Comparison of gene expression profiles between human and mouse monocyte subsets

Infiltration by monocytes of the central nervous system and its role in multiple sclerosis: reflections on therapeutic strategies

Mononuclear macrophage infiltration in the central nervous system is a prominent feature of neuroinflammation. Recent studies on the pathogenesis and progression of multiple sclerosis have highlighted the multiple roles of mononuclear macrophages in the neuroinflammatory process. Monocytes play a significant role in neuroinflammation, and managing neuroinflammation by manipulating peripheral monocytes stands out as an effective strategy for the treatment of multiple sclerosis, leading to improved patient outcomes. This review outlines the steps involved in the entry of myeloid monocytes into the central nervous system that are targets for effective intervention: the activation of bone marrow hematopoiesis, migration of monocytes in the blood, and penetration of the blood-brain barrier by monocytes. Finally, we summarize the different monocyte subpopulations and their effects on the central nervous system based on phenotypic differences. As activated microglia resemble monocyte-derived macrophages, it is important to accurately identify the role of monocyte-derived macrophages in disease. Depending on the roles played by monocyte-derived macrophages at different stages of the disease, several of these processes can be interrupted to limit neuroinflammation and improve patient prognosis. Here, we discuss possible strategies to target monocytes in neurological diseases, focusing on three key aspects of monocyte infiltration into the central nervous system, to provide new ideas for the treatment of neurodegenerative diseases.

Dietary restriction impacts health and lifespan of genetically diverse mice

Caloric restriction extends healthy lifespan in multiple species1. Intermittent fasting, an alternative form of dietary restriction, is potentially more sustainable in humans, but its effectiveness remains largely unexplored2-8. Identifying the most efficacious forms of dietary restriction is key for developing interventions to improve human health and longevity9. Here we performed an extensive assessment of graded levels of caloric restriction (20% and 40%) and intermittent fasting (1 and 2 days fasting per week) on the health and survival of 960 genetically diverse female mice. We show that caloric restriction and intermittent fasting both resulted in lifespan extension in proportion to the degree of restriction. Lifespan was heritable and genetics had a larger influence on lifespan than dietary restriction. The strongest trait associations with lifespan included retention of body weight through periods of handling-an indicator of stress resilience, high lymphocyte proportion, low red blood cell distribution width and high adiposity in late life. Health effects differed between interventions and exhibited inconsistent relationships with lifespan extension. 40% caloric restriction had the strongest lifespan extension effect but led to a loss of lean mass and changes in the immune repertoire that could confer susceptibility to infections. Intermittent fasting did not extend the lifespan of mice with high pre-intervention body weight, and two-day intermittent fasting was associated with disruption of erythroid cell populations. Metabolic responses to dietary restriction, including reduced adiposity and lower fasting glucose, were not associated with increased lifespan, suggesting that dietary restriction does more than just counteract the negative effects of obesity. Our findings indicate that improving health and extending lifespan are not synonymous and raise questions about which end points are the most relevant for evaluating aging interventions in preclinical models and clinical trials.

Sulfotransferase homolog 2 receptors blockade on monocyte subsets along with their inflammatory cytokines for septic lung injury

PURPOSE OF THE STUDY

To observe the dynamic changes in monocyte subsets during septic lung injury and to assess the anti-inflammatory role of the sulfotransferase homolog 2 (ST2) receptor.

MATERIALS AND METHODS

Dynamic changes of monocyte subsets from patients with septic lung injury and mice post-cecal ligation and puncture (CLP) were monitored. ST2 receptors on mice monocytes and concentrations of IL-33, IL-1β, IL-12, and IL-27 from peripheral blood or culture supernatant were detected.

RESULTS

CD14lowCD16- (Mo0) and CD14++CD16+ (Mo2) monocyte subsets were significantly expanded in patients with sepsis-related acute respiratory distress syndrome. In sepsis model mice, monocyte counts, particularly of Ly6Cint and CDLy6Cint+hi monocytes, were significantly increased. The mean optical density value of TNF-α after CLP mainly increased after 24 h, whereas that of IL-6 was significantly increased at all time points assessed after CLP. The levels of IL-1β, IL-12, IL-27, and IL-33 increased to variable degrees at 6, 12, 24, and 48h after CLP, and ST2+ monocytes were significantly expanded in sepsis model mice compared to sham-operated mice. ST2 receptor blockade suppressed IL-1β and IL-12 production in cell culture.

CONCLUSIONS

Changes in monocyte subsets expressing the ST2 receptor play an important role in septic lung injury by modulating inflammatory cytokine secretion.

Macrophage and Neutrophil Dysfunction in Diabetic Wounds

Significance: The incidence of diabetes continues to rise throughout the world in an alarming rate. Diabetic patients often develop diabetic foot ulcers (DFUs), many of which do not heal. Non-healing DFUs are a major cause of hospitalization, amputation, and increased morbidity. Understanding the underlying mechanisms of impaired healing in DFU is crucial for its management. Recent Advances: This review focuses on the recent advancements on macrophages and neutrophils in diabetic wounds and DFUs. In particular, we discuss diabetes-induced dysregulations and dysfunctions of macrophages and neutrophils. Critical Issues: It is well established that diabetic wounds are characterized by stalled inflammation that results in impaired healing. Recent findings in the field suggest that dysregulation of macrophages and neutrophils plays a critical role in impaired healing in DFUs. The delineation of mechanisms that restore macrophage and neutrophil function in diabetic wound healing is the focus of intense investigation. Future Directions: The breadth of recently generated knowledge on the activity of macrophages and neutrophils in diabetic wound healing is impressive. Experimental models have delineated pathways that hold promise for the treatment of diabetic wounds and DFUs. These pathways may be useful targets for further clinical investigation.

CD4 + T cells recruit, then engage macrophages in cognate interactions to clear Mycobacterium tuberculosis from the lungs

IFN-γ-producing CD4 + T cells are required for protection against lethal Mycobacterium tuberculosis ( Mtb ) infections. However, the ability of CD4 + T cells to suppress Mtb growth cannot be fully explained by IFN-γ or other known T cell products. In this study, we show that CD4 + T cell-derived IFN-γ promoted the recruitment of monocyte-derived macrophages (MDMs) to the lungs of Mtb -infected mice. Although the recruited MDMs became quickly and preferentially infected with Mtb , CD4 + T cells rapidly disinfected the MDMs. Clearance of Mtb from MDMs was not explained by IFN-γ, but rather by MHCII-mediated cognate interactions with CD4 + T cells. These interactions promoted MDM expression of glycolysis genes essential for Mtb control. Thus, by recruiting MDMs, CD4 + T cells initiate a cycle of bacterial phagocytosis, Mtb antigen presentation and disinfection in an attempt to clear the bacteria from the lungs.

Th1 cells reduce the osteoblast-like phenotype in valvular interstitial cells by inhibiting NLRP3 inflammasome activation in macrophages

BACKGROUND AND AIMS

Inflammation is initiates the propagation phase of aortic valve calcification. The activation of NLRP3 signaling in macrophages plays a crucial role in the progression of calcific aortic valve stenosis (CAVS). IFN-γ regulates NLRP3 activity in macrophages. This study aimed to explore the mechanism of IFN-γ regulation and its impact on CAVS progression and valve interstitial cell transdifferentiation.

METHODS AND RESULTS

The number of Th1 cells and the expression of IFN-γ and STAT1 in the aortic valve, spleen and peripheral blood increased significantly as CAVS progressed. To explore the mechanisms underlying the roles of Th1 cells and IFN-γ, we treated CAVS mice with IFN-γ-AAV9 or an anti-IFN-γ neutralizing antibody. While IFN-γ promoted aortic valve calcification and dysfunction, it significantly decreased NLRP3 signaling in splenic macrophages and Ly6C+ monocytes. In vitro coculture showed that Th1 cells inhibited NLPR3 activation in ox-LDL-treated macrophages through the IFN-γR1/IFN-γR2-STAT1 pathway. Compared with untreated medium, conditioned medium from Th1-treated bone marrow-derived macrophages reduced the osteogenic calcification of valvular interstitial cells.

