Macrophage Pool Research Articles

Astragalus polysaccharides (PG2) Enhances the M1 Polarization of Macrophages, Functional Maturation of Dendritic Cells, and T Cell-Mediated Anticancer Immune Responses in Patients with Lung Cancer.

Background: Recently, we demonstrated that Astragalus polysaccharide (PG2), the active ingredient in dried roots of astragalus membranaceus, ameliorates cancer symptom clusters and improves quality of life (QoL) in patients with metastatic disease by modulating inflammatory cascade against the background roles of inflammatory cells, including macrophages, dendritic cells (DCs), and cytotoxic T lymphocytes (CTLs) in tumor initiation, metastasis, and progression. Nevertheless, the role of PG2 in the modulation of anticancer immunogenicity and therapeutic response remains relatively underexplored and unclear. Purpose: The present study investigates how and to what extent PG2 modulates cellular and biochemical components of the inflammatory cascade and enhances anticancer immunity, as well as the therapeutic implication of these bio-events in patients with lung cancer. Methods and Results: Herein, we demonstrated that PG2 significantly increased the M1/M2 macrophage polarization ratio in non-small cell carcinoma (NSCLC) H441 and H1299 cells. This PG2-induced preferential pharmacologic up-regulation of tumoral M1 population in vitro positively correlated with the downregulation of tumor-promoting IL-6 and IL-10 expression in NSCLC cell-conditioned medium, with concomitant marked inhibition of cell proliferation, clonogenicity, and tumorsphere formation. Our ex vivo results, using clinical sample from our NSCLC cohort, demonstrated that PG2 also promoted the functional maturation of DCs with consequent enhancement of T cell-mediated anticancer immune responses. Consistent with the in vitro and ex vivo results, our in vivo studies showed that treatment with PG2 elicited significant time-dependent depletion of the tumor-associated M2 population, synergistically enhanced the anti-M2-based anticancer effect of cisplatin, and inhibited xenograft tumor growth in the NSCLC mice models. Moreover, in the presence of PG2, cisplatin-associated dyscrasia and weight-loss was markedly suppressed. Conclusion: These results do indicate a therapeutically-relevant role for PG2 in modulating the M1/M2 macrophage pool, facilitating DC maturation and synergistically enhancing the anticancer effect of conventional chemotherapeutic agent, cisplatin, thus laying the foundation for further exploration of the curative relevance of PG2 as surrogate immunotherapy and/or clinical feasibility of its use for maintenance therapy in patients with lung cancer.

Using High-Dimensional Approaches to Probe Monocytes and Macrophages in Cardiovascular Disease.

High dimensional approaches that characterize single cells at unprecedented depth have helped uncover unappreciated heterogeneity, a better understanding of myeloid cell origins, developmental relationships and functions. These advancements are particularly important in cardiovascular disease, which remains the leading cause of death worldwide. Gradual, monocyte-dependent inflammatory processes, such as the development of atherosclerotic plaque within arterial vessels, contrasts with the robust acute response within the myocardium that occurs when a vessel is occluded. Monocytes and macrophages differentially contribute to tissue injury, repair and regeneration in these contexts, yet many questions remain about which myeloid cell types are involved in a coordinated, organ-level sterile inflammatory response. Single cell RNA sequencing, combined with functional analyses have demonstrated that at least three populations of resident cardiac macrophages exist, and after tissue injury, there is significant diversification of the tissue macrophage pool driven by recruited monocytes. While these studies have provided important insights, they raise many new questions and avenues for future exploration. For example, how do transcriptionally defined sub-populations of cardiac macrophages relate to each other? Are they different activation states along a pre-defined trajectory of macrophage differentiation or do local microenvironments drive newly recruited monocytes into distinct functions? The answers to these questions will require integration of high-dimensional approaches into biologically relevant in vivo experimental systems to ensure the predicted heterogeneity possess a functional outcome.

