Macrophage Polarization Modulates FcγR- and CD13-Mediated Phagocytosis and Reactive Oxygen Species Production, Independently of Receptor Membrane Expression

Prediction of six macrophage phenotypes and their IL-10 content based on single-cell morphology using artificial intelligence

Introduction

The last decade has led to rapid developments and increased usage of computational tools at the single-cell level. However, our knowledge remains limited in how extracellular cues alter quantitative macrophage morphology and how such morphological changes can be used to predict macrophage phenotype as well as cytokine content at the single-cell level.

Methods

Using an artificial intelligence (AI) based approach, this study determined whether (i) accurate macrophage classification and (ii) prediction of intracellular IL-10 at the single-cell level was possible, using only morphological features as predictors for AI. Using a quantitative panel of shape descriptors, our study assessed image-based original and synthetic single-cell data in two different datasets in which CD14+ monocyte-derived macrophages generated from human peripheral blood monocytes were initially primed with GM-CSF or M-CSF followed by polarization with specific stimuli in the presence/absence of continuous GM-CSF or M-CSF. Specifically, M0, M1 (GM-CSF-M1, TNFα/IFNγ-M1, GM-CSF/TNFα/IFNγ-M1) and M2 (M-CSF-M2, IL-4-M2a, M-CSF/IL-4-M2a, IL-10-M2c, M-CSF/IL-10-M2c) macrophages were examined.

Results

Phenotypes were confirmed by ELISA and immunostaining of CD markers. Variations of polarization techniques significantly changed multiple macrophage morphological features, demonstrating that macrophage morphology is a highly sensitive, dynamic marker of phenotype. Using original and synthetic single-cell data, cell morphology alone yielded an accuracy of 93% for the classification of 6 different human macrophage phenotypes (with continuous GM-CSF or M-CSF). A similarly high phenotype classification accuracy of 95% was reached with data generated with different stimuli (discontinuous GM-CSF or M-CSF) and measured at a different time point. These comparably high accuracies clearly validated the here chosen AI-based approach. Quantitative morphology also allowed prediction of intracellular IL-10 with 95% accuracy using only original data.

Discussion

Thus, image-based machine learning using morphology-based features not only (i) classified M0, M1 and M2 macrophages but also (ii) classified M2a and M2c subtypes and (iii) predicted intracellular IL-10 at the single-cell level among six phenotypes. This simple approach can be used as a general strategy not only for macrophage phenotyping but also for prediction of IL-10 content of any IL-10 producing cell, which can help improve our understanding of cytokine biology at the single-cell level.

Diesel exhaust particles induce polarization state-dependent functional and transcriptional changes in human monocyte-derived macrophages

Macrophage populations exist on a spectrum between the proinflammatory M1 and proresolution M2 states and have demonstrated the ability to reprogram between them after exposure to opposing polarization stimuli. Particulate matter (PM) has been repeatedly linked to worsening morbidity and mortality following respiratory infections and has been demonstrated to modify macrophage function and polarization. The purpose of this study was to determine whether diesel exhaust particles (DEP), a key component of airborne PM, would demonstrate polarization state-dependent effects on human monocyte-derived macrophages (hMDMs) and whether DEP would modify macrophage reprogramming. CD14+CD16- monocytes were isolated from the blood of healthy human volunteers and differentiated into macrophages with macrophage colony-stimulating factor (M-CSF). Resulting macrophages were left unpolarized or polarized into the proresolution M2 state before being exposed to DEP, M1-polarizing conditions (IFN-γ and LPS), or both and tested for phagocytic function, secretory profile, gene expression patterns, and bioenergetic properties. Contrary to previous reports, we observed a mixed M1/M2 phenotype in reprogrammed M2 cells when considering the broader range of functional readouts. In addition, we determined that DEP exposure dampens phagocytic function in all polarization states while modifying bioenergetic properties in M1 macrophages preferentially. Together, these data suggest that DEP exposure of reprogrammed M2 macrophages results in a highly inflammatory, highly energetic subpopulation of macrophages that may contribute to the poor health outcomes following PM exposure during respiratory infections.NEW & NOTEWORTHY We determined that reprogramming M2 macrophages in the presence of diesel exhaust particles (DEP) results in a highly inflammatory mixed M1/M2 phenotype. We also demonstrated that M1 macrophages are particularly vulnerable to particulate matter (PM) exposure as seen by dampened phagocytic function and modified bioenergetics. Our study suggests that PM causes reprogrammed M2 macrophages to become a highly energetic, highly secretory subpopulation of macrophages that may contribute to negative health outcomes observed in humans after PM exposure.

Characterization of polarization states of canine monocyte derived macrophages

Macrophages can reversibly polarize into multiple functional subsets depending on their micro-environment. Identification and understanding the functionality of these subsets is relevant for the study of immune‑related diseases. However, knowledge about canine macrophage polarization is still in its infancy. In this study, we polarized canine monocytes using GM-CSF/IFN- γ and LPS towards M1 macrophages or M-CSF and IL-4 towards M2 macrophages and compared them to undifferentiated monocytes (M0). Polarized M1 and M2 macrophages were thoroughly characterized for morphology, surface marker features, gene profiles and functional properties. Our results showed that canine M1-polarized macrophages obtained a characteristic large, roundish, or amoeboid shape, while M2-polarized macrophages were smaller and adopted an elongated spindle-like morphology. Phenotypically, all macrophage subsets expressed the pan-macrophage markers CD14 and CD11b. M1-polarized macrophages expressed increased levels of CD40, CD80 CD86 and MHC II, while a significant increase in the expression levels of CD206, CD209, and CD163 was observed in M2-polarized macrophages. RNAseq of the three macrophage subsets showed distinct gene expression profiles, which are closely associated with immune responsiveness, cell differentiation and phagocytosis. However, the complexity of the gene expression patterns makes it difficult to assign clear new polarization markers. Functionally, undifferentiated -monocytes, and M1- and M2- like subsets of canine macrophages can all phagocytose latex beads. M2-polarized macrophages exhibited the strongest phagocytic capacity compared to undifferentiated monocytes- and M1-polarized cells. Taken together, this study showed that canine M1 and M2-like macrophages have distinct features largely in parallel to those of well-studied species, such as human, mouse and pig. These findings enable future use of monocyte derived polarized macrophages particularly in studies of immune related diseases in dogs.

TRAIL promotes the polarization of human macrophages toward a proinflammatory M1 phenotype and is associated with increased survival in cancer patients with high tumor macrophage content

Background

TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can either induce cell death or activate survival pathways after binding to death receptors (DRs) DR4 or DR5. TRAIL is investigated as a therapeutic agent in clinical trials due to its selective toxicity to transformed cells. Macrophages can be polarized into pro-inflammatory/tumor-fighting M1 macrophages or anti-inflammatory/tumor-supportive M2 macrophages and an imbalance between M1 and M2 macrophages can promote diseases. Therefore, identifying modulators that regulate macrophage polarization is important to design effective macrophage-targeted immunotherapies. The impact of TRAIL on macrophage polarization is not known.

Methods

Primary human monocyte-derived macrophages were pre-treated with either TRAIL or with DR4 or DR5-specific ligands and then polarized into M1, M2a, or M2c phenotypes in vitro. The expression of M1 and M2 markers in macrophage subtypes was analyzed by RNA sequencing, qPCR, ELISA, and flow cytometry. Furthermore, the cytotoxicity of the macrophages against U937 AML tumor targets was assessed by flow cytometry. TCGA datasets were also analyzed to correlate TRAIL with M1/M2 markers, and the overall survival of cancer patients.

Results

TRAIL increased the expression of M1 markers at both mRNA and protein levels while decreasing the expression of M2 markers at the mRNA level in human macrophages. TRAIL also shifted M2 macrophages towards an M1 phenotype. Our data showed that both DR4 and DR5 death receptors play a role in macrophage polarization. Furthermore, TRAIL enhanced the cytotoxicity of macrophages against the AML cancer cells in vitro. Finally, TRAIL expression was positively correlated with increased expression of M1 markers in the tumors from ovarian and sarcoma cancer patients and longer overall survival in cases with high, but not low, tumor macrophage content.