CONCLUSION

Inhibition of the NLRP3 inflammasome by Th1 cells protects against valvular interstitial cell calcification as a negative feedback mechanism of adaptive immunity toward innate immunity. This study provides a precision medicine strategy for CAVS based on the targeting of anti-inflammatory mechanisms.

Macrophage heterogeneity in myocardial infarction: Evolution and implications for diverse therapeutic approaches

Given the extensive participation of myeloid cells (especially monocytes and macrophages) in both inflammation and resolution phases post-myocardial infarction (MI) owing to their biphasic role, these cells are considered as crucial players in the disease pathogenesis. Multiple studies have agreed on the significant contribution of macrophage polarization theory (M2 vs. M1) while determining the underlying reasons behind the observed biphasic effects; nevertheless, this simplistic classification attracts severe drawbacks. The advent of multiple advanced technologies based on OMICS platforms facilitated a successful path to explore comprehensive cellular signatures that could expedite our understanding of macrophage heterogeneity and plasticity. While providing an overall basis behind the MI disease pathogenesis, this review delves into the literature to discuss the current knowledge on multiple macrophage clusters, including the future directions in this research arena. In the end, our focus will be on outlining the possible therapeutic implications based on the emerging observations.

Harnessing the potential of monocytes/macrophages to regenerate tissue-engineered vascular grafts

Cell-free tissue-engineered vascular grafts provide a promising alternative to treat cardiovascular disease, but timely endothelialization is essential for ensuring patency and proper functioning post-implantation. Recent studies from our lab showed that blood cells like monocytes (MCs) and macrophages (Mϕ) may contribute directly to cellularization and regeneration of bioengineered arteries in small and large animal models. While MCs and Mϕ are leucocytes that are part of the innate immune response, they share common developmental origins with endothelial cells (ECs) and are known to play crucial roles during vessel formation (angiogenesis) and vessel repair after inflammation/injury. They are highly plastic cells that polarize into pro-inflammatory and anti-inflammatory phenotypes upon exposure to cytokines and differentiate into other cell types, including EC-like cells, in the presence of appropriate chemical and mechanical stimuli. This review focuses on the developmental origins of MCs and ECs; the role of MCs and Mϕ in vessel repair/regeneration during inflammation/injury; and the role of chemical signalling and mechanical forces in Mϕ inflammation that mediates vascular graft regeneration. We postulate that comprehensive understanding of these mechanisms will better inform the development of strategies to coax MCs/Mϕ into endothelializing the lumen and regenerate the smooth muscle layers of cell-free bioengineered arteries and veins that are designed to treat cardiovascular diseases and perhaps the native vasculature as well.

Helminth induced monocytosis conveys protection from respiratory syncytial virus infection in mice

BACKGROUND

Respiratory syncytial virus (RSV) infection in infants is a major cause of viral bronchiolitis and hospitalisation. We have previously shown in a murine model that ongoing infection with the gut helminth Heligmosomoides polygyrus protects against RSV infection through type I interferon (IFN-I) dependent reduction of viral load. Yet, the cellular basis for this protection has remained elusive. Given that recruitment of mononuclear phagocytes to the lung is critical for early RSV infection control, we assessed their role in this coinfection model.

METHODS

Mice were infected by oral gavage with H. polygyrus. Myeloid immune cell populations were assessed by flow cytometry in lung, blood and bone marrow throughout infection and after secondary infection with RSV. Monocyte numbers were depleted by anti-CCR2 antibody or increased by intravenous transfer of enriched monocytes.

RESULTS

H. polygyrus infection induces bone marrow monopoiesis, increasing circulatory monocytes and lung mononuclear phagocytes in a IFN-I signalling dependent manner. This expansion causes enhanced lung mononuclear phagocyte counts early in RSV infection that may contribute to the reduction of RSV load. Depletion or supplementation of circulatory monocytes prior to RSV infection confirms that these are both necessary and sufficient for helminth induced antiviral protection.

CONCLUSIONS

H. polygyrus infection induces systemic monocytosis contributing to elevated mononuclear phagocyte numbers in the lung. These cells are central to an anti-viral effect that reduces the peak viral load in RSV infection. Treatments to promote or modulate these cells may provide novel paths to control RSV infection in high risk individuals.

A subpopulation of tissue remodeling monocytes stimulates revascularization of the ischemic limb

Despite decades of effort aimed at developing clinically effective cell therapies, including mixed population mononuclear cells, to revascularize the ischemic limb, there remains a paucity of patient-based studies that inform the function and fate of candidate cell types. In this study, we showed that circulating proangiogenic/arteriogenic monocytes (PAMs) expressing the FcγIIIA receptor CD16 were elevated in patients with chronic limb-threatening ischemia (CLTI), and these amounts decreased after revascularization. Unlike CD16-negative monocytes, PAMs showed large vessel remodeling properties in vitro when cultured with endothelial cells and smooth muscle cells and promoted salvage of the ischemic limb in vivo in a mouse model of hindlimb ischemia. PAMs showed a propensity to migrate toward and bind to ischemic muscle and to secrete angiogenic/arteriogenic factors, vascular endothelial growth factor A (VEGF-A) and heparin-binding epidermal growth factor. We instigated a first-in-human single-arm cohort study in which autologous PAMs were injected into the ischemic limbs of five patients with CLTI. Greater than 25% of injected cells were retained in the leg for at least 72 hours, of which greater than 80% were viable, with evidence of enhanced large vessel remodeling in the injected muscle area. In summary, we identified up-regulation of a circulatory PAM subpopulation as an endogenous response to limb ischemia in CLTI and tested a potentially clinically relevant therapeutic strategy.

Inducing the "re-development state" of periodontal ligament cells via tuning macrophage mediated immune microenvironment

INTRODUCTION

Periodontal regeneration, specifically the restoration of the cementum-periodontal ligament (PDL)-alveolar bone complex, remains a formidable challenge in the field of regenerative dentistry. In light of periodontal development, harnessing the multi-tissue developmental capabilities of periodontal ligament cells (PDLCs) and reinitiating the periodontal developmental process hold great promise as an effective strategy to foster the regeneration of the periodontal complex.

OBJECTIVES

This study aims to delve into the potential effects of the macrophage-mediated immune microenvironment on the "developmental engineering" regeneration strategy and its underlying molecular mechanisms.

METHODS

In this study, we conducted a comprehensive examination of the periodontium developmental process in the rat mandibular first molar using histological staining. Through the induction of diverse immune microenvironments in macrophages, we evaluated their potential effects on periodontal re-development events using a cytokine array. Additionally, we investigated PDLC-mediated periodontal re-development events under these distinct immune microenvironments through transcriptome sequencing and relevant functional assays. Furthermore, the underlying molecular mechanism was also performed.

RESULTS

The activation of development-related functions in PDLCs proved challenging due to their declined activity. However, our findings suggest that modulating the macrophage immune response can effectively regulate PDLCs-mediated periodontium development-related events. The M1 type macrophage immune microenvironment was found to promote PDLC activities associated with epithelial-mesenchymal transition, fiber degradation, osteoclastogenesis, and inflammation through the Wnt, IL-17, and TNF signaling pathways. Conversely, the M2 type macrophage immune microenvironment demonstrated superiority in inducing epithelium induction, fibers formation, and mineralization performance of PDLCs by upregulating the TGFβ and PI3K-Akt signaling pathway.

CONCLUSION

The results of this study could provide some favorable theoretical bases for applying periodontal development engineering strategy in resolving the difficulties in periodontal multi-tissue regeneration.

The role of tumor-associated macrophages in tumor immune evasion

BACKGROUND

Tumor growth is closely linked to the activities of various cells in the tumor microenvironment (TME), particularly immune cells. During tumor progression, circulating monocytes and macrophages are recruited, altering the TME and accelerating growth. These macrophages adjust their functions in response to signals from tumor and stromal cells. Tumor-associated macrophages (TAMs), similar to M2 macrophages, are key regulators in the TME.

