Mature monocytic cells enter tissues and engraft

Why nanoparticles prefer liver macrophage cell uptake in vivo

Effective delivery of therapeutic and diagnostic nanoparticles is dependent on their ability to accumulate in diseased tissues. However, most nanoparticles end up in liver macrophages regardless of nanoparticle design after administration. In this review, we describe the interactions of liver macrophages with nanoparticles. Liver macrophages have significant advantages in interacting with circulating nanoparticles over most target cells and tissues in the body. We describe these advantages in this article. Understanding these advantages will enable the development of strategies to overcome liver macrophages and deliver nanoparticles to targeted diseased tissues effectively. Ultimately, these approaches will increase the therapeutic efficacy and diagnostic signal of nanoparticles.

Microglia and Microglia-Like Cells: Similar but Different

Microglia are the tissue-resident macrophages of the central nervous parenchyma. In mammals, microglia are thought to originate from yolk sac precursors and posteriorly maintained through the entire life of the organism. However, the contribution of microglial cells from other sources should also be considered. In addition to “true” or “bona-fide” microglia, which are of embryonic origin, the so-called “microglia-like cells” are hematopoietic cells of bone marrow origin that can engraft the mature brain mainly under pathological conditions. These cells implement great parts of the microglial immune phenotype, but they do not completely adopt the “true microglia” features. Because of their pronounced similarity, true microglia and microglia-like cells are usually considered together as one population. In this review, we discuss the origin and development of these two distinct cell types and their differences. We will also review the factors determining the appearance and presence of microglia-like cells, which can vary among species. This knowledge might contribute to the development of therapeutic strategies aiming at microglial cells for the treatment of diseases in which they are involved, for example neurodegenerative disorders like Alzheimer’s and Parkinson’s diseases.

Cell Origin and iNOS Function Are Critical to Macrophage Activation Following Acute Lung Injury

In the intratracheal bleomycin (ITB) model of acute lung injury (ALI), macrophages are recruited to the lung and participate in the inflammation and resolution that follows injury. Macrophage origin is influential in determining activation; however, the specific phenotype of recruited and resident macrophages is not known. Inducible nitric oxide synthase (iNOS) has been implicated in the pathogenesis of ALI; however, the effects of its inhibition are mixed. Here we examined how macrophage origin determines the phenotypic response to ALI. Further, we hypothesize cell specific iNOS is key to determining activation and recruitment. Using a chimeric mouse approach, we have identified recruited and resident macrophage populations. We also used the chimeric mouse approach to create either pulmonary or bone marrow NOS2^-/- mice and systemically inhibited iNOS via 1400 W. We evaluated macrophage populations at the peak of inflammation (8 days) and the beginning of resolution (15 days) following ITB. These studies demonstrate tissue resident macrophages adopt a M2 phenotype specifically, but monocyte originated macrophages activate along a spectrum. Additionally, we demonstrated that monocyte originating macrophage derived iNOS is responsible for recruitment to the lung during the inflammatory phase. Further, we show that macrophage activation is dependent upon cellular origin. Finally, these studies suggest pulmonary derived iNOS is detrimental to the lung following ITB. In conclusion, macrophage origin is a key determinant in response to ALI and iNOS is central to recruitment and activation.

Long-term smoking alters abundance of over half of the proteome in bronchoalveolar lavage cell in smokers with normal spirometry, with effects on molecular pathways associated with COPD

Background

Smoking represents a significant risk factor for many chronic inflammatory diseases, including chronic obstructive pulmonary disease (COPD).

Methods

To identify dysregulation of specific proteins and pathways in bronchoalveolar lavage (BAL) cells associated with smoking, isobaric tags for relative and absolute quantitation (iTRAQ)-based shotgun proteomics analyses were performed on BAL cells from healthy never-smokers and smokers with normal lung function from the Karolinska COSMIC cohort. Multivariate statistical modeling, multivariate correlations with clinical data, and pathway enrichment analysis were performed.

Results

Smoking exerted a significant impact on the BAL cell proteome, with more than 500 proteins representing 15 molecular pathways altered due to smoking. The majority of these alterations occurred in a gender-independent manner. The phagosomal- and leukocyte trans endothelial migration (LTM) pathways significantly correlated with FEV₁/FVC as well as the percentage of CD8⁺ T-cells and CD8⁺CD69⁺ T-cells in smokers. The correlations to clinical parameters in healthy never-smokers were minor.