Conclusions

TRAIL promotes the polarization of human macrophages toward a proinflammatory M1 phenotype via both DR4 and DR5. Our study defines TRAIL as a new regulator of macrophage polarization and suggests that targeting DRs can enhance the anti-tumorigenic response of macrophages in the tumor microenvironment by increasing M1 polarization.

SOCS1-KIR Peptide in PEGDA Hydrogels Reduces Pro-Inflammatory Macrophage Activation

Macrophages modulate the wound healing cascade by adopting different phenotypes such as pro-inflammatory (M1) or pro-wound healing (M2). To reduce M1 activation, the JAK/STAT pathway can be targeted by using suppressors of cytokine signaling (SOCS1) proteins. Recently a peptide mimicking the kinase inhibitory region (KIR) of SOCS1 has been utilized to manipulate the adaptive immune response. However, the utilization of SOCS1-KIR to reduce pro-inflammatory phenotype in macrophages is yet to be investigated in a biomaterial formulation. This study introduces a PEGDA hydrogel platform to investigate SOCS1-KIR as a macrophage phenotype manipulating peptide. Immunocytochemistry, cytokine secretion assays, and gene expression analysis for pro-inflammatory macrophage markers in 2D and 3D experiments demonstrate a reduction in M1 activation due to SOCS1-KIR treatment. The retention of SOCS1-KIR in the hydrogel through release assays and diffusion tests is demonstrated. The swelling ratio of the hydrogel also remains unaffected with the entrapment of SOCS1-KIR. This study elucidates how SOCS1-KIR peptide in PEGDA hydrogels can be utilized as an effective therapeutic for macrophage manipulation.

Silica nanoparticles promoted pro-inflammatory macrophage and foam cell transformation via ROS/PPARγ/NF-κB signaling

Experimental evidence has pointed out silica nanoparticles (SiNPs) possessing a proatherogenic capability. However, the interplay between SiNPs and macrophages in the pathogenesis of atherosclerosis was poorly understood. Here, we demonstrated SiNPs could promote macrophage adhesion to endothelial cells, accompanied by elevated Vcam1 and Mcp1. Upon SiNPs stimuli, macrophages manifested enhanced phagocytic activity and a pro-inflammatory phenotype, as reflected by the transcriptional determination of M1/M2-related biomarkers. In particular, our data certified the increased macrophage M1 subset facilitated more lipid accumulation and resultant foam cell transformation in comparison to the M2 phenotype. More importantly, the mechanistic investigations revealed ROS-mediated PPARγ/NF-κB signaling was a key contributor to the above phenomena. That was, SiNPs caused ROS accumulation in macrophages, resulting in the deactivation of PPARγ, nuclear translocation of NF-κB, ultimately contributing to macrophage phenotype shift toward M1 and foam cell transformation. Collectively, we first revealed SiNPs facilitated pro-inflammatory macrophage and foam cell transformation via ROS/PPARγ/NF-κB signaling. These data would provide new insight into the atherogenic property of SiNPs in a macrophage model.

The presence of activating IgG Fc receptors in macrophages aggravates the development of experimental abdominal aortic aneurysm

INTRODUCTION

Abdominal aortic aneurysm (AAA) is a multifactorial, degenerative disease characterized by progressive aortic dilation and chronic activation of inflammation, proteolytic activity, and oxidative stress in the aortic wall. The immune response triggered by antibodies against antigens present in the vascular wall participates in the formation and progression of AAA through mechanisms not completely understood. This work analyses the function of specific IgG receptors (FcγR), especially those expressed by monocytes/macrophages, in the development of experimental AAA.

METHODS

In the elastase-induced AAA model, the abdominal aortas from wildtype and FcγR deficient mice with/without macrophage adoptive transfer were analysed by histology and quantitative PCR. In vitro, mouse macrophages were transfected with RNA interference of FcγRIV/CD16.2 or treated with Syk kinase inhibitor before stimulation with IgG immune complexes.

RESULTS

Macrophage adoptive transfer in FcγR deficient mice increased the susceptibility to AAA development. Mice receiving macrophages with functional FcγR exhibited higher aortic diameter increase, higher content of macrophages and B lymphocytes, and upregulated expression of chemokine CCL2, cytokines (TNF-α and IL-17), metalloproteinase MMP2, prooxidant enzyme NADPH oxidase-2, and the isoforms FcγRIII/CD16 and FcγRIV/CD16.2. In vitro, both FcγRIV/CD16.2 gene silencing and Syk inhibition reduced cytokines and reactive oxygen species production induced by immune complexes in macrophages.

CONCLUSIONS

Activation of macrophage FcγR contributes to AAA development by inducing mediators of inflammation, proteolysis, and oxidative stress. Modulation of FcγR or effector molecules may represent a potential target for AAA treatment.

Decidual macrophages in recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is defined as two or more pregnancy loss, affecting the happiness index of fertility couples. The mechanisms involved in the occurrence of RSA are not clear to date. The primary problem for the maternal immune system is how to establish and maintain the immune tolerance to the semi-allogeneic fetuses. During the pregnancy, decidual macrophages mainly play an important role in the immunologic dialogue. The purpose of this study is to explore decidual macrophages, and to understand whether there is a connection between these cells and RSA by analyzing their phenotypes and functions. Pubmed, Web of Science and Embase were searched. The eligibility criterion for this review was evaluating the literature about the pregnancy and macrophages. Any disagreement between the authors was resolved upon discussion and if required by the judgment of the corresponding author. We summarized the latest views on the phenotype, function and dysfunction of decidual macrophages to illuminate its relationship with RSA.

Monocytes educated by cancer-associated fibroblasts secrete exosomal miR-181a to activate AKT signaling in breast cancer cells

BACKGROUND

Cancer-associated fibroblasts (CAFs), one of the major components of the tumor stroma, contribute to an immunosuppressive tumor microenvironment (TME) through the induction and functional polarization of protumoral macrophages. We have herein investigated the contribution of CAFs to monocyte recruitment and macrophage polarization. We also sought to identify a possible paracrine mechanism by which CAF-educated monocytes affect breast cancer (BC) cell progression.

METHODS

Monocytes were educated by primary CAFs and normal fibroblast (NF); the phenotypic alterations of CAF- or NF-educated monocytes were measured by flow cytometry. Exosomes isolated from the cultured conditioned media of the educated monocytes were characterized. An in vivo experiment using a subcutaneous transplantation tumor model in athymic nude mice was conducted to uncover the effect of exosomes derived from CAF- or NF-educated monocytes on breast tumor growth. Gain- and loss-of-function experiments were performed to explore the role of miR-181a in BC progression with the involvement of the AKT signaling pathway. Western blotting, enzyme-linked immunosorbent assay, RT-qPCR, flow cytometry staining, migration assay, immunohistochemical staining, and bioinformatics analysis were performed to reveal the underlying mechanisms.

RESULTS

We illustrated that primary CAFs recruited monocytes and established pro-tumoral M2 macrophages. CAF may also differentiate human monocyte THP-1 cells into anti-inflammatory M2 macrophages. Besides, we revealed that CAFs increased reactive oxygen species (ROS) generation in THP-1 monocytes, as differentiating into M2 macrophages requires a level of ROS for proper polarization. Importantly, T-cell proliferation was suppressed by CAF-educated monocytes and their exosomes, resulting in an immunosuppressive TME. Interestingly, CAF-activated, polarized monocytes lost their tumoricidal abilities, and their derived exosomes promoted BC cell proliferation and migration. In turn, CAF-educated monocyte exosomes exhibited a significant promoting effect on BC tumorigenicity in vivo. Of clinical significance, we observed that up-regulation of circulating miR-181a in BC was positively correlated with tumor aggressiveness and found a high level of this miRNA in CAF-educated monocytes and their exosomes. We further clarified that the pro-oncogenic effect of CAF-educated monocytes may depend in part on the exosomal transfer of miR-181a through modulating the PTEN/Akt signaling axis in BC cells.

