Local macrophage proliferation, rather than recruitment from the blood, is a signature of TH2 inflammation

SENP1-Sirt3 signaling promotes α-ketoglutarate production during M2 macrophage polarization

The metabolic program is altered during macrophage activation and influences macrophage polarization. Glutaminolysis promotes accumulation of α-ketoglutarate (αKG), leading to Jumonji domain-containing protein D3 (Jmjd3)-dependent demethylation at H3K27me3 during M2 polarization of macrophages. However, it remains unclear how αKG accumulation is regulated during M2 polarization of macrophages. This study shows that SENP1-Sirt3 signaling controls glutaminolysis, leading to αKG accumulation during IL-4-stimulated M2 polarization. Activation of the SENP1-Sirt3 axis augments M2 macrophage polarization through the accumulation of αKG via glutaminolysis. We also identify glutamate dehydrogenase 1 (GLUD1) as an acetylated protein in mitochondria. The SENP1-Sirt3 axis deacetylates GLUD1 and increases its activity in glutaminolysis to promote αKG production, leading to M2 polarization of macrophages. Therefore, SENP1-Sirt3 signaling plays a critical role in αKG accumulation via glutaminolysis to promote M2 polarization.

Targeted Accumulation of Macrophages Induced by Microbeam Irradiation in a Tissue-Dependent Manner

Radiation therapy (RT) is a vital component of multimodal cancer treatment, and its immunomodulatory effects are a major focus of current therapeutic strategies. Macrophages are some of the first cells recruited to sites of radiation-induced injury where they can aid in tissue repair, propagate radiation-induced fibrogenesis and influence tumour dynamics. Microbeam radiation therapy (MRT) is a unique, spatially fractionated radiation modality that has demonstrated exceptional tumour control and reduction in normal tissue toxicity, including fibrosis. We conducted a morphological analysis of MRT-irradiated normal liver, lung and skin tissues as well as lung and melanoma tumours. MRT induced distinct patterns of DNA damage, reflecting the geometry of the microbeam array. Macrophages infiltrated these regions of peak dose deposition at variable timepoints post-irradiation depending on the tissue type. In normal liver and lung tissue, macrophages clearly demarcated the beam path by 48 h and 7 days post-irradiation, respectively. This was not reflected, however, in normal skin tissue, despite clear DNA damage marking the beam path. Persistent DNA damage was observed in MRT-irradiated lung carcinoma, with an accompanying geometry-specific influx of mixed M1/M2-like macrophage populations. These data indicate the unique potential of MRT as a tool to induce a remarkable accumulation of macrophages in an organ/tissue-specific manner. Further characterization of these macrophage populations is warranted to identify their organ-specific roles in normal tissue sparing and anti-tumour responses.

The interaction between nanoparticles and immune system: application in the treatment of inflammatory diseases

Nanoparticle (NP) is an emerging tool applied in the biomedical field. With combination of different materials and adjustment of their physical and chemical properties, nanoparticles can have diverse effects on the organism and may change the treating paradigm of multiple diseases in the future. More and more results show that nanoparticles can function as immunomodulators and some formulas have been approved for the treatment of inflammation-related diseases. However, our current understanding of the mechanisms that nanoparticles can influence immune responses is still limited, and systemic clinical trials are necessary for the evaluation of their security and long-term effects. This review provides an overview of the recent advances in nanoparticles that can interact with different cellular and molecular components of the immune system and their application in the management of inflammatory diseases, which are caused by abnormal immune reactions. This article focuses on the mechanisms of interaction between nanoparticles and the immune system and tries to provide a reference for the future design of nanotechnology for the treatment of inflammatory diseases.

Adoptive transfer of metabolically reprogrammed macrophages for atherosclerosis treatment in diabetic ApoE−/- mice

Atherosclerosis is characterized by inflammation in the arterial wall, which is known to be exacerbated by diabetes. Therapeutic repression of inflammation is a promising strategy for treating atherosclerosis. In this study, we showed that diabetes aggravated atherosclerosis in apolipoproteinE knockout (ApoE^−/-) mice, in which increased expression of long-chain acyl-CoA synthetase 1 (Acsl1) in macrophages played an important role. Knockdown of Acsl1 in macrophages (Mφ^shAcsl1) reprogrammed macrophages to an anti-inflammatory phenotype, especially under hyperglycemic conditions. Injection of Mφ^shAcsl1 reprogrammed macrophages into streptozotocin (STZ)-induced diabetic ApoE^−/- mice (ApoE^−/-+ STZ) alleviated inflammation locally in the plaque, liver and spleen. Consistent with the reduction in inflammation, plaques became smaller and more stable after the adoptive transfer of reprogrammed macrophages. Taken together, our findings indicate that increased Acsl1 expression in macrophages play a key role in aggravated atherosclerosis of diabetic mice, possibly by promoting inflammation. Adoptive transfer of Acsl1 silenced macrophages may serve as a potential therapeutic strategy for atherosclerosis.

1

Increased Acsl1 in macrophages is responsible for the exacerbated inflammation in diabetes

2

Mφ^shAcsl1 is characterized as anti-inflammatory phenotype

3

Adoptive transfer of Mφ^shAcsl1 alleviates atherosclerosis in diabetic ApoE^−/- mice

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Mφ^shAcsl1 inhibits both local and systemic inflammation in vivo

Helminth resistance is mediated by differential activation of recruited monocyte-derived alveolar macrophages and arginine depletion

Macrophages are known to mediate anti-helminth responses, but it remains uncertain which subsets are involved or how macrophages actually kill helminths. Here, we show rapid monocyte recruitment to the lung after infection with the nematode parasite Nippostrongylus brasiliensis. In this inflamed tissue microenvironment, these monocytes differentiate into an alveolar macrophage (AM)-like phenotype, expressing both SiglecF and CD11c, surround invading parasitic larvae, and preferentially kill parasites in vitro. Monocyte-derived AMs (Mo-AMs) express type 2-associated markers and show a distinct remodeling of the chromatin landscape relative to tissue-derived AMs (TD-AMs). In particular, they express high amounts of arginase-1 (Arg1), which we demonstrate mediates helminth killing through L-arginine depletion. These studies indicate that recruited monocytes are selectively programmed in the pulmonary environment to express AM markers and an anti-helminth phenotype.

Low-Dose Lung Radiation Therapy for COVID-19 Lung Disease: A Preclinical Efficacy Study in a Bleomycin Model of Pneumonitis

PURPOSE

Low-dose whole lung radiation therapy (LDLR) has been proposed as a treatment for patients with acute respiratory distress syndrome associated with SARS-CoV-2 infection, and clinical trials are underway. There is an urgent need for preclinical evidence to justify this approach and inform dose, scheduling, and mechanisms of action.

METHODS AND MATERIALS

Female C57BL/6 mice were treated with intranasal bleomycin sulfate (7.5 or 11.25 units/kg, day 0) and then exposed to whole lung radiation therapy (0.5, 1.0, or 1.5 Gy, or sham; day 3). Bodyweight was measured daily, and lung tissue was harvested for histology and flow cytometry on day 10. Computed tomography lung imaging was performed before radiation (day 3) and pre-endpoint (day 10).

RESULTS

Bleomycin caused pneumonitis of variable severity, which correlated with weight loss. LDLR at 1.0 Gy was associated with a significant increase in the proportion of mice recovering to 98% of initial bodyweight, and a proportion of these mice exhibited less severe histopathologic lung changes. Mice experiencing moderate initial weight loss were more likely to respond to LDLR than those experiencing severe initial weight loss. In addition, LDLR (1.0 Gy) significantly reduced bleomycin-induced increases in interstitial macrophages, CD103+ dendritic cells (DCs), and neutrophil-DC hybrids. Overall, bleomycin-treated mice exhibited significantly higher percentages of nonaerated lung in left than right lungs, and LDLR (1.0 Gy) limited further reductions in aerated lung volume in right but not left lungs. LDLR at 0.5 and 1.5 Gy did not improve bodyweight, flow cytometric, or radiologic readouts of bleomycin-induced pneumonitis.