METHODS

We review the origins, characteristics, and functions of TAMs within the TME. This analysis includes the mechanisms through which TAMs facilitate immune evasion and promote tumor metastasis. Additionally, we explore potential therapeutic strategies that target TAMs.

RESULTS

TAMs are instrumental in mediating tumor immune evasion and malignant behaviors. They release cytokines that inhibit effector immune cells and attract additional immunosuppressive cells to the TME. TAMs primarily target effector T cells, inducing exhaustion directly, influencing activity indirectly through cellular interactions, or suppressing through immune checkpoints. Additionally, TAMs are directly involved in tumor proliferation, angiogenesis, invasion, and metastasis. Developing innovative tumor-targeted therapies and immunotherapeutic strategies is currently a promising focus in oncology. Given the pivotal role of TAMs in immune evasion, several therapeutic approaches have been devised to target them. These include leveraging epigenetics, metabolic reprogramming, and cellular engineering to repolarize TAMs, inhibiting their recruitment and activity, and using TAMs as drug delivery vehicles. Although some of these strategies remain distant from clinical application, we believe that future therapies targeting TAMs will offer significant benefits to cancer patients.

How Mycobacterium tuberculosis builds a home: Single-cell analysis reveals M. tuberculosis ESX-1-mediated accumulation of anti-inflammatory macrophages in infected mouse lungs

Mycobacterium tuberculosis (MTB) infects and replicates in lung mononuclear phagocytes (MNPs) with astounding ability to evade elimination. ESX-1, a type VII secretion system, acts as a virulence determinant that contributes to MTB's ability to survive within MNPs, but its effect on MNP recruitment and/or differentiation remains unknown. Here, using single-cell RNA sequencing, we studied the role of ESX-1 in MNP heterogeneity and response in mice and murine bone marrow-derived macrophages (BMDM). We found that ESX-1 is required for MTB to recruit diverse MNP subsets with high MTB burden. Further, MTB induces an anti-inflammatory signature in MNPs and BMDM in an ESX-1 dependent manner. Similarly, spatial transcriptomics revealed an upregulation of anti-inflammatory signals in MTB lesions, where monocyte-derived macrophages concentrate near MTB-infected cells. Together, our findings suggest that MTB ESX-1 mediates the recruitment and differentiation of anti-inflammatory MNPs, which MTB can infect and manipulate for survival.

Transcription factor C/EBPα is required for the development of Ly6Chi monocytes but not Ly6Clo monocytes

Monocytes comprise two major subsets, Ly6Chi classical monocytes and Ly6Clo nonclassical monocytes. Notch2 signaling in Ly6Chi monocytes triggers transition to Ly6Clo monocytes, which require Nr4a1, Bcl6, Irf2, and Cebpb. By comparison, less is known about transcriptional requirements for Ly6Chi monocytes. We find transcription factor CCAAT/enhancer-binding protein alpha (C/EBPα) is highly expressed in Ly6Chi monocytes, but down-regulated in Ly6Clo monocytes. A few previous studies described the requirement of C/EBPα in the development of neutrophils and eosinophils. However, the role of C/EBPα for in vivo monocyte development has not been understood. We deleted the Cebpa +37 kb enhancer in mice, eliminating hematopoietic expression of C/EBPα, reproducing the expected neutrophil defect. Surprisingly, we also found a severe and selective loss of Ly6Chi monocytes, while preserving Ly6Clo monocytes. We find that BM progenitors from Cebpa +37-/- mice rapidly progress through the monocyte progenitor stage to develop directly into Ly6Clo monocytes even in the absence of Notch2 signaling. These results identify a previously unrecognized role for C/EBPα in maintaining Ly6Chi monocyte identity.

The role of foam cells in spinal cord injury: challenges and opportunities for intervention

Spinal cord injury (SCI) results in a large amount of tissue cell debris in the lesion site, which interacts with various cytokines, including inflammatory factors, and the intrinsic glial environment of the central nervous system (CNS) to form an inhibitory microenvironment that impedes nerve regeneration. The efficient clearance of tissue debris is crucial for the resolution of the inhibitory microenvironment after SCI. Macrophages are the main cells responsible for tissue debris removal after SCI. However, the high lipid content in tissue debris and the dysregulation of lipid metabolism within macrophages lead to their transformation into foamy macrophages during the phagocytic process. This phenotypic shift is associated with a further pro-inflammatory polarization that may aggravate neurological deterioration and hamper nerve repair. In this review, we summarize the phenotype and metabolism of macrophages under inflammatory conditions, as well as the mechanisms and consequences of foam cell formation after SCI. Moreover, we discuss two strategies for foam cell modulation and several potential therapeutic targets that may enhance the treatment of SCI.

Advances in lung ischemia/reperfusion injury: unraveling the role of innate immunity

BACKGROUND

Lung ischemia/reperfusion injury (LIRI) is a common occurrence in clinical practice and represents a significant complication following pulmonary transplantation and various diseases. At the core of pulmonary ischemia/reperfusion injury lies sterile inflammation, where the innate immune response plays a pivotal role. This review aims to investigate recent advancements in comprehending the role of innate immunity in LIRI.

METHODS

A computer-based online search was performed using the PubMed database and Web of Science database for published articles concerning lung ischemia/reperfusion injury, cell death, damage-associated molecular pattern molecules (DAMPs), innate immune cells, innate immunity, inflammation.

RESULTS

During the process of lung ischemia/reperfusion, cellular injury even death can occur. When cells are injured or undergo cell death, endogenous ligands known as DAMPs are released. These molecules can be recognized and bound by pattern recognition receptors (PRRs), leading to the recruitment and activation of innate immune cells. Subsequently, a cascade of inflammatory responses is triggered, ultimately exacerbating pulmonary injury. These steps are complex and interrelated rather than being in a linear relationship. In recent years, significant progress has been made in understanding the immunological mechanisms of LIRI, involving novel types of cell death, the ability of receptors other than PRRs to recognize DAMPs, and a more detailed mechanism of action of innate immune cells in ischemia/reperfusion injury (IRI), laying the groundwork for the development of novel diagnostic and therapeutic approaches.

CONCLUSIONS

Various immune components of the innate immune system play critical roles in lung injury after ischemia/reperfusion. Preventing cell death and the release of DAMPs, interrupting DAMPs receptor interactions, disrupting intracellular inflammatory signaling pathways, and minimizing immune cell recruitment are essential for lung protection in LIRI.

Immunomodulatory effects of curcumin on macrophage polarization in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by synovial inflammation, cartilage destruction, pannus formation and bone erosion. Various immune cells, including macrophages, are involved in RA pathogenesis. The heterogeneity and plasticity of macrophages render them pivotal regulators of both the induction and resolution of the inflammatory response. Predominantly, two different phenotypes of macrophages have been identified: classically activated M1 macrophages exacerbate inflammation via the production of cytokines, chemokines and other inflammatory mediators, while alternatively activated M2 macrophages inhibit inflammation and facilitate tissue repair. An imbalance in the M1/M2 macrophage ratio is critical during the initiation and progression of RA. Macrophage polarization is modulated by various transcription factors, epigenetic elements and metabolic reprogramming. Curcumin, an active component of turmeric, exhibits potent immunomodulatory effects and is administered in the treatment of multiple autoimmune diseases, including RA. The regulation of macrophage polarization and subsequent cytokine production as well as macrophage migration is involved in the mechanisms underlying the therapeutic effect of curcumin on RA. In this review, we summarize the underlying mechanisms by which curcumin modulates macrophage function and polarization in the context of RA to provide evidence for the clinical application of curcumin in RA treatment.