Abstract P138: Perivascular Adipose Tissues (pvats) Home Distinct 'Active' Immune Cell Niches, Denser Than Non-pvat Adipose Tissues of Healthy Rats

Perivascular adipose tissue (PVAT) is protective and reduces the contraction of blood vessels in health. Eosinophils are one of the key players to the anti-contractile nature of PVAT in health. This finding led to our hypothesis that an ‘active’ immune complement exists in healthy PVAT. Male and female Sprague Dawley rats (12-14 weeks age) were used. PVATs from the thoracic aorta (brown APVAT), mesenteric resistance vessels (white MRPVAT), non-PVATs: subscapular (brown SS fat), retroperitoneal (white RP fat) and spleen (positive control) were harvested from each animal. T cells (CD4 and CD8), B cells, NK cells, macrophages, mast cells and neutrophils in the stromal vascular fraction were quantified using 9-color flow cytometry. Activation status (effector/ memory/ regulatory) of macrophages, T and B cells were also determined by flow cytometry. The number of immune cells are normalized to tissue weight (table). MRPVAT has denser total immune population (both sexes) and active macrophage pool (females) vs RP fat. APVAT homes a denser immune niche (females) and active T cell, B cell pools (both sexes) vs SS fat. This is the first study to characterize ‘active’ immune populations in healthy PVATs vs non-PVATs in male and female rats. Further studies to understand the functions of basally active immune cells in healthy PVATs are warranted.

Ontogeny of Tumor-Associated Macrophages.

Tumor-associated macrophages (TAM) represent the main immune cell population of the tumor microenvironment in most cancer. For decades, TAM have been the focus of intense investigation to understand how they modulate the tumor microenvironment and their implication in therapy failure. One consensus is that TAM are considered to exclusively originate from circulating monocyte precursors released from the bone marrow, fitting the original dogma of tissue-resident macrophage ontogeny. A second consensus proposed that TAM harbor either a classically activated M1 or alternatively activated M2 polarization profile, with almost opposite anti- and pro-tumoral activity respectively. These fundamental pillars are now revised in face of the latest discoveries on macrophage biology. Embryonic-derived macrophages were recently characterized as major contributors to the pool of tissue-resident macrophages in many tissues. Their turnover with macrophages derived from precursors of adult hematopoiesis seems to follow a regulation at the subtissular level. This has shed light on an ever more complex macrophage diversity in the tumor microenvironment than once thought and raise the question of their respective implication in tumor development compared to classical monocyte-derived macrophages. These recent advances highlight that TAM have actually not fully revealed their usefulness and deserve to be reconsidered. Understanding the link between TAM ontogeny and their various functions in tumor growth and interaction with the immune system represents one of the future challenges for cancer therapy.

Monocytes and cancer: promising role as a diagnostic marker and application in therapy

Interrelationship between a malignant tumor and the immunity are provided by the involvement of both adaptive and innate immune systems. Monocytes are major participants in nonspecific immune response and mediate their key function through refilling the pool of tumor-associated macrophages, dendritic cells and myeloid suppressor cells. All these populations regulate the relationship of tumor-infiltrating immunocompetent cells with tumor cells and with other components of the microenvironment, as well as tumor cell proliferation, angiogenesis, and dissemination. Monocytes, being direct participants of the chronic persistent inflammation, are involved in the inflammation impact on both tumor origin and progression. The study of the molecular mechanisms of monocyte recruitment and differentiation in malignant neoplasms seems to be a promising direction, both for a diagnostic purpose and as a search for targeting molecules for the control of macrophages and dendritic cells in the tumor microenvironment. In this review, the characteristics of peripheral blood monocytes are given, taking into account the heterogeneity of their population. Tie2+ cells and macrophage-polarized CD163+ and CD204+ -monocytes, as well as cancer-associated macrophage-like cells (CAMLs), are described as contributors to cancer disease progression and outcome. The involvement of monocyte subpopulations in the pathogenesis of oncological diseases of different localizations at the stages of the formation of monocyte precursors in the bone marrow, circulation in peripheral blood and differentiation in tumor tissue is shown.

Liver Macrophages: Old Dogmas and New Insights.