CONCLUSIONS

Our findings established a connection between tumor stromal communication and tumor progression and demonstrated an inductive function for CAF-educated monocytes in BC cell progression. We also proposed a supporting model in which exosomal transfer of miR-181a from CAF-educated monocytes activates AKT signaling by regulating PTEN in BC cells.

Crosslinking of membrane CD13 in human neutrophils mediates phagocytosis and production of reactive oxygen species, neutrophil extracellular traps and proinflammatory cytokines

Aminopeptidase N, or CD13, is a cell membrane ectopeptidase highly expressed in myeloid cells. Through its enzymatic activity, CD13 regulates the activity of several bioactive peptides, such as endorphins and enkephalins, chemotactic peptides like MCP-1 and IL-8, angiotensin III, bradikinin, etc. In recent years, it has been appreciated that independently of its peptidase activity, CD13 can activate signal transduction pathways and mediate effector functions such as phagocytosis and cytokine secretion in monocytes and macrophages. Although neutrophils are known to express CD13 on its membrane, it is currently unknown if CD13 can mediate effector functions in these cells. Here, we show that in human neutrophils CD13 can mediate phagocytosis, which is dependent on a signaling pathway that involves Syk, and PI3-K. Phagocytosis mediated by CD13 is associated with production of reactive oxygen species (ROS). The level of phagocytosis and ROS production mediated by CD13 are similar to those through FcγRIII (CD16b), a widely studied receptor of human neutrophils. Also, CD13 ligation induces the release of neutrophil extracellular traps (NETs) as well as cytokine secretion from neutrophils. These results support the hypothesis that CD13 is a membrane receptor able to activate effector functions in human neutrophils.

Cyclic Attractors Are Critical for Macrophage Differentiation, Heterogeneity, and Plasticity

Adaptability, heterogeneity, and plasticity are the hallmarks of macrophages. How these complex properties emerge from the molecular interactions is an open question. Thus, in this study we propose an actualized regulatory network of cytokines, signaling pathways, and transcription factors to survey the differentiation, heterogeneity, and plasticity of macrophages. The network recovers attractors, which in regulatory networks correspond to cell types, that correspond to M0, M1, M2a, M2b, M2c, M2d, M2-like, and IL-6 producing cells, including multiple cyclic attractors that are stable to perturbations. These cyclic attractors reproduce experimental observations and show that oscillations result from the structure of the network. We also study the effect of the environment in the differentiation and plasticity of macrophages, showing that the observed heterogeneity in macrophage populations is a result of the regulatory network and its interaction with the micro-environment. The macrophage regulatory network gives a mechanistic explanation to the heterogeneity and plasticity of macrophages seen in vivo and in vitro, and offers insights into the mechanism that allows the immune system to react to a complex dynamic environment.

β‐Glucan receptors on IL‐4 activated macrophages are required for hookworm larvae recognition and trapping

Recent advances in the field of host immunity against parasitic nematodes have revealed the importance of macrophages in trapping tissue migratory larvae. Protective immune mechanisms against the rodent hookworm Nippostrongylus brasiliensis (Nb) are mediated, at least in part, by IL‐4‐activated macrophages that bind and trap larvae in the lung. However, it is still not clear how host macrophages recognize the parasite. An in vitro co‐culture system of bone marrow‐derived macrophages and Nb infective larvae was utilized to screen for the possible ligand–receptor pair involved in macrophage attack of larvae. Competitive binding assays revealed an important role for β‐glucan recognition in the process. We further identified a role for CD11b and the non‐classical pattern recognition receptor ephrin‐A2 (EphA2), but not the highly expressed β‐glucan dectin‐1 receptor, in this process of recognition. This work raises the possibility that parasitic nematodes synthesize β‐glucans and it identifies CD11b and ephrin‐A2 as important pattern recognition receptors involved in the host recognition of these evolutionary old pathogens. To our knowledge, this is the first time that EphA2 has been implicated in immune responses to a helminth.

IL-4 plays an essential role in DnaJ-ΔA146Ply-mediated immunoprotection against Streptococcus pneumoniae in mice

The fusion protein DnaJ-ΔA146Ply is protective against pneumococcal infections in mice. However, we found that immunized IL-4-/- mice showed significant lower survival rates and higher bacterial loads than did wild-type (WT) mice after being challenged. We explored the role of IL-4 in the protective immunity conferred by DnaJ-ΔA146Ply. Our results showed that there were no significant differences in antibody titers between immunized WT mice and IL-4-/- mice. The bacterial loads of passively immunized IL-4-/- mice were significantly higher than those of WT mice, while mice immunized with anti-DnaJ-ΔA146Ply serum from WT and IL-4-/- mice showed similar capacity for bacterial clearance. DnaJ-ΔA146Ply-dependent phagocytosis of IL-4-/- neutrophils was significant decreased compared with that of WT neutrophils. The levels of Syk and phosphor-Syk in IL-4-/- neutrophils were decreased compared with those in WT neutrophils. Additionally, Splenocytes in IL-4-/- mice triggered significantly higher levels of IFN-γ and IL-17A than did splenocytes in WT mice. Taken together, our findings illustrate that IL-4 deficiency does not influence the antibody production or antibody effect, but change the cellular immune response induced by DnaJ-ΔA146Ply. Additionally, IL-4 can enhance the antibody-dependent phagocytosis of neutrophils partially by activating Syk and participate in the protective immunity induced by DnaJ-ΔA146Ply.

Analyses of the Impact of Immunosuppressive Cytokines on Porcine Macrophage Responses and Susceptibility to Infection to African Swine Fever Viruses

African swine fever viruses (ASFV), currently a serious threat to the global pig industry, primarily target porcine macrophages. Macrophages are characterized by their remarkable plasticity, being able to modify their phenotype and functions in response to diverse stimuli. Since IL-10 and TGF-β polarize macrophages toward an anti-inflammatory phenotype, we analyzed their impact on porcine monocyte-derived macrophages’ (moMΦ) susceptibility to infection and their responses to two genotype I ASFV strains, virulent 26544/OG10 and attenuated NH/P68. At a low multiplicity of infection (MOI), NH/P68, but not 26544/OG10, presented a higher ability to infect moM(IL-10) compared to moMΦ and moM(TGF-β), but no differences were appreciated at a higher MOI. Both strains replicated efficiently in all moMΦ subsets, with no differences at later times post-infection. Both strains downregulated CD14 and CD16 expression on moMΦ, irrespective of the activation status. ASFV’s modulation of CD163 and MHC II DR expression and cytokine responses to NH/P68 or 26544/OG10 ASFV were not affected by either IL-10 or TGF-β pre-treatment. Our results revealed little impact of these anti-inflammatory cytokines on moMΦ interaction with ASFV, which likely reflects the ability of the virus to effectively modulate macrophage responses.

A Review of Antimicrobial Activity of Dental Mesenchymal Stromal Cells: Is There Any Potential?

Antimicrobial defense is an essential component of host-microbial homeostasis and contributes substantially to oral health maintenance. Dental mesenchymal stromal cells (MSCs) possess multilineage differentiation potential, immunomodulatory properties and play an important role in various processes like regeneration and disease progression. Recent studies show that dental MSCs might also be involved in antibacterial defense. This occurs by producing antimicrobial peptides or attracting professional phagocytic immune cells and modulating their activity. The production of antimicrobial peptides and immunomodulatory abilities of dental MSCs are enhanced by an inflammatory environment and influenced by vitamin D3. Antimicrobial peptides also have anti-inflammatory effects in dental MSCs and improve their differentiation potential. Augmentation of antibacterial efficiency of dental MSCs could broaden their clinical application in dentistry.

Leukocyte Membrane Enzymes Play the Cell Adhesion Game

For a long time, proteins with enzymatic activity have not been usually considered to carry out other functions different from catalyzing chemical reactions within or outside the cell. Nevertheless, in the last few years several reports have uncovered the participation of numerous enzymes in other processes, placing them in the category of moonlighting proteins. Some moonlighting enzymes have been shown to participate in complex processes such as cell adhesion. Cell adhesion plays a physiological role in multiple processes: it enables cells to establish close contact with one another, allowing communication; it is a key step during cell migration; it is also involved in tightly binding neighboring cells in tissues, etc. Importantly, cell adhesion is also of great importance in pathophysiological scenarios like migration and metastasis establishment of cancer cells. Cell adhesion is strictly regulated through numerous switches: proteins, glycoproteins and other components of the cell membrane. Recently, several cell membrane enzymes have been reported to participate in distinct steps of the cell adhesion process. Here, we review a variety of examples of membrane bound enzymes participating in adhesion of immune cells.

