Glucocorticoids induce differentiation of monocytes towards macrophages that share functional and phenotypical aspects with erythroblastic island macrophages

Differentiating erythroblasts adapt to mechanical stimulation by upregulation of cholesterol biosynthesis via S1P/SREBP-induced HMGCR expression

Understanding how mechanical stress affects erythropoiesis is crucial to produce transfusable erythrocytes in fluid-turbulent bioreactors. We investigated the effects of shear-stress on differentiating CD49d+CD235a+ primary human erythroblasts (EBL) at molecular, cellular, and functional level. Shear-stress, at differentiation onset, enhanced EBL maturation and induced upregulation of genes regulating cholesterol/lipids biosynthesis, causing changes in cell lipid composition. Of note, the osmotic resistance, and the expression of 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGCR), the rate-limiting enzyme of the cholesterol biosynthesis pathway, were higher in dynamic cultures. Inhibition of the S1P-induced proteolytic cleavage, activating SREBPs, led to abrogation of HMCGR expression, and loss of EBL in dynamic cultures, similar to lovastatin administration. This data reveals a role for the S1P-SREBP-HMGCR-axis in the regulation of shear-stress induced adaptation during erythropoiesis, shedding light into mechanisms that will assist the upscaling of erythroid differentiation into bioreactors. Moreover, as shear-stress on hematopoietic cells occurs within the bone-marrow, these results introduce a novel signalling axis in the transduction pathways controlling erythropoiesis.

Reprogramming macrophages with R848-loaded artificial protocells to modulate skin and skeletal wound healing

After tissue injury, inflammatory cells are rapidly recruited to the wound where they clear microbes and other debris, and coordinate the behaviour of other cell lineages at the repair site in both positive and negative ways. In this study, we take advantage of the translucency and genetic tractability of zebrafish to evaluate the feasibility of reprogramming innate immune cells in vivo with cargo-loaded protocells and investigate how this alters the inflammatory response in the context of skin and skeletal repair. Using live imaging, we show that protocells loaded with R848 cargo (which targets TLR7 and TLR8 signalling), are engulfed by macrophages resulting in their switching to a pro-inflammatory phenotype and altering their regulation of angiogenesis, collagen deposition and re-epithelialization during skin wound healing, as well as dampening osteoblast and osteoclast recruitment and bone mineralization during fracture repair. For infected skin wounds, R848-reprogrammed macrophages exhibited enhanced bactericidal activities leading to improved healing. We replicated our zebrafish studies in cultured human macrophages, and showed that R848-loaded protocells similarly reprogramme human cells, indicating how this strategy might be used to modulate wound inflammation in the clinic.

Surface Markers and Chemokines/Cytokines of Tumor-Associated Macrophages in Osteosarcoma and Other Carcinoma Microenviornments-Contradictions and Comparisons

Osteosarcoma (OS) is the most common primary bone tumor in children and adolescents. Prognosis is improving with advances in multidisciplinary treatment strategies, but the development of new anticancer agents has not, and improvement in prognosis for patients with pulmonary metastases has stalled. In recent years, the tumor microenvironment (TME) has gained attention as a therapeutic target for cancer. The immune component of OS TME consists mainly of tumor-associated macrophages (TAMs). They exhibit remarkable plasticity, and their phenotype is influenced by the TME. In general, surface markers such as CD68 and CD80 show anti-tumor effects, while CD163 and CD204 show tumor-promoting effects. Surface markers have potential value as diagnostic and prognostic biomarkers. The cytokines and chemokines produced by TAMs promote tumor growth and metastasis. However, the role of TAMs in OS remains unclear to date. In this review, we describe the role of TAMs in OS by focusing on TAM surface markers and the TAM-produced cytokines and chemokines in the TME, and by comparing their behaviors in other carcinomas. We found contrary results from different studies. These findings highlight the urgency for further research in this field to improve the stalled OS prognosis percentages.

Biomaterial-mediated intracellular control of macrophages for cell therapy in pro-inflammatory and pro-fibrotic conditions

Macrophages are key modulators of all inflammatory diseases and essential for their resolution, making macrophage cell therapy a promising strategy for regenerative medicine. However, since macrophages change rapidly in response to microenvironmental cues, their phenotype must be controlled post-administration. We present a tunable biomaterial-based strategy to control macrophages intracellularly via small molecule-releasing microparticles. Poly(lactic-co-glycolic acid) microparticles encapsulating the anti-inflammatory and anti-fibrotic drug dexamethasone were administered to macrophages in vitro, with uptake rates controlled by different loading regimes. Microparticle dose and dexamethasone content directly affected macrophage phenotype and phagocytic capacity, independent of particle content per cell, leading to an overall pro-reparative, anti-inflammatory, anti-fibrotic phenotype with increased phagocytic and ECM degrading functionality. Intracellularly controlled macrophages partially maintained this phenotype in vivo in a murine pulmonary fibrosis model, with more prominent effects in a pro-fibrotic environment compared to pro-inflammatory. These results suggest that intracellular control using biomaterials has the potential to control macrophage phenotype post-administration, which is essential for successful macrophage cell therapy.

Exploring effect of M2 macrophages on experimental full-thickness wound healing in streptozotocin-induced diabetic rats

Diabetes mellitus is one of the most prevalent medical conditions, in both humans and animals. People with diabetes mellitus often experience slower than normal wound healing, making it a serious health concern. This study investigates the effect of M2 differentiated macrophages on full-thickness wound healing in white Westar rats exposed to streptozocin 70 mg/kg. A full-thickness skin defect with dimensions of 2 × 2 cm was created on the back of all the animals, and their blood sugar was simultaneously assessed. The monocytes were isolated from blood samples using the plastic adherence method and were exposed to dexamethasone (5-10 μ) for 24 h. Subsequently, they were washed with PBS and incubated in fresh cell culture medium for 5 days. The differentiated M2 cells were injected into four points of the experimental ulcers of the treatment group. Macroscopic and microscopic changes were evaluated and compared over a period of two weeks between the test and control groups. The infusion of these cells a few days after wounding enhances wound healing parameters significantly, as evidenced by an increase in germinating tissue formation, wound contraction, inflammation reduction, and collagen increase in the treated group.

The effects of the differentiated macrophages by dexamethasone on the immune responses

The characteristics of M2 macrophages suggest immunotherapeutic approaches for inducing immunological tolerance. The current study aimed to evaluate the effect of Dexamethasone (Dex) treatment on monocytes polarization and its impact on immune responses. The monocytes were extracted from the rat's blood samples. The effects of Dex concentration and treatment duration on monocyte viability, phagocytosis of rabbit red blood cell (RRBC) antigens, and cytokine gene expression were evaluated using MTT, ELISA, and Real-Time PCR analysis, respectively. The monocytes treated with Dex were injected into the rats as an autograft. The effects of the grafted cells were assessed on immune responses, monocyte differentiation, and pathological lesions, in comparison to the control groups. Treatment of monocytes with 10-5 M of Dex for 48 h increased the expression of IL-10 and TGF-β genes, while reducing the expression of TNF-α and IL-1 genes. The monocytes treated with antigen and Dex showed higher CD206 gene expression compared to CD80. The cells that were treated with Dex had the highest concentration of antigens after five days. Administration of the grafted cells to the animals has some significant effects on innate immune responses and no impact on pathological lesions. The group that received cells treated with Dex and antigen experienced a significant decrease in anti-RBC antibody titers. Additionally, there was a significant difference in the expression of cytokine genes and M2 differentiation markers among the groups that were evaluated. The effects of Dex on the viability and differentiation of monocytes depend on the dosage, timing, and duration of the treatment.

