Macrophage development: I. Rationale for using Griffonia simplicifolia isolectin B4 as a marker for the line

Role of NLRP3 Inflammasomes in Monocyte and Microglial Recruitments in Choroidal Neovascularization

Although the pathogenesis of choroidal neovascularization (CNV) is largely unknown in age-related macular degeneration (AMD), inflammasomes may contribute to CNV development and progression. To understand the role NLRP3 inflammasomes in CNV, we used Ccr2RFPCx3cr1GFP dual-reporter mice and immunostaining techniques to confirm localization of NLRP3 inflammasomes in the laser-induced CNV (LCNV) lesions. Confocal microscopy was used to image and quantify LCNV volumes. MCC950 was used as NLRP3 inhibitor. ELISA and quantitative RT-PCR were used to confirm the activation of NLRP3 by monitoring the expression of IL-1β protein and mRNA in choroidal tissues from LCNV mice. In addition, NLRP3 (-/-) LCNV mice were used to investigate whether NLRP3 inflammasomes contribute to the development of LCNV lesions. We observed that red fluorescent protein (RFP)-positive monocyte-derived macrophages and GFP-positive microglia-derived macrophages, in addition to other cell types, were localized in LCNV lesions at day 7 post-laser injury. In addition, NLRP3 inflammasomes are associated with LCNV lesions. Inhibition of NLRP3 inflammasomes, using MCC950, caused an increased Ccr2RFP-positive macrophages, Cx3cr1GFP-positive microglia, and other cells, resulting in an increase in total lesion size. NLRP3 (-/-) LCNV mice showed significantly increased lesion size compared with age-matched controls. Inhibition of NLRP3 resulted in decreased IL-1β mRNA and protein expression in the choroidal tissues, suggesting that increased lesion size may not be directly related to IL-1β.

Role of NLRP3 inflammasomes in monocyte and microglial recruitments in choroidal neovascularization

Though the pathogenesis of choroidal neovascularization (CNV) is largely unknown in age-related macular degeneration (AMD), inflammasomes may contribute to CNV development and progression. To understand the role NLRP3 inflammasomes in CNV, we used Ccr2RFPCx3cr1GFP dual-reporter mice to characterize migration of Ccr2RFP positive monocytes and Cx3cr1GFP positive microglial cells into CNV lesions after laser-induced rupture of Bruch's membrane. MCC950 was used as NLRP3 inhibitor. Immunostaining was used to confirm localization of NLRP3 inflammasomes in the LCNV lesions. Confocal microscopy was used to image and quantify LCNV volumes. ELISA and qRT-PCR were used to confirm the activation of NLRP3 by monitoring the expression of IL-1β protein and mRNA in choroidal tissues from LCNV mice. In addition, NLRP3 (-/-) LCNV mice were used to investigate whether NLRP3 inflammasomes contribute to the development of LCNV lesions. We observed that RFP positive monocyte-derived macrophages and GFP positive microglia-derived macrophages, in addition to other cell types, were localized in LCNV lesions at day 7 post-laser injury. In addition, NLRP3 inflammasomes are associated with LCNV lesions. Inhibition of NLRP3 inflammasomes, using MCC950, caused an increased Ccr2RFP positive macrophages, Cx3cr1GFP positive microglia, and other cells resulting in an increase in total lesion size. NLRP3 (-/-) LCNV mice, showed significantly increased lesion size compared to age-matched controls. Inhibition of NLRP3, resulted in decreased IL-1β mRNA and protein expression in the choroidal tissues, suggesting that increased lesion size may not be directly related to IL-1β.

A novel optical imaging probe for targeted visualization of NLRP3 inflammasomes in a mouse model of age-related macular degeneration

Purpose

Wet form of age-related macular degeneration (wet AMD) is a progressive vascular disease that mainly affects older adults and causes severe and irreversible vision loss. A key complication of wet AMD is choroidal neovascularization (CNV), which may be driven in part by NLRP3 inflammasomes that are associated with macrophages migration to CNV lesions. Since activated NLRP3 is correlated with CNV, visualizing NLRP3 inflammasomes and their associated macrophages is of great interest to monitor wet AMD progression and develop effective therapies against it. However, to the best of our knowledge, current ophthalmic imaging systems do not permit such targeted imaging. Therefore, in this study, we developed InflammaProbe-1, an optical imaging probe for targeted visualization of NLRP3 inflammasomes in CNV lesions.

Methods

InflammaProbe-1 was synthesized by conjugating a clinically relevant fluorophore, Oregon Green^® 488, to the selective NLRP3 inhibitor, CY-09. The ability of InflammaProbe-1 to target NLRP3 was assessed with an enzyme-linked immunosorbent assay by comparing its ability to inhibit NLRP3-mediated secretion of IL-1β to that of CY-09 in LPS-primed and nigericin-stimulated BMDMs. In vitro confocal imaging of NLRP3 was performed on InflammaProbe-1-stained BMDMs that had been induced to express NLRP3 with LPS. In vivo imaging of NLRP3 was conducted on mouse laser induced choroidal neovascularization (LCNV), a model of AMD, 6 h after an intraperitoneal injection of InflammaProbe-1 at 10 mg/kg on day 4 post-LCNV.