Statins and Bempedoic Acid: Different Actions of Cholesterol Inhibitors on Macrophage Activation

Statins represent the most prescribed class of drugs for the treatment of hypercholesterolemia. Effects that go beyond lipid-lowering actions have been suggested to contribute to their beneficial pharmacological properties. Whether and how statins act on macrophages has been a matter of debate. In the present study, we aimed at characterizing the impact of statins on macrophage polarization and comparing these to the effects of bempedoic acid, a recently registered drug for the treatment of hypercholesterolemia, which has been suggested to have a similar beneficial profile but fewer side effects. Treatment of primary murine macrophages with two different statins, i.e., simvastatin and cerivastatin, impaired phagocytotic activity and, concurrently, enhanced pro-inflammatory responses upon short-term lipopolysaccharide challenge, as characterized by an induction of tumor necrosis factor (TNF), interleukin (IL) 1β, and IL6. In contrast, no differences were observed under long-term inflammatory (M1) or anti-inflammatory (M2) conditions, and neither inducible NO synthase (iNOS) expression nor nitric oxide production was altered. Statin treatment led to extracellular-signal regulated kinase (ERK) activation, and the pro-inflammatory statin effects were abolished by ERK inhibition. Bempedoic acid only had a negligible impact on macrophage responses when compared with statins. Taken together, our data point toward an immunomodulatory effect of statins on macrophage polarization, which is absent upon bempedoic acid treatment.

Building a better antibody through the Fc: advances and challenges in harnessing antibody Fc effector functions for antiviral protection

Antibodies can provide antiviral protection through neutralization and recruitment of innate effector functions through the Fc domain. While neutralization has long been appreciated for its role in antibody-mediated protection, a growing body of work indicates that the antibody Fc domain also significantly contributes to antiviral protection. Recruitment of innate immune cells such as natural killer cells, neutrophils, monocytes, macrophages, dendritic cells and the complement system by antibodies can lead to direct restriction of viral infection as well as promoting long-term antiviral immunity. Monoclonal antibody therapeutics against viruses are increasingly incorporating Fc-enhancing features to take advantage of the Fc domain, uncovering a surprising breadth of mechanisms through which antibodies can control viral infection. Here, we review the recent advances in our understanding of antibody-mediated innate immune effector functions in protection from viral infection and review the current approaches and challenges to effectively leverage innate immune cells via antibodies.

Fcγ receptor activation mediates vascular inflammation and abdominal aortic aneurysm development

BACKGROUND

Abdominal aortic aneurysm (AAA), a degenerative vascular pathology characterized by permanent dilation of the aorta, is considered a chronic inflammatory disease involving innate/adaptive immunity. However, the functional role of antibody-dependent immune response against antigens present in the damaged vessel remains unresolved. We hypothesized that engagement of immunoglobulin G (IgG) Fc receptors (FcγR) by immune complexes (IC) in the aortic wall contributes to AAA development. We therefore evaluated FcγR expression in AAA lesions and analysed whether inhibition of FcγR signaling molecules (γ-chain and Syk kinase) influences AAA formation in mice.

METHODS

FcγR gene/protein expression was assessed in human and mouse AAA tissues. Experimental AAA was induced by aortic elastase perfusion in wild-type (WT) mice and γ-chain knockout (γKO) mice (devoid of activating FcγR) in combination with macrophage adoptive transfer or Syk inhibitor treatment. To verify the mechanisms of FcγR in vitro, vascular smooth muscle cells (VSMC) and macrophages were stimulated with IgG IC.

RESULTS

FcγR overexpression was detected in adventitia and media layers of human and mouse AAA. Elastase-perfused γKO mice exhibited a decrease in AAA incidence, aortic dilation, elastin degradation, and VSMC loss. This was associated with (1) reduced infiltrating leukocytes and immune deposits in AAA lesions, (2) inflammatory genes and metalloproteinases downregulation, (3) redox balance restoration, and (4) converse phenotype of anti-inflammatory macrophage M2 and contractile VSMC. Adoptive transfer of FcγR-expressing macrophages aggravated aneurysm in γKO mice. In vitro, FcγR deficiency attenuated inflammatory gene expression, oxidative stress, and phenotypic switch triggered by IC. Additionally, Syk inhibition prevented IC-mediated cell responses, reduced inflammation, and mitigated AAA formation.

CONCLUSION

Our findings provide insight into the role and mechanisms mediating IgG-FcγR-associated inflammation and aortic wall injury in AAA, which might represent therapeutic targets against AAA disease.

TREM2 is a receptor for non-glycosylated mycolic acids of mycobacteria that limits anti-mycobacterial macrophage activation

Mycobacterial cell-wall glycolipids elicit an anti-mycobacterial immune response via FcRγ-associated C-type lectin receptors, including Mincle, and caspase-recruitment domain family member 9 (CARD9). Additionally, mycobacteria harbor immuno-evasive cell-wall lipids associated with virulence and latency; however, a mechanism of action is unclear. Here, we show that the DAP12-associated triggering receptor expressed on myeloid cells 2 (TREM2) recognizes mycobacterial cell-wall mycolic acid (MA)-containing lipids and suggest a mechanism by which mycobacteria control host immunity via TREM2. Macrophages respond to glycosylated MA-containing lipids in a Mincle/FcRγ/CARD9-dependent manner to produce inflammatory cytokines and recruit inducible nitric oxide synthase (iNOS)-positive mycobactericidal macrophages. Conversely, macrophages respond to non-glycosylated MAs in a TREM2/DAP12-dependent but CARD9-independent manner to recruit iNOS-negative mycobacterium-permissive macrophages. Furthermore, TREM2 deletion enhances Mincle-induced macrophage activation in vitro and inflammation in vivo and accelerates the elimination of mycobacterial infection, suggesting that TREM2-DAP12 signaling counteracts Mincle-FcRγ-CARD9-mediated anti-mycobacterial immunity. Mycobacteria, therefore, harness TREM2 for immune evasion.

Mycobacterial cell wall lipids can drive immunoevasion, but underlying mechanisms are incompletely understood. Here the authors show TREM2 is a pattern recognition receptor that binds non-glycosylated mycolic acid-containing lipids and inhibits Mincle-induced anti-mycobacterial macrophage responses.

Small extracellular vesicles derived from interferon-γ pre-conditioned mesenchymal stromal cells effectively treat liver fibrosis

Mesenchymal stromal cells (MSCs) are used for ameliorating liver fibrosis and aiding liver regeneration after cirrhosis; Here, we analyzed the therapeutic potential of small extracellular vesicles (sEVs) derived from interferon-γ (IFN-γ) pre-conditioned MSCs (γ-sEVs). γ-sEVs effectively induced anti-inflammatory macrophages with high motility and phagocytic abilities in vitro, while not preventing hepatic stellate cell (HSC; the major source of collagen fiber) activation in vitro. The proteome analysis of MSC-derived sEVs revealed anti-inflammatory macrophage inducible proteins (e.g., annexin-A1, lactotransferrin, and aminopeptidase N) upon IFN-γ stimulation. Furthermore, by enabling CX₃CR1+ macrophage accumulation in the damaged area, γ-sEVs ameliorated inflammation and fibrosis in the cirrhosis mouse model more effectively than sEVs. Single cell RNA-Seq analysis revealed diverse effects, such as induction of anti-inflammatory macrophages and regulatory T cells, in the cirrhotic liver after γ-sEV administration. Overall, IFN-γ pre-conditioning altered sEVs resulted in efficient tissue repair indicating a new therapeutic strategy.