RBP-J regulates homeostasis and function of circulating Ly6Clo monocytes

Notch-RBP-J signaling plays an essential role in the maintenance of myeloid homeostasis. However, its role in monocyte cell fate decisions is not fully understood. Here, we showed that conditional deletion of transcription factor RBP-J in myeloid cells resulted in marked accumulation of blood Ly6Clo monocytes that highly expressed chemokine receptor CCR2. Bone marrow transplantation and parabiosis experiments revealed a cell-intrinsic requirement of RBP-J for controlling blood Ly6CloCCR2hi monocytes. RBP-J-deficient Ly6Clo monocytes exhibited enhanced capacity competing with wildtype counterparts in blood circulation. In accordance with alterations of circulating monocytes, RBP-J deficiency led to markedly increased population of lung tissues with Ly6Clo monocytes and CD16.2+ interstitial macrophages. Furthermore, RBP-J deficiency-associated phenotypes could be genetically corrected by further deleting Ccr2 in myeloid cells. These results demonstrate that RBP-J functions as a crucial regulator of blood Ly6Clo monocytes and thus derived lung-resident myeloid populations, at least in part through regulation of CCR2.

Role of immune inflammation regulated by macrophage in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) can lead to irreversible impairment of visual function, and the number of patients with AMD has been increasing globally. The immunoinflammatory theory is an important pathogenic mechanism of AMD, with macrophages serving as the primary inflammatory infiltrating cells in AMD lesions. Its powerful immunoinflammatory regulatory function has attracted considerable attention. Herein, we provide an overview of the involvement of macrophage-regulated immunoinflammation in different stages of AMD. Additionally, we summarize novel therapeutic approaches for AMD, focusing on targeting macrophages, such as macrophage/microglia modulators, reduction of macrophage aggregation in the subretinal space, modulation of macrophage effector function, macrophage phenotypic alterations, and novel biomimetic nanocomposites development based on macrophage-associated functional properties. We aimed to provide a basis and reference for the further exploration of AMD pathogenesis, developmental influences, and new therapeutic approaches.

Interleukin 28A aggravates Con A-induced acute liver injury by promoting the recruitment of M1 macrophages

Immune-mediated acute hepatic injury is characterized by the destruction of a large number of hepatocytes and severe liver function damage. Interleukin-28A (IL-28A), a member of the IL-10 family, is notable for its antiviral properties. However, despite advances in our understanding of IL-28A, its role in immune-mediated acute injury remains unclear. The present study investigated the role of IL-28A in concanavalin A (Con A)-induced acute immune liver injury. After Con A injection in mice, IL-28A level significantly increased. IL-28A deficiency was found to protect mice from acute liver injury, prolong survival time, and reduce serum aspartate aminotransferase and alanine aminotransferase levels. In contrast, recombinant IL-28A aggravated liver injury in mice. The proportion of activated M1 macrophages was significantly lower in the IL-28A-deficiency group than in the wild-type mouse group. In adoptive transfer experiments, M1 macrophages from WT could exacerbate mice acute liver injury symptoms in the IL-28A deficiency group. Furthermore, the expression of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), IL-12, IL-6, and IL-1β, by M1 macrophages decreased significantly in the IL-28A-deficiency group. Western blotting demonstrated that IL-28A deficiency could limit M1 macrophage polarization by modulating the nuclear factor (NF)-κB, mitogen-activated protein kinase (MAPK), and interferon regulatory factor (IRF) signaling pathways. In summary, IL-28A deletion plays an important protective role in the Con A-induced acute liver injury model and IL-28A deficiency inhibits the activation of M1 macrophages by inhibiting the NF-κB, MAPK, and IRF signaling pathways. These results provide a potential new target for the treatment of immune-related hepatic injury.

Therapy-induced normal tissue damage promotes breast cancer metastasis

Disseminated tumor cells frequently exhibit a period of dormancy, rendering them chemotherapy insensitive; conversely, the systemic delivery of chemotherapies can result in normal tissue damage. Using multiple mouse and human breast cancer models, we demonstrate that prior chemotherapy administration enhances metastatic colonization and outgrowth. In vitro, chemotherapy-treated fibroblasts display a pro-tumorigenic senescence-associated secretory phenotype (SASP) and are effectively eliminated by targeting the anti-apoptotic protein BCL-xL. In vivo, chemotherapy treatment induces SASP expression in normal tissues; however, the accumulation of senescent cells is limited, and BCL-xL inhibitors are unable to reduce chemotherapy-enhanced metastasis. This likely reflects that chemotherapy-exposed stromal cells do not enter a BCL-xL-dependent phenotype or switch their dependency to other anti-apoptotic BCL-2 family members. This study highlights the role of the metastatic microenvironment in controlling outgrowth of disseminated tumor cells and the need to identify additional approaches to limit the pro-tumorigenic effects of therapy-induced normal tissue damage.

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

Introduction

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

Methods

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

Results

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

Discussion

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

CD115+ monocytes protect microbially experienced mice against E. coli-induced sepsis

Uropathogenic E. coli (UPEC) is a primary organism responsible for urinary tract infections and a common cause of sepsis. Microbially experienced laboratory mice, generated by cohousing with pet store mice, exhibit increased morbidity and mortality to polymicrobial sepsis or lipopolysaccharide challenge. By contrast, cohoused mice display significant resistance, compared with specific pathogen-free mice, to a monomicrobial sepsis model using UPEC. CD115+ monocytes mediate protection in the cohoused mice, as depletion of these cells leads to increased mortality and UPEC pathogen burden. Further study of the cohoused mice reveals increased TNF-α production by monocytes, a skewing toward Ly6ChiCD115+ "classical" monocytes, and enhanced egress of Ly6ChiCD115+ monocytes from the bone marrow. Analysis of cohoused bone marrow also finds increased frequency and number of myeloid multipotent progenitor cells. These results show that a history of microbial exposure impacts innate immunity in mice, which can have important implications for the preclinical study of sepsis.

The Influence of Maternal High Fat Diet During Lactation on Offspring Hematopoietic Priming

Obesity and metabolic diseases are rising among women of reproductive age, increasing offspring metabolic risk. Maternal nutritional interventions during lactation present an opportunity to modify offspring outcomes. We previously demonstrated in mice that adult male offspring have metabolic impairments and increased adipose tissue macrophages (ATM) when dams are fed high fat diet (HFD) during the postnatal lactation window (HFD PN). We sought to understand the effect of HFD during lactation on early-life inflammation. HFD PN offspring were evaluated at postnatal day 16 to 19 for tissue weight and gene expression. Profiling of adipose tissue and bone marrow immune cells was conducted through lipidomics, in vitro myeloid colony forming unit assays, and flow cytometry. HFD PN mice had more visceral gonadal white adipose tissue (GWAT) and subcutaneous fat. Adipose tissue RNA sequencing demonstrated enrichment of inflammation, chemotaxis, and fatty acid metabolism and concordant changes in GWAT lipidomics. Bone marrow (BM) of both HFD PN male and female offspring had increased monocytes (CD45+Ly6G-CD11b+CD115+) and B cells (CD45+Ly6G-CD11b-CD19+). Similarly, serum from HFD PN offspring enhanced in vitro BM myeloid colonies in a toll-like receptor 4-dependent manner. We identified that male HFD PN offspring had increased GWAT pro-inflammatory CD11c+ ATMs (CD45+CD64+). Maternal exposure to HFD alters milk lipids enhancing adiposity and myeloid inflammation even in early life. Future studies are needed to understand the mechanisms driving this pro-inflammatory state of both BM and ATMs, the causes of the sexually dimorphic phenotypes, and the feasibility of intervening in this window to improve metabolic health.

Immune cell-mediated venous thrombus resolution

Herein, we review the current processes that govern experimental deep vein thrombus (DVT) resolution. How the human DVT resolves at the molecular and cellular level is not well known due to limited specimen availability. Experimentally, the thrombus resolution resembles wound healing, with early neutrophil-mediated actions followed by monocyte/macrophage-mediated events, including neovascularization, fibrinolysis, and eventually collagen replacement. Potential therapeutic targets are described, and coupling with site-directed approaches to mitigate off-target effects is the long-term goal. Similarly, timing of adjunctive agents to accelerate DVT resolution is an area that is only starting to be considered. There is much critical research that is needed in this area.