Defining the proteomic landscape of cultured macrophages and their polarization continuum

Macrophages have previously been characterized based on phenotypical and functional differences into suggested simplified subtypes of MØ, M1, M2a and M2c. These macrophage subtypes can be generated in a well-established primary monocyte culture model that produces cells expressing accepted subtype surface markers. To determine how these subtypes retain functional similarities and better understand their formation, we generated all four subtypes from the same donors. Comparative whole-cell proteomics confirmed that four distinct macrophage subtypes could be induced from the same donor material, with > 50% of 5435 identified proteins being significantly altered in abundance between subtypes. Functional assessment highlighted that these distinct protein expression profiles are primed to enable specific cell functions, indicating that this shifting proteome is predictive of meaningful changes in cell characteristics. Importantly, the 2552 proteins remained consistent in abundance across all macrophage subtypes examined, demonstrating maintenance of a stable core proteome that likely enables swift polarity changes. We next explored the cross-polarization capabilities of preactivated M1 macrophages treated with dexamethasone. Importantly, these treated cells undergo a partial repolarization toward the M2c surface markers but still retain the M1 functional phenotype. Our investigation of polarized macrophage subtypes therefore provides evidence of a sliding scale of macrophage functionality, with these data sets providing a valuable benchmark resource for further studies of macrophage polarity, with relevance for cell therapy development and drug discovery.

Stress induces behavioral abnormalities by increasing expression of phagocytic receptor MERTK in astrocytes to promote synapse phagocytosis

Childhood neglect and/or abuse can induce mental health conditions with unknown mechanisms. Here, we identified stress hormones as strong inducers of astrocyte-mediated synapse phagocytosis. Using in vitro, in vivo, and human brain organoid experiments, we showed that stress hormones increased the expression of the Mertk phagocytic receptor in astrocytes through glucocorticoid receptor (GR). In post-natal mice, exposure to early social deprivation (ESD) specifically activated the GR-MERTK pathway in astrocytes, but not in microglia. The excitatory post-synaptic density in cortical regions was reduced in ESD mice, and there was an increase in the astrocytic engulfment of these synapses. The loss of excitatory synapses, abnormal neuronal network activities, and behavioral abnormalities in ESD mice were largely prevented by ablating GR or MERTK in astrocytes. Our work reveals the critical roles of astrocytic GR-MERTK activation in evoking stress-induced abnormal behaviors in mice, suggesting GR-MERTK signaling as a therapeutic target for stress-induced mental health conditions.

Navigating the marrow sea towards erythromyeloblastic islands under normal and inflammatory conditions

PURPOSE OF REVIEW

Terminal erythroid differentiation occurs in specialized niches called erythroblastic islands. Since their discovery in 1958, these niches have been described as a central macrophage surrounded by differentiating erythroblasts. Here, we review the recent advances made in the characterization of these islands and the role they could play in anaemia of inflammation.

RECENT FINDINGS

The utilization of multispectral imaging flow cytometry (flow cytometry with microscopy) has enabled for a more precise characterization of the niche that revealed the presence of maturing granulocytes in close contact with the central macrophage. These erythromyeloblastic islands (EMBIs) can adapt depending on the peripheral needs. Indeed, during inflammation wherein inflammatory cytokines limit erythropoiesis and promote granulopoiesis, EMBIs present altered structures with increased maturing granulocytes and decreased erythroid precursors.

SUMMARY

Regulation of the structure and function of the EMBI in the bone marrow emerges as a potential player in the pathophysiology of acute and chronic inflammation and its associated anaemia.

Role of Macrophages in Sickle Cell Disease Erythrophagocytosis and Erythropoiesis

Sickle cell disease (SCD) is an inherited blood disorder caused by a β-globin gene point mutation that results in the production of sickle hemoglobin that polymerizes upon deoxygenation, causing the sickling of red blood cells (RBCs). RBC deformation initiates a sequence of events leading to multiple complications, such as hemolytic anemia, vaso-occlusion, chronic inflammation, and tissue damage. Macrophages participate in extravascular hemolysis by removing damaged RBCs, hence preventing the release of free hemoglobin and heme, and triggering inflammation. Upon erythrophagocytosis, macrophages metabolize RBC-derived hemoglobin, activating mechanisms responsible for recycling iron, which is then used for the generation of new RBCs to try to compensate for anemia. In the bone marrow, macrophages can create specialized niches, known as erythroblastic islands (EBIs), which regulate erythropoiesis. Anemia and inflammation present in SCD may trigger mechanisms of stress erythropoiesis, intensifying RBC generation by expanding the number of EBIs in the bone marrow and creating new ones in extramedullary sites. In the current review, we discuss the distinct mechanisms that could induce stress erythropoiesis in SCD, potentially shifting the macrophage phenotype to an inflammatory profile, and changing their supporting role necessary for the proliferation and differentiation of erythroid cells in the disease. The knowledge of the soluble factors, cell surface and intracellular molecules expressed by EBI macrophages that contribute to begin and end the RBC’s lifespan, as well as the understanding of their signaling pathways in SCD, may reveal potential targets to control the pathophysiology of the disease.

Digital image analysis of erythroblastic islands in myelodysplastic syndromes

INTRODUCTION

Myelodysplastic syndromes (MDS) encompass a diverse group of myeloid neoplasms for which the diagnosis of low-grade subtypes remains challenging. Erythroblastic islands (EBIs) are highly organized units of erythroid proliferation, differentiation, and enucleation. EBI disruption is frequently observed and is believed to be one of the early changes in MDS.

METHODS

In this study, we digitally analyzed bone marrow biopsies dual stained with alpha-hemoglobin stabilizing protein (AHSP) and CD163 to quantitatively study features of EBIs in MDS, among MDS subtypes, as well as those in normal marrows and marrows with other causes of anemia.

RESULTS

EBIs in MDS specimens were smaller in size and higher in density compared to both normal and non-MDS anemia specimens. Increased CD163 expression within the EBIs is observed in both MDS and other causes of anemia. A combination of increased EBI density and CD163 expression is seen in association with MDS with high-risk cytogenetics and multiple adverse mutations.

CONCLUSION

As a proof-of-concept study, we show that EBI features can be relatively easily quantified with AHSP/CD163 dual immunohistochemistry and open-source imaging analysis software, highlighting those that are unique to MDS, and which may be prognostically relevant. Further studies of the measurable EBI features may provide valuable and novel tools to aid MDS diagnosis and prognostication in the era of digital pathology.

Apoptosis Evaluation in Circulating CD34+-Enriched Hematopoietic Stem and Progenitor Cells in Patients with Abnormally Increased Production of Endogenous Glucocorticoids in Course of Cushing's Syndrome

Abnormalities in hematological parameters of peripheral blood have been noted in patients with endogenous Cushing's Syndrome (CS) in the corticotropin (ACTH)-dependent and ACTH-independent forms. Nevertheless, the exact mechanism of glucocorticoids (GCs) action on human hematopoiesis is still not entirely clear. The aim of the study was to determine whether endogenous excessive production of GCs could affect apoptosis of CD34+ cells enriched in hematopoietic stem and progenitor cells (HSPCs) collected from the peripheral blood of newly diagnosed CS patients. Flow cytometry, Annexin-V enzyme-linked immunosorbent assay, TUNEL assay, real-time quantitative PCR, and microarray RNA/miRNA techniques were used to characterize CS patients' HSPCs. We found that the glucocorticoid receptor (GR) protein expression levels in CS were higher than in healthy controls. A complex analysis of apoptotic status of CS patients' HSPC cells showed that GCs significantly augmented apoptosis in peripheral blood-derived CD34+ cells and results obtained using different methods to detect early and late apoptosis in analyzed cell population were consistent. CS was also associated with significant upregulation in several members of the BCL-2 superfamily and other genes associated with apoptosis control. Furthermore, global gene expression analysis revealed significantly higher expression of genes associated with programmed cell death control in HSPCs from CS patients. These findings suggest that human endogenous GCs have a direct pro-apoptotic activity in hematopoietic CD34+ cells derived from CS subjects before treatment.

Macrophage Reprogramming with Anti-miR223-Loaded Artificial Protocells Enhances In Vivo Cancer Therapeutic Potential

Several immune cell-expressed miRNAs (miRs) are associated with altered prognostic outcome in cancer patients, suggesting that they may be potential targets for development of cancer therapies. Here, translucent zebrafish (Danio rerio) is utilized to demonstrate that genetic knockout or knockdown of one such miR, microRNA-223 (miR223), globally or specifically in leukocytes, does indeed lead to reduced cancer progression. As a first step toward potential translation to a clinical therapy, a novel strategy is described for reprogramming neutrophils and macrophages utilizing miniature artificial protocells (PCs) to deliver anti-miRs against the anti-inflammatory miR223. Using genetic and live imaging approaches, it is shown that phagocytic uptake of anti-miR223-loaded PCs by leukocytes in zebrafish (and by human macrophages in vitro) effectively prolongs their pro-inflammatory state by blocking the suppression of pro-inflammatory cytokines, which, in turn, drives altered immune cell-cancer cell interactions and ultimately leads to a reduced cancer burden by driving reduced proliferation and increased cell death of tumor cells. This PC cargo delivery strategy for reprogramming leukocytes toward beneficial phenotypes has implications also for treating other systemic or local immune-mediated pathologies.

