IL-4 dependent alternatively-activated macrophages have a distinctive in vivo gene expression phenotype

25-Hydroxycholesterol regulates lysosome AMP kinase activation and metabolic reprogramming to educate immunosuppressive macrophages

Macrophages are critical to turn noninflamed "cold tumors" into inflamed "hot tumors". Emerging evidence indicates abnormal cholesterol metabolites in the tumor microenvironment (TME) with unclear function. Here, we uncovered the inducible expression of cholesterol-25-hydroxylase (Ch25h) by interleukin-4 (IL-4) and interleukin-13 (IL-13) via the transcription factor STAT6, causing 25-hydroxycholesterol (25HC) accumulation. scRNA-seq analysis confirmed that CH25Hhi subsets were enriched in immunosuppressive macrophage subsets and correlated to lower survival rates in pan-cancers. Targeting CH25H abrogated macrophage immunosuppressive function to enhance infiltrating T cell numbers and activation, which synergized with anti-PD-1 to improve anti-tumor efficacy. Mechanically, lysosome-accumulated 25HC competed with cholesterol for GPR155 binding to inhibit the kinase mTORC1, leading to AMPKα activation and metabolic reprogramming. AMPKα also phosphorylated STAT6 Ser564 to enhance STAT6 activation and ARG1 production. Together, we propose CH25H as an immunometabolic checkpoint, which manipulates macrophage fate to reshape CD8+ T cell surveillance and anti-tumor response.

Axon guidance cue SEMA3A promotes the aggressive phenotype of basal-like PDAC

OBJECTIVE

The dysregulation of the axon guidance pathway is common in pancreatic ductal adenocarcinoma (PDAC), yet our understanding of its biological relevance is limited. Here, we investigated the functional role of the axon guidance cue SEMA3A in supporting PDAC progression.

DESIGN

We integrated bulk and single-cell transcriptomic datasets of human PDAC with in situ hybridisation analyses of patients' tissues to evaluate SEMA3A expression in molecular subtypes of PDAC. Gain and loss of function experiments in PDAC cell lines and organoids were performed to dissect how SEMA3A contributes to define a biologically aggressive phenotype.

RESULTS

In PDAC tissues, SEMA3A is expressed by stromal elements and selectively enriched in basal-like/squamous epithelial cells. Accordingly, expression of SEMA3A in PDAC cells is induced by both cell-intrinsic and cell-extrinsic determinants of the basal-like phenotype. In vitro, SEMA3A promotes cell migration as well as anoikis resistance. At the molecular level, these phenotypes are associated with increased focal adhesion kinase signalling through canonical SEMA3A-NRP1 axis. SEMA3A provides mouse PDAC cells with greater metastatic competence and favours intratumoural infiltration of tumour-associated macrophages and reduced density of T cells. Mechanistically, SEMA3A functions as chemoattractant for macrophages and skews their polarisation towards an M2-like phenotype. In SEMA3Ahigh tumours, depletion of macrophages results in greater intratumour infiltration by CD8+T cells and better control of the disease from antitumour treatment.

CONCLUSIONS

Here, we show that SEMA3A is a stress-sensitive locus that promotes the malignant phenotype of basal-like PDAC through both cell-intrinsic and cell-extrinsic mechanisms.

Dynamics of ex vivo cytokine transcription during experimental Toxocara canis infection in Balb/c mice

The cytokine microenvironment is crucial in generating and polarizing the immune response. A means of monitoring this environment would be of great value for better understanding Toxocara canis immune modulation. The aim of this study was to analyze the dynamics of cytokine transcription ex vivo, during early (24-48 hours) and late (15-30 days) times post-infection, in the mesenteric lymph nodes, spleen and intestinal mucosa of Balb/c mice experimentally infected with T. canis larvae. Mice in the treated group were infected with 100 third-stage larvae (L3), whereas mice in the control group were not infected. Analyses were performed at different times: 24-48 hours post-infection (HPI), 15-30 days post-infection (DPI). IL4, IL10, IL12 and Ym1 mRNA transcriptions were analyzed through qPCR. This study showed cytokine transcription mediated by migrating larvae in the mesenteric lymph nodes and spleen at 24-48 HPI, whereas cytokine transcription in the intestinal mucosa was observed only at late times (15-30 DPI). These results suggest that the T. canis larvae migration during infection might play a role in cytokine dynamics. Since the cytokine microenvironment is crucial in modulating immune response, knowledge of cytokine dynamics during T. canis infections pave the way to better understand its interaction with the host.

Eosinophils Are an Endogenous Source of Interleukin-4 during Filarial Infections and Contribute to the Development of an Optimal T Helper 2 Response

INTRODUCTION

Interleukin-4 (IL-4) is a central regulator of type 2 immunity, crucial for the defense against multicellular parasites like helminths. This study focuses on its roles and cellular sources during Litomosoides sigmodontis infection, a model for human filarial infections.

METHODS

Utilizing an IL-4 secretion assay, investigation into the sources of IL-4 during the progression of L. sigmodontis infection was conducted. The impact of eosinophils on the Th2 response was investigated through experiments involving dblGATA mice, which lack eosinophils and, consequently, eosinophil-derived IL-4.

RESULTS

The absence of eosinophils notably influenced Th2 polarization, leading to impaired production of type 2 cytokines. Interestingly, despite this eosinophil deficiency, macrophage polarization, proliferation, and antibody production remained unaffected.

CONCLUSION

Our research uncovers eosinophils as a major source of IL-4, especially during the early phase of filarial infection. Consequently, these findings shed new light on IL-4 dynamics and eosinophil effector functions in filarial infections.

Characterization of the immunosuppressive environment induced by larval Echinococcus granulosus during chronic experimental infection

The larval stage of Echinococcus granulosus causes the chronic infection known as cystic echinococcosis, deploying strong inhibitory mechanisms on host immune responses. Using experimental intraperitoneal infection in C57BL/6 mice, we carried out an in-depth analysis of the local changes in macrophage populations associated with chronic infection. In addition, we analyzed T cells and relevant soluble mediators. Infected animals showed an increase in local cell numbers, mostly accounted for by eosinophils, T cells, and macrophages. Within macrophage populations, the largest increases in cell numbers corresponded to resident large peritoneal macrophages (LPM). Monocyte recruitment appeared to be active, as judged by the increased number of monocytes and cells in the process of differentiation towards LPM, including small (SPM) and converting peritoneal macrophages (CPM). In contrast, we found no evidence of macrophage proliferation. Infection induced the expression of M2 markers in SPM, CPM, and LPM. It also enhanced the expression of the co-inhibitor PD-L1 in LPM, SPM, and CPM and induced the co-inhibitor PD-L2 in SPM and CPM. Therefore, local macrophages acquire M2-like phenotypes with probable suppressive capacities. Regarding T cells, infection induced an increase in the percentage of CD4+ cells that are PD-1+, which represent a potential target of suppression by PD-L1+/PD-L2+ macrophages. In possible agreement, CD4+ T cells from infected animals showed blunted proliferative responses to in vitro stimulation with anti-CD3. Further evidence of immune suppression in the parasite vicinity arose from the observation of an expansion in FoxP3+ CD4+ regulatory T cells and increases in the local concentrations of the anti-inflammatory cytokines TGF-β and IL-1Ra.

Macrophage polarization in spinal cord injury repair and the possible role of microRNAs: A review

The prevention, treatment, and rehabilitation of spinal cord injury (SCI) have always posed significant medical challenges. After mechanical injury, disturbances in microcirculation, edema formation, and the generation of free radicals lead to additional damage, impeding effective repair processes and potentially exacerbating further dysfunction. In this context, inflammatory responses, especially the activation of macrophages, play a pivotal role. Different phenotypes of macrophages have distinct effects on inflammation. Activation of classical macrophage cells (M1) promotes inflammation, while activation of alternative macrophage cells (M2) inhibits inflammation. The polarization of macrophages is crucial for disease healing. A non-coding RNA, known as microRNA (miRNA), governs the polarization of macrophages, thereby reducing inflammation following SCI and facilitating functional recovery. This study elucidates the inflammatory response to SCI, focusing on the infiltration of immune cells, specifically macrophages. It examines their phenotype and provides an explanation of their polarization mechanisms. Finally, this paper introduces several well-known miRNAs that contribute to macrophage polarization following SCI, including miR-155, miR-130a, and miR-27 for M1 polarization, as well as miR-22, miR-146a, miR-21, miR-124, miR-223, miR-93, miR-132, and miR-34a for M2 polarization. The emphasis is placed on their potential therapeutic role in SCI by modulating macrophage polarization, as well as the present developments and obstacles of miRNA clinical therapy.