Conclusion

The significant correlations of proteins in the phagosome- and LTM pathways with activated cytotoxic T-cells (CD69+) and the level of airway obstruction (FEV₁/FVC) in smokers, both hallmarks of COPD, suggests that these two pathways may play a role in the molecular events preceding the development of COPD in susceptible smokers. Both pathways were found to be further dysregulated in COPD patients from the same cohort, thereby providing further support to this hypothesis. Given that not all smokers develop COPD in spite of decades of smoking, it is also plausible that some of the molecular pathways associated with response to smoking exert protective mechanisms to smoking-related pathologies in resilient individuals.

Trial registration

ClinicalTrials.gov identifier NCT02627872; Retrospectively registered on December 9, 2015.

Electronic supplementary material

The online version of this article (10.1186/s12931-017-0695-6) contains supplementary material, which is available to authorized users.

Monocyte Trafficking, Engraftment, and Delivery of Nanoparticles and an Exogenous Gene into the Acutely Inflamed Brain Tissue - Evaluations on Monocyte-Based Delivery System for the Central Nervous System

The ability of monocytes and monocyte-derived macrophages (MDM) to travel towards chemotactic gradient, traverse tissue barriers, and accumulate precisely at diseased sites makes them attractive candidates as drug carriers and therapeutic gene delivery vehicles targeting the brain, where treatments are often hampered by the blockade of the blood brain barrier (BBB). This study was designed to fully establish an optimized cell-based delivery system using monocytes and MDM, by evaluating their homing efficiency, engraftment potential, as well as carriage and delivery ability to transport nano-scaled particles and exogenous genes into the brain, following the non-invasive intravenous (IV) cell adoptive transfer in an acute neuroinflammation mouse model induced by intracranial injection of Escherichia coli lipopolysaccharides. We demonstrated that freshly isolated monocytes had superior inflamed-brain homing ability over MDM cultured in the presence of macrophage colony stimulating factor. In addition, brain trafficking of IV infused monocytes was positively correlated with the number of adoptive transferred cells, and could be further enhanced by transient disruption of the BBB with IV administration of Mannitol, Bradykinin or Serotonin right before cell infusion. A small portion of transmigrated cells was detected to differentiate into IBA-1 positive cells with microglia morphology in the brain. Finally, with the use of superparamagnetic iron oxide nanoparticles SHP30, the ability of nanoscale agent-carriage monocytes to enter the inflamed brain region was validated. In addition, lentiviral vector DHIV-101 was used to introduce green fluorescent protein (GFP) gene into monocytes, and the exogenous GFP gene was detected in the brain at 48 hours following IV infusion of the transduced monocytes. All together, our study has set up the optimized conditions for the more-in-depth tests and development of monocyte-mediated delivery, and our data supported the notion to use monocytes as a non-invasive cell-based delivery system for the brain.

High-Affinity Fc Receptor Expression Indicates Relative Immaturity in Human Monocytes

Within monocyte heterogeneity, subsets represent discrete, well-characterized phenotypes. Although many studies have highlighted differences between subsets, there is evidence that subpopulations represent contiguous stages in a maturational series. As CD14(hi)CD64(hi) monocytes have higher proliferative potential than CD14(hi)CD64(lo) monocytes, the surface marker profile on 4 subsets defined by CD14 and CD64 was measured. The profiles were compared to that of subsets defined by the high-affinity IgE receptor (FcɛRIα), CD16, and CD14; further differences in size, granularity, and buoyancy were measured in subsets delineated by these markers. There was a positive correlation between proliferative monocyte (PM) prevalence and CD64 expression on the classical monocyte subset, and also between PM prevalence and circulating FcɛRIα(+) monocytes. The expression of CD64, the high-affinity IgG receptor, on canonical human monocyte subsets was determined before and after short-term culture, and in response to interleukin (IL)-6, IL-10, macrophage colony-stimulating factor, granulocyte/macrophage colony-stimulating factor and interferon-γ; the influence of these cytokines on monocyte subset transition was also measured. The loss of FcɛRIα expression preceded an increase in CD16 expression in whole blood cultures. These data indicate that high-affinity Fc receptors are expressed on less mature monocytes and that FcɛRIα(+) monocytes are developmentally antecedent to the canonical classical and intermediate monocyte subsets.