Macrophages: key players in erythrocyte turnover

The development of red blood cells (RBCs), or erythropoiesis, occurs in specialized niches in the bone marrow, called erythroblastic islands, composed of a central macrophage surrounded by erythroblasts at different stages of differentiation. Upon anemia or hypoxemia, erythropoiesis extends to extramedullary sites, mainly spleen and liver, a process known as stress erythropoiesis, leading to the expansion of erythroid progenitors, iron recruitment and increased production of reticulocytes and mature RBCs. Macrophages are key cells in both homeostatic and stress erythropoiesis, providing conditions for erythroid cells to survive, proliferate and differentiate. During RBCs aging and injury, macrophages play a fundamental role again, performing the clearance of these cells and recycling iron for new erythroblasts in development. Thus, macrophages are crucial components of the RBCs turnover and in this review, we aimed to cover the main known mechanisms involved in the process of birth and death of RBCs, highlighting the importance of macrophage functions in the whole RBC lifecycle.

Effects of glucocorticoids on leukocytes: Genomic and non-genomic mechanisms

Glucocorticoids (GCs) have been widely used as immunosuppressants and anti-inflammatory agents to treat a variety of autoimmune and inflammatory diseases, and they fully exert their anti-inflammatory and immune-regulating effects in the body. The effect of GCs on white blood cells is an important part of their action. GCs can cause changes in peripheral blood white blood cell counts by regulating the proliferation, differentiation, and apoptosis of white blood cells. Although the total number of white blood cells, neutrophil counts, lymphocytes, and eosinophils increases, the counts of basic granulocytes and macrophages decreases. In addition, GCs can regulate the activation and secretion of white blood cells, inhibit the secretion of a variety of pro-inflammatory cytokines, the expression of chemokines, and promote the production of anti-inflammatory cytokines. For patients on GC therapy, the effects of GCs on leukocytes were similar to the changes in peripheral blood caused by bacterial infections. Thus, we suggest that clinicians should be more cautious in assessing the presence of infection in children with long-term use of GCs and avoid overuse of antibiotics in the presence of elevated leukocytes. GCs work through genomic and non-genomic mechanisms in the human body, which are mediated by GC receptors. In recent years, studies have not fully clarified the mechanism of GCs, and further research on these mechanisms will help to develop new therapeutic strategies.

GM-CSF impairs erythropoiesis by disrupting erythroblastic island formation via macrophages

Anemia is a significant complication of chronic inflammation and may be related to dysregulated activities among erythroblastic island (EBI) macrophages. GM-CSF was reported to be upregulated and attracted as a therapeutic target in many inflammatory diseases. Among EBIs, we found that the GM-CSF receptor is preferentially and highly expressed among EBI macrophages but not among erythroblasts. GM-CSF treatment significantly decreases human EBI formation in vitro by decreasing the adhesion molecule expression of CD163. RNA-sequence analysis suggests that GM-CSF treatment impairs the supporting function of human EBI macrophages during erythropoiesis. GM-CSF treatment also polarizes human EBI macrophages from M2-like type to M1-like type. In addition, GM-CSF decreases mouse bone marrow (BM) erythroblasts as well as EBI macrophages, leading to a reduction in EBI numbers. In defining the molecular mechanism at work, we found that GM-CSF treatment significantly decreases the adhesion molecule expression of CD163 and Vcam1 in vivo. Importantly, GM-CSF treatment also decreases the phagocytosis rate of EBI macrophages in mouse BM as well as decreases the expression of the engulfment-related molecules Mertk, Axl, and Timd4. In addition, GM-CSF treatment polarizes mouse BM EBI macrophages from M2-like type to M1-like type. Thus, we document that GM-CSF impairs EBI formation in mice and humans. Our findings support that targeting GM-CSF or reprogramming EBI macrophages might be a novel strategy to treat anemia resulting from inflammatory diseases.

Transcriptional Control of Gene Expression and the Heterogeneous Cellular Identity of Erythroblastic Island Macrophages

During definitive erythropoiesis, maturation of erythroid progenitors into enucleated reticulocytes requires the erythroblastic island (EBI) niche comprising a central macrophage attached to differentiating erythroid progenitors. Normally, the macrophage provides a nurturing environment for maturation of erythroid cells. Its critical physiologic importance entails aiding in recovery from anemic insults, such as systemic stress or acquired disease. Considerable interest in characterizing the central macrophage of the island niche led to the identification of putative cell surface markers enriched in island macrophages, enabling isolation and characterization. Recent studies focus on bulk and single cell transcriptomics of the island macrophage during adult steady-state erythropoiesis and embryonic erythropoiesis. They reveal that the island macrophage is a distinct cell type but with widespread cellular heterogeneity, likely suggesting distinct developmental origins and biological function. These studies have also uncovered transcriptional programs that drive gene expression in the island macrophage. Strikingly, the master erythroid regulator EKLF/Klf1 seems to also play a major role in specifying gene expression in island macrophages, including a putative EKLF/Klf1-dependent transcription circuit. Our present review and analysis of mouse single cell genetic patterns suggest novel expression characteristics that will enable a clear enrichment of EBI subtypes and resolution of island macrophage heterogeneity. Specifically, the discovery of markers such as Epor, and specific features for EKLF/Klf1-expressing island macrophages such as Sptb and Add2, or for SpiC-expressing island macrophage such as Timd4, or for Maf/Nr1h3-expressing island macrophage such as Vcam1, opens exciting possibilities for further characterization of these unique macrophage cell types in the context of their critical developmental function.

Coordinated glucocorticoid receptor and MAFB action induces tolerogenesis and epigenome remodeling in dendritic cells

Glucocorticoids (GCs) exert potent anti-inflammatory effects in immune cells through the glucocorticoid receptor (GR). Dendritic cells (DCs), central actors for coordinating immune responses, acquire tolerogenic properties in response to GCs. Tolerogenic DCs (tolDCs) have emerged as a potential treatment for various inflammatory diseases. To date, the underlying cell type-specific regulatory mechanisms orchestrating GC-mediated acquisition of immunosuppressive properties remain poorly understood. In this study, we investigated the transcriptomic and epigenomic remodeling associated with differentiation to DCs in the presence of GCs. Our analysis demonstrates a major role of MAFB in this process, in synergy with GR. GR and MAFB both interact with methylcytosine dioxygenase TET2 and bind to genomic loci that undergo specific demethylation in tolDCs. We also show that the role of MAFB is more extensive, binding to thousands of genomic loci in tolDCs. Finally, MAFB knockdown erases the tolerogenic properties of tolDCs and reverts the specific DNA demethylation and gene upregulation. The preeminent role of MAFB is also demonstrated in vivo for myeloid cells from synovium in rheumatoid arthritis following GC treatment. Our results imply that, once directly activated by GR, MAFB plays a critical role in orchestrating the epigenomic and transcriptomic remodeling that define the tolerogenic phenotype.

Pleiotropic Effects of Glucocorticoids on the Immune System in Circadian Rhythm and Stress

Glucocorticoids (GCs) are a class of steroid hormones secreted from the adrenal cortex. Their production is controlled by circadian rhythm and stress, the latter of which includes physical restraint, hunger, and inflammation. Importantly, GCs have various effects on immunity, metabolism, and cognition, including pleiotropic effects on the immune system. In general, GCs have strong anti-inflammatory and immunosuppressive effects. Indeed, they suppress inflammatory cytokine expression and cell-mediated immunity, leading to increased risks of some infections. However, recent studies have shown that endogenous GCs induced by the diurnal cycle and dietary restriction enhance immune responses against some infections by promoting the survival, redistribution, and response of T and B cells via cytokine and chemokine receptors. Furthermore, although GCs are reported to reduce expression of Th2 cytokines, GCs enhance type 2 immunity and IL-17-associated immunity in some stress conditions. Taken together, GCs have both immunoenhancing and immunosuppressive effects on the immune system.