Inflammation is a hallmark of virtually all liver diseases, such as liver cancer, fibrosis, nonalcoholic steatohepatitis, alcoholic liver disease, and cholangiopathies. Liver macrophages have been thoroughly studied in human disease and mouse models, unravelling that the hepatic mononuclear phagocyte system is more versatile and complex than previously believed. Liver macrophages mainly consist of liver‐resident phagocytes, or Kupffer cells (KCs), and bone marrow‐derived recruited monocytes. Although both cell populations in the liver demonstrate principal functions of macrophages, such as phagocytosis, danger signal recognition, cytokine release, antigen processing, and the ability to orchestrate immune responses, KCs and recruited monocytes retain characteristic ontogeny markers and remain remarkably distinct on several functional aspects. While KCs dominate the hepatic macrophage pool in homeostasis (“sentinel function”), monocyte‐derived macrophages prevail in acute or chronic injury (“emergency response team”), making them an interesting target for novel therapeutic approaches in liver disease. In addition, recent data acquired by unbiased large‐scale techniques, such as single‐cell RNA sequencing, unraveled a previously unrecognized complexity of human and murine macrophage polarization abilities, far beyond the old dogma of inflammatory (M1) and anti‐inflammatory (M2) macrophages. Despite tremendous progress, numerous challenges remain in deciphering the full spectrum of macrophage activation and its implication in either promoting liver disease progression or repairing injured liver tissue. Being aware of such heterogeneity in cell origin and function is of crucial importance when studying liver diseases, developing novel therapeutic interventions, defining macrophage‐based prognostic biomarkers, or designing clinical trials. Growing knowledge in gene expression modulation and emerging technologies in drug delivery may soon allow shaping macrophage populations toward orchestrating beneficial rather than detrimental inflammatory responses.

Functions of Macrophages in the Maintenance of Intestinal Homeostasis.

Intestinal macrophages constitute the largest pool of macrophages in the body and have emerged as crucial sentinels for pathogen recognition and elimination. The source and development of intestinal macrophages, as well as their distinct properties have been well documented. Intestinal macrophages exert their functions in the maintenance of intestinal homeostasis by shaping host-microbiota symbiosis, managing gut inflammation, crosstalking with T cells, and facilitating wound repair. Recently, nutritional regulation of intestinal macrophages has attracted substantial attention and is becoming a promising approach to disease prevention and control. Understanding the mechanisms employed by intestinal macrophages in mediating intestinal immune homeostasis and inflammation, as well as the mode of action of dietary nutrients in the modulating functions of intestinal macrophages, represents an opportunity to prevent and control inflammatory bowel diseases.

Reconstruction of Transcriptional Programs of Monocyte to Macrophage Sequential Cell Fate Transition Using Single Cell RNA Sequencing in Sex Mis-Matched Lung Transplantation

Purpose Alveolar macrophages are key regulators of the innate immune response and participate in the stem cell niche to organise tissue repair and lung homeostasis . The fate of donor alveolar macrophages is poorly understood as existing studies have relied on sex chromosome labelling or HLA typing methodologies. We sought to confirm the existence of a long-lived pool of donor-derived alveolar macrophages using single cell RNA sequencing in sex mismatched lung transplant patients. Methods BAL cells from 17 individuals, including 11 non-transplant (7 female) and 6 lung transplant recipients (3 male->female, 1 female->male) were isolated and sorted for live cells. Single cells were captured and barcoded using the 10X Genomics Single Cell 3′ Gene Expression platform. Sequencing data was filtered and aligned to human reference genome and count tables analysed in Seurat and Monocle packages. Results Our analysis revealed 2 transcripts specific to female and male cells respectively; XIST (X-inactive specific transcript) and RPS4Y1 (Ribosomal Protein S4 Y-Linked 1) with 70% of cells able to be sex matched (Table1). Of 4 sex mismatched lung transplant patients, only 1 male 8.4 months post-transplant, had alveolar macrophages of donor origin (17.5%). Engrafting monocytes acquired a near identical phenotype to donor macrophages, with trajectory inference of recipient cells revealing arrested expression of genes associated with chemotaxis (CCL2) and tissue remodelling (TIMP1) and upregulation of scavenger receptor (MSR1) and lipid metabolism (FABP4 and SCD) genes (Figure 1). Conclusion Our work questions the existence of long-lived self-renewing populations of alveolar macrophages. Knowledge of the transcriptional programs associated with cell fate transition from peripheral blood derived monocyte to alveolar macrophage will aid in deciphering the pathogenesis of lung diseases involving monocyte/macrophage lineages.