CONCLUSIONS

Our data support the concept that LDLR can ameliorate acute inflammatory lung injury, identify 1.0 Gy as the most effective dose, and provide evidence that it is more effective in the context of moderate than severe pneumonitis. Mechanistically, LDLR at 1.0 Gy significantly suppressed bleomycin-induced accumulation of pulmonary interstitial macrophages, CD103+ DCs, and neutrophil-DC hybrids.

Tissue-resident immunity in the lung: a first-line defense at the environmental interface

The lung is a vital organ that incessantly faces external environmental challenges. Its homeostasis and unimpeded vital function are ensured by the respiratory epithelium working hand in hand with an intricate fine-tuned tissue-resident immune cell network. Lung tissue-resident immune cells span across the innate and adaptive immunity and protect from infectious agents but can also prove to be pathogenic if dysregulated. Here, we review the innate and adaptive immune cell subtypes comprising lung-resident immunity and discuss their ontogeny and role in distinct respiratory diseases. An improved understanding of the role of lung-resident immunity and how its function is dysregulated under pathological conditions can shed light on the pathogenesis of respiratory diseases.

Transcriptional and Histochemical Signatures of Bone Marrow Mononuclear Cell-Mediated Resolution of Synovitis

Osteoarthritis (OA) may result from impaired ability of synovial macrophages to resolve joint inflammation. Increasing macrophage counts in inflamed joints through injection with bone marrow mononuclear cells (BMNC) induces lasting resolution of synovial inflammation. To uncover mechanisms by which BMNC may affect resolution, in this study, differential transcriptional signatures of BMNC in response to normal (SF) and inflamed synovial fluid (ISF) were analyzed. We demonstrate the temporal behavior of co-expressed gene networks associated with traits from related in vivo and in vitro studies. We also identified activated and inhibited signaling pathways and upstream regulators, further determining their protein expression in the synovium of inflamed joints treated with BMNC or DPBS controls. BMNC responded to ISF with an early pro-inflammatory response characterized by a short spike in the expression of a NF-ƙB- and mitogen-related gene network. This response was associated with sustained increased expression of two gene networks comprising known drivers of resolution (IL-10, IGF-1, PPARG, isoprenoid biosynthesis). These networks were common to SF and ISF, but more highly expressed in ISF. Most highly activated pathways in ISF included the mevalonate pathway and PPAR-γ signaling, with pro-resolving functional annotations that improve mitochondrial metabolism and deactivate NF-ƙB signaling. Lower expression of mevalonate kinase and phospho-PPARγ in synovium from inflamed joints treated with BMNC, and equivalent IL-1β staining between BMNC- and DPBS-treated joints, associates with accomplished resolution in BMNC-treated joints and emphasize the intricate balance of pro- and anti-inflammatory mechanisms required for resolution. Combined, our data suggest that BMNC-mediated resolution is characterized by constitutively expressed homeostatic mechanisms, whose expression are enhanced following inflammatory stimulus. These mechanisms translate into macrophage proliferation optimizing their capacity to counteract inflammatory damage and improving their general and mitochondrial metabolism to endure oxidative stress while driving tissue repair. Such effect is largely achieved through the synthesis of several lipids that mediate recovery of homeostasis. Our study reveals candidate mechanisms by which BMNC provide lasting improvement in patients with OA and suggests further investigation on the effects of PPAR-γ signaling enhancement for the treatment of arthritic conditions.

Hematopoietic Stem Cell Requirement for Macrophage Regeneration Is Tissue Specific

Tissue-resident macrophages (TRMΦ) are important immune sentinels responsible for maintaining tissue and immune homeostasis within their specific niche. Recently, the origins of TRMΦ have undergone intense scrutiny, in which now most TRMΦ are thought to originate early during embryonic development independent of hematopoietic stem cells (HSCs). We previously characterized two distinct subsets of mouse peritoneal cavity macrophages (MΦ) (large and small peritoneal MΦ) whose origins and relationship to both fetal and adult long-term (LT) HSCs have not been fully investigated. In this study, we employ highly purified LT-HSC transplantation and in vivo lineage tracing to show a dual ontogeny for large and small peritoneal MΦ, in which the initial wave of peritoneal MΦ is seeded from yolk sac-derived precursors, which later require LT-HSCs for regeneration. In contrast, transplanted fetal and adult LT-HSCs are not able to regenerate brain-resident microglia. Thus, we demonstrate that LT-HSCs retain the potential to develop into TRMΦ, but their requirement is tissue specific in the peritoneum and brain.

Macrophage plasticity in Duchenne muscular dystrophy: a nexus of pathological remodelling with therapeutic implications

Duchenne muscular dystrophy (DMD) is characterized by chronic skeletal muscle necrosis, leading to muscle regeneration failure and fibrosis. Although macrophages (MPs) are normally essential for muscle regeneration, dysregulated MP function promotes pathological muscle remodelling. Infiltrating MPs can be predominantly pro-inflammatory (M1 biased), anti-inflammatory (M2 biased) or of a mixed phenotype and can originate from the adult bone marrow (monocyte dependent) or embryonic precursors (monocyte independent). In mdx mice (genetic model of DMD) lacking either Toll-like receptor (Tlr) 2 or Tlr4, it is found that MP infiltration of dystrophic muscle is significantly reduced and that the MP phenotype is shifted toward a more anti-inflammatory profile. This is accompanied by significant improvements in muscle histology and force production. Lack of the chemokine receptor CCR2, which impedes monocyte release from the bone marrow, leads to similar beneficial effects in mdx mice. Evidence was also found for Tlr4-regulated induction of trained innate immunity in MPs cultured from the bone marrow of mdx mice before their entry into the muscle. These MPs exhibit epigenetic and metabolic alterations, accompanied by non-specific hyper-responsiveness to multiple stimuli, which is manifested by potentiated upregulation of both pro- and anti-inflammatory genes. In summary, exaggerated recruitment of monocyte-derived MPs and signs of trained innate immunity at the level of the bone marrow are features of the immunophenotype associated with dystrophic muscle disease. These phenomena are regulated by Toll-like receptors that bind endogenous damage-associated molecular pattern (DAMP) molecules, suggesting that DAMP release from dystrophic muscles modulates MP plasticity at the bone marrow level through Toll-like receptor-driven mechanisms.

Efferocytosis induces macrophage proliferation to help resolve tissue injury

Apoptotic cell clearance by macrophages (efferocytosis) promotes resolution signaling pathways, which can be triggered by molecules derived from the phagolysosomal degradation of apoptotic cells. We show here that nucleotides derived from the hydrolysis of apoptotic cell DNA by phagolysosomal DNase2a activate a DNA-PKcs-mTORC2/Rictor pathway that increases Myc to promote non-inflammatory macrophage proliferation. Efferocytosis-induced proliferation expands the pool of resolving macrophages in vitro and in mice, including zymosan-induced peritonitis, dexamethasone-induced thymocyte apoptosis, and atherosclerosis regression. In the dexamethasone-thymus model, hematopoietic Rictor deletion blocked efferocytosing macrophage proliferation, apoptotic cell clearance, and tissue resolution. In atherosclerosis regression, silencing macrophage Rictor or DNase2a blocked efferocyte proliferation, apoptotic cell clearance, and plaque stabilization. In view of previous work showing that other types of apoptotic cell cargo can promote resolution in individual efferocytosing macrophages, the findings here suggest that signaling-triggered apoptotic cell-derived nucleotides can amplify this benefit by increasing the number of these macrophages.