Results

InflammaProbe-1 was just as effective as CY-09 at inhibiting IL-1β secretion (p < 0.01 at 10 μM for both the InflammaProbe-1 and CY-09 groups relative to the control). InflammaProbe-1-stained BMDMs that had been induced to express NLRP3 showed significantly brighter fluorescence than untreated cells (p < 0.0001 for LPS treatment group and p < 0.001 for LPS and nigericin treatment group). Furthermore, in vivo molecular imaging of NLRP3 was achieved in mouse LCNV.

Conclusion

We propose that InflammaProbe-1 may be a useful molecular imaging probe to monitor the onset, progression, and therapeutic response of AMD and other NLRP3-mediated diseases.

Identification of the Adult Hematopoietic Liver as the Primary Reservoir for the Recruitment of Pro-regenerative Macrophages Required for Salamander Limb Regeneration

The lack of scar-free healing and regeneration in many adult human tissues imposes severe limitations on the recovery of function after injury. In stark contrast, salamanders can functionally repair a range of clinically relevant tissues throughout adult life. The impressive ability to regenerate whole limbs after amputation, or regenerate following cardiac injury, is critically dependent on the recruitment of (myeloid) macrophage white blood cells to the site of injury. Amputation in the absence of macrophages results in regeneration failure and scar tissue induction. Identifying the exact hematopoietic source or reservoir of myeloid cells supporting regeneration is a necessary step in characterizing differences in macrophage phenotypes regulating scarring or regeneration across species. Mammalian wounds are dominated by splenic-derived monocytes that originate in the bone marrow and differentiate into macrophages within the wound. Unlike mammals, adult axolotls do not have functional bone marrow but instead utilize liver and spleen tissues as major sites for adult hematopoiesis. To interrogate leukocyte identity, tissue origins, and modes of recruitment, we established several transgenic axolotl hematopoietic tissue transplant models and flow cytometry protocols to study cell migration and identify the source of pro-regenerative macrophages. We identified that although bidirectional trafficking of leukocytes can occur between spleen and liver tissues, the liver is the major source of leukocytes recruited to regenerating limbs. Recruitment of leukocytes and limb regeneration occurs in the absence of the spleen, thus confirming the dependence of liver-derived myeloid cells in regeneration and that splenic maturation is dispensable for the education of pro-regenerative macrophages. This work provides an important foundation for understanding the hematopoietic origins and education of myeloid cells recruited to, and essential for, adult tissue regeneration.

Origins and diversity of macrophages in health and disease

Macrophages are the first immune cells in the developing embryo and have a central role in organ development, homeostasis, immunity and repair. Over the last century, our understanding of these cells has evolved from being thought of as simple phagocytic cells to master regulators involved in governing a myriad of cellular processes. A better appreciation of macrophage biology has been matched with a clearer understanding of their diverse origins and the flexibility of their metabolic and transcriptional machinery. The understanding of the classical mononuclear phagocyte system in its original form has now been expanded to include the embryonic origin of tissue‐resident macrophages. A better knowledge of the intrinsic similarities and differences between macrophages of embryonic or monocyte origin has highlighted the importance of ontogeny in macrophage dysfunction in disease. In this review, we provide an update on origin and classification of tissue macrophages, the mechanisms of macrophage specialisation and their role in health and disease. The importance of the macrophage niche in providing trophic factors and a specialised environment for macrophage differentiation and specialisation is also discussed.

No Evidence for Erythro-Myeloid Progenitor-Derived Vascular Endothelial Cells in Multiple Organs

RATIONALE

Endothelial cells are thought to emerge de novo from the mesoderm to form the entire circulatory system. Recently, erythro-myeloid progenitors (EMPs) have been proposed to be another remarkable developmental origin for blood vessels in multiple organs, including the hindbrain, liver, lung, and heart, as demonstrated by lineage tracing studies using different genetic tools. These observations challenge the current consensus that intraembryonic vessels are thought to expand solely by the proliferation of preexisting endothelial cells. Resolution of this controversy over the developmental origin of endothelial cells is crucial for developing future therapeutics for vessel-dependent organ repair and regeneration.

OBJECTIVE

To examine the contribution of EMPs to intraembryonic endothelial cells.

METHODS AND RESULTS

We first used a transgenic mouse expressing a tamoxifen-inducible Mer-iCre fusion protein driven by the Csf1r (colony stimulating factor 1 receptor) promoter. Genetic lineage tracing based on Csf1r-Mer-iCre-Mer showed no contribution of EMPs to brain endothelial cells identified by several markers. We also generated a knock-in mouse line by inserting an internal ribosome entry site-iCre cassette into the 3' untranslated region of Csf1r gene to further investigate the cellular fates of EMPs. Similarly, we did not find any Csf1r-ires-iCre traced endothelial cells in brain, liver, lung, or heart in development either. Additionally, we found that Kit (KIT proto-oncogene receptor tyrosine kinase) was expressed not only in EMPs but also in embryonic hindbrain endothelial cells. Therefore, Kit promoter-driven recombinase, such as Kit-CreER, is a flawed tool for lineage tracing when examining the contribution of EMPs to hindbrain endothelial cells. We also traced CD45 (protein tyrosine phosphatase receptor type C; Ptprc)⁺ circulating EMPs and did not find any CD45 lineage-derived endothelial cells during development.