The role of macrophages in the innate immune response to Streptococcus pneumoniae and Staphylococcus aureus: mechanisms and contrasts

Macrophages are critical mediators of innate immune responses against bacteria. The Gram-positive bacteria Streptococcus pneumoniae and Staphylococcus aureus express a range of virulence factors, which challenge macrophages' immune competence. We review how macrophages respond to this challenge. Macrophages employ a range of strategies to phagocytose and kill each pathogen. When the macrophages capacity to clear bacteria is overwhelmed macrophages play important roles in orchestrating the inflammatory response through pattern recognition receptor-mediated responses. Macrophages also ensure the inflammatory response is tightly constrained, to avoid tissue damage, and play an important role in downregulating the inflammatory response once initial bacterial replication is controlled.

Normalization and improvement of CNS deficits in mice with Hurler syndrome after long-term peripheral delivery of BBB-targeted iduronidase

Mucopolysaccharidosis type I (MPS I) is a progressive lysosomal storage disorder with systemic and central nervous system (CNS) involvement due to deficiency of α-L-iduronidase (IDUA). We previously identified a receptor-binding peptide from apolipoprotein E (e) that facilitated a widespread delivery of IDUAe fusion protein into CNS. In this study, we evaluated the long-term CNS biodistribution, dose-correlation, and therapeutic benefits of IDUAe after systemic, sustained delivery via hematopoietic stem cell (HSC)-mediated gene therapy with expression restricted to erythroid/megakaryocyte lineages. Compared to the highest dosage group treated by nontargeted control IDUAc (165 U/ml), physiological levels of IDUAe in the circulation (12 U/ml) led to better CNS benefits in MPS I mice as demonstrated in glycosaminoglycan accumulation, histopathology analysis, and neurological behavior. Long-term brain metabolic correction and normalization of exploratory behavior deficits in MPS I mice were observed by peripheral enzyme therapy with physiological levels of IDUAe derived from clinically attainable levels of HSC transduction efficiency (0.1). Importantly, these levels of IDUAe proved to be more beneficial on correction of cerebrum pathology and behavioral deficits in MPS I mice than wild-type HSCs fully engrafted in MPS I chimeras. These results provide compelling evidence for CNS efficacy of IDUAe and its prospective translation to clinical application.

Properties of human blood monocytes. II. Monocytes from healthy adults are highly heterogeneous within and among individuals

BACKGROUND

Human blood monocytes are known to include subsets defined by the expression of CD14 and CD16 but otherwise are often assumed to be relatively homogeneous. However, we had observed additional heterogeneity that led us to a more extensive examination of monocytes.

METHODS

Blood samples from 200 healthy adults without known immunological abnormalities were examined by analysis with a hematology analyzer and by flow cytometry (FCM) to determine leukocyte differential counts, to identify subsets and to measure expression of monocyte-associated molecules.

RESULTS

The estimated cell counts of monocytes, neutrophils, total lymphocytes, and T cells all varied to a similar extent, that is, ±30-35%. The fractions of monocyte subsets defined by CD14 and CD16 or by CD163 expression also varied among individuals. FCM examinations showed that all the monocyte-associated molecules that were examined varied in expression in this increasing order-CD244, CD4, CD38, CD91, CD11b, toll-like receptor 2 (TLR2), TIA-1, CD14 (on CD14(Br+) cells), CD86, CD80, HLA-DQ, CD33, and HLA-DR.

CONCLUSIONS

Human blood monocytes are heterogeneous among healthy adults with respect to cell counts, subsets, and the levels of expression of monocyte-associated molecules. An increase in the "non-classical" (CD14(Lo/Neg) /CD16(+) ) monocyte subset or in the expression of CD11b or TLR2 have known diagnostic/prognostic implications. CD244 and CD4 have well-defined functions on lymphocytes but perform unknown activities on monocytes although their expression appears more narrowly controlled. Together, these data suggest that monocytes should be more extensively examined in both clinical and basic contexts.