Macrophages of distinct origins contribute to tumor development in the lung.

Tissue-resident macrophages can self-maintain without contribution of adult hematopoiesis. Herein we show that tissue-resident interstitial macrophages (Res-TAMs) in mouse lungs contribute to the pool of tumor-associated macrophages (TAMs) together with CCR2-dependent recruited macrophages (MoD-TAMs). Res-TAMs largely correlated with tumor cell growth in vivo, while MoD-TAMs accumulation was associated with enhanced tumor spreading. Both cell subsets were depleted after chemotherapy, but MoD-TAMs rapidly recovered and performed phagocytosis-mediated tumor clearance. Interestingly, anti-VEGF treatment combined with chemotherapy inhibited both Res and Mod-TAM reconstitution without affecting monocyte infiltration and improved its efficacy. Our results reveal that the developmental origin of TAMs dictates their relative distribution, function, and response to cancer therapies in lung tumors.

Understanding the Biology of Self-Renewing Macrophages.

Macrophages reside in specific territories in organs, where they contribute to the development, homeostasis, and repair of tissues. Recent work has shown that the size of tissue macrophage populations has an impact on tissue functions and is determined by the balance between replenishment and elimination. Macrophage replenishment is mainly due to self-renewal of macrophages, with a secondary contribution from blood monocytes. Self-renewal is a recently discovered trait of macrophages, which can have a major impact on their physiological functions and hence on the wellbeing of the organism. In this review, I discuss our current understanding of the developmental origin of self-renewing macrophages and the mechanisms used to maintain a physiologically stable macrophage pool.

Functional phenotype and role of resident and recruited bone marrow derived exudate macrophages in influenza virus-induced lung injury and repair

Background: Alveolar macrophages (AM) play an important role in host defense and tissue homeostasis. Even though macrophage polarization has been extensively studied in different disease models, the generation of macrophage phenotypes with specific functional profiles, their lineage relation and particular roles during pathogen-induced acute lung injury (ALI), resolution and tissue repair has not been convincingly elucidated. Methods & Materials: C57BL/6 mice were infected with influenza virus (IV) PR8 by intra-tracheal (i.t) application. BAL and lungs were harvested during the acute and resolution and repair phases of infection. The polarization profiles of different AM subsets were characterized by FACS during the course of infection. Bone marrow transplantation (BMT) experiments using CD45.2/1 mice were performed to demonstrate lineage-relation between recruited and resident macrophages. Adoptive transfer of BMM with diverse polarization patterns (isolated from IV-challenged wild type mice) into the lungs of IV-infected CCR2-/- mice (lacking BMM recruitment) was performed to address their functional phenotypes during injury, resolution and lung repair. Gene expression profiles in different BMM phenotypes were screened by genome wide transcriptome analysis. Results: Our flow cytometry analyses demonstrated that alveolar and interstitial BMM show an M1 phenotype in the acute phase and shift to an M2 phenotype in the late phase of infection. BMT experiments revealed that M2 BMM substantially contributed to replenishment of the depleted resident alveolar macrophage (rAM) pool, indicating a high functional plasticity of BMM recruited after infection. In addition, M1 and M2BMM adoptive transfer experiments showed that intra-tracheal transferred M1BMM increased alveolar barrier dysfunction whereas M2BMM preserved the rAM pool and induced alveolar epithelial cell proliferation and barrier repair. Further, our genome-wide transcriptome analysis on flow-sorted M1/M2BMM showed significant up-regulation of a distinct set of growth factors, repair mediators and pro-survival genes in M2 when compared with M1BMM, some of which were found to be central mediators of the beneficial functions of M2BMM in vivo. Conclusion: These data support that mediators produced by M2BMM contribute to replenishment and preservation of the rAM pool and improved lung barrier function. In summary, our data demonstrate high functional plasticity of BMM during IV pneumonia and highlight these cells as targets for therapeutic approaches.