CONCLUSIONS

Our study suggested that EMPs are not the origin of intraembryonic endothelial cells.

Hepatocyte growth factor is upregulated in ischemic retina and contributes to retinal vascular leakage and neovascularization

In patients with macular edema due to ischemic retinopathy, aqueous levels of hepatocyte growth factor (HGF) correlate with edema severity. We tested whether HGF expression and activity in mice with oxygen-induced ischemic retinopathy supports a role in macular edema. In ischemic retina, HGF was increased in endogenous cells and macrophages associated with retinal neovascularization (NV). HGF activator was increased in and around retinal vessels potentially providing vascular targeting. One day after intravitreous injection of HGF, VE-cadherin was reduced and albumin levels in retina and vitreous were significantly increased indicating vascular leakage. Injection of VEGF caused higher levels of vitreous albumin than HGF, and co-injection of both growth factors caused significantly higher levels than either alone. HGF increased the number of macrophages on the retinal surface, which was blocked by anti-c-Met and abrogated in chemokine (C-C motif) ligand 2 (CCL2)-/- mice. Injection of anti-c-Met significantly decreased leakage within 24 hours and after 5 days it reduced retinal NV in mice with ischemic retinopathy, but had no effect on choroidal NV. These data indicate that HGF is a pro-permeability, pro-inflammatory, and pro-angiogenic factor and along with its activator is increased in ischemic retina providing support for a potential role of HGF in macular edema in ischemic retinopathies.

Imaging methods used to study mouse and human HSC niches: Current and emerging technologies

Bone marrow contains numerous different cell types arising from hematopoietic stem cells (HSCs) and non-hematopoietic mesenchymal/skeletal stem cells, in addition to other cell types such as endothelial cells- these non-hematopoietic cells are commonly referred to as stromal cells or microenvironment cells. HSC function is intimately linked to complex signals integrated by their niches, formed by combinations of hematopoietic and stromal cells. Studies of hematopoietic cells have been significantly advanced by flow cytometry methods, enabling the quantitation of each cell type in normal and perturbed situations, in addition to the isolation of these cells for molecular and functional studies. Less is known, however, about the specific niches for distinct developing hematopoietic lineages, or the changes occurring in the niche size and function in these distinct anatomical sites in the bone marrow under stress situations and ageing. Significant advances in imaging technology during the last decade have permitted studies of HSC niches in mice. Additional imaging technologies are emerging that will facilitate the study of human HSC niches in trephine BM biopsies. Here we provide an overview of imaging technologies used to study HSC niches, in addition to highlighting emerging technology that will help us to more precisely identify and characterize HSC niches in normal and diseased states.

Reciprocal analyses in zebrafish and medaka reveal that harnessing the immune response promotes cardiac regeneration

Zebrafish display a distinct ability to regenerate their heart following injury. However, this ability is not shared by another teleost, the medaka. In order to identify cellular and molecular bases for this difference, we performed comparative transcriptomic analyses following cardiac cryoinjury. This comparison points to major differences in immune cell dynamics between these models. Upon closer examination, we observed delayed and reduced macrophage recruitment in medaka, along with delayed neutrophil clearance. To investigate the role of immune responses in cardiac regeneration, we delayed macrophage recruitment in zebrafish and observed compromised neovascularization, neutrophil clearance, cardiomyocyte proliferation and scar resolution. In contrast, stimulating Toll-like receptor signaling in medaka enhanced immune cell dynamics and promoted neovascularization, neutrophil clearance, cardiomyocyte proliferation and scar resolution. Altogether, these data provide further insight into the complex role of the immune response during regeneration, and serve as a platform to identify and test additional regulators of cardiac repair.

DOI:http://dx.doi.org/10.7554/eLife.25605.001

Quantitative assessment of angiogenesis, perfused blood vessels and endothelial tip cells in the postnatal mouse brain

During development and in various diseases of the CNS, new blood vessel formation starts with endothelial tip cell selection and vascular sprout migration, followed by the establishment of functional, perfused blood vessels. Here we describe a method that allows the assessment of these distinct angiogenic steps together with antibody-based protein detection in the postnatal mouse brain. Intravascular and perivascular markers such as Evans blue (EB), isolectin B4 (IB4) or laminin (LN) are used alongside simultaneous immunofluorescence on the same sections. By using confocal laser-scanning microscopy and stereological methods for analysis, detailed quantification of the 3D postnatal brain vasculature for perfused and nonperfused vessels (e.g., vascular volume fraction, vessel length and number, number of branch points and perfusion status of the newly formed vessels) and characterization of sprouting activity (e.g., endothelial tip cell density, filopodia number) can be obtained. The entire protocol, from mouse perfusion to vessel analysis, takes ∼10 d.