Alveolar macrophages develop from fetal monocytes that differentiate into long-lived cells in the first week of life via GM-CSF

Alveolar macrophages differentiate from fetal monocytes in a GM-CSF–dependent fashion and colonize the alveolar space within a few days after birth.

Tissue-resident macrophages can develop from circulating adult monocytes or from primitive yolk sac–derived macrophages. The precise ontogeny of alveolar macrophages (AMFs) is unknown. By performing BrdU labeling and parabiosis experiments in adult mice, we found that circulating monocytes contributed minimally to the steady-state AMF pool. Mature AMFs were undetectable before birth and only fully colonized the alveolar space by 3 d after birth. Before birth, F4/80^hiCD11b^lo primitive macrophages and Ly6C^hiCD11b^hi fetal monocytes sequentially colonized the developing lung around E12.5 and E16.5, respectively. The first signs of AMF differentiation appeared around the saccular stage of lung development (E18.5). Adoptive transfer identified fetal monocytes, and not primitive macrophages, as the main precursors of AMFs. Fetal monocytes transferred to the lung of neonatal mice acquired an AMF phenotype via defined developmental stages over the course of one week, and persisted for at least three months. Early AMF commitment from fetal monocytes was absent in GM-CSF–deficient mice, whereas short-term perinatal intrapulmonary GM-CSF therapy rescued AMF development for weeks, although the resulting AMFs displayed an immature phenotype. This demonstrates that tissue-resident macrophages can also develop from fetal monocytes that adopt a stable phenotype shortly after birth in response to instructive cytokines, and then self-maintain throughout life.

On the origin of cancer metastasis

Metastasis involves the spread of cancer cells from the primary tumor to surrounding tissues and to distant organs and is the primary cause of cancer morbidity and mortality. In order to complete the metastatic cascade, cancer cells must detach from the primary tumor, intravasate into the circulatory and lymphatic systems, evade immune attack, extravasate at distant capillary beds, and invade and proliferate in distant organs. Currently, several hypotheses have been advanced to explain the origin of cancer metastasis. These involve an epithelial mesenchymal transition, an accumulation of mutations in stem cells, a macrophage facilitation process, and a macrophage origin involving either transformation or fusion hybridization with neoplastic cells. Many of the properties of metastatic cancer cells are also seen in normal macrophages. A macrophage origin of metastasis can also explain the long-standing "seed and soil" hypothesis and the absence of metastasis in plant cancers. The view of metastasis as a macrophage metabolic disease can provide novel insight for therapeutic management.

Production of monocytic cells from bone marrow stem cells: therapeutic usage in Alzheimer's disease

Accumulation of amyloid β (Aβ) is a major hallmark in Alzheimer’s disease (AD). Bone marrow derived monocytic cells (BMM) have been shown to reduce Aβ burden in mouse models of AD, alleviating the AD pathology. BMM have been shown to be more efficient phagocytes in AD than the endogenous brain microglia. Because BMM have a natural tendency to infiltrate into the injured area, they could be regarded as optimal candidates for cell-based therapy in AD. In this study, we describe a method to obtain monocytic cells from BM-derived haematopoietic stem cells (HSC). Mouse or human HSC were isolated and differentiated in the presence of macrophage colony stimulating factor (MCSF). The cells were characterized by assessing the expression profile of monocyte markers and cytokine response to inflammatory stimulus. The phagocytic capacity was determined with Aβ uptake assay in vitro and Aβ degradation assay of natively formed Aβ deposits ex vivo and in a transgenic APdE9 mouse model of AD in vivo. HSC were lentivirally transduced with enhanced green fluorescent protein (eGFP) to determine the effect of gene modification on the potential of HSC-derived cells for therapeutic purposes. HSC-derived monocytic cells (HSCM) displayed inflammatory responses comparable to microglia and peripheral monocytes. We also show that HSCM contributed to Aβ reduction and could be genetically modified without compromising their function. These monocytic cells could be obtained from human BM or mobilized peripheral blood HSC, indicating a potential therapeutic relevance for AD.