Industrially Compatible Transfusable iPSC-Derived RBCs: Progress, Challenges and Prospective Solutions

Amidst the global shortfalls in blood supply, storage limitations of donor blood and the availability of potential blood substitutes for transfusion applications, society has pivoted towards in vitro generation of red blood cells (RBCs) as a means to solve these issues. Many conventional research studies over the past few decades have found success in differentiating hematopoietic stem and progenitor cells (HSPCs) from cord blood, adult bone marrow and peripheral blood sources. More recently, techniques that involve immortalization of erythroblast sources have also gained traction in tackling this problem. However, the RBCs generated from human induced pluripotent stem cells (hiPSCs) still remain as the most favorable solution due to many of its added advantages. In this review, we focus on the breakthroughs for high-density cultures of hiPSC-derived RBCs, and highlight the major challenges and prospective solutions throughout the whole process of erythropoiesis for hiPSC-derived RBCs. Furthermore, we elaborate on the recent advances and techniques used to achieve cost-effective, high-density cultures of GMP-compliant RBCs, and on their relevant novel applications after downstream processing and purification.

Macrophages form erythropoietic niches and regulate iron homeostasis to adapt erythropoiesis in response to infections and inflammation

It has recently emerged that tissue-resident macrophages are key regulators of several stem cell niches orchestrating tissue formation during development, as well as postnatally, when they also organize the repair and regeneration of many tissues including the hemopoietic tissue. The fact that macrophages are also master regulators and effectors of innate immunity and inflammation allows them to coordinate hematopoietic response to infections, injuries, and inflammation. After recently reviewing the roles of phagocytes and macrophages in regulating normal and pathologic hematopoietic stem cell niches, we now focus on the key roles of macrophages in regulating erythropoiesis and iron homeostasis. We review herein the recent advances in understanding how macrophages at the center of erythroblastic islands form an erythropoietic niche that controls the terminal differentiation and maturation of erythroblasts into reticulocytes; how red pulp macrophages in the spleen control iron recycling and homeostasis; how these macrophages coordinate emergency erythropoiesis in response to blood loss, infections, and inflammation; and how persistent infections or inflammation can lead to anemia of inflammation via macrophages. Finally, we discuss the technical challenges associated with the molecular characterization of erythroid island macrophages and red pulp macrophages.

Towards manufactured red blood cells for the treatment of inherited anemia

Patients with inherited anemia and hemoglobinopathies (such as sickle cell disease and β-thalassemia) are treated with red blood cell (RBC) transfusions to alleviate their symptoms. Some of these patients may have rare blood group types or go on to develop alloimmune reactions, which can make it difficult to source compatible blood in the donor population. Laboratory-grown RBC represent a particularly attractive alternative which could satisfy an unmet clinical need. The challenge, however, is to produce - from a limited number of stem cells - the 2x1012 RBC required for a standard adult therapeutic dose. Encouraging progress has been made in RBC production from adult stem cells under good manufacturing practice. In 2011, the Douay group conducted a successful proof-of-principle mini-transfusion of autologous manufactured RBC in a single volunteer. In the UK, a trial is planned to assess whether manufactured RBC are equivalent to RBC produced naturally in donors, by testing an allogeneic mini-dose of laboratory-grown manufactured RBC in multiple volunteers. This review discusses recent progress in the erythroid culture field as well as opportunities for further scaling up of manufactured RBC production for transfusion practice.

Early use of dexamethasone increases Nr4a1 in Kupffer cells ameliorating acute liver failure in mice in a glucocorticoid receptor-dependent manner

BACKGROUND AND OBJECTIVE

Acute liver failure (ALF) is a type of disease with high mortality and rapid progression with no specific treatment methods currently available. Glucocorticoids exert beneficial clinical effects on therapy for ALF. However, the mechanism of this effect remains unclear and when to use glucocorticoids in patients with ALF is difficult to determine. The purpose of this study was to investigate the specific immunological mechanism of dexamethasone (Dex) on treatment of ALF induced by lipopolysaccharide (LPS)/D-galactosamine (D-GaIN) in mice.

METHODS

Male C57BL/6 mice were given LPS and D-GaIN by intraperitoneal injection to establish an animal model of ALF. Dex was administrated to these mice and its therapeutic effect was observed. Hematoxylin and eosin (H&E) staining was used to determine liver pathology. Multicolor flow cytometry, cytometric bead array (CBA) method, and next-generation sequencing were performed to detect changes of messenger RNA (mRNA) in immune cells, cytokines, and Kupffer cells, respectively.

RESULTS

A mouse model of ALF can be constructed successfully using LPS/D-GaIN, which causes a cytokine storm in early disease progression. Innate immune cells change markedly with progression of liver failure. Earlier use of Dex, at 0 h rather than 1 h, could significantly improve the progression of ALF induced by LPS/D-GaIN in mice. Numbers of innate immune cells, especially Kupffer cells and neutrophils, increased significantly in the Dex-treated group. In vivo experiments indicated that the therapeutic effect of Dex is exerted mainly via the glucocorticoid receptor (Gr). Sequencing of Kupffer cells revealed that Dex could increase mRNA transcription level of nuclear receptor subfamily 4 group A member 1 (Nr4a1), and that this effect disappeared after Gr inhibition.

CONCLUSIONS

In LPS/D-GaIN-induced ALF mice, early administration of Dex improved ALF by increasing the numbers of innate immune cells, especially Kupffer cells and neutrophils. Gr-dependent Nr4a1 upregulation in Kupffer cells may be an important ALF effect regulated by Dex in this process.

The role of macrophages in anti-tumor immune responses: pathological significance and potential as therapeutic targets

Malignant tumors comprise various types of normal cells and tumor cells, and are infiltrated by large numbers of immune cells, including macrophages. The results of numerous studies on the function and significance of intratumoral macrophages (tumor-associated macrophages) suggest that these macrophages generally enhance tumor progression rather than act as anti-tumor immune agents. Although much remains unknown, in this review, we attempt to describe the role of macrophages in the tumor microenvironment, and discuss their potential mechanisms on the recent immunotherapy.

Erythroblastic Island Macrophages Shape Normal Erythropoiesis and Drive Associated Disorders in Erythroid Hematopoietic Diseases

Erythroblastic islands (EBIs), discovered more than 60 years ago, are specialized microenvironments for erythropoiesis. This island consists of a central macrophage with surrounding developing erythroid cells. EBI macrophages have received intense interest in the verifications of the supporting erythropoiesis hypothesis. Most of these investigations have focused on the identification and functional analyses of EBI macrophages, yielding significant progresses in identifying and isolating EBI macrophages, as well as verifying the potential roles of EBI macrophages in erythropoiesis. EBI macrophages express erythropoietin receptor (Epor) both in mouse and human, and Epo acts on both erythroid cells and EBI macrophages simultaneously in the niche, thereby promoting erythropoiesis. Impaired Epor signaling in splenic niche macrophages significantly inhibit the differentiation of stress erythroid progenitors. Moreover, accumulating evidence suggests that EBI macrophage dysfunction may lead to certain erythroid hematological disorders. In this review, the heterogeneity, identification, and functions of EBI macrophages during erythropoiesis under both steady-state and stress conditions are outlined. By reviewing the historical data, we discuss the influence of EBI macrophages on erythroid hematopoietic disorders and propose a new hypothesis that erythroid hematopoietic disorders are driven by EBI macrophages.

EKLF/KLF1 expression defines a unique macrophage subset during mouse erythropoiesis

Erythroblastic islands are a specialized niche that contain a central macrophage surrounded by erythroid cells at various stages of maturation. However, identifying the precise genetic and transcriptional control mechanisms in the island macrophage remains difficult due to macrophage heterogeneity. Using unbiased global sequencing and directed genetic approaches focused on early mammalian development, we find that fetal liver macrophages exhibit a unique expression signature that differentiates them from erythroid and adult macrophage cells. The importance of erythroid Krüppel-like factor (EKLF)/KLF1 in this identity is shown by expression analyses in EKLF-/- and in EKLF-marked macrophage cells. Single-cell sequence analysis simplifies heterogeneity and identifies clusters of genes important for EKLF-dependent macrophage function and novel cell surface biomarkers. Remarkably, this singular set of macrophage island cells appears transiently during embryogenesis. Together, these studies provide a detailed perspective on the importance of EKLF in the establishment of the dynamic gene expression network within erythroblastic islands in the developing embryo and provide the means for their efficient isolation.