Expression of dual nucleotides/cysteinyl-leukotrienes receptor GPR17 in early trafficking of cardiac stromal cells after myocardial infarction

GPR17 is a G_i-coupled dual receptor activated by uracil-nucleotides and cysteinyl-leukotrienes. These mediators are massively released into hypoxic tissues. In the normal heart, GPR17 expression has been reported. By contrast, its role in myocardial ischaemia has not yet been assessed. In the present report, the expression of GPR17 was investigated in mice before and at early stages after myocardial infarction by using immunofluorescence, flow cytometry and RT-PCR. Before induction of ischaemia, results indicated the presence of the receptor in a population of stromal cells expressing the stem-cell antigen-1 (Sca-1). At early stages after ligation of the coronary artery, the receptor was expressed in Sca-1⁺ cells, and cells stained with Isolectin-B4 and anti-CD45 antibody. GPR17⁺ cells also expressed mesenchymal marker CD44. GPR17 function was investigated in vitro in a Sca-1⁺/CD31⁻ cell line derived from normal hearts. These experiments showed a migratory function of the receptor by treatment with UDP-glucose and leukotriene LTD4, two GPR17 pharmacological agonists. The GPR17 function was finally assessed in vivo by treating infarcted mice with Cangrelor, a pharmacological receptor antagonist, which, at least in part, inhibited early recruitment of GPR17⁺ and CD45⁺ cells. These findings suggest a regulation of heart-resident mesenchymal cells and blood-borne cellular species recruitment following myocardial infarction, orchestrated by GPR17.

Hyperforin attenuates microglia activation and inhibits p65-Ser276 NFκB phosphorylation in the rat piriform cortex following status epilepticus

Hyperforin, a lipophilic constituent of medicinal herb St. John's Wort, has neurobiological effects including antidepressant activity, antibiotic potency, anti-inflammatory activity and anti-tumoral properties. Furthermore, hyperforin activates transient receptor potential conical channel-6 (TRPC6), a nonselective cation channel. To elucidate the roles of hyperforin and TRPC6 in neuroinflammation in vivo, we investigated the effect of hyperforin on neuroinflammatory responses and its related events in the rat piriform cortex (PC) following status epilepticus (SE). Hyperforin attenuated microglial activation, p65-serine 276 NFκB phosphorylation, and suppressed TNF-α expression in the PC following SE. Hyperforin also effectively alleviated SE-induced vasogenic edema formation, neuronal damage, microglial TRPC6 induction and blood-derived monocyte infiltration. Our findings suggest that hyperforin may effectively attenuate microglia-mediated neuroinflammation in the TRPC6-independent manner.

Toona sinensis leaf aqueous extract displays activity against sepsis in both in vitro and in vivo models

Toona sinensis (TS) leaves are used as a vegetable and in traditional Chinese medicine. However, in vivo experiments regarding the anti-inflammatory function of TS leaves have not previously been conducted. The aim of this study was to investigate the potential role of TS leaf extract (TSL) in the prevention of sepsis-induced lung injury in vivo and on macrophage activation in vitro. The results showed that oral gavage pretreatment with TSL in rats for 30 days improved the survival of cecal ligation and puncture-induced sepsis, potentially by attenuating sepsis-induced histological lung damage rather than inflammatory cell infiltration. Furthermore, we demonstrated that pretreatment with TSL attenuated the lipopolysaccharide (LPS)-induced expression of inducible nitric oxide synthase, thereby inhibiting nitric oxide production and release in murine macrophage-like RAW 264.7 cells. Interestingly, TSL did not affect the LPS-induced release of other cytokines (e.g., tumor necrosis factor α and interleukin 1β) but increased LPS-induced heme-oxygenase-1 expression. In conclusion, the study provides preliminary data for TSL on cecal ligation and puncture-induced sepsis. The beneficial impact of TSL needs extensive study to get solid evidence.

A critical role for pannexin-1 in activation of innate immune cells of the choroid plexus

Epiplexus cells are a population of innate immune cells in the choroid plexus of the brain ventricles. They are thought to contribute to the immune component of the blood-cerebrospinal-fluid-barrier (BCSFB). Here we have developed a novel technique for studying epiplexus cells in acutely isolated, live and intact choroid plexus. We show that epiplexus cells are potently activated by exogenous ATP, increasing their motility within the tissue. This ATP-induced chemokinesis required activation of pannexin-1 channels, which are expressed by the epithelial cells of the choroid plexus and not the epiplexus cells themselves. Furthermore, ATP acts at least in part through the P2X4 ionotropic purinergic receptor. Thus, the resident immune cells of the choroid plexus appear to be in communication with the epithelial cells through pannexin-1 channels.

The embryonic mouse hindbrain as a qualitative and quantitative model for studying the molecular and cellular mechanisms of angiogenesis

The mouse embryo hindbrain is a robust and adaptable model for studying sprouting angiogenesis. It permits the spatiotemporal analysis of organ vascularization in normal mice and in mouse strains with genetic mutations that result in late embryonic or perinatal lethality. Unlike postnatal models such as retinal angiogenesis or Matrigel implants, there is no requirement for the breeding of conditional knockout mice. The unique architecture of the hindbrain vasculature allows whole-mount immunolabeling of blood vessels and high-resolution imaging, as well as easy quantification of angiogenic sprouting, network density and vessel caliber. The hindbrain model also permits the visualization of ligand binding to blood vessels in situ and the analysis of blood vessel growth within a natural multicellular microenvironment in which endothelial cells (ECs) interact with non-ECs to refine the 3D organ architecture. The entire procedure, from embryo isolation to imaging and through to results analysis, takes approximately 4 d.