The helminth TGF-β mimic TGM4 is a modular ligand that binds CD44, CD49d and TGF-β receptors to preferentially target myeloid cells

The murine helminth parasite Heligmosomoides polygyrus expresses a family of modular proteins which, replicating the functional activity of the immunomodulatory cytokine TGF-β, have been named TGM (TGF-β Μimic). Multiple domains bind to different receptors, including TGF-β receptors TβRI (ALK5) and TβRII through domains 1-3, and prototypic family member TGM1 binds the cell surface co-receptor CD44 through domains 4-5. This allows TGM1 to induce T lymphocyte Foxp3 expression, characteristic of regulatory (Treg) cells, and to activate a range of TGF-β-responsive cell types. In contrast, a related protein, TGM4, targets a much more restricted cell repertoire, primarily acting on myeloid cells, with less potent effects on T cells and lacking activity on other TGF-β-responsive cell types. TGM4 binds avidly to myeloid cells by flow cytometry, and can outcompete TGM1 for cell binding. Analysis of receptor binding in comparison to TGM1 reveals a 10-fold higher affinity than TGM1 for TGFβR-I (TβRI), but a 100-fold lower affinity for TβRII through Domain 3. Consequently, TGM4 is more dependent on co-receptor binding; in addition to CD44, TGM4 also engages CD49d (Itga4) through Domains 1-3, as well as CD206 and Neuropilin-1 through Domains 4 and 5. TGM4 was found to effectively modulate macrophage populations, inhibiting lipopolysaccharide-driven inflammatory cytokine production and boosting interleukin (IL)-4-stimulated responses such as Arginase-1 in vitro and in vivo. These results reveal that the modular nature of TGMs has allowed the fine tuning of the binding affinities of the TβR- and co-receptor binding domains to establish cell specificity for TGF-β signalling in a manner that cannot be attained by the mammalian cytokine.

Exposure to lung-migrating helminth protects against murine SARS-CoV-2 infection through macrophage-dependent T cell activation

Helminth endemic regions report lower COVID-19 morbidity and mortality. Here, we show that lung remodeling from a prior infection with a lung-migrating helminth, Nippostrongylus brasiliensis, enhances viral clearance and survival of human-ACE2 transgenic mice challenged with SARS-CoV-2 (SCV2). This protection is associated with a lymphocytic infiltrate, including increased accumulation of pulmonary SCV2-specific CD8+ T cells, and anti-CD8 antibody depletion abrogated the N. brasiliensis-mediated reduction in viral loads. Pulmonary macrophages with a type 2 transcriptional and epigenetic signature persist in the lungs of N. brasiliensis-exposed mice after clearance of the parasite and establish a primed environment for increased CD8+ T cell recruitment and activation. Accordingly, depletion of macrophages ablated the augmented viral clearance and accumulation of CD8+ T cells driven by prior N. brasiliensis infection. Together, these findings support the concept that lung-migrating helminths can limit disease severity during SCV2 infection through macrophage-dependent enhancement of antiviral CD8+ T cell responses.

M1/M2 macrophages and their overlaps - myth or reality?

Macrophages represent heterogeneous cell population with important roles in defence mechanisms and in homoeostasis. Tissue macrophages from diverse anatomical locations adopt distinct activation states. M1 and M2 macrophages are two polarized forms of mononuclear phagocyte in vitro differentiation with distinct phenotypic patterns and functional properties, but in vivo, there is a wide range of different macrophage phenotypes in between depending on the microenvironment and natural signals they receive. In human infections, pathogens use different strategies to combat macrophages and these strategies include shaping the macrophage polarization towards one or another phenotype. Macrophages infiltrating the tumours can affect the patient's prognosis. M2 macrophages have been shown to promote tumour growth, while M1 macrophages provide both tumour-promoting and anti-tumour properties. In autoimmune diseases, both prolonged M1 activation, as well as altered M2 function can contribute to their onset and activity. In human atherosclerotic lesions, macrophages expressing both M1 and M2 profiles have been detected as one of the potential factors affecting occurrence of cardiovascular diseases. In allergic inflammation, T2 cytokines drive macrophage polarization towards M2 profiles, which promote airway inflammation and remodelling. M1 macrophages in transplantations seem to contribute to acute rejection, while M2 macrophages promote the fibrosis of the graft. The view of pro-inflammatory M1 macrophages and M2 macrophages suppressing inflammation seems to be an oversimplification because these cells exploit very high level of plasticity and represent a large scale of different immunophenotypes with overlapping properties. In this respect, it would be more precise to describe macrophages as M1-like and M2-like.

The transcriptional control of the VEGFA-VEGFR1 (FLT1) axis in alternatively polarized murine and human macrophages

Introduction

Macrophages significantly contribute to the regulation of vessel formation under physiological and pathological conditions. Although the angiogenesis-regulating role of alternatively polarized macrophages is quite controversial, a growing number of evidence shows that they can participate in the later phases of angiogenesis, including vessel sprouting and remodeling or regression. However, the epigenetic and transcriptional regulatory mechanisms controlling this angiogenesis-modulating program are not fully understood.

Results

Here we show that IL-4 can coordinately regulate the VEGFA-VEGFR1 (FLT1) axis via simultaneously inhibiting the proangiogenic Vegfa and inducing the antiangiogenic Flt1 expression in murine bone marrow-derived macrophages, which leads to the attenuated proangiogenic activity of alternatively polarized macrophages. The IL-4-activated STAT6 and IL-4-STAT6 signaling pathway-induced EGR2 transcription factors play a direct role in the transcriptional regulation of the Vegfa-Flt1 axis. We demonstrated that this phenomenon is not restricted to the murine bone marrow-derived macrophages, but can also be observed in different murine tissue-resident macrophages ex vivo and parasites-elicited macrophages in vivo with minor cell type-specific differences. Furthermore, IL-4 exposure can modulate the hypoxic response of genes in both murine and human macrophages leading to a blunted Vegfa/VEGFA and synergistically induced Flt1/FLT1 expression.

Discussion

Our findings establish that the IL-4-activated epigenetic and transcriptional program can determine angiogenesis-regulating properties in alternatively polarized macrophages under normoxic and hypoxic conditions.

IL-4 and IL-13: Regulators and Effectors of Wound Repair

Type 2 immunity mediates protective responses to helminths and pathological responses to allergens, but it also has broad roles in the maintenance of tissue integrity, including wound repair. Type 2 cytokines are known to promote fibrosis, an overzealous repair response, but their contribution to healthy wound repair is less well understood. This review discusses the evidence that the canonical type 2 cytokines, IL-4 and IL-13, are integral to the tissue repair process through two main pathways. First, essential for the progression of effective tissue repair, IL-4 and IL-13 suppress the initial inflammatory response to injury. Second, these cytokines regulate how the extracellular matrix is modified, broken down, and rebuilt for effective repair. IL-4 and/or IL-13 amplifies multiple aspects of the tissue repair response, but many of these pathways are highly redundant and can be induced by other signals. Therefore, the exact contribution of IL-4Rα signaling remains difficult to unravel.

Effective Reversal of Macrophage Polarization by Inhibitory Combinations Predicted by a Boolean Protein–Protein Interaction Model

Background: The function and polarization of macrophages has a significant impact on the outcome of many diseases. Targeting tumor-associated macrophages (TAMs) is among the greatest challenges to solve because of the low in vitro reproducibility of the heterogeneous tumor microenvironment (TME). To create a more comprehensive model and to understand the inner workings of the macrophage and its dependence on extracellular signals driving polarization, we propose an in silico approach. Methods: A Boolean control network was built based on systematic manual curation of the scientific literature to model the early response events of macrophages by connecting extracellular signals (input) with gene transcription (output). The network consists of 106 nodes, classified as 9 input, 75 inner and 22 output nodes, that are connected by 217 edges. The direction and polarity of edges were manually verified and only included in the model if the literature plainly supported these parameters. Single or combinatory inhibitions were simulated mimicking therapeutic interventions, and output patterns were analyzed to interpret changes in polarization and cell function. Results: We show that inhibiting a single target is inadequate to modify an established polarization, and that in combination therapy, inhibiting numerous targets with individually small effects is frequently required. Our findings show the importance of JAK1, JAK3 and STAT6, and to a lesser extent STK4, Sp1 and Tyk2, in establishing an M1-like pro-inflammatory polarization, and NFAT5 in creating an anti-inflammatory M2-like phenotype. Conclusions: Here, we demonstrate a protein–protein interaction (PPI) network modeling the intracellular signalization driving macrophage polarization, offering the possibility of therapeutic repolarization and demonstrating evidence for multi-target methods.