Role of anti-allergic agents on attenuating transfusion reactions in adults: A systematic review and meta-analysis

BACKGROUND

Anti-allergic agents (e.g. dexamethasone, chlorpheniramine or promethazine) are commonly administered to patients prior to blood product transfusions. However, the use of these agents is largely experience-based instead of evidence-based. This meta-analysis aimed to explore the evidence behind using anti-allergic agents to attenuate transfusion reactions.

MATERIALS AND METHODS

The Pubmed, EMBASE, Cochrane Library, Wanfang, Chinese National Knowledge Infrastructure (CNKI), and Chinese Biomedical literature (CMB) databases were all queried for related articles. Data from groups treated with and without anti-allergic agents were collected for meta-analysis using RevMan 5.3. Baseline characteristics and univariate statistics between groups were compared using SPSS 19.0.

RESULTS

Eight eligible articles (six case control studies and two randomized controlled trials, all with high risks of bias) were identified (22060 total cases). Administered anti-allergic agents in these studies only included dexamethasone, chlorpheniramine or promethazine. Baseline characteristics showed no significant age or gender differences between treatment or control groups. There were no significant differences between the pooled experimental or control groups (for each of the three medications) in terms of fever, pruritis, rash, airway spasm or overall transfusion reaction rates.

CONCLUSION

There is no evidence that dexamethasone, chlorpheniramine or promethazine can prevent transfusion reactions. Avoiding the arbitrary use of such anti-allergic agents before blood transfusions may potentially avoid needless adverse drug reactions.

CD14+ monocytes repress gamma globin expression at early stages of erythropoiesis

In β-hemoglobinopathies, reactivation of gamma- at the expense of beta-globin is a prominent therapeutic option. Expression of the globin genes is not strictly intrinsically regulated during erythropoiesis, supported by the observation that fetal erythroid cells switch to adult hemoglobin expression when injected in mice. We show cultured erythroblasts are a mix of HbA restrictive and HbA/HbF expressing cells and that the proportion of cells in the latter population depends on the starting material. Cultures started from CD34+ cells contain more HbA/HbF expressing cells compared to erythroblasts cultured from total peripheral blood mononuclear cells (PBMC). Depletion of CD14+ cells from PBMC resulted in higher HbF/HbA percentages. Conversely, CD34+ co-culture with CD14+ cells reduced the HbF/HbA population through cell–cell proximity, indicating that CD14+ actively repressed HbF expression in adult erythroid cultures. RNA-sequencing showed that HbA and HbA/HbF populations contain a limited number of differentially expressed genes, aside from HBG1/2. Co-culture of CD14+ cells with sorted uncommitted hematopoietic progenitors and CD34-CD36+ erythroblasts showed that hematopoietic progenitors prior to the hemoglobinized erythroid stages are more readily influenced by CD14+ cells to downregulate expression of HBG1/2, suggesting temporal regulation of these genes. This possibly provides a novel therapeutic avenue to develop β-hemoglobinopathies treatments.

Neutrophilic asthma features increased airway classical monocytes

BACKGROUND

Monocytes and macrophages are critical innate immune cells of the airways. Despite their differing functions, few clinical studies discriminate between them and little is known about their regulation in asthma.

OBJECTIVE

We aimed to distinguish and quantify macrophages, monocytes and monocyte subsets in induced sputum and blood and examine their relationship with inflammatory and clinical features of asthma.

METHODS

We applied flow cytometry to distinguish macrophages, monocytes and subsets in sputum and blood (n = 53; 45 asthma, 8 non-asthma) and a second asthma sputum cohort (n = 26). Monocyte subsets were identified by surface CD14/CD16 (CD14⁺⁺ CD16^- classical, CD14⁺ CD16⁺ intermediate and CD14⁺ CD16⁺⁺ non-classical monocytes). Surface CD206, a marker of monocyte tissue differentiation, was measured in sputum. Relationship to airway inflammatory phenotype (neutrophilic n = 9, eosinophilic n = 14, paucigranulocytic n = 22) and asthma severity (severe n = 12, non-severe n = 33) was assessed.

RESULTS

Flow cytometry- and microscope-quantified sputum differential cell proportions were significantly correlated. Sputum macrophage number was reduced (p = .036), while classical monocyte proportion was increased in asthma vs non-asthma (p = .032). Sputum classical monocyte number was significantly higher in neutrophilic vs paucigranulocytic asthma (p = .013). CD206^- monocyte proportion and number were increased in neutrophilic vs eosinophilic asthma (p < .001, p = .013). Increased sputum classical and CD206^- monocyte numbers in neutrophilic asthma were confirmed in the second cohort. Blood monocytes did not vary with airway inflammatory phenotype, but blood classical monocyte proportion and number were increased in severe vs non-severe asthma (p = .022, p = .011).

CONCLUSION AND CLINICAL RELEVANCE

Flow cytometry allowed distinction of sputum macrophages, monocytes and subsets, revealing compartment-specific dysregulation of monocytes in asthma. We observed an increase in classical and CD206^- monocytes in sputum in neutrophilic asthma, suggesting co-recruitment of monocytes and neutrophils to the airways in asthma. Our data suggest further investigation of how airway monocyte dysregulation impacts on asthma-related disease activity is merited.

Glucocorticoid treatment in patients with newly diagnosed immune thrombocytopenia switches CD14++ CD16+ intermediate monocytes from a pro-inflammatory to an anti-inflammatory phenotype

Immune thrombocytopenia (ITP) is thought to result from an aberrant adaptive autoimmune response, involving autoantibodies, B and T lymphocytes, directed at platelets and megakaryocytes. Previous reports have demonstrated skewed CD4⁺ T-helper subset distribution and enhanced production of pro-inflammatory cytokines such as interleukin 17A and interferon gamma. The role of monocytes (MCs) in ITP is less widely described, but innate immune cells have a role in shaping CD4⁺ T-cell phenotypes. Glucocorticoids (GCs) are commonly used for first-line ITP treatment and modulate a broad range of immune cells including T cells and MCs. Using multiparameter flow cytometry analysis, we demonstrate the expansion of intermediate MCs (CD14⁺⁺ CD16⁺ ) in untreated patients with newly diagnosed ITP, with these cells displaying a pro-inflammatory phenotype, characterised by enhanced expression of CD64 and CD80. After 2 weeks of prednisolone treatment (1 mg/kg daily), the proportion of intermediate MCs reduced, with enhanced expression of the anti-inflammatory markers CD206 and CD163. Healthy control MCs were distinctly different than MCs from patients with ITP before and after GC treatment. Furthermore, the GC-induced phenotype was not observed in patients with chronic ITP receiving thrombopoietin receptor agonists. These data suggest a role of MCs in ITP pathogenesis and clinical response to GC therapy.

Large-scale in vitro production of red blood cells from human peripheral blood mononuclear cells

Transfusion of donor-derived red blood cells (RBC) is the most common form of cellular therapy. Donor availability and the potential risk of alloimmunization and other transfusion-related complications may, however, limit the availability of transfusion units, especially for chronically transfused patients. In vitro cultured, customizable RBC would negate these concerns and further increase precision medicine. Large-scale, cost-effective production depends on optimization of culture conditions. We developed a defined medium and adapted our protocols to good manufacturing practice (GMP) culture requirements, which reproducibly provided pure erythroid cultures from peripheral blood mononuclear cells without prior CD34+ isolation, and a 3 × 107-fold increase in erythroblasts in 25 days (or from 100 million peripheral blood mononuclear cells, 2 to 4 mL packed red cells can be produced). Expanded erythroblast cultures could be differentiated to CD71dimCD235a+CD44+CD117-DRAQ5- RBC in 12 days. More than 90% of the cells enucleated and expressed adult hemoglobin as well as the correct blood group antigens. Deformability and oxygen-binding capacity of cultured RBC was comparable to in vivo reticulocytes. Daily RNA sampling during differentiation followed by RNA-sequencing provided a high-resolution map/resource of changes occurring during terminal erythropoiesis. The culture process was compatible with upscaling using a G-Rex bioreactor with a capacity of 1 L per reactor, allowing transition toward clinical studies and small-scale applications.