Contribution of resident and recruited macrophages in vascular physiology and pathology

Macrophages are generally believed to originate entirely from the bone marrow; however, this paradigm is challenged by the discovery of yolk-sac-derived resident macrophages. Here, we provide an overview of recent advances in the ontogeny and function of resident macrophages. Macrophage precursors from three distinct embryonic sources (yolk sac, fetal liver and bone marrow) are found to colonize various tissues via the blood circulation early during embryogenesis until shortly after birth. They differentiate into distinct long-lived resident macrophages in response to the expression of tissue-specific transcription factors. Resident macrophages are proficient at taking up tissue-specific cellular debris and consequently acquire tissue-specific imprints. They are primarily involved in homeostasis but can also support the functionality of various tissues. Under pathological settings, dysregulation of resident macrophages can promote disease progression. Resident macrophages maintain themselves via in-situ proliferation under steady state. Following injury, bone marrow monocytes can contribute to the resident macrophage pool in adult animal. Embryonically and postnatally derived resident macrophages are similar but not identical: the former are more efficient at efferocytosis, whereas the latter are more competent at host defense. Thus, specific targeting of these two different resident macrophage populations may lead to better therapeutic strategies.

Macrophages play an essential role in trauma-induced sterile inflammation and tissue repair.

Severe trauma is accompanied by a profound activation of the immune system. Patients with polytrauma develop systemic inflammatory response syndrome (SIRS) and often sepsis, which contributes substantially to high mortality of this condition. On a cellular level, necrosis and loss of plasma membrane integrity lead to the release of endogenous "damage-associated molecular patterns" (DAMPs) as danger signals, which in turn activate innate immune cells. Inflammation that occurs in the absence of invading pathogens has been termed sterile inflammation and trauma with tissue damage represents an acute form of sterile inflammation. Macrophages are a heterogeneous group of phagocytes of the innate immune system and serve as sentinels to detect loss of tissue integrity. Macrophages show a remarkable plasticity and undergo phenotypical changes in response to injury and repair. Under basal conditions, tissue-resident macrophages are distributed in various organ systems and have critical functions in tissue development and the maintenance of homeostasis. Inflammatory conditions, such as major trauma, lead to the rapid recruitment of blood-derived monocytes that mature into macrophages as well as direct recruitment of macrophages from the cavity that surrounds the injured organ. This leads to augmentation of the pool of tissue-resident macrophages. Besides their essential role in sensing tissue damage and initiating inflammation, macrophages contribution critically to tissue repair and wound healing, ultimately allowing full restoration. Dysregulated sterile inflammation and defective healing result in chronic inflammatory disease with persistent tissue damage. In this review, we summarize the cellular and molecular mechanisms that lead to activation of sterile inflammation, recruitment of immune cells and initiation of wound healing. We focus on the pivotal role of macrophages played in this context.

The tumour microenvironment creates a niche for the self-renewal of tumour-promoting macrophages in colon adenoma

Circulating CCR2+ monocytes are crucial for maintaining the adult tissue-resident F4/80hiMHCIIhi macrophage pool in the intestinal lamina propria. Here we show that a subpopulation of CCR2-independent F4/80hiMHCIIlow macrophages, which are the most abundant F4/80hi cells in neonates, gradually decline in number in adulthood; these macrophages likely represent the fetal contribution to F4/80hi cells. In colon adenomas of ApcMin/+ mice, F4/80hiMHCIIlow macrophages are not only preserved, but become the dominant subpopulation among tumour-resident macrophages during tumour progression. Furthermore, these pro-tumoural F4/80hiMHCIIlow and F4/80hiMHCIIhi macrophages can self-renew in the tumour and maintain their numbers mostly independent from bone marrow contribution. Analyses of colon adenomas indicate that CSF1 may be a key facilitator of macrophage self-renewal. In summary, the tumour microenvironment creates an isolated niche for tissue-resident macrophages that favours macrophage survival and self-renewal.