Regulatory T-cells and IL-5 mediate pain outcomes in a preclinical model of chronic muscle pain

Fibromyalgia (FM) is a chronic musculoskeletal pain disorder primarily diagnosed in women. Historically, clinical literature focusing on cytokines and immune cells has been inconsistent. However, recent key studies show several layers of immune system dysfunction in FM. Preclinically, studies of the immune system have focused on monocytes with little focus on other immune cells. Importantly, T-cells are implicated in the development and resolution of chronic pain states, particularly in females. Our previous work showed that monocytes from women with FM produced more interleukin 5 (IL-5) and systemic treatment of IL-5 reversed mechanical hypersensitivity in a preclinical model of FM. Typically, IL-5 is produced by T_H2-cells, so in this study we assessed T-cell populations and cytokine production in female mice using the acid-induced chronic muscle pain model of FM before and after treatment with IL-5. Two unilateral injections of pH4.0 saline, five days apart, into the gastrocnemius muscle induce long-lasting widespread pain. We found that peripheral (blood) regulatory T_helper-cells (CD4⁺ FOXP3+) are downregulated in pH4.0-injected mice, with no differences in tissue (lymph nodes) or CD8⁺ T-cell populations. We tested the analgesic properties of IL-5 using a battery of spontaneous and evoked pain measures. Interestingly, IL-5 treatment induced place preference in mice previously injected with pH4.0 saline. Mice treated with IL-5 show limited changes in T-cell populations compared to controls, with a rescue in regulatory T-cells which positively correlates with improved mechanical hypersensitivity. The experiments in this study provide novel evidence that downregulation of regulatory T-cells play a role in chronic muscle pain pathology in the acidic saline model of FM and that IL-5 signaling is a promising target for future development of therapeutics.

Helminth exposure protects against murine SARS-CoV-2 infection through macrophage dependent T cell activation

Helminth endemic regions report lower COVID-19 morbidity and mortality. Here, we show that lung remodeling from a prior infection with a lung migrating helminth, Nippostrongylus brasiliensis , enhances viral clearance and survival of human-ACE2 transgenic mice challenged with SARS-CoV-2 (SCV2). This protection is associated with a lymphocytic infiltrate including an increased accumulation of pulmonary SCV2-specific CD8+ T cells and anti-CD8 antibody depletion abrogated the N. brasiliensis -mediated reduction in viral loads. Pulmonary macrophages with a type-2 transcriptional signature persist in the lungs of N. brasiliensis exposed mice after clearance of the parasite and establish a primed environment for increased antigen presentation. Accordingly, depletion of macrophages ablated the augmented viral clearance and accumulation of CD8+ T cells driven by prior N. brasiliensis infection. Together, these findings support the concept that lung migrating helminths can limit disease severity during SCV2 infection through macrophage-dependent enhancement of anti-viral CD8+ T cell responses.

Abstract Figure

An update on Ym1 and its immunoregulatory role in diseases

Ym1 is a rodent-specific chitinase-like protein (CLP) lacking catalytic activity, whose cellular origins are mainly macrophages, neutrophils and other cells. Although the detailed function of Ym1 remains poorly understood, Ym1 has been generally recognized as a fundamental feature of alternative activation of macrophages in mice and hence one of the prevalent detecting targets in macrophage phenotype distinguishment. Studies have pointed out that Ym1 may have regulatory effects, which are multifaceted and even contradictory, far more than just a mere marker. Allergic lung inflammation, parasite infection, autoimmune diseases, and central nervous system diseases have been found associations with Ym1 to varying degrees. Thus, insights into Ym1’s role in diseases would help us understand the pathogenesis of different diseases and clarify the genuine roles of CLPs in mammals. This review summarizes the information on Ym1 from the gene to its expression and regulation and focuses on the association between Ym1 and diseases.

Fungal-mediated lung allergic airway disease: The critical role of macrophages and dendritic cells

Fungi are abundant in the environment, causing our lungs to be constantly exposed to a diverse range of species. While the majority of these are cleared effectively in healthy individuals, constant exposure to spores (especially Aspergillus spp.) can lead to the development of allergic inflammation that underpins and worsen diseases such as asthma. Despite this, the precise mechanisms that underpin the development of fungal allergic disease are poorly understood. Innate immune cells, such as macrophages (MΦs) and dendritic cells (DCs), have been shown to be critical for mediating allergic inflammation to a range of different allergens. This review will focus on the crucial role of MΦ and DCs in mediating antifungal immunity, evaluating how these immune cells mediate allergic inflammation within the context of the lung environment. Ultimately, we aim to highlight important future research questions that will lead to novel therapeutic strategies for fungal allergic diseases.

Redefining inflammatory macrophage phenotypes across stages and tissues by single-cell transcriptomics

Single-cell transcriptomic data identifies major activation paths of monocyte-derived macrophages as a framework for inflammatory tissue macrophages.

The effect of short-chain fatty acids on M2 macrophages polarization in vitro and in vivo

Alternatively activated macrophages (M2 polarization) play an important role in asthma. Short-chain fatty acids (SCFAs) possessed immune-regulatory functions, but their effects on M2 polarization of alveolar macrophages and its underlying mechanisms are still unclear. In our study, murine alveolar macrophage MH-S cell line and human monocyte-derived macrophages were used to polarize to M2 subset with interleukin-4 (IL-4) treatment. The underlying mechanisms involved were investigated using molecule inhibitors/agonists. In vivo, female C57BL/6 mice were divided into five groups: CON group, ovalbumin (OVA) asthma group, OVA+Acetate group, OVA+Butyrate group, and OVA+Propionate group. Mice were fed with or without SCFAs (Acetate, Butyrate, Propionate) in drinking water for 20 days before developing OVA-induced asthma model. In MH-S, SCFAs inhibited IL-4-incuced protein or mRNA expressions of M2-associated genes in a dose-dependent manner. G-protein-coupled receptor 43 (GPR43) agonist 4-CMTB and histone deacetylase (HDAC) inhibitor (trichostatin A, TSA), but not GPR41 agonist AR420626 could inhibit the protein or mRNA expressions M2-associated genes. 4-CMTB, but not TSA, had no synergistic role in the inhibitory effect of SCFAs on M2 polarization. In vivo study indicated Butyrate and Propionate, but not Acetate, attenuated OVA-induced M2 polarization in the lung and airway inflammation. We also found the inhibitory effect of SCFAs on M2 polarization in human-derived macrophages. Therefore, SCFAs inhibited M2 polarization in MH-S likely through GPR43 activation and/or HDAC inhibition. Butyrate and Propionate but not Acetate could inhibit M2 polarization and airway inflammation in asthma model. SCFAs also abrogated M2 polarization in human-derived macrophages.

Acute and chronic immunomodulatory response mechanisms against Toxocara canis larvae infection in mice

Abstract The objective of this work was to evaluate the early and late immunological modulation of an experimental infection of T. canis larvae in mice. Mice were infected with 100 infective larvae and euthanized at different period: 24, 48 hours post infection (HPI), 15- and 30 days post infection (DPI). The humoral response was evaluated by indirect ELISA. Quantitative RT–PCR (qPCR) was used to quantify the mRNA transcription of cytokines IL4, IL10, IL12 and Ym1 in the early and late infection periods. Infection with T. canis was able to generate specific total IgG at 15- and 30- DPI. Analyzing the IgG isotype revealed a significant differentiation for IgG1 compared with IgG2a, IgG2b and IgG3, characterizing a Th-2 response. Evaluating the gene transcription at the early phase of infection, higher transcription levels of IL10, IL4 and Ym1 and a downregulation of IL12 were observed. By the late phase, increased transcription levels of IL4, Ym1 and IL12 were observed, and downregulation of IL-10 transcription was observed. The data obtained suggest that during experimental infection with T. canis, the participation of the IL4, IL10, IL12 cytokines and Ym1 can play an important role in T. canis immunomodulation.