NRP1 acts cell autonomously in endothelium to promote tip cell function during sprouting angiogenesis

Neuropilin (NRP) 1 is a receptor for the vascular endothelial growth factor (VEGF)-A and is essential for normal angiogenesis. Previous in vitro experiments identified NRP1 interactions with VEGF-A's main signaling receptor VEGFR2 within endothelial cells, but also between nonendothelial NRP1 and endothelial VEGFR2. Consistent with an endothelial role for NRP1 in angiogenesis, we found that VEGFR2 and NRP1 were coexpressed in endothelial tip and stalk cells in the developing brain. In addition, NRP1 was expressed on two cell types that interact with growing brain vessels-the neural progenitors that secrete VEGF-A to stimulate tip cell activity and the pro-angiogenic macrophages that promote tip cell anastomosis. Selective targeting of Nrp1 in each of these cell types demonstrated that neural progenitor- and macrophage-derived NRP1 were dispensable, whereas endothelial NRP1 was essential for normal brain vessel growth. NRP1 therefore promotes brain angiogenesis cell autonomously in endothelium, independently of heterotypic interactions with nonendothelial cells. Genetic mosaic analyses demonstrated a key role for NRP1 in endothelial tip rather than stalk cells during vessel sprouting. Thus, NRP1-expressing endothelial cells attained the tip cell position when competing with NRP1-negative endothelial cells in chimeric vessel sprouts. Taken together, these findings demonstrate that NRP1 promotes endothelial tip cell function during angiogenesis.

CXCR4 antagonist AMD3100 accelerates impaired wound healing in diabetic mice

The antagonism of CXC-chemokine receptor 4 (CXCR4) with AMD3100 improves cardiac performance after myocardial infarction by augmenting the recruitment of endothelial progenitor cells (EPCs) from the bone marrow to the regenerating vasculature. We investigated whether AMD3100 may accelerate diabetes-impaired wound healing through a similar mechanism. Skin wounds were made on the backs of leptin-receptor–deficient mice and treated with AMD3100 or saline. Fourteen days after treatment, wound closure was significantly more complete in AMD3100-treated mice (AMD3100: 87.0±2.6%, Saline: 33.1±1.8%; P<0.0001) and was accompanied by greater collagen-fiber formation, capillary density, smooth-muscle-containing vessel density, and monocyte/macrophage infiltration. On day 7 after treatment, AMD3100 was associated with higher circulating EPC and macrophage counts and with significantly upregulated mRNA levels of stromal-cell–derived factor 1 and platelet-derived growth-factor B in the wound bed. AMD3100 also promoted macrophage proliferation and phagocytosis and the migration and proliferation of diabetic mouse primary dermal fibroblasts and 3T3 fibroblasts, which express very little CXCR4. In conclusion, a single topical application of AMD3100 promoted wound healing in diabetic mice by increasing cytokine production, mobilizing bone-marrow EPCs, and enhancing the activity of fibroblasts and monocytes/macrophages, thereby increasing both angiogenesis and vasculogenesis. Not all of the AMD3100-mediated effects evolved through CXCR4 antagonism.

Immunohistochemical localization of galectin-3 in the reproductive organs of the cow

The protein levels and immunohistochemical localization of galectin-3, which is a beta-galactoside-binding protein, were studied in the cow reproductive organs. Using Western blot analysis, galectin-3 was detected at low levels in the ovary and oviduct, at moderate levels in the uterus, and at high levels in the cervix. Using immunohistochemistry, galectin-3 was immunolocalized in macrophages in the interstitium, in cells in the atretic follicles, and in luteal cells in the regressing corpus luteum, but not in the growing follicles in the ovary. In the oviduct, galectin-3 was detected in some macrophages in the lamina propria, submucosa and muscle layers, as well as in some cells in the covering epithelium. In the uterus, galectin-3 was immunolocalized in some epithelial cells and in some macrophages in the submucosa, but not in the endometrial glands at the non-pregnant stage. In the cervix, galectin-3 was immunolocalized in many mucus-secreting cells in the mucosa and in a few macrophages in the submucosa and muscle layers. Based on its localization, we postulate that galectin-3 in the covering epithelium is involved in the mucosal defense system, and that galectin-3-positive macrophages in all tissues are involved in either cell survival or death. In addition, galectin-3 plays an important role in the regression of follicles and the corpus luteum.

Changes in quinolinic acid production and its related enzymes following D-galactosamine and lipopolysaccharide-induced hepatic injury

Increases in quinolinic acid (QUIN), a neurotoxic L-tryptophan metabolite, have been observed in human serum and cerebrospinal fluid and in animal models of severe hepatic injury. The aim of this study was to evaluate the changes in QUIN accumulation and its related enzymes after acute hepatic injury induced by D-galactosamine and endotoxin. Gerbils were given an intraperitoneal injection of pyrogen-free saline alone as control, lipopolysaccharide (LPS) alone (150 ng/kg), D-galactosamine alone (500 mg/kg) or a combination of D-galactosamine with LPS. Concentrations of QUIN, its related metabolites, and related enzyme activities were determined. D-Galactosamine treatment significantly decreased activities of hepatic aminocarboxymuconate-semialdehyde decarboxylase (ACMSDase) resulting in increased QUIN concentrations in serum and tissues. The magnitude of QUIN responses was markedly increased by endotoxin due to the increased availability of L-kynurenine, a rate-limiting substrate for QUIN synthesis. Further, infiltration of monocytes/macrophages, which is a possible major source of QUIN production in the liver, was shown by immunohistochemistry after hepatic injury induced by D-galactosamine and endotoxin. Increased serum QUIN concentrations are probably due to the increased substrate availability and the decreased activity of aminocarboxymuconate-semialdehyde decarboxylase in the liver, accompanying the increased monocyte/macrophage infiltration into the liver after hepatic injury.