Mitochondrial metabolism coordinates stage-specific repair processes in macrophages during wound healing

Wound healing is a coordinated process that initially relies on pro-inflammatory macrophages, followed by a pro-resolution function of these cells. Changes in cellular metabolism likely dictate these distinct activities, but the nature of these changes has been unclear. Here, we profiled early- versus late-stage skin wound macrophages in mice at both the transcriptional and functional levels. We found that glycolytic metabolism in the early phase is not sufficient to ensure productive repair. Instead, by combining conditional disruption of the electron transport chain with deletion of mitochondrial aspartyl-tRNA synthetase, followed by single-cell sequencing analysis, we found that a subpopulation of early-stage wound macrophages are marked by mitochondrial ROS (mtROS) production and HIF1α stabilization, which ultimately drives a pro-angiogenic program essential for timely healing. In contrast, late-phase, pro-resolving wound macrophages are marked by IL-4Rα-mediated mitochondrial respiration and mitohormesis. Collectively, we identify changes in mitochondrial metabolism as a critical control mechanism for macrophage effector functions during wound healing.

Human filariasis-contributions of the Litomosoides sigmodontis and Acanthocheilonema viteae animal model

Filariae are vector-borne parasitic nematodes that are endemic worldwide, in tropical and subtropical regions. Important human filariae spp. include Onchocerca volvulus, Wuchereria bancrofti and Brugia spp., and Loa loa and Mansonella spp. causing onchocerciasis (river blindness), lymphatic filariasis (lymphedema and hydrocele), loiasis (eye worm), and mansonelliasis, respectively. It is estimated that over 1 billion individuals live in endemic regions where filarial diseases are a public health concern contributing to significant disability adjusted life years (DALYs). Thus, efforts to control and eliminate filarial diseases were already launched by the WHO in the 1970s, especially against lymphatic filariasis and onchocerciasis, and are mainly based on mass drug administration (MDA) of microfilaricidal drugs (ivermectin, diethylcarbamazine, albendazole) to filarial endemic areas accompanied with vector control strategies with the goal to reduce the transmission. With the United Nations Sustainable Development Goals (SDGs), it was decided to eliminate transmission of onchocerciasis and stop lymphatic filariasis as a public health problem by 2030. It was also requested that novel drugs and treatment strategies be developed. Mouse models provide an important platform for anti-filarial drug research in a preclinical setting. This review presents an overview about the Litomosoides sigmodontis and Acanthocheilonema viteae filarial mouse models and their role in immunological research as well as preclinical studies about novel anti-filarial drugs and treatment strategies.

IL-33: A central cytokine in helminth infections

IL-33 is an alarmin cytokine which has been implicated in allergy, fibrosis, inflammation, tumorigenesis, metabolism, and homeostasis. However, amongst its strongest roles are in helminth infections, where IL-33 usually (but not always) is central to induction of an effective anti-parasitic immune response. In this review, we will summarise the literature around this fascinating cytokine, its activity on immune and non-immune cells, the unique (and sometimes counterintuitive) responses it induces, and how it can coordinate the immune response during infections by parasitic helminths. Finally, we will summarise some of the ways that parasites have developed to modulate the IL-33 pathway for their own benefit.

Analysis of the Influence of Jaw Periosteal Cells on Macrophages Phenotype Using an Innovative Horizontal Coculture System

Jaw periosteum-derived mesenchymal stem cells (JPCs) represent a promising cell source for bone tissue engineering in oral and maxillofacial surgery due to their high osteogenic potential and good accessibility. Our previous work demonstrated that JPCs are able to regulate THP-1-derived macrophage polarization in a direct coculture model. In the present study, we used an innovative horizontal coculture system in order to understand the underlying paracrine effects of JPCs on macrophage phenotype polarization. Therefore, JPCs and THP-1-derived M1/M2 macrophages were cocultured in parallel chambers under the same conditions. After five days of horizontal coculture, flow cytometric, gene and protein expression analyses revealed inhibitory effects on costimulatory and proinflammatory molecules/factors as well as activating effects on anti-inflammatory factors in M1 macrophages, originating from multiple cytokines/chemokines released by untreated and osteogenically induced JPCs. A flow cytometric assessment of DNA synthesis reflected significantly decreased numbers of proliferating M1/M2 cells when cocultured with JPCs. In this study, we demonstrated that untreated and osteogenically induced JPCs are able to switch macrophage polarization from a classical M1 to an alternative M2-specific phenotype by paracrine secretion, and by inhibition of THP-1-derived M1/M2 macrophage proliferation.

Macrophage regulation & function in helminth infection

Macrophages are innate immune cells with essential roles in host defense, inflammation, immune regulation and repair. During infection with multicellular helminth parasites, macrophages contribute to pathogen trapping and killing as well as to tissue repair and the resolution of type 2 inflammation. Macrophages produce a broad repertoire of effector molecules, including enzymes, cytokines, chemokines and growth factors that govern anti-helminth immunity and repair of parasite-induced tissue damage. Helminth infection and the associated type 2 immune response induces an alternatively activated macrophage (AAM) phenotype that - beyond driving host defense - prevents aberrant Th2 cell activation and type 2 immunopathology. The immune regulatory potential of macrophages is exploited by helminth parasites that induce the production of anti-inflammatory mediators such as interleukin 10 or prostaglandin E₂ to evade host immunity. Here, we summarize current insights into the mechanisms of macrophage-mediated host defense and repair during helminth infection and highlight recent progress on the immune regulatory crosstalk between macrophages and helminth parasites. We also point out important remaining questions such as the translation of findings from murine models to human settings of helminth infection as well as long-term consequences of helminth-induced macrophage reprogramming for subsequent host immunity.

Myeloid Cell-Specific IL-4 Receptor Knockout Partially Protects from Adipose Tissue Inflammation

IL-4 receptor signaling is supposed to play a major role in anti-inflammatory polarization and proliferation of adipose tissue macrophages. In this study, we examined the metabolic and inflammatory phenotype of C57BL/6J mice (IIl4ra) with LysM-dependent knockout (IIl4ra ^Δmyel) of the IL-4 receptor α-chain (IL-4Rα), the mandatory signaling component of IL-4 and IL-13, on chow and high-fat diet. Lean IIl4ra ^Δmyel mice showed decreased insulin sensitivity, no divergent adipose tissue macrophage polarization, but an increased percentage of CD8⁺ T cells in visceral adipose tissue. After 20 wk of a high-fat diet, IIl4ra ^Δmyel mice exhibited higher glucose tolerance, no changes in the lymphocyte compartment and fewer M1 macrophages in visceral adipose tissue. In vivo adipose tissue macrophage proliferation measured by BrdU incorporation was unaffected by Il4ra knockout. Interestingly, we show that IL-4Rα signaling directly augmented Itgax (Cd11c) gene expression in bone marrow-derived macrophages and increased the amount of CD11c⁺ macrophages in adipose tissue explants. Myeloid cell-specific knockout of Il4ra deteriorated insulin sensitivity in lean mice but improved parameters of glucose homeostasis and partially protected from adipose tissue inflammation in obese mice. Hence, IL-4Rα signaling probably plays a minor role in maintaining the macrophage M2 population and proliferation rates in vivo. Moreover, our data indicate that IL-4 signaling plays a proinflammatory role in adipose tissue inflammation by directly upregulating CD11c on adipose tissue macrophages.