Differences in Cell-Intrinsic Inflammatory Programs of Yolk Sac and Bone Marrow Macrophages

BACKGROUND

Tissue-resident macrophages have mixed developmental origins. They derive in variable extent from yolk sac (YS) hematopoiesis during embryonic development. Bone marrow (BM) hematopoietic progenitors give rise to tissue macrophages in postnatal life, and their contribution increases upon organ injury. Since the phenotype and functions of macrophages are modulated by the tissue of residence, the impact of their origin and developmental paths has remained incompletely understood.

METHODS

In order to decipher cell-intrinsic macrophage programs, we immortalized hematopoietic progenitors from YS and BM using conditional HoxB8, and carried out an in-depth functional and molecular analysis of differentiated macrophages.

RESULTS

While YS and BM macrophages demonstrate close similarities in terms of cellular growth, differentiation, cell death susceptibility and phagocytic properties, they display differences in cell metabolism, expression of inflammatory markers and inflammasome activation. Reduced abundance of PYCARD (ASC) and CASPASE-1 proteins in YS macrophages abrogated interleukin-1β production in response to canonical and non-canonical inflammasome activation.

CONCLUSIONS

Macrophage ontogeny is associated with distinct cellular programs and immune response. Our findings contribute to the understanding of the regulation and programming of macrophage functions.

CCR2 deficiency alters activation of microglia subsets in traumatic brain injury

In traumatic brain injury (TBI), a diversity of brain resident and peripherally derived myeloid cells have the potential to worsen damage and/or to assist in healing. We define the heterogeneity of microglia and macrophage phenotypes during TBI in wild-type (WT) mice and Ccr2^−/− mice, which lack macrophage influx following TBI and are resistant to brain damage. We use unbiased single-cell RNA sequencing methods to uncover 25 microglia, monocyte/macrophage, and dendritic cell subsets in acute TBI and normal brains. We find alterations in transcriptional profiles of microglia subsets in Ccr2^−/− TBI mice compared to WT TBI mice indicating that infiltrating monocytes/macrophages influence microglia activation to promote a type I IFN response. Preclinical pharmacological blockade of hCCR2 after injury reduces expression of IFN-responsive gene, Irf7, and improves outcomes. These data extend our understanding of myeloid cell diversity and crosstalk in brain trauma and identify therapeutic targets in myeloid subsets.

By single-cell RNA sequencing of traumatically injured and normal brains from wild-type and Ccr2^−/− mice, Somebang et al. define microglia, macrophage, and dendritic cell phenotypes in TBI. Targeting mouse and/or human CCR2 reduces specific TBI brain CNS myeloid compartments, dampens type I interferon responses, and improves cognition after TBI.

Trichuris muris infection drives cell-intrinsic IL4R alpha independent colonic RELMα+ macrophages

The intestinal nematode parasite Trichuris muris dwells in the caecum and proximal colon driving an acute resolving intestinal inflammation dominated by the presence of macrophages. Notably, these macrophages are characterised by their expression of RELMα during the resolution phase of the infection. The RELMα+ macrophage phenotype associates with the presence of alternatively activated macrophages and work in other model systems has demonstrated that the balance of classically and alternatively activated macrophages is critically important in enabling the resolution of inflammation. Moreover, in the context of type 2 immunity, RELMα+ alternatively activated macrophages are associated with the activation of macrophages via the IL4Rα. Despite a breadth of inflammatory pathologies associated with the large intestine, including those that accompany parasitic infection, it is not known how colonic macrophages are activated towards an alternatively activated phenotype. Here, we address this important knowledge gap by using Trichuris muris infection, in combination with transgenic mice (IL4Rαfl/fl.CX3CR1Cre) and IL4Rα-deficient/wild-type mixed bone marrow chimaeras. We make the unexpected finding that education of colonic macrophages towards a RELMα+, alternatively activated macrophage phenotype during T. muris infection does not require IL4Rα expression on macrophages. Further, this independence is maintained even when the mice are treated with an anti-IFNγ antibody during infection to create a strongly polarised Th2 environment. In contrast to RELMα, PD-L2 expression on macrophages post infection was dependent on IL4Rα signalling in the macrophages. These novel data sets are important, revealing a surprising cell-intrinsic IL4R alpha independence of the colonic RELMα+ alternatively activated macrophage during Trichuris muris infection.

Infection of mice with Trichuris muris, a whipworm parasite results in inflammation of the large intestine. Inflammation is temporary; once the parasite has been cleared, damage to the intestinal tissue heals. During inflammation white blood cells move in to the gut tissue. These cells are dominated by a cell type called the macrophage. Macrophages which accumulate in the intestine post-infection express a protein called RELMα. These RELMα-expressing macrophages are thought to help resolve inflammation and have traditionally been associated with IL-4 and IL-13-driven activation. We set out to determine whether the macrophages which emerge during T. muris infection need to respond to IL-4 and/or IL-13 in order to express RELMα. We did this by creating a transgenic mouse where the common IL4Rα chain of the IL-4 and IL-13 receptor was absent from macrophages. To our surprise, macrophages were able to express RELMα regardless of whether the macrophage could or could not respond to IL-14/IL-13. This new knowledge is important as in some inflammatory conditions, treatments seeking to encourage alternatively activated macrophages have been proposed. Such treatments require an understanding of both the important and the redundant signals as well as recognition that activating signals may be disparate in different tissue environments.

Revisiting the Mechanisms of Immune Evasion Employed by Human Parasites

For the establishment of a successful infection, i.e., long-term parasitism and a complete life cycle, parasites use various diverse mechanisms and factors, which they may be inherently bestowed with, or may acquire from the natural vector biting the host at the infection prelude, or may take over from the infecting host, to outmaneuver, evade, overcome, and/or suppress the host immunity, both innately and adaptively. This narrative review summarizes the up-to-date strategies exploited by a number of representative human parasites (protozoa and helminths) to counteract the target host immune defense. The revisited information should be useful for designing diagnostics and therapeutics as well as vaccines against the respective parasitic infections.

Anti-F4/80 treatment attenuates Th2 cell responses: Implications for the role of lung interstitial macrophages in the asthmatic mice

Lung interstitial macrophages (IMs) can be polarized towards an alternative activation phenotype in ovalbumin (OVA)-induced asthmatic mice. However, the role of alternative activation of lung IMs in Th2 cell responses in the asthmatic murine is still unclear. Here, we leverage an anti-F4/80 treatment which has been shown to selectively deplete IMs in mice and investigate how this treatment modulates Th2 cell responses in lung and whether the modulation is dependent on lung IMs in murine models of asthma. We show that anti-F4/80 treatment alleviates Th2 cell responses in mice immunized and challenged with OVA or house dust mite (HDM). The anti-F4/80 treatment does not target lung alveolar macrophages (AMs) in OVA-induced asthmatic mice or impact the abundance of other immune cell types, including B cells, T cells, and NK cells in wild-type mice. However, this treatment does inhibit the expression of polarized markers of alternatively activated macrophages, including arginase-1, Ym-1, and Fizz-1 in the lung tissues from OVA-induced asthmatic mice. Furthermore, we find that the inhibitory effects of anti-F4/80 treatment on Th2 cell responses can be reversed upon adoptive transfer of lung IMs. Taken together, our data show that anti-F4/80 treatment attenuates Th2 cell responses, which is at least partially related to depletion of lung IMs in murine models of asthma. This suggests that targeted lung IMs may provide a potential therapeutic protocol for the treatment of asthmatics.

Resistin: A journey from metabolism to cancer

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Resistin levels have been associated with several pathological disorders such as metabolic disorders, cancers etc.

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Resistin exists in three isoforms namely RELM-α, β and γ.

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High resistin level activates inflammatory pathways, promotes metabolic disorders and is associated with carcinogenesis.

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Increase in the resistin level impairs the therapeutic response by inducing stemness or resistance, in cancer cells.

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Conventional drugs which alter resistin level could have therapeutic implications in several pathological disorders.