Stress erythropoiesis: definitions and models for its study

Steady-state erythropoiesis generates new erythrocytes at a constant rate, and it has enormous productive capacity. This production is balanced by the removal of senescent erythrocytes by macrophages in the spleen and liver. Erythroid homeostasis is highly regulated to maintain sufficient erythrocytes for efficient oxygen delivery to the tissues, while avoiding viscosity problems associated with overproduction. However, there are times when this constant production of erythrocytes is inhibited or is inadequate; at these times, erythroid output is increased to compensate for the loss of production. In some cases, increased steady-state erythropoiesis can offset the loss of erythrocytes but, in response to inflammation caused by infection or tissue damage, steady-state erythropoiesis is inhibited. To maintain homeostasis under these conditions, an alternative stress erythropoiesis pathway is activated. Emerging data suggest that the bone morphogenetic protein 4 (BMP4)-dependent stress erythropoiesis pathway is integrated into the inflammatory response and generates a bolus of new erythrocytes that maintain homeostasis until steady-state erythropoiesis can resume. In this perspective, we define the mechanisms that generate new erythrocytes when steady-state erythropoiesis is impaired and discuss experimental models to study human stress erythropoiesis.

Inside Out Integrin Activation Mediated by PIEZO1 Signaling in Erythroblasts

The non-selective mechanosensitive ion channel PIEZO1 controls erythrocyte volume homeostasis. Different missense gain-of-function mutations in PIEZO1 gene have been identified that cause Hereditary Xerocytosis (HX), a rare autosomal dominant haemolytic anemia. PIEZO1 expression is not limited to erythrocytes and expression levels are significantly higher in erythroid precursors, hinting to a role in erythropoiesis. During erythropoiesis, interactions between erythroblasts, central macrophages, and extracellular matrix within erythroblastic islands are important. Integrin α4β1 and α5β1 present on erythroblasts facilitate such interactions in erythroblastic islands. Here we found that chemical activation of PIEZO1 using Yoda1 leads to increased adhesion to VCAM1 and fibronectin in flowing conditions. Integrin α4, α5, and β1 blocking antibodies prevented this PIEZO1-induced adhesion suggesting inside-out activation of integrin on erythroblasts. Blocking the Ca²⁺ dependent Calpain and PKC pathways by using specific inhibitors also blocked increased erythroid adhesion to VCAM1 and fibronectins. Cleavage of Talin was observed as a result of Calpain and PKC activity. In conclusion, PIEZO1 activation results in inside-out integrin activation, facilitated by calcium-dependent activation of PKC and Calpain. The data introduces novel concepts in Ca²⁺ signaling during erythropoiesis with ramification on erythroblastic island homeostasis in health and disease like Hereditary Xerocytosis.

Stress Erythropoiesis is a Key Inflammatory Response

Bone marrow medullary erythropoiesis is primarily homeostatic. It produces new erythrocytes at a constant rate, which is balanced by the turnover of senescent erythrocytes by macrophages in the spleen. Despite the enormous capacity of the bone marrow to produce erythrocytes, there are times when it is unable to keep pace with erythroid demand. At these times stress erythropoiesis predominates. Stress erythropoiesis generates a large bolus of new erythrocytes to maintain homeostasis until steady state erythropoiesis can resume. In this review, we outline the mechanistic differences between stress erythropoiesis and steady state erythropoiesis and show that their responses to inflammation are complementary. We propose a new hypothesis that stress erythropoiesis is induced by inflammation and plays a key role in maintaining erythroid homeostasis during inflammatory responses.

Glucocorticoids mobilize macrophages by transcriptionally up-regulating the exopeptidase DPP4

Glucocorticoids are potent endogenous anti-inflammatory molecules, and their cognate receptor, glucocorticoid receptor (GR), is expressed in nearly all immune cells. Macrophages are heterogeneous immune cells having a central role in both tissue homeostasis and inflammation and also play a role in the pathogenesis of some inflammatory diseases. Paradoxically, glucocorticoids have only a limited efficacy in controlling the resolution of these macrophage-related diseases. Here, we report that the transcriptomes of monocyte-like THP-1 cells and macrophage-like THP-1 cells (THP1-MΦ) have largely conserved gene expression patterns. In contrast, the differentiation to THP1-MΦ significantly altered the sensitivity of gene transcription to glucocorticoids. Among glucocorticoid-regulated genes, we identified the exopeptidase dipeptidyl peptidase-4 (DPP4) as a critical glucocorticoid-responsive gene in THP1-MΦ. We found that GR directly induces DPP4 gene expression by binding to two glucocorticoid-responsive elements (GREs) within the DPP4 promoter. Additionally, we show that glucocorticoid-induced DPP4 expression is blocked by the GR antagonist RU-486 and by GR siRNA transfection and that DPP4 enzyme activity is reduced by DPP4 inhibitors. Of note, glucocorticoids highly stimulated macrophage mobility; unexpectedly, DPP4 mediated the glucocorticoid-induced macrophage migration, and siRNA-mediated knockdowns of GR and DPP4 blocked dexamethasone-induced THP1-MΦ migration. Moreover, glucocorticoid-induced DPP4 activation was also observed in proinflammatory M1-polarized murine macrophages, as well as peritoneal macrophages, and was associated with increased macrophage migration. Our results indicate that glucocorticoids directly up-regulate DPP4 expression and thereby induce migration in macrophages, potentially explaining why glucocorticoid therapy is less effective in controlling macrophage-dominated inflammatory disorders.

A Shift in Myeloid Cell Phenotype via Down Regulation of Siglec-1 in Island Macrophages of Bone Marrow Is Associated With Decreased Late Erythroblasts Seen in Anemia of Critical Illness

Burn injury has been shown to significantly dampen erythropoiesis in both burn patients and in murine models. Our previous findings elucidated the erythropoietin independent defects in red cell development stages involving erythroid progenitor production and late stage erythroblast enucleation processes. We hypothesized that macrophages (MØ) in erythroblast islands (EBI) could be yet another roadblock impeding erythropoiesis following burn injury. Here we highlight that the methodology to study EBI can be achieved with single cell suspensions using a simple technique such as flow cytometry, as obtaining the central erythroblast island macrophages (EBIMØs) of interest is a delicate process. We elucidated the requisite of EBIMØ from the erythroblast as well as the MØ perspective. In addition to the primary erythropoiesis organ, the bone marrow (BM), spleens were also examined for extra-medullary erythropoiesis. Femurs and spleens were harvested from adult mice (B₆D₂F₁) subjected to 15% total body surface area (TBSA) scald burn (B) or sham burn (S). Total bone marrow cells (TBM) and splenocytes were probed for total erythrons, early and late erythroblasts and EBIMØ by flow cytometry. There was only a marginal increase in the number of EBIMØ after burn, but, between the signatures of EBIMØ, Siglec-1 expression (MFI) was reduced by 40% in B with and a parallel 44% decrease in TBM erythrons in the BM. There were more (2.5-fold) EEBs and less LEBs (2.4-fold) per million TBM cells in B; with a corresponding decrease in Siglec-1 and Ly6G expressions in EBIMØ associated with EEB. Conversely, extra-medullary erythropoiesis was robust in spleens from B. Not only were the numbers of EBIMØs increased in B (p < 0.002), both EEBs and LEBs associated with EBIMØ were higher by 30 and 75%, respectively. Importantly, an increase in Siglec-1 and Vcam1 expressing F480⁺ splenic macrophages was observed after burn injury. Therefore, stagnant EEBs in the BM after burn injury could be due to low Siglec1 expressing EBIMØ, which perhaps impede their maturation into LEBs and reticulocytes. Repercussion of myeloid cell phenotype specific to BM after burn injury could plausibly account for a defective late stage RBC maturation resulting in anemia of critical illness.

Summary Sentence: Characterization of erythroblast island macrophages (EBIMØ) in the bone marrow and spleen at different stages of erythropoiesis after burn injury.