The Antidepressant Mirtazapine Activates Hepatic Macrophages, Facilitating Pathogen Clearance While Limiting Tissue Damage in Mice

Background and Aims

Mirtazapine is an atypical antidepressant with antagonist activity for serotonin and histamine receptors. Clinical and experimental evidence suggests that, in addition to treating depression, mirtazapine also alters liver innate immunity and suppresses immune-driven hepatic macrophage activation. Liver macrophages, Kupffer cells, represent the largest collection of fixed macrophages in the body and are critical in regulating hepatic immunity. In addition to their capacity to regulate inflammation, Kupffer cells are key sentinels for clearing blood-borne pathogens, preventing their dissemination within the body. This process involves pathogen capture, phagocytosis, and activation-induced killing via reactive oxygen species (ROS) production. Therefore, we speculated that mirtazapine might adversely alter Kupffer cell pathogen-associated activation and killing.

Methods

Mice were treated with mirtazapine and time-dependent changes in Kupffer cells were characterized using intravital microscopy. Macrophage and neutrophil responses, bacterial dissemination, and liver damage were assessed following i.v. infection with a pathogenic strain of S. aureus.

Results

Mirtazapine rapidly (within 1.5 h) activates Kupffer cells, indicated by a loss of elongated shape with cellular rounding. However, this shape change did not result in impaired pathogen capture function, and, in fact, generated enhanced ROS production in response to S. aureus-induced sepsis. Neutrophil dynamics were altered with reduced cellular recruitment to the liver following infection. Bacterial dissemination post-intravenous administration was not altered by mirtazapine treatment; however, hepatic abscess formation was significantly reduced.

Conclusions

Mirtazapine rapidly activates Kupffer cells, associated with preserved bacterial capture functions and enhanced ROS generation capacity. Moreover, these changes in Kupffer cells were linked to a beneficial reduction in hepatic abscess size. In contrast to our initial speculation, mirtazapine may have beneficial effects in sepsis and warrants further exploration.

Immunological effects of Chondrus armatus carrageenans and their low molecular weight degradation products

Ability of high molecular weight (HMW) κ- and λ-carrageenans of the red marine algae Chondrus armatus and their low molecular weight degradation products (LMWDPs) (0.7-20 and 10-170 kDa respectively) to influence functional properties (motility and phagocytosis) of murine peritoneal macrophages was assessed in this study as an in vitro and a weeklong feeding experiment. We demonstrated that, with an exception of one, all carrageenan samples at 100 μg/ml increased cellular motility and dose-dependently decreased phagocytic activity; LMWDPs of λ-carrageenan suppressed motility and had no effect on phagocytosis. Oral administration of all the carrageenan samples at 100 μg/kg/day for 7 days to mice had no effect on their clinical appearance, body weight, weight of their liver, spleen or thymus or development of noticeable changes to their inner organs. All samples induced a shift of the cell composition of the peritoneal cavity towards macrophages. Consumption of LMWDPs of κ-carrageenan resulted in development of leukopenia, however, no changes to relative WBC count were introduced by either of the samples. All samples decreased murine peritoneal macrophages phagocytic activity, with λ-samples possessing higher efficacy than their κ-counterparts; all LMWDPs stimulated peritoneal macrophages motility, with κ-samples possessing higher efficacy than their λ-counterparts In conclusion, we have shown that κ- and λ-carrageenans of the C. armatus and their LMWDPs suppress phagocytotic activity of peritoneal macrophages under both in vitro and in vivo conditions. This allows them to be viewed as pharmacologically active substances andpropagates the need for their further investigation as such.

Serum From Melioidosis Survivors Diminished Intracellular Burkholderia pseudomallei Growth in Macrophages: A Brief Research Report

Melioidosis is a neglected tropical disease with high mortality rate. It is caused by the Gram-negative, CDC category B select agent Burkholderia pseudomallei (B. ps) that is intrinsically resistant to first-line antibiotics. An antibody-based vaccine is likely to be the most effective control measure. Previous studies have demonstrated significant mechanistic roles of antibodies in protection against death in animal models, but data from human melioidosis is scarce. Herein, we used in-vitro antibody-dependent cellular phagocytosis and growth inhibition assays to assess the mechanism of protective antibodies in patients with acute melioidosis. We found that serum from patients who survived the disease enable more live B. ps to be engulfed by THP-1 derived macrophages (median 1.7 × 10³ CFU/ml, IQR 1.1 × 10³-2.5 × 10³ CFU/ml) than serum from patients who did not survive (median 1.2 × 10³ CFU/ml, IQR 0.7 × 10³-1.8 × 10³, p = 0.02). In addition, the intracellular growth rate of B. ps pre-opsonized with serum from survivors (median 7.89, IQR 5.58–10.85) was diminished when compared with those with serum from non-survivors (median 10.88, IQR 5.42–14.88, p = 0.04). However, the difference of intracellular bacterial growth rate failed to reach statistical significance when using purified IgG antibodies (p = 0.09). These results provide new insights into a mechanistic role of serum in protection against death in human melioidosis for antibody-based vaccine development.

Children with oligoarticular juvenile idiopathic arthritis have skewed synovial monocyte polarization pattern with functional impairment-a distinct inflammatory pattern for oligoarticular juvenile arthritis

BACKGROUND

Juvenile idiopathic arthritis (JIA) is an umbrella term of inflammatory joint diseases in children. Oligoarthritis is the most common form in the Western world, representing roughly 60% of all patients. Monocytes and macrophages play an important role in adult arthritides, but their role in oligoarticular JIA is less studied. Polarization highly influences monocytes' and macrophages' effector functions, broadly separated into pro-inflammatory M1 or anti-inflammatory M2 phenotypes. Here, we set out to investigate the polarization pattern and functional aspects of synovial monocytes in oligoarticular juvenile idiopathic arthritis (JIA).

METHODS

Paired synovial fluid, blood samples (n = 13), and synovial biopsies (n = 3) were collected from patients with untreated oligoarticular JIA. Monocytes were analyzed for polarization markers by flow cytometry and qPCR. Effector function was analyzed by a phagocytosis assay. Polarization of healthy monocytes was investigated by stimulation with synovial fluid in vitro. Monocyte/macrophage distribution, polarization, and mRNA expression were investigated in biopsies by immunohistochemistry, immunofluorescence, and in situ hybridization.

RESULTS

Children with oligoarticular JIA have polarized synovial fluid monocytes of a specific M1(IFNγ)/M2(IL-4)-like pattern. This was evidenced by increased surface expression of CD40 (p < 0.001), CD86 (p < 0.001), and CD206 (p < 0.001), but not CD163, as compared to paired circulating monocytes. Additionally, polarization was extensively explored at the mRNA level and synovial fluid monocytes differentially expressed classical markers of M1(IFNγ)/M2(IL-4) polarization compared to circulating monocytes. Synovial fluid monocytes were functionally affected, as assessed by reduced capacity to phagocytose (p < 0.01). Synovial fluid induced M2 markers (CD16 and CD206), but not M1 (CD40) or CD86 in healthy monocytes and did not induce cytokine production. Single and co-expression of surface CD40 and CD206, as well as mRNA expression of IL-10 and TNF, was observed in monocytes/macrophages in synovial biopsies.

CONCLUSION

Children with untreated oligoarticular JIA have similar and distinct synovial fluid monocyte polarization pattern of mixed pro- and anti-inflammatory features. This pattern was not exclusively a result of the synovial fluid milieu as monocytes/macrophages in the synovial membrane show similar patterns. Our study highlights a distinct polarization pattern in oligoarticular JIA, which could be utilized for future treatment strategies.

Neutrophil Extracellular Trap Degradation by Differently Polarized Macrophage Subsets

Supplemental Digital Content is available in the text.

Macrophages are immune cells, capable to remodel the extracellular matrix, which can harbor extracellular DNA incorporated into neutrophil extracellular traps (NETs). To study the breakdown of NETs we studied the capability of macrophage subsets to degrade these structures in vitro and in vivo in a murine thrombosis model. Furthermore, we analyzed human abdominal aortic aneurysm samples in support of our in vitro and in vivo results.