Resistin, a small secretory molecule, has been implicated to play an important role in the development of insulin resistance under obese condition. For the past few decades, it has been linked to various cellular and metabolic functions. It has been associated with diseases like metabolic disorders, cardiovascular diseases and cancers. Numerous clinical studies have indicated an increased serum resistin level in pathological disorders which have been reported to increase mortality rate in comparison to low resistin expressing subjects. Various molecular studies suggest resistin plays a pivotal role in proliferation, metastasis, angiogenesis, inflammation as well as in regulating metabolism in cancer cells. Therefore, understanding the role of resistin and elucidating its’ associated molecular mechanism will give a better insight into the management of these disorders. In this article, we summarize the diverse roles of resistin in pathological disorders based on the available literature, clinicopathological data, and a compiled study from various databases. The article mainly provides comprehensive information of its role as a target in different treatment modalities in pre as well as post-clinical studies.

Comparative Transcriptomics of IBD Patients Indicates Induction of Type 2 Immunity Irrespective of the Disease Ideotype

Inflammatory cytokines initiate and sustain the perpetuation of processes leading to chronic inflammatory conditions such as inflammatory bowel diseases (IBD). The nature of the trigger causing an inflammatory reaction decides whether type 1, type 17, or type 2 immune responses, typically characterized by the respective T- helper cell subsets, come into effect. In the intestine, Type 2 responses have been linked with mucosal healing and resolution upon an immune challenge involving parasitic infections. However, type 2 cytokines are frequently elevated in certain types of IBD in particular ulcerative colitis (UC) leading to the assumption that Th2 cells might critically support the pathogenesis of UC raising the question of whether such elevated type 2 responses in IBD are beneficial or detrimental. In line with this, previous studies showed that suppression of IL-13 and other type 2 related molecules in murine models could improve the outcomes of intestinal inflammation. However, therapeutic attempts of neutralizing IL-13 in ulcerative colitis patients have yielded no benefits. Thus, a better understanding of the role of type 2 cytokines in regulating intestinal inflammation is required. Here, we took a comparative transcriptomic approach to address how Th2 responses evolve in different mouse models of colitis and human IBD datasets. Our data show that type 2 immune-related transcripts are induced in the inflamed gut of IBD patients in both Crohn's disease and UC and across widely used mouse models of IBD. Collectively our data implicate that the presence of a type 2 signature rather defines a distinct state of intestinal inflammation than a disease-specific pathomechanism.

Dermal bacterial LPS-stimulation reduces susceptibility to intradermal Trypanosoma brucei infection

Infections with Trypanosoma brucei sp. are established after the injection of metacyclic trypomastigotes into the skin dermis by the tsetse fly vector. The parasites then gain access to the local lymphatic vessels to infect the local draining lymph nodes and disseminate systemically via the bloodstream. Macrophages are considered to play an important role in host protection during the early stage of systemic trypanosome infections. Macrophages are abundant in the skin dermis, but relatively little is known of their impact on susceptibility to intradermal (ID) trypanosome infections. We show that although dermal injection of colony stimulating factor 1 (CSF1) increased the local abundance of macrophages in the skin, this did not affect susceptibility to ID T. brucei infection. However, bacterial LPS-stimulation in the dermis prior to ID trypanosome infection significantly reduced disease susceptibility. In vitro assays showed that LPS-stimulated macrophage-like RAW264.7 cells had enhanced cytotoxicity towards T. brucei, implying that dermal LPS-treatment may similarly enhance the ability of dermal macrophages to eliminate ID injected T. brucei parasites in the skin. A thorough understanding of the factors that reduce susceptibility to ID injected T. brucei infections may lead to the development of novel strategies to help reduce the transmission of African trypanosomes.

Azithromycin alleviates systemic lupus erythematosus via the promotion of M2 polarisation in lupus mice

Our previous study demonstrated that azithromycin could promote alternatively activated (M2) macrophages under lupus conditions in vitro, which might be beneficial for lupus treatment. Thus, the aim of this study was to further confirm whether azithromycin can drive M2 polarisation in lupus and ultimately alleviate systemic lupus erythematosus (SLE) in vivo. Lymphocyte-derived DNA (ALD-DNA)-induced mice (induced lupus model) and MRL-Fas^lpr mice (spontaneous lupus model) were both used in the experiment. First, we observed symptoms of lupus by assessing the levels of serum anti-dsDNA antibodies and serum creatinine and renal pathology. We found that both murine models showed increased levels of serum anti-dsDNA antibodies and creatinine, enhanced glomerular fibrosis and cell infiltration, basement membrane thickening and elevated IgG deposition. After azithromycin treatment, all these medical indexes were alleviated, and kidney damage was effectively reversed. Next, macrophage polarisation was assessed in the spleen and kidneys. Macrophage infiltration in the spleen was notably decreased after azithromycin treatment in both murine models, with a remarkably elevated proportion of M2 macrophages. In addition, the expression of interleukin (IL)-1, IL-6, tumour necrosis factor (TNF)-α, inducible nitric oxide synthase (iNOS), CD86, toll-like receptor (TLR)2 and TLR4 was extremely downregulated, while the expression of transforming growth factor (TGF)-β, arginase-1 (Arg-1), chitinase-like 3 (Ym-1), found in inflammatory zone (Fizz-1) and mannose receptor (CD206) was significantly upregulated in the kidneys after azithromycin treatment. Taken together, our results indicated for the first time that azithromycin could alleviate lupus by promoting M2 polarisation in vivo. These findings exploited the newly discovered potential of azithromycin, a conventional drug with verified safety, affordability and global availability, which could be a novel treat-to-target strategy for SLE via macrophage modulation.

M-CSF, IL-6, and TGF-β promote generation of a new subset of tissue repair macrophage for traumatic brain injury recovery

Traumatic brain injury (TBI) leads to high mortality rate. We aimed to identify the key cytokines favoring TBI repair and found that patients with TBI with a better outcome robustly increased concentrations of macrophage colony-stimulating factor, interleukin-6, and transforming growth factor-β (termed M6T) in cerebrospinal fluid or plasma. Using TBI mice, we identified that M2-like macrophage, microglia, and endothelial cell were major sources to produce M6T. Together with the in vivo tracking of mCherry+ macrophages in zebrafish models, we confirmed that M6T treatment accelerated blood-borne macrophage infiltration and polarization toward a subset of tissue repair macrophages that expressed similar genes as microglia for neuroprotection, angiogenesis and cell migration. M6T therapy in TBI mice and zebrafish improved neurological function while blocking M6T-exacerbated brain injury. Considering low concentrations of M6T in some patients with poor prognostic, M6T treatment might repair TBI via generating a previously unidentified subset of tissue repair macrophages.

Integration of IL-2 and IL-4 signals coordinates divergent regulatory T cell responses and drives therapeutic efficacy

Cells exist within complex milieus of communicating factors, such as cytokines, that combine to generate context-specific responses, yet nearly all knowledge about the function of each cytokine and the signaling propagated downstream of their recognition is based on the response to individual cytokines. Here, we found that regulatory T cells (Tregs) integrate concurrent signaling initiated by IL-2 and IL-4 to generate a response divergent from the sum of the two pathways in isolation. IL-4 stimulation of STAT6 phosphorylation was blocked by IL-2, while IL-2 and IL-4 synergized to enhance STAT5 phosphorylation, IL-10 production, and the selective proliferation of IL-10-producing Tregs, leading to increased inhibition of conventional T cell activation and the reversal of asthma and multiple sclerosis in mice. These data define a mechanism of combinatorial cytokine signaling and lay the foundation upon which to better understand the origins of cytokine pleiotropy while informing improved the clinical use of cytokines.

Lung toxicity and gene expression changes in response to whole-body inhalation exposure to cellulose nanocrystal in rats

OBJECTIVE

Human exposure to cellulose nanocrystal (CNC) is possible during the production and/or use of products containing CNC. The objectives of the current study were to determine the lung toxicity of CNC and the underlying molecular mechanisms of the toxicity.

METHODS

Rats were exposed to air or CNC (20 mg/m3, six hours/day, 14 d) by whole-body inhalation and lung toxicity and global gene expression profile were determined.

RESULTS

Significant increases in lactate dehydrogenase activity, pro-inflammatory cytokine levels, phagocyte oxidant production, and macrophage and neutrophil counts were detected in the bronchoalveolar lavage cells or fluid from the CNC exposed rats. Mild lung histological changes, such as the accumulation of macrophages and neutrophils, were detected in the CNC exposed rats. Gene expression profiling by next generation sequencing identified 531 genes whose expressions were significantly different in the lungs of the CNC exposed rats, compared with the controls. Bioinformatic analysis of the lung gene expression data identified significant enrichment in several biological functions and canonical pathways including those related to inflammation (cellular movement, immune cell trafficking, inflammatory diseases and response, respiratory disease, complement system, acute phase response, leukocyte extravasation signaling, granulocyte and agranulocyte adhesion and diapedesis, IL-10 signaling, and phagosome formation and maturation) and oxidative stress (NRF2-mediated oxidative stress response, production of nitric oxide and reactive oxygen species in macrophages, and free radical scavenging).