Loss of Diacylglycerol Kinase α Enhances Macrophage Responsiveness

The diacylglycerol kinases (DGKs) are a family of enzymes responsible for the conversion of diacylglycerol (DAG) to phosphatidic acid (PA). In addition to their primary function in lipid metabolism, DGKs have recently been identified as potential therapeutic targets in multiple cancers, including glioblastoma (GBM) and melanoma. Aside from its tumorigenic properties, DGKα is also a known promoter of T-cell anergy, supporting a role as a recently-recognized T cell checkpoint. In fact, the only significant phenotype previously observed in Dgka knockout (KO) mice is the enhancement of T-cell activity. Herein we reveal a novel, macrophage-specific, immune-regulatory function of DGKα. In bone marrow-derived macrophages (BMDMs) cultured from wild-type (WT) and KO mice, we observed increased responsiveness of KO macrophages to diverse stimuli that yield different phenotypes, including LPS, IL-4, and the chemoattractant MCP-1. Knockdown (KD) of Dgka in a murine macrophage cell line resulted in similar increased responsiveness. Demonstrating in vivo relevance, we observed significantly smaller wounds in Dgka-/- mice with full-thickness cutaneous burns, a complex wound healing process in which macrophages play a key role. The burned area also demonstrated increased numbers of macrophages. In a cortical stab wound model, Dgka-/- brains show increased Iba1+ cell numbers at the needle track versus that in WT brains. Taken together, these findings identify a novel immune-regulatory checkpoint function of DGKα in macrophages with potential implications for wound healing, cancer therapy, and other settings.

Implantable blood clot loaded with BMP-2 for regulation of osteoimmunology and enhancement of bone repair

The treatment of large-area bone defects still faces many difficulties and challenges. Here, we developed a blood clot delivery platform loaded with BMP-2 protein (BMP-2@BC) for enhanced bone regeneration. Blood clot gel platform as natural biomaterials can be engineered from autologous blood. Once implanted into the large bone defect site, it can be used for BMP-2 local delivery, as well as modulating osteoimmunology by recruiting a great number of macrophages and regulating their polarization at different stages. Moreover, due to the deep-red color of blood clot gel, mild localized hyperthermia under laser irradiation further accelerated bone repair and regeneration. We find that the immune niche within the bone defect microenvironment can be modulated in a controllable manner by the blood clots implantation and laser treatment. We further demonstrate that the newly formed bone covered almost 95% of the skull defect area by our strategy in both mice and rat disease models. Due to the great biocompatibility, photothermal potential, and osteoimmunomodulation capacity, such technology shows great promise to be used in further clinical translation.

Precision-porous polyurethane elastomers engineered for application in pro-healing vascular grafts: Synthesis, fabrication and detailed biocompatibility assessment

Unmet needs for small diameter, non-biologic vascular grafts and the less-than-ideal performance of medium diameter grafts suggest opportunities for major improvements. Biomaterials that are mechanically matched to native blood vessels, reduce the foreign body capsule (FBC) and demonstrate improved integration and healing are expected to improve graft performance. In this study, we developed biostable, crosslinked polyurethane formulations and used them to fabricate scaffolds with precision-engineered 40 μm pores. We matched the scaffold mechanical properties with those of native blood vessels by optimizing the polyurethane compositions. We hypothesized that such scaffolds promote healing and mitigate the FBC. To test our hypothesis, polyurethanes with 40 μm pores, 100 μm pores, and non-porous slabs were implanted subcutaneously in mice for 3 weeks, and then were examined histologically. Our results show that 40 μm porous scaffolds elicit the highest level of angiogenesis, cellularization, and the least severe foreign body capsule (based on a refined assessment method). This study presents the first biomaterial with tuned mechanical properties and a precision engineered porous structure optimized for healing, thus can be ideal for pro-healing vascular grafts and in situ vascular engineering. In addition, these scaffolds may have wide applications in tissue engineering, drug delivery, and implantable device.

The Role of PPAR-γ in Allergic Disease

PURPOSE OF REVIEW

The incidence of allergic diseases such as asthma, rhinitis and atopic dermatitis has risen at an alarming rate over the last century. Thus, there is a clear need to understand the critical factors that drive such pathologic immune responses. Peroxisome proliferator-activated receptor-γ (PPAR-γ) is a nuclear receptor that has emerged as an important regulator of multiple cell types involved in the inflammatory response to allergens; from airway epithelial cells to T Helper (TH) cells.

RECENT FINDINGS

Initial studies suggested that agonists of PPAR-γ could be employed to temper allergic inflammation, suppressing pro-inflammatory gene expression programs in epithelial cells. Several lines of work now suggest that PPAR-γ plays an essential in promoting 'type 2' immune responses that are typically associated with allergic disease. PPAR-γ has been found to promote the functions of TH2 cells, type 2 innate lymphoid cells, M2 macrophages and dendritic cells, regulating lipid metabolism and directly inducing effector gene expression. Moreover, preclinical models of allergy in gene-targeted mice have increasingly implicated PPAR-γ in driving allergic inflammation. Herein, we highlight the contrasting roles of PPAR-γ in allergic inflammation and hypothesize that the availability of environmental ligands for PPAR-γ may be at the heart of the rise in allergic diseases worldwide.

Pro-inflammatory polarization primes Macrophages to transition into a distinct M2-like phenotype in response to IL-4

Tissue repair is largely regulated by diverse Mϕ populations whose functions are timing- and context-dependent. The early phase of healing is dominated by pro-inflammatory Mϕs, also known as M1, followed by the emergence of a distinct and diverse population that is collectively referred to as M2. The extent of the diversity of the M2 population is unknown. M2 Mϕs may originate directly from circulating monocytes or from phenotypic switching of pre-existing M1 Mϕs within the site of injury. The differences between these groups are poorly understood, but have major implications for understanding and treating pathologies characterized by deficient M2 activation, such as chronic wounds, which also exhibit diminished M1 Mϕ behavior. This study investigated the influence of prior M1 activation on human Mϕ polarization to an M2 phenotype in response to IL-4 treatment in vitro. Compared to unactivated (M0) Mϕs, M1 Mϕs up-regulated several receptors that promote the M2 phenotype, including the primary receptor for IL-4. M1 Mϕs also up-regulated M2 markers in response to lower doses of IL-4, including doses as low as 10 pg/mL, and accelerated STAT6 phosphorylation. However, M1 activation appeared to also change the Mϕ response to treatment with IL-4, generating an M2-like phenotype with a distinct gene and protein expression signature compared to M2 Mϕs prepared directly from M0 Mϕs. Functionally, compared to M0-derived M2 Mϕs, M1-derived M2 Mϕs demonstrated increased migratory response to SDF-1α, and conditioned media from these Mϕs promoted increased migration of endothelial cells in transwell assays, although other common Mϕ-associated functions such as phagocytosis were not affected by prior polarization state. In summary, M1 polarization appears to prime Mϕs to transition into a distinct M2 phenotype in response to IL4, which leads to increased expression of some genes and proteins and decreased expression of others, as well as functional differences. Together, these findings indicate the importance of prior M1 activation in regulating subsequent M2 behavior, and suggest that correcting M1 behavior may be a therapeutic target in dysfunctional M2 activation.