Fast processes of nanoparticle blood clearance: Comprehensive study

Blood circulation is the key parameter that determines the in vivo efficiency of nanoagents. Despite clinical success of the stealth liposomal agents with their inert and shielded surfaces, a great number of non-stealth nanomaterials is being developed due to their potential of enhanced functionality. By harnessing surface phenomena, such agents can offer advanced control over drug release through intricately designed nanopores, catalysis-propelled motion, computer-like analysis of several disease markers for precise target identification, etc. However, investigation of pharmacokinetic behavior of these agents becomes a great challenge due to ultra-short circulation (usually around several minutes) and impossibility to use the invasive blood-sampling techniques. Accordingly, the data on circulation of such agents has been scarce and irregular. Here, we demonstrate high-throughput capabilities of the developed magnetic particle quantification technique for nanoparticle circulation measurements and present a comprehensive investigation of factors that affect blood circulation of the non-stealth nanoparticles. Namely, we studied the following 9 factors: particle size, zeta-potential, coating, injection dose, repetitive administration, induction of anesthesia, mice strain, absence/presence of tumors, tumor size. Our fundamental findings demonstrate potential ways to extend the half-life of the agents in blood thereby giving them a better chance of achieving their goal in the organism. The study will be valuable for design of the next generation nanomaterials with advanced biomedical functionality.

Growth Hormone Reprograms Macrophages toward an Anti-Inflammatory and Reparative Profile in an MAFB-Dependent Manner

Growth hormone (GH), a pleiotropic hormone secreted by the pituitary gland, regulates immune and inflammatory responses. In this study, we show that GH regulates the phenotypic and functional plasticity of macrophages both in vitro and in vivo. Specifically, GH treatment of GM-CSF-primed monocyte-derived macrophages promotes a significant enrichment of anti-inflammatory genes and dampens the proinflammatory cytokine profile through PI3K-mediated downregulation of activin A and upregulation of MAFB, a critical transcription factor for anti-inflammatory polarization of human macrophages. These in vitro data correlate with improved remission of inflammation and mucosal repair during recovery in the acute dextran sodium sulfate-induced colitis model in GH-overexpressing mice. In this model, in addition to the GH-mediated effects on other immune cells, we observed that macrophages from inflamed gut acquire an anti-inflammatory/reparative profile. Overall, these data indicate that GH reprograms inflammatory macrophages to an anti-inflammatory phenotype and improves resolution during pathologic inflammatory responses.

Antibody combinations for optimized staining of macrophages in human lung tumours

The analysis of tumour-associated macrophages (TAMs) has a high potential to predict cancer recurrence and response to immunotherapy. However, the heterogeneity of TAMs poses a challenge for quantitative and qualitative measurements. Here, we critically evaluated by immunohistochemistry and flow cytometry two commonly used pan-macrophage markers (CD14 and CD68) as well as some suggested markers for tumour-promoting M2 macrophages (CD163, CD204, CD206 and CD209) in human non-small cell lung cancer (NSCLC). Tumour, non-cancerous lung tissue and blood were investigated. For immunohistochemistry, CD68 was confirmed to be a useful pan-macrophage marker although careful selection of antibody was found to be critical. The widely used anti-CD68 antibody clone KP-1 stains both macrophages and neutrophils, which is problematic for TAM quantification because lung tumours contain many neutrophils. For TAM counting in tumour sections, we recommend combined labelling of CD68 with a cell membrane marker such as CD14, CD163 or CD206. In flow cytometry, the commonly used combination of CD14 and HLA-DR was found to not be optimal because some TAMs do not express CD14. Instead, combined staining of CD68 and HLA-DR is preferable to gate all TAMs. Concerning macrophage phenotypic markers, the scavenger receptor CD163 was found to be expressed by a substantial fraction (50%-86%) of TAMs with a large patient-to-patient variation. Approximately 50% of TAMs were positive for CD206. Surprisingly, there was no clear overlap between CD163 and CD206 positivity, and three distinct TAM sub-populations were identified in NSCLC tumours: CD163⁺ CD206⁺ , CD163⁺ CD206^- and CD163^- CD206^- . This work should help develop macrophage-based prognostic tools for cancer.

Cracking the Cell Death Code

Cell death is an invariant feature throughout our life span, starting with extensive scheduled cell death during morphogenesis and continuing with death under homeostasis in adult tissues. Additionally, cells become victims of accidental, unscheduled death following injury and infection. Cell death in each of these occasions triggers specific and specialized responses in the living cells that surround them or are attracted to the dying/dead cells. These responses sculpt tissues during morphogenesis, replenish lost cells in homeostasis to maintain tissue/system function, and repair damaged tissues after injury. Wherein lies the information that sets in motion the cascade of effector responses culminating in remodeling, renewal, or repair? Here, we attempt to provide a framework for thinking about cell death in terms of the specific effector responses that accompanies various modalities of cell death. We also propose an integrated threefold "cell death code" consisting of information intrinsic to the dying/dead cell, the surroundings of the dying cell, and the identity of the responder.

CD4+ T cell phenotypes in the pathogenesis of immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by low platelet counts due to enhanced platelet clearance and compromised production. Traditionally, ITP was regarded a B cell mediated disorder as anti-platelet antibodies are detected in most patients. The very nature of self-antigens, evident processes of isotype switching and the affinity maturation of anti-platelet antibodies indicate that B cells in order to mount anti-platelet immune response require assistance of auto-reactive CD4⁺ T cells. For a long time, ITP pathogenesis has been exclusively reviewed through the prism of the disturbed balance between Th1 and Th2 subsets of CD4⁺ T cells, however, more recently new subsets of these cells have been described including Th17, Th9, Th22, T follicular helper and regulatory T cells. In this paper, we review the current understanding of the role and immunological mechanisms by which CD4⁺ T cells contribute to the pathogenesis of ITP.

Standardized protocols for differentiation of THP-1 cells to macrophages with distinct M(IFNγ+LPS), M(IL-4) and M(IL-10) phenotypes

In vitro models of differing macrophage functions are useful since human monocyte-derived macrophages are short-lived, finite and vary from donor to donor. Published protocols using the promonocytic cell line THP-1 have tended to result in cells that closely resemble classically-activated macrophages, differentiated in IFNγ and LPS. However, no protocol, to date, has fully recapitulated polarization of THP-1 to the M(IL-4) or M(IL-10) macrophage phenotypes seen when human monocyte-derived macrophages are exposed to each cytokine. Here we present protocols that can be used to prepare M(IL-4) polarized THP-1 that transcribe CCL17, CCL26, CD200R and MRC1 and M(IL-10) cells which transcribe CD163, C1QA and SEPP1. We show that the inhibitory Fcγ Receptor IIb is preferentially expressed on the surface of M(IL-4) cells, altering the balance of activating to inhibitory Fcγ Receptors. Adoption of standardized experimental conditions for macrophage polarization will make it easier to compare downstream effector functions of different macrophage polarization states, where the impact of PMA exposure is minimized and rest periods and cytokine exposure have been optimized.

Phagocytosis assays with different pH-sensitive fluorescent particles and various readouts

Phagocytosis is a fundamental mechanism of innate immunity and its impairment is associated with severe chronic diseases, for example, chronic obstructive pulmonary disease. Investigating phagocytosis requires flexible tools and assay conditions, such as different fluorescent particle types, detection colors and readouts. We comprehensively evaluated and optimized phagocytosis assays using particles labeled with fluorescent pH-sensitive pHrodo^® dyes, facilitating the specific detection of phagocytosed particles. Beads, bacterial and yeast particles labeled with pHrodo red and green were tested for their uptake by THP-1 cells and primary human macrophages by flow cytometry and high-content imaging. Whereas the latter allowed kinetic phagocytosis measurement, the former demonstrated the feasibility of using cell sorting for periods of up to 6 h, enabling downstream applications such as pooled genetic screens.