Macrophage polarization and metabolism in atherosclerosis

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of fatty deposits in the inner walls of vessels. These plaques restrict blood flow and lead to complications such as heart attack or stroke. The development of atherosclerosis is influenced by a variety of factors, including age, genetics, lifestyle, and underlying health conditions such as high blood pressure or diabetes. Atherosclerotic plaques in stable form are characterized by slow growth, which leads to luminal stenosis, with low embolic potential or in unstable form, which contributes to high risk for thrombotic and embolic complications with rapid clinical onset. In this complex scenario of atherosclerosis, macrophages participate in the whole process, including the initiation, growth and eventually rupture and wound healing stages of artery plaque formation. Macrophages in plaques exhibit high heterogeneity and plasticity, which affect the evolving plaque microenvironment, e.g., leading to excessive lipid accumulation, cytokine hyperactivation, hypoxia, apoptosis and necroptosis. The metabolic and functional transitions of plaque macrophages in response to plaque microenvironmental factors not only influence ongoing and imminent inflammatory responses within the lesions but also directly dictate atherosclerotic progression or regression. In this review, we discuss the origin of macrophages within plaques, their phenotypic diversity, metabolic shifts, and fate and the roles they play in the dynamic progression of atherosclerosis. It also describes how macrophages interact with other plaque cells, particularly T cells. Ultimately, targeting pathways involved in macrophage polarization may lead to innovative and promising approaches for precision medicine. Further insights into the landscape and biological features of macrophages within atherosclerotic plaques may offer valuable information for optimizing future clinical treatment for atherosclerosis by targeting macrophages.

Atherosclerosis from Newborn to Adult-Epidemiology, Pathological Aspects, and Risk Factors

Cardiovascular disease is the leading cause of mortality and morbidity throughout the world, accounting for 16.7 million deaths each year. The underlying pathological process for the majority of cardiovascular diseases is atherosclerosis, a slowly progressing, multifocal, chronic, immune-inflammatory disease that involves the intima of large and medium-sized arteries. The process of atherosclerosis begins in childhood as fatty streaks-an accumulation of lipids, inflammatory cells, and smooth muscle cells in the arterial wall. Over time, a more complex lesion develops into an atheroma and characteristic fibrous plaques. Atherosclerosis alone is rarely fatal; it is the further changes that render fibrous plaques vulnerable to rupture; plaque rupture represents the most common cause of coronary thrombosis. The prevalence of atherosclerosis is increasing worldwide and more than 50% of people with circulatory disease die of it, mostly in modern societies. Epidemiological studies have revealed several environmental and genetic risk factors that are associated with the early formation of a pathogenic foundation for atherosclerosis, such as dyslipidemia, hypertension, diabetes mellitus, obesity, and smoking. The purpose of this review is to bring together the current information concerning the origin and progression of atherosclerosis in childhood as well as the identification of known risk factors for atherosclerotic cardiovascular disease in children.

Monocytes as primary defenders against Toxoplasma gondii infection

Monocytes are recruited from the bone marrow to sites of infection where they release cytokines and chemokines, function in antimicrobial immunity, and differentiate into macrophages and dendritic cells to control infection. Although many studies have focused on monocyte-derived macrophages and dendritic cells, recent work has examined the unique roles of monocytes during infection to promote immune defense. We focus on the effector functions of monocytes during infection with the parasite Toxoplasma gondii, and discuss the signals that mobilize monocytes to sites of infection, their production of inflammatory cytokines and antimicrobial mediators, their ability to shape the adaptive immune response, and their immunoregulatory functions. Insights from other infections, including Plasmodium and Listeria are also included for comparison and context.

Monocyte heterogeneity in cardiovascular disease

Monocytes circulate the vasculature at steady state and are recruited to sites of inflammation where they differentiate into macrophages (MФ) to replenish tissue-resident MФ populations and engage in the development of cardiovascular disease (CVD). Monocytes display considerable heterogeneity, currently reflected by a nomenclature based on their expression of cluster of differentiation (CD) 14 and CD16, distinguishing CD14++CD16- classical (cMo), CD14++CD16+ intermediate (intMo) and CD14+CD16++ non-classical (ncMo) monocytes. Several reports point to shifted subset distributions in the context of CVD, with significant association of intMo numbers with atherosclerosis, myocardial infarction, and heart failure. However, clear indications of their causal involvement as well as their predictive value for CVD are lacking. As recent high-parameter cytometry and single-cell RNA sequencing (scRNA-Seq) studies suggest an even higher degree of heterogeneity, better understanding of the functionalities of these subsets is pivotal. Considering their high heterogeneity, surprisingly little is known about functional differences between MФ originating from monocytes belonging to different subsets, and implications thereof for CVD pathogenesis. This paper provides an overview of recent findings on monocyte heterogeneity in the context of homeostasis and disease as well as functional differences between the subsets and their potential to differentiate into MФ, focusing on their role in vessels and the heart. The emerging paradigm of monocyte heterogeneity transcending the current tripartite subset division argues for an updated nomenclature and functional studies to substantiate marker-based subdivision and to clarify subset-specific implications for CVD.

Bcl6, Irf2, and Notch2 promote nonclassical monocyte development

Ly6Clo monocytes are a myeloid subset that specializes in the surveillance of vascular endothelium. Ly6Clo monocytes have been shown to derive from Ly6Chi monocytes. NOTCH2 signaling has been implicated as a trigger for Ly6Clo monocyte development, but the basis for this effect is unclear. Here, we examined the impact of NOTCH2 signaling of myeloid progenitors on the development of Ly6Clo monocytes in vitro. NOTCH2 signaling induced by delta-like ligand 1 (DLL1) efficiently induced the transition of Ly6Chi TREML4- monocytes into Ly6Clo TREML4+ monocytes. We further identified two additional transcriptional requirements for development of Ly6Clo monocytes. Deletion of BCL6 from myeloid progenitors abrogated development of Ly6Clo monocytes. IRF2 was also required for Ly6Clo monocyte development in a cell-intrinsic manner. DLL1-induced in vitro transition into Ly6Clo TREML4+ monocytes required IRF2 but unexpectedly could occur in the absence of NUR77 or BCL6. These results imply a transcriptional hierarchy for these factors in controlling Ly6Clo monocyte development.

Hepatocytes reprogram liver macrophages involving control of TGF-β activation, influencing liver regeneration and injury

BACKGROUND

Macrophages play an important role in maintaining liver homeostasis and regeneration. However, it is not clear to what extent the different macrophage populations of the liver differ in terms of their activation state and which other liver cell populations may play a role in regulating the same.

METHODS

Reverse transcription PCR, flow cytometry, transcriptome, proteome, secretome, single cell analysis, and immunohistochemical methods were used to study changes in gene expression as well as the activation state of macrophages in vitro and in vivo under homeostatic conditions and after partial hepatectomy.

RESULTS

We show that F4/80+/CD11bhi/CD14hi macrophages of the liver are recruited in a C-C motif chemokine receptor (CCR2)-dependent manner and exhibit an activation state that differs substantially from that of the other liver macrophage populations, which can be distinguished on the basis of CD11b and CD14 expressions. Thereby, primary hepatocytes are capable of creating an environment in vitro that elicits the same specific activation state in bone marrow-derived macrophages as observed in F4/80+/CD11bhi/CD14hi liver macrophages in vivo. Subsequent analyses, including studies in mice with a myeloid cell-specific deletion of the TGF-β type II receptor, suggest that the availability of activated TGF-β and its downregulation by a hepatocyte-conditioned milieu are critical. Reduction of TGF-βRII-mediated signal transduction in myeloid cells leads to upregulation of IL-6, IL-10, and SIGLEC1 expression, a hallmark of the activation state of F4/80+/CD11bhi/CD14hi macrophages, and enhances liver regeneration.

CONCLUSIONS

The availability of activated TGF-β determines the activation state of specific macrophage populations in the liver, and the observed rapid transient activation of TGF-β may represent an important regulatory mechanism in the early phase of liver regeneration in this context.