Delivery of nanoparticles to brain metastases of breast cancer using a cellular Trojan horse

As systemic cancer therapies improve and are able to control metastatic disease outside the central nervous system, the brain is increasingly the first site of relapse. The blood-brain barrier (BBB) represents a major challenge to the delivery of therapeutics to the brain. Macrophages originating from circulating monocytes are able to infiltrate brain metastases while the BBB is intact. Here, we show that this ability can be exploited to deliver both diagnostic and therapeutic nanoparticles specifically to experimental brain metastases of breast cancer.

In situ proliferation and differentiation of macrophages in dental pulp

The presence of macrophages in dental pulp is well known. However, whether these macrophages proliferate and differentiate in the dental pulp in situ, or whether they constantly migrate from the blood stream into the dental pulp remains unknown. We have examined and compared the development of dental pulp macrophages in an organ culture system with in vivo tooth organs to clarify the developmental mechanism of these macrophages. The first mandibular molar tooth organs from ICR mice aged between 16 days of gestation (E16) to 5 days postnatally were used for in vivo experiments. Those from E16 were cultured for up to 14 days with or without 10% fetal bovine serum. Dental pulp tissues were analyzed with immunohistochemistry to detect the macrophages and with reverse transcription and the polymerase chain reaction (RT-PCR) for the detection of factors related to macrophage development. The growth curves for the in vivo and in vitro cultured cells revealed similar numbers of F4/80-positive macrophages in the dental pulp. RT-PCR analysis indicated the constant expression of myeloid colony-stimulating factor (M-CSF) in both in-vivo- and in-vitro-cultured dental pulp tissues. Anti-M-CSF antibodies significantly inhibited the increase in the number of macrophages in the dental pulp. These results suggest that (1) most of the dental pulp macrophages proliferate and differentiate in the dental pulp without a supply of precursor cells from the blood stream, (2) M-CSF might be a candidate molecule for dental pulp macrophage development, and (3) serum factors might not directly affect the development of macrophages.

How to get from here to there: macrophage recruitment in Alzheimer's disease

Alzheimer's disease (AD) is pathologically defined by presence of intracellular neurofibrillary tangles and extracellular amyloid plaques comprised of amyoid-β (Aβ) peptides. Despite local recruitment of brain microglia to sites of amyloid deposition, these mononuclear phagocytes ultimately fail at restricting β-amyloid plaque formation. On the other hand, it is becoming increasingly clear that professional phagocytes from the periphery possess Aβ clearance aptitude. Yet, in order to harness this beneficial innate immune response, effective strategies must be developed to coax monocytes/macrophages from the periphery into the brain. It has previously been suggested that Aβ 'immunotherapy' clears cerebral Aβ deposits via mononuclear phagocytes, and recent evidence suggests that targeting transforming growth factor-β-Smad 2/3 signaling and chemokine pathways such as Ccr2 impacts blood-to-brain trafficking of these cells in transgenic mouse models of AD. It has also been shown that the fractalkine receptor (Cx3cr1) pathway plays a critical role in chemotaxis of mononuclear phagocytes toward neurons destined for death in AD model mice. In order to translate these basic science findings into AD treatments, a key challenge will be to develop a new generation of pharmacotherapeutics that safely and effectively promote recruitment of peripheral amyloid phagocytes into the AD brain.

An all-feline retroviral packaging system for transduction of human cells

Abstract The subgroup C feline leukemia virus (FeLV-C) receptor FLVCR is a widely expressed 12-transmembrane domain transporter that exports cytoplasmic heme and is a promising target for retrovirus-mediated gene delivery. Previous studies demonstrated that FeLV-C pseudotype vectors were more efficient at targeting human hematopoietic stem cells than those pseudotyped with gibbon ape leukemia virus (GALV), and thus we developed an all FeLV-C-based packaging system, termed CatPac. CatPac is helper-virus free and can produce higher titer vectors than existing gammaretroviral packaging systems, including systems mixing Moloney murine leukemia virus (MoMLV) Gag-Pol and FeLV-C Env proteins. The vectors can be readily concentrated (>30-fold), refrozen (three to five times), and held on ice (>2 days) with little loss of titer. Furthermore, we demonstrate that CatPac pseudotype vectors efficiently target early CD34(+)CD38(-) stem/progenitor cells, monocytic and erythroid progenitors, activated T cells, mature macrophages, and cancer cell lines, suggesting utility for human cell and cell line transduction and possibly gene therapy.