Application of CNTF or FGF-2 increases the number of M2-like macrophages after optic nerve injury in adult Rana pipiens

We have previously shown that a single application of the growth factors ciliary neurotrophic factor (CNTF) or fibroblast growth factor 2 (FGF-2) to the crushed optic nerve of the frog, Rana pipiens, increases the numbers and elongation rate of regenerating retinal ganglion cell axons. Here we investigate the effects of these factors on the numbers and types of macrophages that invade the regeneration zone. In control PBS-treated nerves, many macrophages are present 100 μm distal to the crush site at 1 week after injury; their numbers halve by 2 weeks. A single application of CNTF at the time of injury triples the numbers of macrophages at 1 week, with this increase compared to control being maintained at 2 weeks. Application of FGF-2 is equally effective at 1 week, but the macrophage numbers have fallen to control levels at 2 weeks. Immunostaining with a pan-macrophage marker, ED1, and a marker for M2-like macrophages, Arg-1, showed that the proportion of the putative M2 phenotype remained at approximately 80% with all treatments. Electron microscopy of the macrophages at 1 week shows strong phagocytic activity with all treatments, with many vacuoles containing axon fragments and membrane debris. At 2 weeks with PBS or FGF-2 treatment the remaining macrophages are less phagocytically active, containing mainly lipid inclusions. With CNTF treatment, at 2 weeks many of the more numerous macrophages are still phagocytosing axonal debris, although they also contain lipid inclusions. We conclude that the increase in macrophage influx seen after growth factor application is beneficial for the regenerating axons, probably due to more extensive removal of degenerating distal axons, but also perhaps to secretion of growth-promoting substances.

Nonglucuronidated Ezetimibe Disrupts CD13- and CD64-Coassembly in Membrane Microdomains and Decreases Cellular Cholesterol Content in Human Monocytes/Macrophages

Ezetimibe (EZE) and glucuronidated EZE (EZE-Glu) differentially target Niemann-Pick C1-like 1 (NPC1L1) and CD13 (aminopeptidase-N) to inhibit intestinal cholesterol absorption and cholesterol processing in other cells, although the precise molecular mechanisms are not fully elucidated. Cellular effects of EZE, EZE-Glu, and the low-absorbable EZE-analogue S6130 were investigated on human monocyte-derived macrophages upon loading with atherogenic lipoproteins. EZE and S6130, but not EZE-Glu disturbed the colocalization of CD13 and its coreceptor CD64 (Fcγ receptor I) in membrane microdomains, and decreased the presence of both receptors in detergent-resistant membrane fractions. Biotinylated cholesterol absorption inhibitor C-5 (i.e., derivative of EZE) was rapidly internalized to perinuclear tubular structures of cells, resembling endoplasmic reticulum (ER), but CD13 was detected on extracellular sites of the plasma membrane and endolysosomal vesicles. Administration of EZE, but not of EZE-Glu or S6130, was associated with decreased cellular cholesteryl ester content, indicating the sterol-O acyltransferase 1 (SOAT1)-inhibition by EZE. Furthermore, EZE decreased the expression of molecules involved in cholesterol uptake and synthesis, in parallel with increased apolipoprotein A-I-mediated cholesterol efflux and upregulation of efflux-effectors. However, NPC1L1 the other claimed molecular target of EZE, was not detected in macrophages, thereby excluding this protein as target for EZE in macrophages. Thus, EZE is very likely a CD13-linked microdomain-disruptor and SOAT1-inhibitor in macrophages leading to in vitro anti-atherosclerotic effects through a decrease of net cellular cholesterol content. © 2019 International Society for Advancement of Cytometry.

Material stiffness influences the polarization state, function and migration mode of macrophages

Biomaterial implantation is followed by an inflammatory cascade dominated by macrophages, which determine implant acceptance or rejection through pro- and anti-inflammatory polarization states (Anderson et al., 2008; Brown and Badylak, 2013). It is known that chemical signals such as bacterial endotoxins and cytokines (IL4) can direct macrophage polarization (Mantovani et al., 2004); however, recent evidence implicates biophysical cues in this process (McWhorter et al., 2015; Patel et al., 2012). Here we report that THP-1 derived macrophages cultured on collagen-coated polyacrylamide gels of varying stiffness adapt their polarization state, functional roles and migration mode according to the stiffness of the underlying substrate. Through gene expression and protein secretion analysis, we show that stiff polyacrylamide gels (323 kPa) prime macrophages towards a pro-inflammatory phenotype with impaired phagocytosis in macrophages, while soft (11 kPa) and medium (88 kPa) stiffness gels prime cells towards an anti-inflammatory, highly phagocytic phenotype. Furthermore, we show that stiffness dictates the migration mode of macrophages; on soft and medium stiffness gels, cells display Rho-A kinase (ROCK)-dependent, podosome-independent fast amoeboid migration and on stiff gels they adopt a ROCK-independent, podosome-dependent slow mesenchymal migration mode. We also provide a mechanistic insight into this process by showing that the anti-inflammatory property of macrophages on soft and medium gels is ROCK-dependent and independent of the ligand presented to them. Together, our results demonstrate that macrophages adapt their polarization, function and migration mode in response to the stiffness of the underlying substrate and suggest that biomaterial stiffness is capable of directing macrophage behaviour independent of the biochemical cues being presented to them. The results from this study establish an important role for substrate stiffness in directing macrophage behaviour, and will lead to the design of immuno-informed biomaterials that are capable of modulating the macrophage response after implantation. STATEMENT OF SIGNIFICANCE: Biomaterial implantation is followed by an inflammatory cascade dominated by macrophages, which determine implant acceptance or rejection through pro- and anti-inflammatory polarization states. It is known that chemical signals can direct macrophage polarization; however, recent evidence implicates biophysical cues in this process. Here we report that macrophages cultured on gels of varying stiffness adapt their polarization state, functional roles and migration mode according to the stiffness of the underlying substrate. The results from this study establish an important role for substrate stiffness in directing macrophage behaviour, and will lead to the design of immuno-informed biomaterials that are capable of modulating the macrophage response after implantation.

A Foreign Body Response-on-a-Chip Platform

Understanding the foreign body response (FBR) and desiging strategies to modulate such a response represent a grand challenge for implant devices and biomaterials. Here, the development of a microfluidic platform is reported, i.e., the FBR-on-a-chip (FBROC) for modeling the cascade of events during immune cell response to implants. The platform models the native implant microenvironment where the implants are interfaced directly with surrounding tissues, as well as vasculature with circulating immune cells. The study demonstrates that the release of cytokines such as monocyte chemoattractant protein 1 (MCP-1) from the extracellular matrix (ECM)-like hydrogels in the bottom tissue chamber induces trans-endothelial migration of circulating monocytes in the vascular channel toward the hydrogels, thus mimicking implant-induced inflammation. Data using patient-derived peripheral blood mononuclear cells further reveal inter-patient differences in FBR, highlighting the potential of this platform for monitoring FBR in a personalized manner. The prototype FBROC platform provides an enabling strategy to interrogate FBR on various implants, including biomaterials and engineered tissue constructs, in a physiologically relevant and individual-specific manner.

Critical Role of Macrophage FcγR Signaling and Reactive Oxygen Species in Alloantibody-Mediated Hepatocyte Rejection

Humoral alloimmunity negatively impacts both short- and long-term cell and solid organ transplant survival. We previously reported that alloantibody-mediated rejection of transplanted hepatocytes is critically dependent on host macrophages. However, the effector mechanism(s) of macrophage-mediated injury to allogeneic liver parenchymal cells is not known. We hypothesized that macrophage-mediated destruction of allogeneic hepatocytes occurs by cell-cell interactions requiring FcγRs. To examine this, alloantibody-dependent hepatocyte rejection in CD8-depleted wild-type (WT) and Fcγ-chain knockout (KO; lacking all functional FcγR) transplant recipients was evaluated. Alloantibody-mediated hepatocellular allograft rejection was abrogated in recipients lacking FcγR compared with WT recipients. We also investigated anti-FcγRI mAb, anti-FcγRIII mAb, and inhibitors of intracellular signaling (to block phagocytosis, cytokines, and reactive oxygen species [ROS]) in an in vitro alloantibody-dependent, macrophage-mediated hepatocytoxicity assay. Results showed that in vitro alloantibody-dependent, macrophage-mediated hepatocytotoxicity was critically dependent on FcγRs and ROS. The adoptive transfer of WT macrophages into CD8-depleted FcγR-deficient recipients was sufficient to induce alloantibody-mediated rejection, whereas adoptive transfer of macrophages from Fcγ-chain KO mice or ROS-deficient (p47 KO) macrophages was not. These results provide the first evidence, to our knowledge, that alloantibody-dependent hepatocellular allograft rejection is mediated by host macrophages through FcγR signaling and ROS cytotoxic effector mechanisms. These results support the investigation of novel immunotherapeutic strategies targeting macrophages, FcγRs, and/or downstream molecules, including ROS, to inhibit humoral immune damage of transplanted hepatocytes and perhaps other cell and solid organ transplants.