Sequelae of parenteral domoic acid administration in rats: comparison of effects on different anatomical markers in brain

Brain damage following administration of domoic acid, a structural analog of the excitatory amino acids glutamic acid and kainic acid, was compared using different anatomic markers in adult rats. Seven days after administration of domoic acid (2.25 mg/kg i.p.) or vehicle, brains were collected and sectioned and stained to visualize Nissl substance using thionin, argyrophilia using a cupric silver staining method, astroglia using immunohistochemistry to detect glial fibrillary acidic protein-like immunoreactivity (GFAP-ir), and activated microglia using lectin histochemistry to detect Griffonia simplicifolia I-B4 isolectin (GSI-B4) binding in adjacent sections. In approximately 60% of rats to which it was administered, domoic acid caused stereotyped behavior within 60 min, followed by convulsions within 2-3 h. Brains of domoic acid-administered rats that did not manifest stereotyped behavior or convulsions did not differ from brains from vehicle-administered controls. In animals that had manifested stereotyped behavior and convulsions, Nissl staining was mostly unremarkable in brain sections. In contrast, there was intense argyrophilia in anterior olfactory nucleus, CA1 hippocampus, lateral septum, parietal (layer IV), piriform, and entorhinal cortices, ventral posterolateral thalamus, and amygdala. This pattern was reminiscent of that seen in postmortem specimens from humans who consumed domoic acid-tainted mussels and in experimental animals after kainic acid administration. Adjacent sections displayed astrogliosis, evidenced by increased GFAP-ir, which was more diffuse than the argyrophilic reaction. Activated microglia were revealed using GSI-B4 histochemistry. These data suggest activation of discrete brain circuits in rats that convulse following domoic acid administration and subsequent pathological alterations. The data strongly suggest that neuropathology following domoic acid occurs only in animals manifesting domoic acid-induced sterotypy and convulsions. The data do not rule out more insidious damage in behaviorally normal rats that receive domoic acid.

Precursors of macrophages in embryonic rat lungs fail to exhibit granulocyte-forming potential

BACKGROUND

Mesenchyme-like macrophage (M) precursors called angular cells are present in rat lungs on the thirteenth day of gestation and by then can differentiate into outright macrophages. Based on studies of bone marrow-derived cells, it is widely believed that the macrophage line necessarily proceeds from a colony-forming unit with dual granulocyte-macrophage potential (CFU-GM). In embryos this seems doubtful since macrophages are already scattered throughout the body before the first granulocytes appear. We examined the question in organ cultured 14 day prenatal rat lungs after having shown earlier that the macrophage population developed in explants is increased by exposure to M- and GM-colony-stimulating factors (CSFs) but is unaffected by multi (IL-3)- or granulocyte (G)-CSF. Reportedly retinoic acid (RA) shifts CFU-GM strongly towards granulocytic differentiation and inhibits mitosis of unipotential macrophage precursors but not differentiated cells. Transforming growth factor beta 1 (TGF) inhibits multipotential blood progenitors but allows proliferation of committed precursors, and TGF together with GM-CSF induces granulocytopoiesis from CFU-GM.

METHODS

Lung pairs were grown on a serum-containing medium or one supplemented either by RA, TGF, or TGF/GM-CSF to form a control and three experimental groups. A fourth experiment compared responses to M-CSF exposure and M-CSF/TGF. Macrophage population growth was estimated by measuring the areas of coronas formed by macrophages emerged from the explants. F-actin was stained with fluorescein-labeled phalloidin.

RESULTS

In all experiments macrophages were produced unmixed with granulocytes. By +8 days they had largely emerged to form coronas about the lungs. In cultures exposed to RA, macrophages were less intensely stained for actin and slower to emerge than controls. At +8 days, however, coronal areas were not significantly different from controls, as was also true for the TGF group. In contrast, coronal areas of cultures grown with TGF/GM-CSF were much larger. At +17 days, mean coronal area of TGF cultures was about half that of controls (P < 0.05), whereas mean coronal area of the TGF/GM-CSF group was 5.4 times greater (P < 0.001). Macrophages from control and TGF-exposed cultures responded to M-CSF by an increase in coronal area which was greater among cultures given M-CSF alone than those given TGF + M-CSF (both P < 0.005).

CONCLUSIONS

Macrophage precursors in embryonic lungs are distinct from CFU-GM.