Tolerogenic properties of CD206+ macrophages appeared in the sublingual mucosa after repeated antigen-painting

The sublingual mucosa (SLM) in the oral cavity is utilized as the site for sublingual immunotherapy to induce tolerance against allergens. We previously reported that CD206+ round-type macrophage-like cells were induced in the SLM after repeated antigen (e.g. cedar pollen or fluorescein isothiocyanate (FITC))-painting. In this study, we examined the phenotypic and functional properties of CD206+ cells induced by repeated FITC-painting on the SLM. CD206+ cells after the repeated FITC-painting possessed a macrophage-like CD11b+Ly6C+ F4/80+CD64+ phenotype and expressed TIM-4, which was expressed in tolerogenic tissue-resident macrophages, at a high level. SLM CD206+ cells preferentially expressed molecules related to endocytosis and homeostatic processes, including the novel B7 family of immune checkpoint molecules, as assessed by microarray analyses. SLM CD206+ cells showed preferential expression of M2-related genes such as Fizz1, Aldh1a1 and Aldh1a2 but not Ym-1 and Arginase-1. A CD206+ cell-rich status inhibited OVA-specific CD4+ T-cell responses but reciprocally enhanced the proportion of both IL-10+CD4+ cells and Foxp3+ regulatory T-cells in regional lymph nodes. Co-culture of CD206+ cells with dendritic cells (DCs) showed that IL-12 production was suppressed in DCs concurrent with the decline of the MHC class IIhiCD86+ population, which was restored by neutralization of IL-10. These results demonstrate SLM CD206+ cells show the feature of tolerogenic macrophages and down-regulate the antigen-presenting cell function of mature DCs resulting in the inhibition of CD4+ T-cell responses.

Metabolic Hormones Modulate Macrophage Inflammatory Responses

Simple Summary

Macrophages are a type of immune cell which play an important role in the development of cancer. Obesity increases the risk of cancer and obesity also causes disruption to the normal levels of hormones that are produced to coordinate metabolism. Recent research now shows that these metabolic hormones also play important roles in macrophage immune responses and so through macrophages, disrupted metabolic hormone levels may promote cancer. This review article aims to highlight and summarise these recent findings so that the scientific community may better understand how important this new area of research is, and how these findings can be capitalised on for future scientific studies.

Abstract

Macrophages are phagocytotic leukocytes that play an important role in the innate immune response and have established roles in metabolic diseases and cancer progression. Increased adiposity in obese individuals leads to dysregulation of many hormones including those whose functions are to coordinate metabolism. Recent evidence suggests additional roles of these metabolic hormones in modulating macrophage inflammatory responses. In this review, we highlight key metabolic hormones and summarise their influence on the inflammatory response of macrophages and consider how, in turn, these hormones may influence the development of different cancer types through the modulation of macrophage functions.

Metabolic orchestration of the wound healing response

Wound healing requires cooperation between different cell types, among which macrophages play a central role. In particular, inflammatory macrophages are engaged in the initial response to wounding, and alternatively activated macrophages are essential for wound closure and the resolution of tissue repair. The links between temporal activation-induced changes in the metabolism of such macrophages and the influence this has on their functional states, along with the realization that metabolites play both intrinsic and extrinsic roles in the cells that produce them, has focused attention on the metabolism of wound healing. Here, we discuss macrophage metabolism during distinct stages of normal healing and its related pathologic processes, such as during cancer and fibrosis. Further, we frame these insights in a broader context of the current understanding of macrophage metabolic reprogramming linked to cellular activation and function. Finally, we discuss parallels between the metabolism of macrophages and fibroblasts, the latter being a key stromal cell type in wound healing, and consider the importance of the metabolic interplay between different cell types in the wound microenvironment.

Methotrexate Ameliorates Systemic Inflammation and Septic Associated-Lung Damage in a Cecal Ligation and Puncture Septic Rat Model

BACKGROUND

Sepsis is a serious, heterogeneous clinical entity produced by a severe and systemic host inflammatory response to infection. Methotrexate (MTX) is a folate-antagonist that induces the generation of adenosine and also inhibits JAK/STAT pathway; MTX it is widely used as an anti-inflammatory drug to control the immune system.

OBJECTIVE

The aim of this study was to assess the beneficial effects of a single and low dose of MTX in the systemic response and acute lung injury (ALI) induced by sepsis. As in the clinics, we treated our animals with antibiotics and fluids and performed the source control to mimic the current clinic treatment.

METHODS AND MAIN RESULTS

Sepsis was induced in rats by a cecal ligation puncture (CLP) procedure. Six hours after induction of sepsis, we proceeded to the source control; fluids and antibiotics were administered at 6 h and 24 h after CLP. MTX (2.5 mg/Kg) was administered 6 h after the first surgery in one CLP experimental group and to one Sham group. A protective effect of MTX was observed through a significant reduction of pro-inflammatory cytokines and a decrease infiltration of inflammatory cells in the lung. In addition, we found a regulation in adenosine receptor A2aR and the metalloproteinases by MTX.

CONCLUSION

A single, low dose of MTX attenuates sepsis lung-associated damage by decreasing pro-inflammatory response, infiltration of pro-inflammatory cells and avoiding defective tissue lung remodeling.

SREBP1-induced fatty acid synthesis depletes macrophages antioxidant defences to promote their alternative activation

Macrophages exhibit a spectrum of activation states ranging from classical to alternative activation¹. Alternatively, activated macrophages are involved in diverse pathophysiological processes such as confining tissue parasites², improving insulin sensitivity³ or promoting an immune-tolerant microenvironment that facilitates tumour growth and metastasis⁴. Recently, the metabolic regulation of macrophage function has come into focus as both the classical and alternative activation programmes require specific regulated metabolic reprogramming⁵. While most of the studies regarding immunometabolism have focussed on the catabolic pathways activated to provide energy, little is known about the anabolic pathways mediating macrophage alternative activation. In this study, we show that the anabolic transcription factor sterol regulatory element binding protein 1 (SREBP1) is activated in response to the canonical T helper 2 cell cytokine interleukin-4 to trigger the de novo lipogenesis (DNL) programme, as a necessary step for macrophage alternative activation. Mechanistically, DNL consumes NADPH, partitioning it away from cellular antioxidant defences and raising reactive oxygen species levels. Reactive oxygen species serves as a second messenger, signalling sufficient DNL, and promoting macrophage alternative activation. The pathophysiological relevance of this mechanism is validated by showing that SREBP1/DNL is essential for macrophage alternative activation in vivo in a helminth infection model.

Kupffer cell restoration after partial hepatectomy is mainly driven by local cell proliferation in IL-6-dependent autocrine and paracrine manners

Kupffer cells (KCs), which are liver-resident macrophages, originate from the fetal yolk sac and represent one of the largest macrophage populations in the body. However, the current data on the origin of the cells that restore macrophages during liver injury and regeneration remain controversial. Here, we address the question of whether liver macrophage restoration results from circulating monocyte infiltration or local KC proliferation in regenerating livers after partial hepatectomy (PHx) and uncover the underlying mechanisms. By using several strains of genetically modified mice and performing immunohistochemical analyses, we demonstrated that local KC proliferation mainly contributed to the restoration of liver macrophages after PHx. Peak KC proliferation was impaired in Il6-knockout (KO) mice and restored after the administration of IL-6 protein, whereas KC proliferation was not affected in Il4-KO or Csf2-KO mice. The source of IL-6 was identified using hepatocyte- and myeloid-specific Il6-KO mice and the results revealed that both hepatocytes and myeloid cells contribute to IL-6 production after PHx. Moreover, peak KC proliferation was also impaired in myeloid-specific Il6 receptor-KO mice after PHx, suggesting that IL-6 signaling directly promotes KC proliferation. Studies using several inhibitors to block the IL-6 signaling pathway revealed that sirtuin 1 (SIRT1) contributed to IL-6-mediated KC proliferation in vitro. Genetic deletion of the Sirt1 gene in myeloid cells, including KCs, impaired KC proliferation after PHx. In conclusion, our data suggest that KC repopulation after PHx is mainly driven by local KC proliferation, which is dependent on IL-6 and SIRT1 activation in KCs.