CONCLUSION

Our data demonstrated that inhalation exposure of rats to CNC resulted in lung toxicity mediated mainly through the induction of inflammation and oxidative stress.

TRPV4 Plays a Role in Matrix Stiffness-Induced Macrophage Polarization

Phenotypic polarization of macrophages is deemed essential in innate immunity and various pathophysiological conditions. We have now determined key aspects of the molecular mechanism by which mechanical cues regulate macrophage polarization. We show that Transient Receptor Potential Vanilloid 4 (TRPV4), a mechanosensitive ion channel, mediates substrate stiffness-induced macrophage polarization. Using atomic force microscopy, we showed that genetic ablation of TRPV4 function abrogated fibrosis-induced matrix stiffness generation in skin tissues. We have determined that stiffer skin tissue promotes the M1 macrophage subtype in a TRPV4-dependent manner; soft tissue does not. These findings were further validated by our in vitro results which showed that stiff matrix (50 kPa) alone increased expression of macrophage M1 markers in a TRPV4-dependent manner, and this response was further augmented by the addition of soluble factors; neither of which occurred with soft matrix (1 kPa). A direct requirement for TRPV4 in M1 macrophage polarization spectrum in response to increased stiffness was evident from results of gain-of-function assays, where reintroduction of TRPV4 significantly upregulated the expression of M1 markers in TRPV4 KO macrophages. Together, these data provide new insights regarding the role of TRPV4 in matrix stiffness-induced macrophage polarization spectrum that may be explored in tissue engineering and regenerative medicine and targeted therapeutics.

CCR2 deficiency in monocytes impairs angiogenesis and functional recovery after ischemic stroke in mice

Inflammatory Ly6C^hiCCR2⁺ monocytes infiltrate the brain after stroke but their functions are not entirely clear. We report that CCR2⁺ monocytes and CCR2⁺ lymphocytes infiltrate the brain after permanent ischemia. To underscore the role of CCR2⁺ monocytes, we generated mice with selective CCR2 deletion in monocytes. One day post-ischemia, these mice showed less infiltrating monocytes and reduced expression of pro-inflammatory cytokines, markers of alternatively macrophage activation, and angiogenesis. Accordingly, Ly6C^hi monocytes sorted from the brain of wild type mice 24 h post-ischemia expressed pro-inflammatory genes, M2 genes, and pro-angiogenic genes. Flow cytometry showed heterogeneous phenotypes within the infiltrating Ly6C^hiCCR2⁺ monocytes, including a subgroup of Arginase-1⁺ cells. Mice with CCR2-deficient monocytes displayed a delayed inflammatory rebound 15 days post-ischemia that was not found in wild type mice. Furthermore, they showed reduced angiogenesis and worse behavioral performance. Administration of CCR2^+/+ bone-marrow monocytes to mice with CCR2-deficient monocytes did not improve the behavioral performance suggesting that immature bone-marrow monocytes lack pro-reparative functions. The results show that CCR2⁺ monocytes contribute to acute post-ischemic inflammation and participate in functional recovery. The study unravels heterogeneity in the population of CCR2⁺ monocytes infiltrating the ischemic brain and suggests that pro-reparative monocyte subsets promote functional recovery after ischemic stroke.

Distinct macrophage populations and phenotypes associated with IL-4 mediated immunomodulation at the host implant interface

The host macrophage response to implants has shown to be affected by tissue location and physio-pathological conditions of the patient. Success in immunomodulatory strategies is thus predicated on the proper understanding of the macrophage populations participating on each one of these contexts. The present study uses an in vivo implantation model to analyze how immunomodulation via an IL-4 eluting implant affects distinct macrophage populations at the tissue-implant interface and how this may affect downstream regenerative processes. Populations identified as F4/80+, CD68+ and CD11b+ macrophages at the peri-implant space showed distinct susceptibility to polarize towards an M2-like phenotype under the effects of delivered IL-4. Also, the presence of the coating resulted in a significant reduction in F4/80+ macrophages, while other populations remained unchanged. These results suggests that the F4/80+ macrophage population may be predominant in the early stages of the host response at the surface of these implants, in contrast to CD11b+ macrophage populations which were either fewer in number or located more distant from the implant surface. Gene expression assays showed increased proteolytic activity and diminished matrix deposition as possible mechanisms explaining the decreased fibrotic capsule deposition and improved peri-implant tissue quality shown in previous studies using IL-4 eluting coatings. The pattern of M2-like gene expression promoted by IL-4 was correlated with glycosaminoglycan production within the site of implantation at early stages of the host response, suggesting a significant role in this response. These findings demonstrate that immunomodulatory strategies can be utilized to design and implement targeted delivery for improving biomaterial performance.

Trichinella spiralis Thioredoxin Peroxidase 2 Regulates Protective Th2 Immune Response in Mice by Directly Inducing Alternatively Activated Macrophages

Trichinella infection can induce macrophages into the alternatively activated phenotype, which is primarily associated with the development of a polarized Th2 immune response. In the present study, we examined the immunomodulatory effect of T. spiralis thioredoxin peroxidase-2 (TsTPX2), a protein derived from T. spiralis ES products, in the regulation of Th2 response through direct activation of macrophages. The location of TsTPX2 was detected by immunohistochemistry and immunofluorescence analyses. The immune response in vivo induced by rTsTPX2 was characterized by analyzing the Th2 cytokines and Th1 cytokines in the peripheral blood. The rTsTPX2-activated macrophages (M_rTsTPX2) were tested for polarization, their ability to evoke naïve CD4⁺ T cells, and resistance to the larval infection after adoptive transfer in BALB/c mice. The immunolocalization analysis showed TsTPX2 in cuticles and stichosome of T. spiralis ML. The immunostaining was detected in cuticles and stichosome of T. spiralis Ad3 and ML, as well as in tissue-dwellings around ML after the intestines and muscle tissues of infected mice were incubated with anti-rTsTPX2 antibody. Immunization of BALB/c mice with rTsTPX2 could induce a Th1-suppressing mixed immune response given the increased levels of Th2 cytokines (IL-4 and IL-10) production along with the decreased levels of Th1 cytokines (IFN-γ, IL-12, and TNF-α). In vitro studies showed that rTsTPX2 could directly drive RAW264.7 and peritoneal macrophages to the M2 phenotype. Moreover, M_rTsTPX2 could promote CD4⁺ T cells polarized into Th2 type in vitro. Adoptive transfer of M_rTsTPX2 into mice suppressed Th1 responses by enhancing Th2 responses and exhibited a 44.7% reduction in adult worm burden following challenge with T. spiralis infective larval, suggesting that the TsTPX2 is a potential vaccine candidate against trichinosis. Our study showed that TsTPX2 would be at least one of the molecules to switch macrophages into the M2 phenotype during T. spiralis infection, which provides a new therapeutic approach to various inflammatory disorders like allergies or autoimmune diseases.

Ontogeny of arterial macrophages defines their functions in homeostasis and inflammation

Arterial macrophages have different developmental origins, but the association of macrophage ontogeny with their phenotypes and functions in adulthood is still unclear. Here, we combine macrophage fate-mapping analysis with single-cell RNA sequencing to establish their cellular identity during homeostasis, and in response to angiotensin-II (AngII)-induced arterial inflammation. Yolk sac erythro-myeloid progenitors (EMP) contribute substantially to adventitial macrophages and give rise to a defined cluster of resident immune cells with homeostatic functions that is stable in adult mice, but declines in numbers during ageing and is not replenished by bone marrow (BM)-derived macrophages. In response to AngII inflammation, increase in adventitial macrophages is driven by recruitment of BM monocytes, while EMP-derived macrophages proliferate locally and provide a distinct transcriptional response that is linked to tissue regeneration. Our findings thus contribute to the understanding of macrophage heterogeneity, and associate macrophage ontogeny with distinct functions in health and disease.