Enhanced Ex Vivo Generation of Erythroid Cells from Human Induced Pluripotent Stem Cells in a Simplified Cell Culture System with Low Cytokine Support

Red blood cell (RBC) differentiation from human induced pluripotent stem cells (hiPSCs) offers great potential for developmental studies and innovative therapies. However, ex vivo erythropoiesis from hiPSCs is currently limited by low efficiency and unphysiological conditions of common culture systems. Especially, the absence of a physiological niche may impair cell growth and lineage-specific differentiation. We here describe a simplified, xeno- and feeder-free culture system for prolonged RBC generation that uses low numbers of supporting cytokines [stem cell factor (SCF), erythropoietin (EPO), and interleukin 3 (IL-3)] and is based on the intermediate development of a “hematopoietic cell forming complex (HCFC).” From this HCFC, CD43⁺ hematopoietic cells (purity >95%) were continuously released into the supernatant and could be collected repeatedly over a period of 6 weeks for further erythroid differentiation. The released cells were mainly CD34⁺/CD45⁺ progenitors with high erythroid colony-forming potential and CD36⁺ erythroid precursors. A total of 1.5 × 10⁷ cells could be harvested from the supernatant of one six-well plate, showing 100- to 1000-fold amplification during subsequent homogeneous differentiation into GPA⁺ erythroid cells. Mean enucleation rates near 40% (up to 60%) further confirmed the potency of the system. These benefits may be explained by the generation of a niche within the HCFC that mimics the spatiotemporal signaling of the physiological microenvironment in which erythropoiesis occurs. Compared to other protocols, this method provides lower complexity, less cytokine and medium consumption, higher cellular output, and better enucleation. In addition, slight modifications in cytokine addition shift the system toward continuous generation of granulocytes and macrophages.

PD1+ tumor associated macrophages predict poor prognosis of locally advanced esophageal squamous cell carcinoma

Aim: Tumor associated macrophages are the most abundant cancer immune cells. However, little was known about the identity of CD68⁺PD1⁺ macrophages as well as the contributions in the prognosis of esophageal squamous cell carcinoma (ESCC). Methods & methods: Immunofluorescence, flowcytometry and RT-PCR were used to analysis PD1⁺ macrophages in ESCC. Results: CD68⁺PD1⁺ macrophages which can express higher M2 markers in cancer tissues, increased about 4.2-times compared with para-cancer tissues. Additionally, PD1^high macrophages were significantly correlated with more malignant phenotypes and poor prognosis. PD1 treatment can enhance phagocytosis of cultured macrophages and redirect this macrophage to M1-like phenotype. Conclusion: Thus, our findings overall indicate that CD68⁺PD1⁺ macrophages are tumor associated macrophagess in ESCC, which can forecast the prognosis of ESCC.

Erythroblast island macrophages: recent discovery and future perspectives

Erythroblastic island (EBI), composed of a central macrophage surrounded by developing erythroid cells, is a structure found in hematopoietic tissues such as fetal liver and bone marrow. It is the first described hematopoietic niche that predominantly supports erythropoiesis. Although it is well accepted that EBIs and EBI macrophage play important roles during erythropoiesis, the mechanisms by which they support erythropoiesis remain largely unclear due to our inability to identify and isolate EBI macrophages. Earlier efforts to identify surface markers for EBI macrophages have focused on the adhesion molecules which are involved in macrophage's interaction with erythroblasts. These include EMP, Vcam1, CD169, CD163, and αV integrin. Findings from these earlier studies suggested that combination of Vcam1, CD169, and mouse macrophage surface marker F4/80 can be used to define mouse EBI macrophage. We found that not all F4/80⁺Vcam1⁺CD169⁺ macrophages are EBI macrophages. Instead, we discovered that EBI macrophages are characterized by the expression of Epor in both mouse and man. RNA-seq analyses of the newly identified EBI macrophages revealed that EBI macrophages have involved specialized function in supporting erythropoiesis. Our findings provide foundation for future studies. Here we will review current knowledge of EBI macrophages and discuss future perspectives.

Glucocorticoids Shape Macrophage Phenotype for Tissue Repair

Inflammation is a complex process which is highly conserved among species. Inflammation occurs in response to injury, infection, and cancer, as an allostatic mechanism to return the tissue and to return the organism back to health and homeostasis. Excessive, or chronic inflammation is associated with numerous diseases, and thus strategies to combat run-away inflammation is required. Anti-inflammatory drugs were therefore developed to switch inflammation off. However, the inflammatory response may be beneficial for the organism, in particular in the case of sterile tissue injury. The inflammatory response can be divided into several parts. The first step is the mounting of the inflammatory reaction itself, characterized by the presence of pro-inflammatory cytokines, and the infiltration of immune cells into the injured area. The second step is the resolution phase, where immune cells move toward an anti-inflammatory phenotype and decrease the secretion of pro-inflammatory cytokines. The last stage of inflammation is the regeneration process, where the tissue is rebuilt. Innate immune cells are major actors in the inflammatory response, of which, macrophages play an important role. Macrophages are highly sensitive to a large number of environmental stimuli, and can adapt their phenotype and function on demand. This change in phenotype in response to the environment allow macrophages to be involved in all steps of inflammation, from the first mounting of the pro-inflammatory response to the post-damage tissue repair.

Ephrin/Eph receptor interaction facilitates macrophage recognition of differentiating human erythroblasts

Erythropoiesis is one of the most efficient cellular processes in the human body producing approximately 2.5 million red blood cells every second. This process occurs in a bone marrow niche comprised of a central resident macrophage surrounded by differentiating erythroblasts, termed an erythroblastic island. It is not known what initially attracts the macrophage to erythroblasts to form these islands. The ephrin/Eph receptor family are known to regulate heterophilic cell-cell adhesion. We find that human VCAM1⁺ and VCAM1^- bone marrow macrophages and in vitro cultured macrophages are ephrin-B2 positive, whereas differentiating human erythroblasts express EPHB4, EPHB6 and EPHA4. Furthermore, we detect a rise in integrin activation on erythroblasts at the stage at which the cells bind which is independent of EPH receptor presence. Using a live cell imaging assay, we show that specific inhibitory peptides or shRNA depletion of EPHB4 cause a significant reduction in the ability of macrophages to interact with erythroblasts but do not affect integrin activation. This study demonstrates for the first time that EPHB4 expression is required on erythroblasts to facilitate the initial recognition and subsequent interaction with macrophages, alongside the presence of active integrins.

Glucocorticoids inhibit macrophage differentiation towards a pro-inflammatory phenotype upon wounding without affecting their migration

Glucocorticoid drugs are widely used to treat immune-related diseases, but their use is limited by side effects and by resistance, which especially occurs in macrophage-dominated diseases. In order to improve glucocorticoid therapies, more research is required into the mechanisms of glucocorticoid action. In the present study, we have used a zebrafish model for inflammation to study glucocorticoid effects on the innate immune response. In zebrafish larvae, the migration of neutrophils towards a site of injury is inhibited upon glucocorticoid treatment, whereas migration of macrophages is glucocorticoid resistant. We show that wounding-induced increases in the expression of genes that encode neutrophil-specific chemoattractants (Il8 and Cxcl18b) are attenuated by the synthetic glucocorticoid beclomethasone, but that beclomethasone does not attenuate the induction of the genes encoding Ccl2 and Cxcl11aa, which are required for macrophage recruitment. RNA sequencing on FACS-sorted macrophages shows that the vast majority of the wounding-induced transcriptional changes in these cells are inhibited by beclomethasone, whereas only a small subset is glucocorticoid-insensitive. As a result, beclomethasone decreases the number of macrophages that differentiate towards a pro-inflammatory (M1) phenotype, which we demonstrated using a tnfa:eGFP-F reporter line and analysis of macrophage morphology. We conclude that differentiation and migration of macrophages are regulated independently, and that glucocorticoids leave the chemotactic migration of macrophages unaffected, but exert their anti-inflammatory effect on these cells by inhibiting their differentiation to an M1 phenotype. The resistance of macrophage-dominated diseases to glucocorticoid therapy can therefore not be attributed to an intrinsic insensitivity of macrophages to glucocorticoids.