Incidence and severity of G6PI-induced arthritis are not increased in genetically distinct mouse strains upon aging

Background

The incidence of rheumatoid arthritis is correlated with age. In this study, we analyzed the association of the incidence and severity of glucose-6-phosphate isomerase (G6PI)-induced arthritis with age in two different mouse strains.

Methods

Young and very old mice from two different arthritis-susceptible wild-type mouse strains were analyzed after a single subcutaneous injection of G6PI s.c. The metabolism and the function of synoviocytes were analyzed in vitro, the production of bioactive lipid mediators by myeloid cells and synoviocytes was assessed in vitro and ex vivo by UPLC-MS-MS, and flow cytometry was used to verify age-related changes of immune cell composition and function.

Results

While the severity of arthritis was independent from age, the onset was delayed in old mice. Old mice showed common signs of immune aging like thymic atrophy associated with decreased CD4⁺ effector T cell numbers. Despite its decrease, the effector T helper (Th) cell compartment in old mice was reactive and functionally intact, and their Tregs exhibited unaltered suppressive capacities. In homeostasis, macrophages and synoviocytes from old mice produced higher amounts of pro-inflammatory cyclooxygenase (COX)-derived products. However, this functional difference did not remain upon challenge in vitro nor upon arthritis reactions ex vivo.

Conclusion

While old mice show a higher baseline of inflammatory functions, this does not result in increased reaction towards self-antigens in arthritis-susceptible mouse strains. Together, our data from two different mouse strains show that the susceptibility for G6PI-induced arthritis is not age-dependent.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02596-7.

Multiple roles of cardiac macrophages in heart homeostasis and failure

Macrophages are essential components of the immune system and play a role in the normal functioning of the cardiovascular system. Depending on their origin and phenotype, cardiac macrophages perform various functions. In a steady-state, these cells play a beneficial role in maintaining cardiac homeostasis by defending the body from pathogens and eliminating apoptotic cells, participating in electrical conduction, vessel patrolling, and arterial tone regulation. However, macrophages also take part in adverse cardiac remodeling that could lead to the development and progression of heart failure (HF) in such HF comorbidities as hypertension, obesity, diabetes, and myocardial infarction. Nevertheless, studies on detailed mechanisms of cardiac macrophage function are still in progress, and could enable potential therapeutic applications of these cells. This review aims to present the latest reports on the origin, heterogeneity, and functions of cardiac macrophages in the healthy heart and in cardiovascular diseases leading to HF. The potential therapeutic use of macrophages is also briefly discussed.

Advances in SIV/SHIV Non-Human Primate Models of NeuroAIDS

Non-human primates (NHPs) are the most relevant model of Acquired Immunodeficiency Syndrome (AIDS) and neuroAIDS, being of great importance in explaining the pathogenesis of HIV-induced nervous system damage. Simian Immunodeficiency Virus (SIV)/ Simian-Human Immunodeficiency Virus (SHIV)-infected monkeys have provided evidence of complex interactions between the virus and host that include host immune response, viral genetic diversity, and genetic susceptibility, which may explain virus-associated central nervous system (CNS) pathology and HIV-associated neurocognitive disorders (HAND). In this article, we review the recent progress contributions obtained using monkey models of HIV infection of the CNS, neuropathogenesis and SIV encephalitis (SIVE), with an emphasis on pharmacologic therapies and dependable markers that predict development of CNS AIDS.

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.

Novel Approaches of Dysregulating Lysosome Functions in Cancer Cells by Specific Drugs and Its Nanoformulations: A Smart Approach of Modern Therapeutics

The smart strategy of cancer cells to bypass the caspase-dependent apoptotic pathway has led to the discovery of novel anti-cancer approaches including the targeting of lysosomes. Recent discoveries observed that lysosomes perform far beyond just recycling of cellular waste, as these organelles are metabolically very active and mediate several signalling pathways to sense the cellular metabolic status. These organelles also play a significant role in mediating the immune system functions. Thus, direct or indirect lysosome-targeting with different drugs can be considered a novel therapeutic approach in different disease including cancer. Recently, some anticancer lysosomotropic drugs (eg, nortriptyline, siramesine, desipramine) and their nanoformulations have been engineered to specifically accumulate within these organelles. These drugs can enhance lysosome membrane permeabilization (LMP) or disrupt the activity of resident enzymes and protein complexes, like v-ATPase and mTORC1. Other anticancer drugs like doxorubicin, quinacrine, chloroquine and DQ661 have also been used which act through multi-target points. In addition, autophagy inhibitors, ferroptosis inducers and fluorescent probes have also been used as novel theranostic agents. Several lysosome-specific drug nanoformulations like mixed charge and peptide conjugated gold nanoparticles (AuNPs), Au-ZnO hybrid NPs, TPP-PEG-biotin NPs, octadecyl-rhodamine-B and cationic liposomes, etc. have been synthesized by diverse methods. These nanoformulations can target cathepsins, glucose-regulated protein 78, or other lysosome specific proteins in different cancers. The specific targeting of cancer cell lysosomes with drug nanoformulations is quite recent and faces tremendous challenges like toxicity concerns to normal tissues, which may be resolved in future research. The anticancer applications of these nanoformulations have led them up to various stages of clinical trials. Here in this review article, we present the recent updates about the lysosome ultrastructure, its cross-talk with other organelles, and the novel strategies of targeting this organelle in tumor cells as a recent innovative approach of cancer management.

Role of Tim4 in the regulation of ABCA1+ adipose tissue macrophages and post-prandial cholesterol levels

Dyslipidemia is a main driver of cardiovascular diseases. The ability of macrophages to scavenge excess lipids implicate them as mediators in this process and understanding the mechanisms underlying macrophage lipid metabolism is key to the development of new treatments. Here, we investigated how adipose tissue macrophages regulate post-prandial cholesterol transport. Single-cell RNA sequencing and protected bone marrow chimeras demonstrated that ingestion of lipids led to specific transcriptional activation of a population of resident macrophages expressing Lyve1, Tim4, and ABCA1. Blocking the phosphatidylserine receptor Tim4 inhibited lysosomal activation and the release of post-prandial high density lipoprotein cholesterol following a high fat meal. Both effects were recapitulated by chloroquine, an inhibitor of lysosomal function. Moreover, clodronate-mediated cell-depletion implicated Tim4+ resident adipose tissue macrophages in this process. Thus, these data indicate that Tim4 is a key regulator of post-prandial cholesterol transport and adipose tissue macrophage function and may represent a novel pathway to treat dyslipidemia.

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.

Macrophage-Regulatory T Cell Interactions Promote Type 2 Immune Homeostasis Through Resistin-Like Molecule α

RELMα is a small, secreted protein expressed by type 2 cytokine-activated “M2” macrophages in helminth infection and allergy. At steady state and in response to type 2 cytokines, RELMα is highly expressed by peritoneal macrophages, however, its function in the serosal cavity is unclear. In this study, we generated RELMα TdTomato (Td) reporter/knockout (Rα^Td) mice and investigated RELMα function in IL-4 complex (IL-4c)-induced peritoneal inflammation. We first validated the RELMα^Td/Td transgenic mice and showed that IL-4c injection led to the significant expansion of large peritoneal macrophages that expressed Td but not RELMα protein, while RELMα^+/+ mice expressed RELMα and not Td. Functionally, RELMα^Td/Td mice had increased IL-4 induced peritoneal macrophage responses and splenomegaly compared to RELMα^+/+ mice. Gene expression analysis indicated that RELMα^Td/Td peritoneal macrophages were more proliferative and activated than RELMα^+/+ macrophages, with increased genes associated with T cell responses, growth factor and cytokine signaling, but decreased genes associated with differentiation and maintenance of myeloid cells. We tested the hypothesis that Rα^Td/Td macrophages drive aberrant T cell activation using peritoneal macrophage and T cell co-culture. There were no differences in CD4⁺ T cell effector responses when co-cultured with RELMα^+/+ or RELMα^Td/Td macrophages, however, RELMα^Td/Td macrophages were impaired in their ability to sustain proliferation of FoxP3⁺ regulatory T cells (Treg). Supportive of the in vitro results, immunofluorescent staining of the spleens revealed significantly decreased FoxP3⁺ cells in the RELMα^Td/Td spleens compared to RELMα^+/+ spleens. Taken together, these studies identify a new RELMα regulatory pathway whereby RELMα-expressing macrophages directly sustain Treg proliferation to limit type 2 inflammatory responses.