Arterial macrophages develop from either yolk sac or bone marrow progenitors. Here, the author show that ageing-induced reduction of arterial macrophages is not replenished by bone marrow-derived cells, but under inflammatory conditions circulating monocytes are recruited to maintain homeostasis, while arterial macrophages of yolk sac origin carry out tissue repair.

Assessment of para-inflammation in a wound healing model

A thorough understanding of the inflammatory process has substantial biological and clinical relevance. Para-inflammation has been described as an adaptive response of the immune system to low levels of tissue stress. However, the role of para-inflammation in wound repair requires further investigation. In the present study, the expression levels of several para-inflammation genes were assessed in a murine cutaneous wound healing model. The results revealed that the expression levels of the para-inflammation genes were significantly altered. Among the genes that were examined, the expression levels of solute carrier family 7 member 11 (Slc7a11) paralleled those of the M2 macrophage-associated genes. Further investigation indicated that the Slc7a11 gene and its encoded protein cystine/glutamate transporter exhibited increased expression levels in IL-4-induced M2 macrophages. Notably, the inhibition of para-inflammation by sulindac prolonged wound healing process. The present study indicated that para-inflammation exhibited a protective effect in wound healing and provided new insight for host tissue repair.

The Network of Colonic Host Defense Peptides as an Innate Immune Defense Against Enteropathogenic Bacteria

Host defense peptides, abundantly secreted by colonic epithelial cells and leukocytes, are proposed to be critical components of an innate immune response in the colon against enteropathogenic bacteria, including Shigella spp., Salmonella spp., Clostridium difficile, and attaching and effacing Escherichia coli and Citrobacter rodentium. These short cationic peptides are bactericidal against both Gram-positive and -negative enteric pathogens, but may also exert killing effects on intestinal luminal microbiota. Simultaneously, these peptides modulate numerous cellular responses crucial for gut defenses, including leukocyte chemotaxis and migration, wound healing, cytokine production, cell proliferation, and pathogen sensing. This review discusses recent advances in our understanding of expression, mechanisms of action and microbicidal and immunomodulatory functions of major colonic host defense peptides, namely cathelicidins, β-defensins, and members of the Regenerating islet-derived protein III (RegIII) and Resistin-like molecule (RELM) families. In a theoretical framework where these peptides work synergistically, aspects of pathogenesis of infectious colitis reviewed herein uncover roles of host defense peptides aimed to promote epithelial defenses and prevent pathogen colonization, mediated through a combination of direct antimicrobial function and fine-tuning of host immune response and inflammation. This interactive host defense peptide network may decode how the intestinal immune system functions to quickly clear infections, restore homeostasis and avoid damaging inflammation associated with pathogen persistence during infectious colitis. This information is of interest in development of host defense peptides (either alone or in combination with reduced doses of antibiotics) as antimicrobial and immunomodulatory therapeutics for controlling infectious colitis.

RELMα-expressing macrophages protect against fatal lung damage and reduce parasite burden during helminth infection

Alternatively activated macrophages (AAMs) can contribute to wound healing, regulation of glucose and fat metabolism, resolution of inflammation, and protective immunity against helminths. Their differentiation, tissue distribution, and effector functions are incompletely understood. Murine AAMs express high levels of resistin-like molecule (RELM) α, an effector protein with potent immunomodulatory functions. To visualize RELMα⁺ macrophages (MΦs) in vivo and evaluate their role in defense against helminths, we generated RELMα reporter/deleter mice. Infection with the helminth Nippostrongylus brasiliensis induced expansion of RELMα⁺ lung interstitial but not alveolar MΦs in a STAT6-dependent manner. RELMα⁺ MΦs were required for prevention of fatal lung damage during primary infection. Furthermore, protective immunity was lost upon specific deletion of RELMα⁺ MΦs during secondary infection. Thus, RELMα reporter/deleter mice reveal compartmentalization of AAMs in different tissues and demonstrate their critical role in resolution of severe lung inflammation and protection against migrating helminths.

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.

The immune response of inbred laboratory mice to Litomosoides sigmodontis: A route to discovery in myeloid cell biology

Litomosoides sigmodontis is the only filarial nematode where the full life cycle, from larval delivery to the skin through to circulating microfilaria, can be completed in immunocompetent laboratory mice. It is thus an invaluable tool for the study of filariasis. It has been used for the study of novel anti‐helminthic therapeutics, the development of vaccines against filariasis, the development of immunomodulatory drugs for the treatment of inflammatory disease and the study of basic immune responses to filarial nematodes. This review will focus on the latter and aims to summarize how the L sigmodontis model has advanced our basic understanding of immune responses to helminths, led to major discoveries in macrophage biology and provided new insights into the immunological functions of the pleural cavity. Finally, and most importantly L sigmodontis represents a suitable platform to study how host genotype affects immune responses, with the potential for further discovery in myeloid cell biology and beyond.

Antibiotics induce sustained dysregulation of intestinal T cell immunity by perturbing macrophage homeostasis

Macrophages in the healthy intestine are highly specialized and usually respond to the gut microbiota without provoking an inflammatory response. A breakdown in this tolerance leads to inflammatory bowel disease (IBD), but the mechanisms by which intestinal macrophages normally become conditioned to promote microbial tolerance are unclear. Strong epidemiological evidence linking disruption of the gut microbiota by antibiotic use early in life to IBD indicates an important role for the gut microbiota in modulating intestinal immunity. Here, we show that antibiotic use causes intestinal macrophages to become hyperresponsive to bacterial stimulation, producing excess inflammatory cytokines. Re-exposure of antibiotic-treated mice to conventional microbiota induced a long-term, macrophage-dependent increase in inflammatory T helper 1 (T_H1) responses in the colon and sustained dysbiosis. The consequences of this dysregulated macrophage activity for T cell function were demonstrated by increased susceptibility to infections requiring T_H17 and T_H2 responses for clearance (bacterial Citrobacter rodentium and helminth Trichuris muris infections), corresponding with increased inflammation. Short-chain fatty acids (SCFAs) were depleted during antibiotic administration; supplementation of antibiotics with the SCFA butyrate restored the characteristic hyporesponsiveness of intestinal macrophages and prevented T cell dysfunction. Butyrate altered the metabolic behavior of macrophages to increase oxidative phosphorylation and also promoted alternative macrophage activation. In summary, the gut microbiota is essential to maintain macrophage-dependent intestinal immune homeostasis, mediated by SCFA-dependent pathways. Oral antibiotics disrupt this process to promote sustained T cell-mediated dysfunction and increased susceptibility to infections, highlighting important implications of repeated broad-spectrum antibiotic use.

Metabolic Programming of Macrophages: Implications in the Pathogenesis of Granulomatous Disease

Metabolic reprogramming is rapidly gaining appreciation in the etiology of immune cell dysfunction in a variety of diseases. Tuberculosis, schistosomiasis, and sarcoidosis represent an important class of diseases characterized by the formation of granulomas, where macrophages are causatively implicated in disease pathogenesis. Recent studies support the incidence of macrophage metabolic reprogramming in granulomas of both infectious and non-infectious origin. These publications identify the mechanistic target of rapamycin (mTOR), as well as the major regulators of lipid metabolism and cellular energy balance, peroxisome proliferator receptor gamma (PPAR-γ) and adenosine monophosphate-activated protein kinase (AMPK), respectively, as key players in the pathological progression of granulomas. In this review, we present a comprehensive breakdown of emerging research on the link between macrophage cell metabolism and granulomas of different etiology, and how parallels can be drawn between different forms of granulomatous disease. In particular, we discuss the role of PPAR-γ signaling and lipid metabolism, which are currently the best-represented metabolic pathways in this context, and we highlight dysregulated lipid metabolism as a common denominator in granulomatous disease progression. This review therefore aims to highlight metabolic mechanisms of granuloma immune cell fate and open up research questions for the identification of potential therapeutic targets in the future.

