, by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), of genes associated with innate and alternative macrophage activation revealed that progesterone down-regulated LPS-induced macrophage nos2, argI and p40 (IL-12/IL-23) expression and IL-4-induced argI, mrc-1 and fizz1 expression. However, progesterone up-regulated IL-4-induced macrophage expression of ym1, while dectin-1 expression remained unaltered. Following treatment of macrophages with LPS and IL-4 in combination a similar pattern was observed, with the exception that progesterone up-regulated macrophage expression of fizz1 as well as ym1 and did not modify mrc-1 expression. Our data demonstrate for the first time that a hormone has the ability to regulate selectively the expression of different genes associated with alternative macrophage activation.

Biotherapeutic target or sink: analysis of the macrophage mannose receptor tissue distribution in murine models of lysosomal storage diseases

Lysosomal storage diseases (LSDs) are metabolic disorders caused by enzyme deficiencies that lead to lysosomal accumulation of undegraded substrates. Enzyme replacement therapies (ERT) have been developed as treatments for patients with Gaucher, Niemann-Pick, Fabry, and Pompe diseases. Depending on the disease, the corresponding therapeutic enzyme is designed to be internalized by diseased cells through receptor-mediated endocytosis via macrophage mannose receptors (MMR) or mannose-6-phosphate receptors (M6PR). Enzymes developed to treat Gaucher and Niemann-Pick diseases are meant to target MMR-expressing cells, and in the case of Cerezyme [recombinant human β-glucocerebrosidase (rhβGC)] for treating Gaucher disease, glycans on the enzyme are modified to increase specificity toward this receptor. Due to heterogeneity in glycosylation on enzymes intended to target the M6PR, however, there may also be some unintended targeting to MMR-expressing cells, which could act as unwanted sinks. Examples include Fabrazyme [recombinant human α-galactosidase A (rhαGal)] for treating Fabry disease and Myozyme [recombinant human acid α-glucosidase (rhGAA)] for treating Pompe disease. It is therefore of great interest to better understand the cell type and tissue distribution of MMR in murine LSD models used to evaluate ERT efficacy and mechanism of action. In this study, we generated affinity-purified polyclonal antibody against murine MMR and used it to carry out a systematic examination of MMR protein localization in murine models of Gaucher, Niemann-Pick, Fabry, and Pompe diseases. Using immunohistochemistry, immunofluorescence, and confocal microscopy, we examined MMR distribution in liver, spleen, lung, kidney, heart, diaphragm, quadriceps, and triceps in these animal models and compared them with MMR distribution in wild-type mice.

Identification of the ovine mannose receptor and its possible role in Visna/Maedi virus infection

This study aims to characterize the mannose receptor (MR) gene in sheep and its role in ovine visna/maedi virus (VMV) infection. The deduced amino acid sequence of ovine MR was compatible with a transmembrane protein having a cysteine-rich ricin-type amino-terminal region, a fibronectin type II repeat, eight tandem C-type lectin carbohydrate-recognition domains (CRD), a transmembrane region, and a cytoplasmic carboxy-terminal tail. The ovine and bovine MR sequences were closer to each other compared to human or swine MR. Concanavalin A (ConA) inhibited VMV productive infection, which was restored by mannan totally in ovine skin fibroblasts (OSF) and partially in blood monocyte-derived macrophages (BMDM), suggesting the involvement of mannosylated residues of the VMV ENV protein in the process. ConA impaired also syncytium formation in OSF transfected with an ENV-encoding pN3-plasmid. MR transcripts were found in two common SRLV targets, BMDM and synovial membrane (GSM) cells, but not in OSF. Viral infection of BMDM and especially GSM cells was inhibited by mannan, strongly suggesting that in these cells the MR is an important route of infection involving VMV Env mannosylated residues. Thus, at least three patterns of viral entry into SRLV-target cells can be proposed, involving mainly MR in GSM cells (target in SRLV-induced arthritis), MR in addition to an alternative route in BMDM (target in SRLV infections), and an alternative route excluding MR in OSF (target in cell culture). Different routes of SRLV infection may thus coexist related to the involvement of MR differential expression.