Intestinal Immune Imbalance is an Alarm in the Development of IBD

Immune regulation plays a crucial role in human health and disease. Inflammatory bowel disease (IBD) is a chronic relapse bowel disease with an increasing incidence worldwide. Clinical treatments for IBD are limited and inefficient. However, the pathogenesis of immune-mediated IBD remains unclear. This review describes the activation of innate and adaptive immune functions by intestinal immune cells to regulate intestinal immune balance and maintain intestinal mucosal integrity. Changes in susceptible genes, autophagy, energy metabolism, and other factors interact in a complex manner with the immune system, eventually leading to intestinal immune imbalance and the onset of IBD. These events indicate that intestinal immune imbalance is an alarm for IBD development, further opening new possibilities for the unprecedented development of immunotherapy for IBD.

A phase 1 study of nivolumab in combination with interferon-gamma for patients with advanced solid tumors

This phase I, dose-escalation trial evaluates the safety of combining interferon-gamma (IFN-γ) and nivolumab in patients with metastatic solid tumors. Twenty-six patients are treated in four cohorts assessing increasing doses of IFN-γ with nivolumab to evaluate the primary endpoint of safety and determine the recommended phase two dose (RP2D). Most common adverse events are low grade and associated with IFN-γ. Three dose limiting toxicities are reported at the highest dose cohorts. We report only one patient with any immune related adverse event (irAE). No irAEs ≥ grade 3 are observed and no patients require corticosteroids. The maximum tolerated dose of IFN-γ is 75 mcg/m², however based on a composite of safety, clinical, and correlative factors the RP2D is 50 mcg/m². Exploratory analyses of efficacy in the phase I cohorts demonstrate one patient with a complete response, and five have achieved stable disease. Pre-planned correlative assessments of circulating immune cells demonstrate intermediate monocytes with increased PD-L1 expression correlating with IFN-γ dose and treatment duration. Interestingly, post-hoc analysis shows that IFN-γ induction increases circulating chemokines and is associated with an observed paucity of irAEs, warranting further evaluation. ClinicalTrials.gov Trial Registration: NCT02614456.

Polarizing Macrophage Functional Phenotype to Foster Cardiac Regeneration

There is an increasing interest in understanding the connection between the immune and cardiovascular systems, which are highly integrated and communicate through finely regulated cross-talking mechanisms. Recent evidence has demonstrated that the immune system does indeed have a key role in the response to cardiac injury and in cardiac regeneration. Among the immune cells, macrophages appear to have a prominent role in this context, with different subtypes described so far that each have a specific influence on cardiac remodeling and repair. Similarly, there are significant differences in how the innate and adaptive immune systems affect the response to cardiac damage. Understanding all these mechanisms may have relevant clinical implications. Several studies have already demonstrated that stem cell-based therapies support myocardial repair. However, the exact role that cardiac macrophages and their modulation may have in this setting is still unclear. The current need to decipher the dual role of immunity in boosting both heart injury and repair is due, at least for a significant part, to unresolved questions related to the complexity of cardiac macrophage phenotypes. The aim of this review is to provide an overview on the role of the immune system, and of macrophages in particular, in the response to cardiac injury and to outline, through the modulation of the immune response, potential novel therapeutic strategies for cardiac regeneration.

Monocyte and macrophage foam cells in diabetes-accelerated atherosclerosis

Diabetes results in an increased risk of atherosclerotic cardiovascular disease. This minireview will discuss whether monocyte and macrophage lipid loading contribute to this increased risk, as monocytes and macrophages are critically involved in the progression of atherosclerosis. Both uptake and efflux pathways have been described as being altered by diabetes or conditions associated with diabetes, which may contribute to the increased accumulation of lipids seen in macrophages in diabetes. More recently, monocytes have also been described as lipid-laden in response to elevated lipids, including triglyceride-rich lipoproteins, the class of lipids often elevated in the setting of diabetes.

Monocyte Differentiation and Heterogeneity: Inter-Subset and Interindividual Differences

The three subsets of human monocytes, classical, intermediate, and nonclassical, show phenotypic heterogeneity, particularly in their expression of CD14 and CD16. This has enabled researchers to delve into the functions of each subset in the steady state as well as in disease. Studies have revealed that monocyte heterogeneity is multi-dimensional. In addition, that their phenotype and function differ between subsets is well established. However, it is becoming evident that heterogeneity also exists within each subset, between health and disease (current or past) states, and even between individuals. This realisation casts long shadows, impacting how we identify and classify the subsets, the functions we assign to them, and how they are examined for alterations in disease. Perhaps the most fascinating is evidence that, even in relative health, interindividual differences in monocyte subsets exist. It is proposed that the individual's microenvironment could cause long-lasting or irreversible changes to monocyte precursors that echo to monocytes and through to their derived macrophages. Here, we will discuss the types of heterogeneity recognised in monocytes, the implications of these for monocyte research, and most importantly, the relevance of this heterogeneity for health and disease.

Crosstalk between macrophages and cardiac cells after myocardial infarction

Cardiovascular diseases, such as myocardial infarction (MI), are a leading cause of death worldwide. Acute MI (AMI) inflicts massive injury to the coronary microcirculation, causing large-scale cardiomyocyte death due to ischemia and hypoxia. Inflammatory cells such as monocytes and macrophages migrate to the damaged area to clear away dead cells post-MI. Macrophages are pleiotropic cells of the innate immune system, which play an essential role in the initial inflammatory response that occurs following MI, inducing subsequent damage and facilitating recovery. Besides their recognized role within the immune response, macrophages participate in crosstalk with other cells (including cardiomyocytes, fibroblasts, immune cells, and vascular endothelial cells) to coordinate post-MI processes within cardiac tissue. Macrophage-secreted exosomes have recently attracted increasing attention, which has led to a more elaborate understanding of macrophage function. Currently, the functional roles of macrophages in the microenvironment of the infarcted heart, particularly with regard to their interaction with surrounding cells, remain unclear. Understanding the specific mechanisms that mediate this crosstalk is essential in treating MI. In this review, we discuss the origin of macrophages, changes in their distribution post-MI, phenotypic and functional plasticity, as well as the specific signaling pathways involved, with a focus on the crosstalk with other cells in the heart. Thus, we provide a new perspective on the treatment of MI. Further in-depth research is required to elucidate the mechanisms underlying crosstalk between macrophages and other cells within cardiac tissue for the identification of potential therapeutic targets. Video Abstract.

Dietary Effects on Monocyte Phenotypes in Subjects With Hypertriglyceridemia and Metabolic Syndrome

In patients with hypertriglyceridemia, a short-term low-saturated fat vs high-saturated fat diet induced lower plasma lipids and improved monocyte phenotypes. These findings highlight the role of diet fat content and composition for monocyte phenotypes and possibly cardiovascular disease risk in these patients. (Effects of Dietary Interventions on Monocytes in Metabolic Syndrome; NCT03591588).

Myocardial Immune Cells: The Basis of Cardiac Immunology

The mammalian heart is characterized by the presence of striated myocytes, which allow continuous rhythmic contraction from early embryonic development until the last moments of life. However, the myocardium contains a significant contingent of leukocytes from every major class. This leukocyte pool includes both resident and nonresident immune cells. Over recent decades, it has become increasingly apparent that the heart is intimately sensitive to immune signaling and that myocardial leukocytes exhibit an array of critical functions, both in homeostasis and in the context of cardiac adaptation to injury. Here, we systematically review current knowledge of all major leukocyte classes in the heart, discussing their functions in health and disease. We also highlight the connection between the myocardium, immune cells, lymphoid organs, and both local and systemic immune responses.