Fetal monocytes and the origins of tissue-resident macrophages

Tissue-resident macrophages have pivotal functions for tissue defense and homeostasis. Two main discoveries have changed our current understanding of macrophage development: Their embryonic origin and their ability to self-renew throughout the lifespan. It is now well accepted that most tissue-resident macrophages are long-lived cells derived from a transient hematopoietic wave of erythro-myeloid progenitors (EMPs) emerging in the yolk sac. At least two distinct pathways derived from EMPs have been implicated in macrophage development. The first one, c-Myb-independent is giving rise to yolk sac macrophages also called primitive macrophages, and bypassing the classical monocytic intermediates. The second requires c-Myb expression and start once EMPs seed the fetal liver where they generate fetal monocytes. Sequentially, primitive macrophages seed every tissue and will ultimately give rise to microglia in the brain, rapidly isolated by the blood brain barrier, while EMP-derived fetal monocytes infiltrate every other tissues and gradually generate the major pool of adult tissue-resident macrophages by diluting the initial primitive macrophage contribution. A third wave of hematopoietic stem cells (HSC)-derived monocytes is also emerging from the fetal liver to contribute to the long-lived macrophage pool established at birth while the adult hematopoiesis is only starting in the bone marrow. We propose here to review recent insights about the different embryonic hematopoietic programs responsible for the generation of long-lived tissue-resident macrophages and their maintenance after birth.

The survival of fetal and bone marrow monocyte-derived alveolar macrophages is promoted by CD44 and its interaction with hyaluronan.

Alveolar macrophages maintain lung homeostasis by performing important roles in immunosurveillance and lung surfactant catabolism. They express high levels of CD44 and are one of the few macrophage populations that constitutively bind hyaluronan, a ligand for CD44 and component of pericellular and extracellular matrices. Using adoptive transfer experiments and a mouse model of inflammation, we found that alveolar macrophages are initially depleted after an inflammatory insult then rapidly self-renew and return to original numbers after the resolution phase. Monocytes recruited to an inflamed lung differentiate and contribute to the alveolar macrophage pool, but this occurs over a much slower time frame than alveolar macrophage self-renewal. CD44 expression on both fetal and bone marrow-derived alveolar macrophages promoted their survival and provided a competitive advantage over CD44-deficient alveolar macrophages at homeostasis and after inflammation. CD44-mediated hyaluronan binding was induced by the alveolar environment, and this interaction promoted alveolar macrophage survival both ex vivo and in vivo. Without CD44, alveolar macrophages lacked a hyaluronan coat, were more susceptible to death, and were present at lower numbers in the alveolar space. This demonstrates a new role for CD44 and hyaluronan in promoting alveolar macrophage survival.

Human Primary Macrophages Derived In Vitro from Circulating Monocytes Comprise Adherent and Non-Adherent Subsets with Differential Expression of Siglec-1 and CD4 and Permissiveness to HIV-1 Infection.

Macrophages are a major target for human immunodeficiency virus type 1 (HIV-1) infection. However, macrophages are largely heterogeneous and may exhibit differences in permissiveness to HIV-1 infection. This study highlights the interplay of macrophage heterogeneity in HIV-1 pathogenesis. We show that monocyte-derived macrophages (MDMs) could be divided into two distinct subsets: CD14+Siglec-1hiCD4+ (non-adherent MDM) and CD14+Siglec-1LoCD4− (adherent MDM). The CD14+Siglec-1hiCD4+MDM subset represented the smaller proportion in the macrophage pool, and varied among different donors. Fractionation and subsequent exposure of the two MDM subsets to HIV-1 revealed opposite outcomes in terms of HIV-1 capture and infection. Although the CD14+Siglec-1hiCD4+MDM captured significantly more HIV-1, infection was significantly higher in the CD14+Siglec-1LoCD4−MDM subset. Thus, CD14+Siglec-1hiCD4+MDM were less permissive to infection. Depletion of CD14+Siglec-1hiCD4+MDM or a decrease in their percentage, resulted in increased infection of MDM, suggestive of a capacity of these cells to capture and sequester HIV-1 in an environment that hinders its infectivity. Increased expression of innate restriction factors and cytokine genes were observed in the non-adherent CD14+Siglec-1hiCD4+MDM, both before and after HIV-1 infection, compared to the adherent CD14+Siglec-1LoCD4−MDM. We speculate that the differential expression of gene expression profiles in the two macrophage subsets may provide an explanation for the differences observed in HIV-1 infectivity.