The Role of Macrophages in the Host's Defense against Sporothrix schenckii

The role of immune cells associated with sporotrichosis caused by Sporothrix schenckii is not yet fully clarified. Macrophages through pattern recognition receptors (PRRs) can recognize pathogen-associated molecular patterns (PAMPs) of Sporothrix, engulf it, activate respiratory burst, and secrete pro-inflammatory or anti-inflammatory biological mediators to control infection. It is important to consider that the characteristics associated with S. schenckii and/or the host may influence macrophage polarization (M1/M2), cell recruitment, and the type of immune response (1, 2, and 17). Currently, with the use of new monocyte-macrophage cell lines, it is possible to evaluate different host-pathogen interaction processes, which allows for the proposal of new mechanisms in human sporotrichosis. Therefore, in order to contribute to the understanding of these host-pathogen interactions, the aim of this review is to summarize and discuss the immune responses induced by macrophage-S. schenckii interactions, as well as the PRRs and PAMPs involved during the recognition of S. schenckii that favor the immune evasion by the fungus.

Role of Macrophages and Related Cytokines in Kidney Disease

Inflammation is a key characteristic of kidney disease, but this immune response is two-faced. In the acute phase of kidney injury, there is an activation of the immune cells to fight against the insult, contributing to kidney repair and regeneration. However, in chronic kidney diseases (CKD), immune cells that infiltrate the kidney play a deleterious role, actively participating in disease progression, and contributing to nephron loss and fibrosis. Importantly, CKD is a chronic inflammatory disease. In early CKD stages, patients present sub-clinical inflammation, activation of immune circulating cells and therefore, anti-inflammatory strategies have been proposed as a common therapeutic target for renal diseases. Recent studies have highlighted the plasticity of immune cells and the complexity of their functions. Among immune cells, monocytes/macrophages play an important role in all steps of kidney injury. However, the phenotype characterization between human and mice immune cells showed different markers; therefore the extrapolation of experimental studies in mice could not reflect human renal diseases. Here we will review the current information about the characteristics of different macrophage phenotypes, mainly focused on macrophage-related cytokines, with special attention to the chemokine CCL18, and its murine functional homolog CCL8, and the macrophage marker CD163, and their role in kidney pathology.

CCR2 Deficiency Impairs Ly6Clo and Ly6Chi Monocyte Responses in Orientia tsutsugamushi Infection

Orientia (O.) tsutsugamushi, the causative agent of scrub typhus, is a neglected, obligate intracellular bacterium that has a prominent tropism for monocytes and macrophages. Complications often involve the lung, where interstitial pneumonia is a typical finding. The severity of scrub typhus in humans has been linked to altered plasma concentrations of chemokines which are known to act as chemoattractants for myeloid cells. The trafficking and function of monocyte responses is critically regulated by interaction of the CC chemokine ligand 2 (CCL2) and its CC chemokine receptor CCR2. In a self-healing mouse model of intradermal infection with the human-pathogenic Karp strain of O. tsutsugamushi, we investigated the role of CCR2 on bacterial dissemination, development of symptoms, lung histology and monocyte subsets in blood and lungs. CCR2-deficient mice showed a delayed onset of disease and resolution of symptoms, higher concentrations and impaired clearance of bacteria in the lung and the liver, accompanied by a slow infiltration of interstitial macrophages into the lungs. In the blood, we found an induction of circulating monocytes that depended on CCR2, while only a small increase in Ly6Chi monocytes was observed in CCR2-/- mice. In the lung, significantly higher numbers of Ly6Chi and Ly6Clo monocytes were found in the C57BL/6 mice compared to CCR2-/- mice. Both wildtype and CCR2-deficient mice developed an inflammatory milieu as shown by cytokine and inos/arg1 mRNA induction in the lung, but with delayed kinetics in CCR2-deficient mice. Histopathology revealed that infiltration of macrophages to the parenchyma, but not into the peribronchial tissue, depended on CCR2. In sum, our data suggest that in Orientia infection, CCR2 drives blood monocytosis and the influx and activation of Ly6Chi and Ly6Clo monocytes into the lung, thereby accelerating bacterial replication and development of interstitial pulmonary inflammation.

The expanding world of tissue-resident macrophages

The term 'macrophage' encompasses tissue cells that typically share dependence on the same transcriptional regulatory pathways (e.g. the transcription factor PU.1) and growth factors (e.g. CSF1/IL-34). They share a core set of functions that largely arise from a uniquely high phagocytic capacity manifest in their ability to clear dying cells, pathogens and scavenge damaged, toxic or modified host molecules. However, macrophages demonstrate a remarkable degree of tissue-specific functionality and have diverse origins that vary by tissue site and inflammation status. With our understanding of this diversity has come an appreciation of the longevity and replicative capacity of tissue-resident macrophages and thus the realisation that macrophages may persist through tissue perturbations and inflammatory events with important consequences for cell function. Here, we discuss our current understanding of the parameters that regulate macrophage survival and function, focusing on the relative importance of the tissue environment versus cell-intrinsic factors, such as origin, how long a cell has been resident within a tissue and prior history of activation. Thus, we reconsider the view of macrophages as wholly plastic cells and raise many unanswered questions about the relative importance of cell life-history versus environment in macrophage programming and function.

Exploiting the obesity-associated immune microenvironment for cancer therapeutics

Obesity causes chronic low-grade inflammation and leads to changes in the immune landscape of multiple organ systems. Given the link between chronic inflammatory conditions and cancer, it is not surprising that obesity is associated with increased risk and worse outcomes in many malignancies. Paradoxically, recent epidemiological studies have shown that high BMI is associated with increased efficacy of immune checkpoint inhibitors (ICI), and a causal relationship has been demonstrated in the preclinical setting. It has been proposed that obesity-associated immune dysregulation underlies this observation by inadvertently creating a favourable microenvironment for increased ICI efficacy. The recent success of ICIs in obese cancer patients raises the possibility that additional immune-targeted therapies may hold therapeutic value in this context. Here we review how obesity affects the immunological composition of the tumor microenvironment in ways that can be exploited for cancer immunotherapies. We discuss existing literature supporting a beneficial role for obesity during ICI therapy in cancer patients, potential opportunities for targeting the innate immune system to mitigate chronic inflammatory processes, and how to pinpoint obese patients who are most likely to benefit from immune interventions without relying solely on body mass index. Given that the incidence of obesity is expanding on an international scale, we propose that understanding obesity-associated inflammation is necessary to reduce cancer mortalities and capitalize on novel therapeutic opportunities in the era of cancer immunotherapy.