B Cell Chronic Lymphocytic Leukemia Development in Mice with Chronic Lung Exposure to Coccidioides Fungal Arthroconidia

Links between repeated microbial infections and B cell chronic lymphocytic leukemia (B-CLL) have been proposed but not tested directly. This study examines how prolonged exposure to a human fungal pathogen impacts B-CLL development in Eµ-hTCL1-transgenic mice. Monthly lung exposure to inactivated Coccidioides arthroconidia, agents of Valley fever, altered leukemia development in a species-specific manner, with Coccidioides posadasii hastening B-CLL diagnosis/progression in a fraction of mice and Coccidioides immitis delaying aggressive B-CLL development, despite fostering more rapid monoclonal B cell lymphocytosis. Overall survival did not differ significantly between control and C. posadasii-treated cohorts but was significantly extended in C. immitis-exposed mice. In vivo doubling time analyses of pooled B-CLL showed no difference in growth rates of early and late leukemias. However, within C. immitis-treated mice, B-CLL manifests longer doubling times, as compared with B-CLL in control or C. posadasii-treated mice, and/or evidence of clonal contraction over time. Through linear regression, positive relationships were noted between circulating levels of CD5+/B220low B cells and hematopoietic cells previously linked to B-CLL growth, albeit in a cohort-specific manner. Neutrophils were positively linked to accelerated growth in mice exposed to either Coccidioides species, but not in control mice. Conversely, only C. posadasii-exposed and control cohorts displayed positive links between CD5+/B220low B cell frequency and abundance of M2 anti-inflammatory monocytes and T cells. The current study provides evidence that chronic lung exposure to fungal arthroconidia affects B-CLL development in a manner dependent on fungal genotype. Correlative studies suggest that fungal species differences in the modulation of nonleukemic hematopoietic cells are involved.

Fibronectin leucine-rich transmembrane protein 2 drives monocyte differentiation into macrophages via the UNC5B-Akt/mTOR axis

Upon migrating into the tissues, hematopoietic stem cell (HSC)-derived monocytes differentiate into macrophages, playing a crucial role in determining innate immune responses towards external pathogens and internal stimuli. However, the regulatory mechanisms underlying monocyte-to-macrophage differentiation remain largely unexplored. Here we divulge a previously uncharacterized but essential role for an axon guidance molecule, fibronectin leucine-rich transmembrane protein 2 (FLRT2), in monocyte-to-macrophage maturation. FLRT2 is almost undetectable in human monocytic cell lines, human peripheral blood mononuclear cells (PBMCs), and mouse primary monocytes but significantly increases in fully differentiated macrophages. Myeloid-specific deletion of FLRT2 (Flrt2ΔMyel) contributes to decreased peritoneal monocyte-to-macrophage generation in mice in vivo, accompanied by impaired macrophage functions. Gain- and loss-of-function studies support the promoting effect of FLRT2 on THP-1 cell and human PBMC differentiation into macrophages. Mechanistically, FLRT2 directly interacts with Unc-5 netrin receptor B (UNC5B) via its extracellular domain (ECD) and activates Akt/mTOR signaling. In vivo administration of mTOR agonist MYH1485 reverses the impaired phenotypes observed in Flrt2ΔMyel mice. Together, these results identify FLRT2 as a novel pivotal endogenous regulator of monocyte differentiation into macrophages. Targeting the FLRT2/UNC5B-Akt/mTOR axis may provide potential therapeutic strategies directly relevant to human diseases associated with aberrant monocyte/macrophage differentiation.

Osteoimmunology in Periodontitis and Orthodontic Tooth Movement

PURPOSE OF REVIEW

To review the role of the immune cells and their interaction with cells found in gingiva, periodontal ligament, and bone that leads to net bone loss in periodontitis or bone remodeling in orthodontic tooth movement.

RECENT FINDINGS

Periodontal disease is one of the most common oral diseases causing inflammation in the soft and hard tissues of the periodontium and is initiated by bacteria that induce a host response. Although the innate and adaptive immune response function cooperatively to prevent bacterial dissemination, they also play a major role in gingival inflammation and destruction of the connective tissue, periodontal ligament, and alveolar bone characteristic of periodontitis. The inflammatory response is triggered by bacteria or their products that bind to pattern recognition receptors that induce transcription factor activity to stimulate cytokine and chemokine expression. Epithelial, fibroblast/stromal, and resident leukocytes play a key role in initiating the host response and contribute to periodontal disease. Single-cell RNA-seq (scRNA-seq) experiments have added new insight into the roles of various cell types in the response to bacterial challenge. This response is modified by systemic conditions such as diabetes and smoking. In contrast to periodontitis, orthodontic tooth movement (OTM) is a sterile inflammatory response induced by mechanical force. Orthodontic force application stimulates acute inflammatory responses in the periodontal ligament and alveolar bone stimulated by cytokines and chemokines that produce bone resorption on the compression side. On the tension side, orthodontic forces induce the production of osteogenic factors, stimulating new bone formation. A number of different cell types, cytokines, and signaling/pathways are involved in this complex process. Inflammatory and mechanical force-induced bone remodeling involves bone resorption and bone formation. The interaction of leukocytes with host stromal cells and osteoblastic cells plays a key role in both initiating the inflammatory events as well as inducing a cellular cascade that results in remodeling in orthodontic tooth movement or in tissue destruction in periodontitis.

Novel technologies for applying immune checkpoint blockers

Cancer cells develop several ways to subdue the immune system among others via upregulation of inhibitory immune checkpoint (ICP) proteins. These ICPs paralyze immune effector cells and thereby enable unfettered tumor growth. Monoclonal antibodies (mAbs) that block ICPs can prevent immune exhaustion. Due to their outstanding effects, mAbs revolutionized the field of cancer immunotherapy. However, current ICP therapy regimens suffer from issues related to systemic administration of mAbs, including the onset of immune related adverse events, poor pharmacokinetics, limited tumor accessibility and immunogenicity. These drawbacks and new insights on spatiality prompted the exploration of novel administration routes for mAbs for instance peritumoral delivery. Moreover, novel ICP drug classes that are adept to novel delivery technologies were developed to circumvent the drawbacks of mAbs. We therefore review the state-of-the-art and novel delivery strategies of ICP drugs.

Pro-inflammatory protein S100A9 alters membrane organization by dispersing ordered domains

Pro-inflammatory, calcium-binding protein S100A9 is localized in the cytoplasm of many cells and regulates several intracellular and extracellular processes. S100A9 is involved in neuroinflammation associated with the pathogenesis of Alzheimer's disease (AD). The number of studies on the impact of S100A9 in co-aggregation processes with amyloid-like proteins is increasing. However, there is still a lack of data on how this protein interacts with lipid membranes. We employed atomic force microscopy (AFM), dynamic light scattering (DLS), and fluorescence measurements (Laurdan and Thioflavin-T) to study the interaction between protein and the membrane surface. We used lipid vesicles in bulk and planar tethered lipid bilayers as biomimetic membrane models. We demonstrated that the protein accumulates on negatively charged lipid bilayers but with no further loss of the bilayer's integrity. The most important result is that the initial adsorption and accumulation of apo-form of S100A9 on the lipid membrane surface is lipid phase-sensitive. The breaking down of raft-like and disappearance of gel-like domains indicate that protein incorporates into the hydrophobic part of the lipid bilayer. We observed the most noticeable loss of integrity in lipid bilayers constructed from a lipid mixture (brain total lipid extract). Understanding the function and interactions of these proteins in cellular environments might expand the development of new diagnostic and therapeutic approaches for AD or other related diseases.

Tumor-associated macrophages employ immunoediting mechanisms in colorectal tumor progression: Current research in Macrophage repolarization immunotherapy

Tumor-associated macrophages (TAMs) constitute the most prolific resident of the tumor microenvironment (TME) that regulate its TME into tumor suppressive or progressive milieu by utilizing immunoediting machinery. Here, the tumor cells construct an immunosuppressive microenvironment that educates TAMs to polarize from anti-tumor TAM-M1 to pro-tumor TAM-M2 phenotype consequently contributing to tumor progression. In colorectal cancer (CRC), the TME displays a prominent pro-tumorigenic immune profile with elevated expression of immune-checkpoint molecules notably PD-1, CTLA4, etc., in both MSI and ultra-mutated MSS tumors. This authenticated immune-checkpoint inhibition (ICI) immunotherapy as a pre-requisite for clinical benefit in CRC. However, in response to ICI, specifically, the MSI^hi tumors evolved to produce novel immune escape variants thus undermining ICI. Lately, TAM-directed therapies extending from macrophage depletion to repolarization have enabled TME alteration. While TAM accrual implicates clinical benefit in CRC, sustained inflammatory insult may program TAMs to shift from M1 to M2 phenotype. Their ability to oscillate on both facets of the spectrum represents macrophage repolarization immunotherapy as an effective approach to treating CRC. In this review, we briefly discuss the differentiation heterogeneity of colonic macrophages that partake in macrophage-directed immunoediting mechanisms in CRC progression and its employment in macrophage re-polarization immunotherapy.