Fra-2-expressing macrophages promote lung fibrosis in mice

Idiopathic Pulmonary Fibrosis (IPF) is a deadly disease with limited therapies. Tissue fibrosis is associated with Type 2 immune response, although the causal contribution of immune cells is not defined. The AP-1 transcription factor Fra-2 is upregulated in IPF lung sections and Fra-2 transgenic mice (Fra-2tg) exhibit spontaneous lung fibrosis. Here we show that Bleomycin-induced lung fibrosis is attenuated upon myeloid-inactivation of Fra-2 and aggravated in Fra-2tg bone marrow chimeras. Type VI collagen (ColVI), a Fra-2 transcriptional target, is up-regulated in three lung fibrosis models, and macrophages promote myofibroblast activation in vitro in a ColVI- and Fra-2-dependent manner. Fra-2 or ColVI inactivation does not affect macrophage recruitment and alternative activation, suggesting that Fra-2/ColVI specifically controls the paracrine pro-fibrotic activity of macrophages. Importantly, ColVI knock-out mice (KO) and ColVI-KO bone marrow chimeras are protected from Bleomycin-induced lung fibrosis. Therapeutic administration of a Fra-2/AP-1 inhibitor reduces ColVI expression and ameliorates fibrosis in Fra-2tg mice and in the Bleomycin model. Finally, Fra-2 and ColVI positively correlate in IPF patient samples and co-localize in lung macrophages. Therefore, the Fra-2/ColVI pro-fibrotic axis is a promising biomarker and therapeutic target for lung fibrosis, and possibly other fibrotic diseases.

MicroRNAs as Molecular Switches in Macrophage Activation

The efficacy of macrophage- mediated inflammatory response relies on the coordinated expression of key factors, which expression is finely regulated at both transcriptional and post-transcriptional level. Several studies have provided compelling evidence that microRNAs play pivotal roles in modulating macrophage activation, polarization, tissue infiltration, and resolution of inflammation. In this review, we highlight the essential molecular mechanisms underlying the different phases of inflammation that are targeted by microRNAs to inhibit or accelerate restoration to tissue integrity and homeostasis. We further review the impact of microRNA-dependent regulation of tumor-associated macrophages and the relative implication for tumor biology.

Role of NADPH oxidase-2 in the progression of the inflammatory response secondary to striatum excitotoxic damage

Background

During excitotoxic damage, neuronal death results from the increase in intracellular calcium, the induction of oxidative stress, and a subsequent inflammatory response. NADPH oxidases (NOX) are relevant sources of reactive oxygen species (ROS) during excitotoxic damage. NADPH oxidase-2 (NOX-2) has been particularly related to neuronal damage and death, as well as to the resolution of the subsequent inflammatory response. As ROS are crucial components of the regulation of inflammatory response, in this work, we evaluated the role of NOX-2 in the progression of inflammation resulting from glutamate-induced excitotoxic damage of the striatum in an in vivo model.

Methods

The striata of wild-type C57BL/6 J and NOX-2 KO mice (gp91^Cybbtm1Din/J) were stereotactically injected with monosodium glutamate either alone or in combination with IL-4 or IL-10. The damage was evaluated in histological sections stained with cresyl violet and Fluoro-Jade B. The enzymatic activity of caspase-3 and NOX were also measured. Additionally, the cytokine profile was identified by ELISA and motor activity was verified by the tests of the cylinder, the adhesive tape removal, and the inverted grid.

Results

Our results show a neuroprotective effect in mice with a genetic inhibition of NOX-2, which is partially due to a differential response to excitotoxic damage, characterized by the production of anti-inflammatory cytokines. In NOX-2 KO animals, the excitotoxic condition increased the production of interleukin-4, which could contribute to the production of interleukin-10 that decreased neuronal apoptotic death and the magnitude of striatal injury. Treatment with interleukin-4 and interleukin-10 protected from excitotoxic damage in wild-type animals.

Conclusions

The release of proinflammatory cytokines during the excitotoxic event promotes an additional apoptotic death of neurons that survived the initial damage. During the subsequent inflammatory response to excitotoxic damage, ROS generated by NOX-2 play a decisive role in the extension of the lesion and consequently in the severity of the functional compromise, probably by regulating the anti-inflammatory cytokines production.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1478-4) contains supplementary material, which is available to authorized users.

Inflammatory monocytes are detrimental to the host immune response during acute infection with Cryptococcus neoformans

Cryptococcus neoformans is a leading cause of invasive fungal infections among immunocompromised patients. However, the cellular constituents of the innate immune response that promote clearance versus progression of infection upon respiratory acquisition of C. neoformans remain poorly defined. In this study, we found that during acute C. neoformans infection, CCR2⁺ Ly6C^hi inflammatory monocytes (IM) rapidly infiltrate the lungs and mediate fungal trafficking to lung-draining lymph nodes. Interestingly, this influx of IM is detrimental to the host, since ablating IM or impairing their recruitment to the lungs improves murine survival and reduces fungal proliferation and dissemination. Using a novel conditional gene deletion strategy, we determined that MHC class II expression by IM did not mediate their deleterious impact on the host. Furthermore, although ablation of IM reduced the number of lymphocytes, innate lymphoid cells, and eosinophils in the lungs, the effects of IM were not dependent on these cells. We ascertained that IM in the lungs upregulated transcripts associated with alternatively activated (M2) macrophages in response to C. neoformans, consistent with the model that IM assume a cellular phenotype that is permissive for fungal growth. We also determined that conditional knockout of the prototypical M2 marker arginase 1 in IM and deletion of the M2-associated transcription factor STAT6 were not sufficient to reverse the harmful effects of IM. Overall, our findings indicate that C. neoformans can subvert the fungicidal potential of IM to enable the progression of infection through a mechanism that is not dependent on lymphocyte priming, eosinophil recruitment, or downstream M2 macrophage polarization pathways. These results give us new insight into the plasticity of IM function during fungal infections and the level of control that C. neoformans can exert on host immune responses.

Cryptococcus neoformans is a fungus that is prevalent throughout the environment and can cause a fatal infection of the central nervous system when inhaled into the lungs by patients with impaired immune systems. Our understanding of the immune responses that either help clear C. neoformans from the lungs or permit development of disease remains limited. In this study, we used a mouse model of lethal C. neoformans infection to determine that inflammatory monocytes, immune cells that are often among the first responders to infections, actually facilitate the progression of infection rather than clearance. These findings establish a foundation for future work to target the immune response of inflammatory monocytes as a strategy to improve the outcomes of patients that develop C. neoformans infections.

CCL2/MCP-1 signaling drives extracellular matrix turnover by diverse macrophage subsets

Macrophage plasticity, cellular origin, and phenotypic heterogeneity are perpetual challenges for studies addressing the biology of this pivotal immune cell in development, homeostasis, and tissue remodeling/repair. Consequently, a myriad of macrophage subtypes has been described in these contexts. To facilitate the identification of functional macrophage subtypes in vivo, here we used a flow cytometry-based assay that allows for detailed phenotyping of macrophages engaged in extracellular matrix (ECM) degradation. Of the five macrophage subtypes identified in the remodeling dermis by using this assay, collagen degradation was primarily executed by Ly6C⁻CCR2⁺ and Ly6C⁻CCR2^low macrophages via mannose receptor-dependent collagen endocytosis, while Ly6C⁺CCR2⁺ macrophages were the dominant fibrin-endocytosing cells. Unexpectedly, the CCL2/MCP1-CCR2 signaling axis was critical for both collagen and fibrin degradation, while collagen degradation was independent of IL-4Ra signaling. Furthermore, the cytokine GM-CSF selectively enhanced collagen degradation by Ly6C⁺CCR2⁺ macrophages. This study reveals distinct subsets of macrophages engaged in ECM turnover and identifies novel wound healing-associated functions for CCL2 and GM-CSF inflammatory cytokines.

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Phenotypically diverse subsets of dermal macrophages undertake the degradation of extracellular matrix

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C-C motif chemokine Ligand 2 (CCL2) signaling is critical for macrophage-mediated endocytosis of collagen and fibrin.

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Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) and Interleukin (IL)-13 stimulate collagen endocytosis.

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The wound healing-associated IL4-IL4 Receptor a (IL4Ra) signaling is dispensable for collagen endocytosis by macrophages.

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The mannose receptor is the principal endocytic collagen receptor utilized by resident dermal macrophages.

Cross-Domain and Viral Interactions in the Microbiome

The importance of the microbiome to human health is increasingly recognized and has become a major focus of recent research. However, much of the work has focused on a few aspects, particularly the bacterial component of the microbiome, most frequently in the gastrointestinal tract. Yet humans and other animals can be colonized by a wide array of organisms spanning all domains of life, including bacteria and archaea, unicellular eukaryotes such as fungi, multicellular eukaryotes such as helminths, and viruses. As they share the same host niches, they can compete with, synergize with, and antagonize each other, with potential impacts on their host. Here, we discuss these major groups making up the human microbiome, with a focus on how they interact with each other and their multicellular host.