Enhanced Skin Incisional Wound Healing With Intracellular ATP Delivery via Macrophage Proliferation and Direct Collagen Production

This study sought to use a newly developed intracellular ATP delivery to enhance incisional wound healing to reduce surgical wound dehiscence and to explore possible mechanism for this effect. Thirty-five adult New Zealand white rabbits were used. Skin incisions were made on the back and closed. ATP-vesicles were mixed with a neutral cream for one side of the wounds while the neutral cream alone was used on the other side of the wounds. Laser speckle contrast imaging (LSCI), biomechanical, histological, and immunohistochemical analyses were performed 7 and 14 days after surgery, and macrophage culture was used to test the enhanced collagen production ability. Among them, 10 were used for wound perfusion study and 25 were used for wound biomechanical and histological/immunohistochemical studies. Wound tissue perfusion was reduced after surgery especially in early days. Wound tissue tensile strength, breaking stress, and elasticity were all much higher in the ATP-vesicle treated group than in the cream treated group at days 7 and 14. The healing was complemented by earlier macrophage accumulation, in situ proliferation, followed by direct collagen production. The results were further confirmed by human macrophage culture. It was concluded that intracellular ATP delivery enhanced healing strength of incisional wounds via multiple mechanisms.

Toxicity of Tetrabromobisphenol A and Its Derivative in the Mouse Liver Following Oral Exposure at Environmentally Relevant Levels

As typical brominated flame retardants (BFRs), tetrabromobisphenol A (TBBPA) and its derivative TBBPA-bis(2,3-dibromopropyl ether) (TBBPA-BDBPE) are ubiquitous in various environmental compartments. However, the potential health risk posed by these compounds, especially at environmentally relevant levels, remains unclear. In this study, using adult male mice, we investigated the toxicity of orally administered TBBPA and TBBPA-BDBPE at an environmentally relevant dose (57 nmol/kg body weight). After a single exposure and daily exposure, we assessed lipid metabolism homeostasis, the transcriptome, and immune cell components in the liver. We found that the single exposure to TBBPA or TBBPA-BDBPE alone increased the number of hepatic macrophages, induced alterations in the levels of lipids, including triacylglycerol and free fatty acids, and caused transcriptome perturbation. The results from the daily administration groups showed that TBBPA and TBBPA-BDBPE both significantly increased the triacylglycerol content; however, the elevation of hepatic macrophages was observed only in the TBBPA-BDBPE treatment group. This study confirmed that environmentally relevant levels of TBBPA and TBBPA-BDBPE are toxic to the liver. Our findings revealed that dysfunction of the liver is a health concern, following exposure to BFRs, even at very low concentrations. The chronic effects induced by TBBPA and its derivatives should be further investigated.

Hepatic Macrophage Responses in Inflammation, a Function of Plasticity, Heterogeneity or Both?

With the increasing availability and accessibility of single cell technologies, much attention has been given to delineating the specific populations of cells present in any given tissue. In recent years, hepatic macrophage heterogeneity has also begun to be examined using these strategies. While previously any macrophage in the liver was considered to be a Kupffer cell (KC), several studies have recently revealed the presence of distinct subsets of hepatic macrophages, including those distinct from KCs both under homeostatic and non-homeostatic conditions. This heterogeneity has brought the concept of macrophage plasticity into question. Are KCs really as plastic as once thought, being capable of responding efficiently and specifically to any given stimuli? Or are the differential responses observed from hepatic macrophages in distinct settings due to the presence of multiple subsets of these cells? With these questions in mind, here we examine what is currently understood regarding hepatic macrophage heterogeneity in mouse and human and examine the role of heterogeneity vs plasticity in regards to hepatic macrophage responses in settings of both pathogen-induced and sterile inflammation.

Fibroblasts and macrophages: Collaborators in tissue homeostasis

Fibroblasts and macrophages are universal cell types across all mammalian tissues. These cells differ in many ways including their cellular origins; dynamics of renewal, recruitment, and motility within tissues; roles in tissue structure and secretion of signaling molecules; and contributions to the activation and progression of immune responses. However, many of the features that make these two cell types unique are not opposing, but instead complementary. This review will present cell-cell communication in this context and discuss how complementarity makes fibroblasts and macrophages highly compatible partners in the maintenance of tissue homeostasis.

Uncoupling of macrophage inflammation from self-renewal modulates host recovery from respiratory viral infection

Tissue macrophages self-renew during homeostasis and produce inflammatory mediators upon microbial infection. We examined the relationship between proliferative and inflammatory properties of tissue macrophages by defining the impact of the Wnt/β-catenin pathway, a central regulator of self-renewal, in alveolar macrophages (AMs). Activation of β-catenin by Wnt ligand inhibited AM proliferation and stemness, but promoted inflammatory activity. In a murine influenza viral pneumonia model, β-catenin-mediated AM inflammatory activity promoted acute host morbidity; in contrast, AM proliferation enabled repopulation of reparative AMs and tissue recovery following viral clearance. Mechanistically, Wnt treatment promoted β-catenin-HIF-1α interaction and glycolysis-dependent inflammation while suppressing mitochondrial metabolism and thereby, AM proliferation. Differential HIF-1α activities distinguished proliferative and inflammatory AMs in vivo. This β-catenin-HIF-1α axis was conserved in human AMs and enhanced HIF-1α expression associated with macrophage inflammation in COVID-19 patients. Thus, inflammatory and reparative activities of lung macrophages are regulated by β-catenin-HIF-1α signaling, with implications for the treatment of severe respiratory diseases.

Treatment with a long-acting chimeric CSF1 molecule enhances fracture healing of healthy and osteoporotic bones

Macrophage-targeted therapies, including macrophage colony-stimulating factor 1 (CSF1), have been shown to have pro-repair impacts post-fracture. Preclinical/clinical applications of CSF1 have been expedited by development of chimeric CSF1-Fc which has extended circulating half-life. Here, we used mouse models to investigate the bone regenerative potential of CSF1-Fc in healthy and osteoporotic fracture. We also explored whether combination of CSF1-Fc with interleukin (IL)-4 provided additional fracture healing benefit in osteopenic bone. Micro-computed tomography, in situ histomorphometry, and bone mechanical parameters were used to assess systemic impacts of CSF1-Fc therapy in naive mice (male and female young, adult and geriatric). An intermittent CSF1-Fc regimen was optimized to mitigate undesirable impacts on bone resorption and hepatosplenomegaly, irrespective of age or gender. The intermittent CSF1-Fc regimen was tested in a mid-diaphyseal femoral fracture model in healthy bones with treatment initiated 1-day post-fracture. Weekly CSF1-Fc did not impact osteoclasts but increased osteal macrophages and improved fracture strength. Importantly, this treatment regimen also improved fracture union and strength in an ovariectomy-model of delayed fracture repair. Combining CSF1-Fc with IL-4 initiated 1-week post-fracture reduced the efficacy of CSF1-Fc. This study describes a novel strategy to specifically achieve bone regenerative actions of CSF1-Fc that has the potential to alleviate fragility fracture morbidity and mortality.

Macro- and microtranscriptomic evidence of the monocyte recruitment to regenerating liver after partial hepatectomy in mouse model

Macrophages are important regulators of liver repair. Participation of migratory monocytes/macrophages in regeneration of hepatic tissues after resection remains disputable. In mouse the resection promotes migration of Ly6C+CD11b+ monocytes/macrophages to the remnant liver accompanied by a reduction in its CD206 + macrophage content. Macrophage proliferation within the liver reaches maximum on day 3 after the surgery. Corresponding macro- and microtranscriptomic profiles of macrophages in regeneration liver cannot be unambiguously defined as pro- or anti-inflammatory. Their typical features include elevated expression of leukocyte chemoattractant factors, and many of the differentially expressed sequences are related to the control of cell growth and metabolic processes in the liver. These findings revealed essential roles of immigration of monocytes/macrophages and macrophages proliferation in maintenance of macrophage populations in the mouse liver during its recovery from a massive resection.