Early development of macrophages in intact and organ cultured hearts of rat embryos

BACKGROUND

Macrophage precursors are present early in embryonic life, being demonstrable in placental and embryonic connective tissues of rats at the neurula stage and as potential macrophages in the brain, liver, and lungs near the onset of organogenesis. We examined the development of macrophages in the heart and the possibility that they initially appear at sites of programmed cell death (apoptosis).

METHODS

Precursors were recognized by the binding of peroxidase-coupled Griffonia simplicifolia isolectin B4 (GSA) on the cell membrane. Their capacity for conversion into macrophages was assayed in organ cultures; confirmation of the progeny as bona fide macrophages was obtained from their responses to particle exposure and macrophage colony-stimulating factor (M-CSF).

RESULTS

GSA+cells were first seen on gestational day 12 (4 mm embryos) as 2-3 cycling, nonvacuolated cells located in cardiac tissue outside the blood vessels. This population increased to approximately 12 cells by day 14 (9 mm embryos). Two-thirds were distributed along the bulbus cordis in the jellylike endocardium and a more densely cellular connective tissue closer to the aortic arches where apoptotic sites are expected to develop. Such sites were not found in serial glycol methacrylate sections through our 14-day specimens, although in whole heart explants of this age an area of necrosis developed along the prospective line of bulbar endocardial fusion on the second day of organ culturing, and by then macrophages were fairly abundant. Organ culturing of 13-day embryonic hearts also yielded large, highly vacuolated, GSA+mononuclear phagocytes. After a few days in culture most of the macrophages migrated onto the medium where they formed a tight corona of cells about the explants. They readily ingested iron oxide particles and concentrated supravitally administered neutral red in their vacuoles. Macrophages from 14-day cultures exposed to M-CSF developed significantly larger coronas than macrophages from explants grown in serum-rich control medium (p < 0.001). In the presence of cytokines, moreover, these cardiac macrophages survived as many as 100 (92 "postnatal") days.

CONCLUSIONS

Macrophage precursors first appear in embryonic rat hearts well before they are needed to clear debris generated by programmed cell death and are capable of rapid conversion into outright phagocytic cells as early as the 13th prenatal day.

Species differences in lectin binding to pulmonary cells: Soybean agglutinin (SBA) as a marker of type I alveolar epithelial cells and alveolar macrophages in mini pigs

We compared lectin staining patterns in rat and mini pig tissues of normal and fibrotic (irradiation-induced) lungs. Two lectins were studied: Dolichos biflorus (DBA) and Soybean (SBA). Both lectins strongly stained a subpopulation of alveolar macrophages. In the rat, DBA positive macrophages were a subpopulation of the SBA binding cells. In mini pig lungs, a further specific binding of DBA and SBA was observed: DBA reacted with endothelia, and SBA stained the alveolar type I cells. Double immunofluorescence experiments using a type II cell-specific cytokeratin antibody confirmed the selective reactivity of SBA with type I cells, which was also present in fibrotic areas with epithelial cell proliferation.

Heterogeneous Dolichos biflorus lectin binding to a subset of rat alveolar macrophages in normal and fibrotic lung tissue

The distribution of Dolichos biflorus lectin in the rat lung and during fibrosis after irradiation was investigated by lectin histochemical and electron microscopical techniques and double immunofluorescence labelling with the monoclonal antibodies RM-1 and ED-1. The results indicate a selective reaction of Dolichos biflorus lectin with a subpopulation of alveolar macrophages. No binding of the lectin was detectable in ED-1-positive macrophages but strong staining occurred in a part of the RM-1-positive cell population. In fibrotic lung specimens an increased number of Dolichos biflorus lectin-positive macrophages was found in which focally ED-1 reactive and RM-1 negative cells appeared. The finding of changing lectin binding pattern in a radiation-induced lung model emphasizes the suitability of the Dolichos biflorus lectin as a marker of macrophage activation or functional specialization.

Macrophage development: IV. Effects of blood factors on macrophages from prenatal rat lung cultures

Effects of colony-stimulating factors M-CSF, GM-CSF, G-CSF, and IL-3 were assessed on cells of macrophage lineage present in organ cultured 14-day prenatal rat lungs. Treatment groups were compared between one another and against control lungs grown on standard medium containing 40% fetal bovine serum without added factors, where a monoculture of macrophages rapidly develops from precursors present at explantation, leading to appearance of a large mature population on the pleural surface outside the lungs. Studies were carried out in living cultures and by light and electron microscopy using peroxidase-coupled isolectin B4 of Griffonia simplicifolia to identify macrophages and their precursors. In the first experiment, 14-day prenatal lung explants (14 + 0 days) containing macrophage precursors but not matured cells were exposed to individual CSFs for 7 days in an attempt to determine whether precursors are committed irrevocably to the macrophage line or can be altered by exposure to factors promoting significant granulocyte development. In succeeding experiments, 4- and 7-day-old cultures (14 + 4, 14 + 7 days) containing matured macrophages were targeted to see whether macrophage survival can be extended beyond expectations in controls and whether mitotic activity is stimulated. Recombinant CSFs were used at dosage levels known to promote colony formation in vitro (200-1,000 CFU/ml). Cultures exposed from prenatal day 14 to M-, GM-, G-CSF, or IL-3 yielded a monoculture of macrophages without exception. Populations developed in the presence of M- or GM-CSF were much larger than in controls or cultures grown with the other blood factors. GM-CSF-exposed cultures produced by far the largest macrophages, among them many multinucleate giant cells. Macrophages developed in the presence of G-CSF were also significantly larger than controls. Growth of the mature macrophage population was greatly stimulated by exposure to M-CSF or GM-CSF but not by IL-3 or G-CSF. Mitotic figures were noted in the coronas of emerged cells surrounding stimulated cultures, compared to none in the controls. Ultrastructurally, macrophages stimulated by M-CSF retained a mature appearance like macrophages in control, IL-3, and G-CSF treatment groups, whereas many in the GM-CSF group became less differentiated. As to long-term survival, a single 14-day explant was grown for 8 days on standard medium (the equivalent date for birth), then placed in a soft agar medium containing M-CSF.(ABSTRACT TRUNCATED AT 400 WORDS)