Biology of Tumor Associated Macrophages in Diffuse Large B Cell Lymphoma

The tumor associated microenvironment is known to play a vital role during the development and progression of different malignant tumors. As a part of tumor microenvironment, tumor associated macrophages (TAMs) are crucial for the genesis, proliferation, metastasis, and survival of tumor cells. Recently, more and more studies showed that TAMs were related with poor clinical status and survival in patients with diffuse large B cell lymphoma (DLBCL). Considering the complex roles which TAMs play in the tumor microenvironment of DLBCL, the aim of this study was to review the biological mechanisms between TAMs and DLBCL cells, including extracellular matrix remodeling and angiogenesis promotion, tumor promotion, immune suppression, and phagocytosis inhibition. This review will help us to further understand the comprehensive impact of TAMs on DLBCL and explore possible prognostic markers and therapeutic targets.

In contrast to morphine, buprenorphine enhances macrophage-induced humoral immunity and, as oxycodone, slightly suppresses the effector phase of cell-mediated immune response in mice

BACKGROUND

Opioid receptors are commonly expressed on various immune cells, macrophages especially. Thus, these cells are prone to stimulation with opioids, which seems to be responsible for opioid-induced immunomodulatory effects. While morphine, fentanyl and methadone influence on mouse immune response was recently studied, little is known about the potential immunomodulatory impact of buprenorphine and oxycodone.

AIM

The current research aimed to investigate the influence of buprenorphine and oxycodone on immune responses in mice under homeostatic conditions.

METHODS AND RESULTS

Repeated administration of morphine led to intensification of CHS response in actively sensitized mice, while buprenorphine or oxycodone administration exerted the opposite effect. Further, hapten-conjugated macrophages from mice treated with morphine, when transferred into naive recipients, induced more potent CHS response. The enhanced generation of reactive oxygen intermediates and nitric oxide by macrophages from mice treated with buprenorphine, oxycodone or morphine was also shown, along with increased release of IL-6, TNFα and TGFβ. Treatment with opioids altered expression of antigen phagocytosis and presentation markers. Finally, the inhibitory effect of morphine treatment on induction of humoral immunity by macrophages was demonstrated, while oxycodone failed to influence humoral immune response and buprenorphine actually enhanced B-cell activation.

CONCLUSIONS

Current observations confirm that macrophages greatly contribute to immunomodulatory effects of opioids. Studies on immunomodulation by opioids have great importance related to the evaluation of its beneficial and adverse effects on patient condition. Our research showed that oxycodone exerts the weakest immunomodulatory properties, allowing us to assume this drug as safer than morphine during prolonged therapy.

Macrophages: Their role, activation and polarization in pulmonary diseases

Macrophages, circulating in the blood or concatenated into different organs and tissues constitute the first barrier against any disease. They are foremost controllers of both innate and acquired immunity, healthy tissue homeostasis, vasculogenesis and congenital metabolism. Two hallmarks of macrophages are diversity and plasticity due to which they acquire a wobbling array of phenotypes. These phenotypes are appropriately synchronized responses to a variety of different stimuli from either the tissue microenvironment or - microbes or their products. Based on the phenotype, macrophages are classified into classically activated/(M1) and alternatively activated/(M2) which are further sub-categorized into M2a, M2b, M2c and M2d based upon gene expression profiles. Macrophage phenotype metamorphosis is the regulating factor in initiation, progression, and termination of numerous inflammatory diseases. Several transcriptional factors and other factors controlling gene expression such as miRNAs contribute to the transformation of macrophages at different points in different diseases. Understanding the mechanisms of macrophage polarization and modulation of their phenotypes to adjust to the micro environmental conditions might provide us a great prospective for designing novel therapeutic strategy. In view of the above, this review summarises the activation of macrophages, the factors intricated in activation along with benefaction of macrophage polarization in response to microbial infections, pulmonary toxicity, lung injury and other inflammatory diseases such as chronic obstructive pulmonary dysplasia (COPD), bronchopulmonary dysplasia (BPD), asthma and sepsis, along with the existing efforts to develop therapies targeting this facet of macrophage biology.

Human Cardiac-Derived Stem/Progenitor Cells Fine-Tune Monocyte-Derived Descendants Activities toward Cardiac Repair

Cardiac repair following MI relies on a finely regulated immune response involving sequential recruitment of monocytes to the injured tissue. Monocyte-derived cells are also critical for tissue homeostasis and healing process. Our previous findings demonstrated the interaction of T and natural killer cells with allogeneic human cardiac-derived stem/progenitor cells (hCPC) and suggested their beneficial effect in the context of cardiac repair. Therefore, we investigated here whether monocytes and their descendants could be also modulated by allogeneic hCPC toward a repair/anti-inflammatory phenotype. Through experimental in vitro assays, we assessed the impact of allogeneic hCPC on the recruitment, functions and differentiation of monocytes. We found that allogeneic hCPC at steady state or under inflammatory conditions can incite CCL-2/CCR2-dependent recruitment of circulating CD14⁺CD16⁻ monocytes and fine-tune their activation toward an anti-inflammatory profile. Allogeneic hCPC also promoted CD14⁺CD16⁻ monocyte polarization into anti-inflammatory/immune-regulatory macrophages with high phagocytic capacity and IL10 secretion. Moreover, hCPC bended the differentiation of CD14⁺CD16⁻ monocytes to dendritic cells (DCs) toward anti-inflammatory macrophage-like features and impaired their antigen-presenting function in favor of immune-modulation. Collectively, our results demonstrate that allogeneic hCPC could reshape monocytes, macrophages as well as DCs responses by favoring their anti-inflammatory/tolerogenic activation/polarization. Thereby, therapeutic allogeneic hCPC might also contribute to post-infarct myocardial healing by modeling the activities of monocytes and their derived descendants.

Autophagy suppresses isoprenaline-induced M2 macrophage polarization via the ROS/ERK and mTOR signaling pathway

The objective of this study was to examine the effect of autophagy on stress-induced M2 macrophage polarization in the tumor microenvironment of breast cancer and to determine whether the underlying mechanism was related to the reactive oxygen species (ROS)/ERK and mTOR pathway. In vitro, we found that the basal autophagy level in mouse RAW 264.7 macrophages decreased with the incubation of tumor cell culture supernatant. Similarly, the polarization of RAW 264.7 to M2 macrophages was inhibited by the autophagy inducer rapamycin and increased by the autophagy inhibitor 3-MA or by siBeclin1. In addition, we found that not only was M2 molecule expression down-regulated but intracellular ROS generation was also blocked by autophagy induction. In vivo, we observed that mice that received an isoprenaline injection as a stress agent exhibited augmented implanted breast tumor growth, lung metastasis, intratumoral mRNA expression of M2 molecules and serum ROS generation. In contrast, the intratumoral expression of LC3-II and Beclin1 was decreased. In addition, we observed that isoprenaline induced the up-regulation of the intratumoral expression of phosphorylated mTOR, phosphorylated ERK1/2, phosphorylated Tyr705-STAT3 and HIF-1α, whereas rapamycin induced an opposite effect on the same molecules and could abolish the effects of isoprenaline. These results suggest that autophagy might suppress M2 macrophage polarization induced by isoprenaline via the ROS/ERK and mTOR signaling pathway. Our findings provide a theoretical basis for why high levels of stress hormones accelerate the progression of breast cancer, and autophagy may play a role in determining the outcomes of cancer therapy.