Non-alcoholic steatohepatitis induces transient changes within the liver macrophage pool

Kupffer cells (KCs) and monocyte-derived macrophages are implicated in non-alcoholic steatohepatitis (NASH) pathogenesis but their functions remain unclear due to the lack of specific markers to distinguish between the different cell types. Additionally, it is unclear if multiple subsets of KCs are present during NASH. Here, we characterized the liver macrophage subsets during methionine/choline deficient (MCD) diet-induced NASH and recovery. We observed a significant reduced contribution of Ly6CloClec4F+Tim4+KCs to the hepatic macrophage pool in MCD fed mice, which normalized during recovery. Ly6CloClec4F-Tim4- monocyte-derived macrophages increased during MCD feeding and returned to baseline during recovery. Ly6CloClec4F+Tim4- monocyte-derived KCs developed during initial recovery but did not self-renew as their numbers were reduced after full recovery. Initial recovery from MCD diet feeding was further characterized by increased proportions of Ki-67+ proliferating KCs. In conclusion, the hepatic macrophage pool undergoes substantial albeit transient changes during NASH and recovery, with the KC pool being maintained by proliferation and differentiation of short-lived monocyte-derived KCs.

Splitting the “Unsplittable”: Dissecting Resident and Infiltrating Macrophages in Experimental Autoimmune Encephalomyelitis

Macrophages predominate the inflammatory landscape within multiple sclerosis (MS) lesions, not only regarding cellularity but also with respect to the diverse functions this cell fraction provides during disease progression and remission. Researchers have been well aware of the fact that the macrophage pool during central nervous system (CNS) autoimmunity consists of a mixture of myeloid cells. Yet, separating these populations to define their unique contribution to disease pathology has long been challenging due to their similar marker expression. Sophisticated lineage tracing approaches as well as comprehensive transcriptome analysis have elevated our insight into macrophage biology to a new level enabling scientists to dissect the roles of resident (microglia and non-parenchymal macrophages) and infiltrating macrophages with unprecedented precision. To do so in an accurate way, researchers have to know their toolbox, which has been filled with diverse, discriminating approaches from decades of studying neuroinflammation in animal models. Every method has its own strengths and weaknesses, which will be addressed in this review. The focus will be on tools to manipulate and/or identify different macrophage subgroups within the injured murine CNS.

Intestinal macrophages in Peyer's patches, sacculus rotundus and appendix of Angora rabbit.

The largest pool of macrophages in the body is harboured by the intestinal mucosa. As the principal phagocytic component of the immune system, macrophages are essential for maintaining mucosal homeostasis as they prevent commensal bacteria from adhering to mucosal epithelial cells. This study provides a RAM11 immunohistochemical and electron microscopic investigation of the existence, localization and distribution of intestinal macrophages in organized gut-associated lymphoid tissue (GALT), including Peyer's patches (PPs), the sacculus rotundus (SR) and the appendix, in the Angora rabbit. Although rabbit intestinal macrophages did not express the tissue macrophage marker macrosialin (CD68), they expressed RAM11. RAM11-positive intestinal macrophages were mostly localized to the subepithelial dome region, interfollicular area and germinal centres (GCs) of the GALT and the lamina propria or submucosa of the ileum and jejunum devoid of PPs and were also observed in the follicle-associated epithelium of PPs, but not in that of the SR and appendix. RAM11-positive macrophages containing engulfed apoptotic bodies were present in the GCs of the lymphoid follicles in the GALT. Electron microscopy further revealed multiple macrophages containing apoptotic bodies within the GCs of the follicles in the GALT. Some macrophage aggregations were observed in the GC and between the GC and the corona region of the follicles in the SR and appendix. Rabbit intestinal macrophages thus undertake both potent phagocytic activity and the efficient scavenging of apoptotic cells. Immunohistochemical data suggest that RAM11 can be reliably used for the determination of intestinal macrophages in the GALT of rabbits.