The early neutrophil-committed progenitors aberrantly differentiate into immunoregulatory monocytes during emergency myelopoiesis

Inflammatory stimuli cause a state of emergency myelopoiesis leading to neutrophil-like monocyte expansion. However, their function, the committed precursors, or growth factors remain elusive. In this study we find that Ym1⁺Ly6C^hi monocytes, an immunoregulatory entity of neutrophil-like monocytes, arise from progenitors of neutrophil 1 (proNeu1). Granulocyte-colony stimulating factor (G-CSF) favors the production of neutrophil-like monocytes through previously unknown CD81⁺CX3CR1^lo monocyte precursors. GFI1 promotes the differentiation of proNeu2 from proNeu1 at the cost of producing neutrophil-like monocytes. The human counterpart of neutrophil-like monocytes that also expands in response to G-CSF is found in CD14⁺CD16^- monocyte fraction. The human neutrophil-like monocytes are discriminated from CD14⁺CD16^- classical monocytes by CXCR1 expression and the capacity to suppress T cell proliferation. Collectively, our findings suggest that the aberrant expansion of neutrophil-like monocytes under inflammatory conditions is a process conserved between mouse and human, which may be beneficial for the resolution of inflammation.

Caspase-11 promotes high-fat diet-induced NAFLD by increasing glycolysis, OXPHOS, and pyroptosis in macrophages

Introduction

Non-alcoholic fatty liver disease (NAFLD) has a global prevalence of 25% of the population and is a leading cause of cirrhosis and hepatocellular carcinoma. NAFLD ranges from simple steatosis (non-alcoholic fatty liver) to non-alcoholic steatohepatitis (NASH). Hepatic macrophages, specifically Kupffer cells (KCs) and monocyte-derived macrophages, act as key players in the progression of NAFLD. Caspases are a family of endoproteases that provide critical connections to cell regulatory networks that sense disease risk factors, control inflammation, and mediate inflammatory cell death (pyroptosis). Caspase-11 can cleave gasdermin D (GSDMD) to induce pyroptosis and specifically defends against bacterial pathogens that invade the cytosol. However, it's still unknown whether high fat diet (HFD)-facilitated gut microbiota-generated cytoplasmic lipopolysaccharides (LPS) activate caspase-11 and promote NAFLD.

Methods

To examine this hypothesis, we performed liver pathological analysis, RNA-seq, FACS, Western blots, Seahorse mitochondrial stress analyses of macrophages and bone marrow transplantation on HFD-induced NAFLD in WT and Casp11-/- mice.

Results and Discussion

Our results showed that 1) HFD increases body wight, liver wight, plasma cholesterol levels, liver fat deposition, and NAFLD activity score (NAS score) in wild-type (WT) mice; 2) HFD increases the expression of caspase-11, GSDMD, interleukin-1β, and guanylate-binding proteins in WT mice; 3) Caspase-11 deficiency decreases fat liver deposition and NAS score; 4) Caspase-11 deficiency decreases bone marrow monocyte-derived macrophage (MDM) pyroptosis (inflammatory cell death) and inflammatory monocyte (IM) surface GSDMD expression; 5) Caspase-11 deficiency re-programs liver transcriptomes and reduces HFD-induced NAFLD; 6) Caspase-11 deficiency decreases extracellular acidification rates (glycolysis) and oxidative phosphorylation (OXPHOS) in inflammatory fatty acid palmitic acid-stimulated macrophages, indicating that caspase-11 significantly contributes to maintain dual fuel bioenergetics-glycolysis and OXPHOS for promoting pyroptosis in macrophages. These results provide novel insights on the roles of the caspase-11-GSDMD pathway in promoting hepatic macrophage inflammation and pyroptosis and novel targets for future therapeutic interventions involving the transition of NAFLD to NASH, hyperlipidemia, type II diabetes, metabolic syndrome, metabolically healthy obesity, atherosclerotic cardiovascular diseases, autoimmune diseases, liver transplantation, and hepatic cancers.

Small Molecule Drugs That Inhibit Phagocytosis

In our initial publication on the in vitro testing of more than 200 compounds, we demonstrated that small molecules can inhibit phagocytosis. We therefore theorized that a small molecule drug discovery-based approach to the treatment of immune cytopenias (ITP, AIHA, HTR, DHTR) is feasible. Those earlier studies showed that small molecules with anti-phagocytic groups, such as the pyrazole core, are good models for producing efficacious phagocytosis inhibitors with low toxicity. We recently screened a chemical library of 80 compounds containing pyrazole/isoxazole/pyrrole core structures and found four hit molecules for further follow-up, all having the pyrazole core structure. Subsequent evaluation via MTT viability, LDH release, and apoptosis, led to the selection of two lead compounds with negligible toxicity and high efficacy. In an in vitro assay for inhibition of phagocytosis, their IC₅₀ values were 2-4 µM. The rational development of these discoveries from hit to lead molecule stage, viz. independent synthesis/scale up of hit molecules, and in vivo activities in mouse models of autoimmune disease, will result in the selection of a lead compound(s) for further pre-clinical evaluation.

Cardiac repair after myocardial infarction: A two-sided role of inflammation-mediated

Myocardial infarction is the leading cause of death and disability worldwide, and the development of new treatments can help reduce the size of myocardial infarction and prevent adverse cardiovascular events. Cardiac repair after myocardial infarction can effectively remove necrotic tissue, induce neovascularization, and ultimately replace granulation tissue. Cardiac inflammation is the primary determinant of whether beneficial cardiac repair occurs after myocardial infarction. Immune cells mediate inflammatory responses and play a dual role in injury and protection during cardiac repair. After myocardial infarction, genetic ablation or blocking of anti-inflammatory pathways is often harmful. However, enhancing endogenous anti-inflammatory pathways or blocking endogenous pro-inflammatory pathways may improve cardiac repair after myocardial infarction. A deficiency of neutrophils or monocytes does not improve overall cardiac function after myocardial infarction but worsens it and aggravates cardiac fibrosis. Several factors are critical in regulating inflammatory genes and immune cells' phenotypes, including DNA methylation, histone modifications, and non-coding RNAs. Therefore, strict control and timely suppression of the inflammatory response, finding a balance between inflammatory cells, preventing excessive tissue degradation, and avoiding infarct expansion can effectively reduce the occurrence of adverse cardiovascular events after myocardial infarction. This article reviews the involvement of neutrophils, monocytes, macrophages, and regulatory T cells in cardiac repair after myocardial infarction. After myocardial infarction, neutrophils are the first to be recruited to the damaged site to engulf necrotic cell debris and secrete chemokines that enhance monocyte recruitment. Monocytes then infiltrate the infarct site and differentiate into macrophages and they release proteases and cytokines that are harmful to surviving myocardial cells in the pre-infarct period. As time progresses, apoptotic neutrophils are cleared, the recruitment of anti-inflammatory monocyte subsets, the polarization of macrophages toward the repair phenotype, and infiltration of regulatory T cells, which secrete anti-inflammatory factors that stimulate angiogenesis and granulation tissue formation for cardiac repair. We also explored how epigenetic modifications regulate the phenotype of inflammatory genes and immune cells to promote cardiac repair after myocardial infarction. This paper also elucidates the roles of alarmin S100A8/A9, secreted frizzled-related protein 1, and podoplanin in the inflammatory response and cardiac repair after myocardial infarction.