Summary: In a zebrafish model for inflammation, glucocorticoids do not affect the migration of macrophages, but inhibit their differentiation towards an M1 phenotype, by strongly attenuating transcriptional responses in these cells.

Exploiting vulnerabilities of cancer by targeting nuclear receptors of stromal cells in tumor microenvironment

The tumor microenvironment is a complex and dynamic cellular community comprising the tumor epithelium and various tumor-supporting cells such as immune cells, fibroblasts, immunosuppressive cells, adipose cells, endothelial cells, and pericytes. The interplay between the tumor microenvironment and tumor cells represents a key contributor to immune evasiveness, physiological hardiness and the local and systemic invasiveness of malignant cells. Nuclear receptors are master regulators of physiological processes and are known to play pro-/anti-oncogenic activities in tumor cells. However, the actions of nuclear receptors in tumor-supporting cells have not been widely studied. Given the excellent druggability and extensive regulatory effects of nuclear receptors, understanding their biological functionality in the tumor microenvironment is of utmost importance. Therefore, the present review aims to summarize recent evidence about the roles of nuclear receptors in tumor-supporting cells and their implications for malignant processes such as tumor proliferation, evasion of immune surveillance, angiogenesis, chemotherapeutic resistance, and metastasis. Based on findings derived mostly from cell culture studies and a few in vivo animal cancer models, the functions of VDR, PPARs, AR, ER and GR in tumor-supporting cells are relatively well-characterized. Evidence for other receptors, such as RARβ, RORγ, and FXR, is limited yet promising. Hence, the nuclear receptor signature in the tumor microenvironment may harbor prognostic value. The clinical prospects of a tumor microenvironment-oriented cancer therapy exploiting the nuclear receptors in different tumor-supporting cells are also encouraging. The major challenge, however, lies in the ability to develop a highly specific drug delivery system to facilitate precision medicine in cancer therapy.

Context-Dependent Effect of Glucocorticoids on the Proliferation, Differentiation, and Apoptosis of Regulatory T Cells: A Review of the Empirical Evidence and Clinical Applications

Glucocorticoids (GCs) are widely used to treat several diseases because of their powerful anti-inflammatory and immunomodulatory effects on immune cells and non-lymphoid tissues. The effects of GCs on T cells are the most relevant in this regard. In this review, we analyze how GCs modulate the survival, maturation, and differentiation of regulatory T (Treg) cell subsets into both murine models and humans. In this way, GCs change the Treg cell number with an impact on the mid-term and long-term efficacy of GC treatment. In vitro studies suggest that the GC-dependent expansion of Treg cells is relevant when they are activated. In agreement with this observation, the GC treatment of patients with established autoimmune, allergic, or (auto)inflammatory diseases causes an expansion of Treg cells. An exception to this appears to be the local GC treatment of psoriatic lesions. Moreover, the effects on Treg number in patients with multiple sclerosis are uncertain. The effects of GCs on Treg cell number in healthy/diseased subjects treated with or exposed to allergens/antigens appear to be context-dependent. Considering the relevance of this effect in the maturation of the immune system (tolerogenic response to antigens), the success of vaccination (including desensitization), and the tolerance to xenografts, the findings must be considered when planning GC treatment.

Extensive epigenomic integration of the glucocorticoid response in primary human monocytes and in vitro derived macrophages

Glucocorticoid receptor is a transcription factor that is ubiquitously expressed. Glucocorticoids are circadian steroids that regulate a wide range of bodily functions, including immunity. Here we report that synthetic glucocorticoids affect 1035 mRNAs in isolated healthy human blood monocytes but only 165 in the respective six day-old monocyte-derived macrophages. The majority of the glucocorticoid response in monocytes concerns genes that are dynamic upon monocyte to macrophage differentiation, whereby macrophage-like mRNA levels are often reached in monocytes within four hours of treatment. Concomitantly, over 5000 chromosomal H3K27ac regions undergo remodelling, of which 60% involve increased H3K27ac signal. We find that chromosomal glucocorticoid receptor binding sites correlate with positive but not with negative local epigenomic effects. To investigate further we assigned our data to topologically associating domains (TADs). This shows that about 10% of macrophage TADs harbour at least one GR binding site and that half of all the glucocorticoid-induced H3K27ac regions are confined to these TADs. Our analyses are therefore consistent with the notion that TADs naturally accommodate information from sets of distal glucocorticoid response elements.

Genetic programming of macrophages generates an in vitro model for the human erythroid island niche

Red blood cells mature within the erythroblastic island (EI) niche that consists of specialized macrophages surrounded by differentiating erythroblasts. Here we establish an in vitro system to model the human EI niche using macrophages that are derived from human induced pluripotent stem cells (iPSCs), and are also genetically programmed to an EI-like phenotype by inducible activation of the transcription factor, KLF1. These EI-like macrophages increase the production of mature, enucleated erythroid cells from umbilical cord blood derived CD34⁺ haematopoietic progenitor cells and iPSCs; this enhanced production is partially retained even when the contact between progenitor cells and macrophages is inhibited, suggesting that KLF1-induced secreted proteins may be involved in this enhancement. Lastly, we find that the addition of three secreted factors, ANGPTL7, IL-33 and SERPINB2, significantly enhances the production of mature enucleated red blood cells. Our study thus contributes to the ultimate goal of replacing blood transfusion with a manufactured product.

In vitro differentiation of red blood cells (RBCs) is a desirable therapy for various disorders. Here the authors develop a culture system using stem cell-derived macrophages to show that inducible expression of a transcription factor, KLF1, enhances RBC production, potentially through the induction of three soluble factors, ANGPTL7, IL33 and SERPINB2.

CD4+ T Cells Alter the Stromal Microenvironment and Repress Medullary Erythropoiesis in Murine Visceral Leishmaniasis

Human visceral leishmaniasis, a parasitic disease of major public health importance in developing countries, is characterized by variable degrees of severity of anemia, but the mechanisms underlying this change in peripheral blood have not been thoroughly explored. Here, we used an experimental model of visceral leishmaniasis in C57BL/6 mice to explore the basis of anemia following infection with Leishmania donovani. 28 days post-infection, mice showed bone marrow dyserythropoiesis by myelogram, with a reduction of TER119+ CD71-/+ erythroblasts. Reduction of medullary erythropoiesis coincided with loss of CD169high bone marrow stromal macrophages and a reduction of CXCL12-expressing stromal cells. Although the spleen is a site of extramedullary erythropoiesis and erythrophagocytosis, splenectomy did not impact the extent of anemia or affect the repression of medullary hematopoiesis that was observed in infected mice. In contrast, these changes in bone marrow erythropoiesis were not evident in B6.Rag2-/- mice, but could be fully reconstituted by adoptive transfer of IFNγ-producing but not IFNγ-deficient CD4+ T cells, mimicking the expansion of IFNγ-producing CD4+ T cells that occurs during infection in wild type mice. Collectively, these data indicate that anemia during experimental murine visceral leishmaniasis can be driven by defects associated with the bone marrow erythropoietic niche, and that this represents a further example of CD4+ T cell-mediated immunopathology affecting hematopoietic competence.

Monocyte-derived macrophages expand the murine stress erythropoietic niche during the recovery from anemia

Anemic stress induces a physiological response that includes the rapid production of new erythrocytes. This process is referred to as stress erythropoiesis. It is best understood in the mouse where it is extramedullary and utilizes signals and progenitor cells that are distinct from bone marrow steady-state erythropoiesis. The development of stress erythroid progenitors occurs in close association with the splenic stress erythropoiesis niche. In particular, macrophages in the niche are required for proper stress erythropoiesis. Here we show that the expansion of the niche occurs in concert with the proliferation and differentiation of stress erythroid progenitors. Using lineage tracing analysis in 2 models of anemic stress, we show that the expansion of the splenic niche is due to the recruitment of monocytes into the spleen, which develop into macrophages that form erythroblastic islands. The influx in monocytes into the spleen depends in part on Ccr2-dependent signaling mediated by Ccl2 and other ligands expressed by spleen resident red pulp macrophages. Overall, these data demonstrate the dynamic nature of the spleen niche, which rapidly expands in concert with the stress erythroid progenitors to coordinate the production of new erythrocytes in response to anemic stress.