Macrophage development: III. Transformation of pulmonary macrophages from precursors in fetal lungs and their later maturation in organ culture

The fate of macrophage precursors residing in 14-day prenatal rat lungs was followed in organ cultures to obtain a detailed, ultrastructurally resolved picture of the sequence and timing of events accompanying their transformation into typical pulmonary macrophages. Cultures were examined at close intervals during the first day (1, 2, 3, 4, 6, 9, 12, 15, 18, and 24 hr) and at wider intervals thereafter (2, 4, 5, 7, 9, and 13 days) to yield a developmental series of cells identified as in the macrophage line based on binding of peroxidase-coupled isolectin B4 of Griffonia simplicifolia (GSA I-B4) to cell membranes and on negligible content of peroxidase-positive granules in the cytoplasm. Organ culturing stimulated virtually all precursors to develop into macrophages. GSA-positive cells in explants occurred outside vessels in pulmonary connective tissue, and at the outset none were typical macrophages: 71% were angular cells, resembling unlabeled mesenchymal cells around them, 16% were undifferentiated leukocytes, and the remainder were irregularly shaped cells with few vacuoles intermediate between the preceding and the macrophages. During the first 12 hr in culture the proportion of angular cells and leukocytes fell to zero, and that of intermediate cells first rose, then receded. In the same interval the proportion of macrophages rose to 87.5%, and by 24 hr all GSA-positive cells were typical macrophages generally engorged with phagocytosed material; about 8 hr appear necessary for converting half the population. Notable ultrastructural changes during this period of transformation involved the centrioles and cytoskeleton, reflecting enhanced cell mobility and phagocytosis. A period of maturation followed, marked by disappearance of cellular debris from phagosomes and an increased prevalence of cells with elaborate lamellipodia. This accords with earlier work showing that macrophage Fc receptor density increases sharply during the first 24 hr, but elevated levels of histochemically demonstrable acid phosphatase appear only later. Mitotic activity was conspicuous in GSA-positive cells throughout both periods. 3H-thymidine labeling indices for precursors and macrophages, determined at six intervals between 1 hr and 24 hr, remained steady at approximately 34%, whereas indices of other categories of lung cells (GSA-negative stromal cells, pleural cells, and airway epithelium) began at this level but rapidly declined, indicating that the GSA-positive cells constitute a single population distinct from others in the lungs. Macrophages found outside the lung cultures after 4-5 days qualify as a mature population, but having migrated away from direct contact with the lung stroma, they survive only a week or two and no longer divide.

Macrophage development: II. Early ontogeny of macrophage populations in brain, liver, and lungs of rat embryos as revealed by a lectin marker

Earliest origins of macrophage populations in the central nervous system, the liver, and the lungs were studied in rat embryos aged between 10.5-11 days and 14 days of gestation, based on light and electron microscopic identification of macrophages using peroxidase-coupled isolectin B4 of Griffonia simplicifolia (GSA I-B4), which recognizes alpha-D-galactose groups on the cell membrane. During embryonic life macrophages and their precursors are GSA I-B4-positive and generally bereft of peroxidase-positive granules. At 10.5 days the yolk sac and embryonic circulations have just become joined, the brain has five vesicles but nerve cells are little differentiated, the liver exists as a diverticulum of the gut with fingerlike extensions of hepatocytes, and the lungs as a laryngotracheal groove. Macrophages and/or their precursors occurred in small numbers in embryonic mesenchyme and blood vessels but showed no special affinity for either liver or lung rudiments. The developing brain was the first organ to be colonized, beginning on prenatal day 12. The liver followed between days 12 and 13 and was succeeded by the lungs, beginning between days 13 and 14. Dividing macrophages were present in these organs at the outset of colonization and throughout the duration of the embryo series, indicating that from the beginning, replication of resident cells contributes to growth of the local population. Granulocyte precursors were first apparent in the liver around day 13; they are also GSA-positive but are distinguished from macrophages by their content of peroxidase-positive granules. Organ cultures of 13-day liver and lungs, and 14-day brain tissue, indicate that whereas isolated liver fragments support the formation of both granulocytes and macrophages, only the latter develop in brain or lung cultures. A resident population of macrophages evidently is set up very early in these organs, well before white cells colonize the spleen, bone marrow, and other future blood forming regions. The events outlined are seen as stages in an embryo-wide process that leads to establishment of macrophage populations in various organs.