Successful allogeneic bone marrow transplant for Niemann-Pick disease type C2 is likely to be associated with a severe 'graft versus substrate' effect

Niemann-Pick disease type C2 (NPC2) is caused by the inherited deficiency of a lysosomal cholesterol transport protein, NPC2 protein. Many cases of NPC2 present in early infancy with inflammatory lung disease, with subsequent severe neurological disease and death in early childhood. This disease is theoretically correctable by bone marrow transplantation (BMT), as the NPC2 protein is small and soluble and secreted and recaptured by the mannose-6-phosphate pathway. In this report we describe the first successful allogeneic bone marrow transplantation for this condition in a 16-month-old boy homozygous for the NPC2 p.E20X mutation, which has hitherto been reported to cause disease with a severe phenotype. During BMT there was an initial improvement of the established respiratory illness, with the immune suppression associated with transplant conditioning, but there was subsequent marked deterioration at the time of immune reconstitution and donor cell engraftment. This 'graft versus substrate' reaction was managed with intensive immune suppressant therapy, and it gradually resolved as the substrate was cleared by the engrafted donor macrophages. All immune suppression was withdrawn 18 months after transplantation, and his respiratory illness has resolved. He walked independently at 24 months and is continuing to reach development milestones after receiving his transplant. We conclude that the successful treatment of Niemann-Pick C2 therefore seems likely to be associated with a severe post-transplantation 'graft versus substrate' reaction that requires intense immune suppression before eventual resolution.

Macrophages in Alzheimer's disease: the blood-borne identity

Alzheimer’s disease (AD) is a progressive and incurable neurodegenerative disorder clinically characterized by cognitive decline involving loss of memory, reasoning and linguistic ability. The amyloid cascade hypothesis holds that mismetabolism and aggregation of neurotoxic amyloid-β (Aβ) peptides, which are deposited as amyloid plaques, are the central etiological events in AD. Recent evidence from AD mouse models suggests that blood-borne mononuclear phagocytes are capable of infiltrating the brain and restricting β-amyloid plaques, thereby limiting disease progression. These observations raise at least three key questions: (1) what is the cell of origin for macrophages in the AD brain, (2) do blood-borne macrophages impact the pathophysiology of AD and (3) could these enigmatic cells be therapeutically targeted to curb cerebral amyloidosis and thereby slow disease progression? This review begins with a historical perspective of peripheral mononuclear phagocytes in AD, and moves on to critically consider the controversy surrounding their identity as distinct from brain-resident microglia and their potential impact on AD pathology.

Reprogramming erythroid cells for lysosomal enzyme production leads to visceral and CNS cross-correction in mice with Hurler syndrome

Restricting transgene expression to maturing erythroid cells can reduce the risk for activating oncogenes in hematopoietic stem cells (HSCs) and their progeny, yet take advantage of their robust protein synthesis machinery for high-level protein production. This study sought to evaluate the feasibility and efficacy of reprogramming erythroid cells for production of a lysosomal enzyme, alpha-L-iduronidase (IDUA). An erythroid-specific hybrid promoter provided inducible IDUA expression and release during in vitro erythroid differentiation in murine erythroleukemia cells, resulting in phenotypical cross-correction in an enzyme-deficient lymphoblastoid cell line derived from patients with mucopolysaccharidosis type I (MPS I). Stable and higher than normal plasma IDUA levels were achieved in vivo in primary and secondary MPS I chimeras for at least 9 months after transplantation of HSCs transduced with the erythroid-specific IDUA-containing lentiviral vector (LV). Moreover, long-term metabolic correction was demonstrated by normalized urinary glycosaminoglycan accumulation in all treated MPS I mice. Complete normalization of tissue pathology was observed in heart, liver, and spleen. Notably, neurological function and brain pathology were significantly improved in MPS I mice by erythroid-derived, higher than normal peripheral IDUA protein. These data demonstrate that late-stage erythroid cells, transduced with a tissue-specific LV, can deliver a lysosomal enzyme continuously at supraphysiological levels to the bloodstream and can correct the disease phenotype in both viscera and CNS of MPS I mice. This approach provides a paradigm for the utilization of RBC precursors as a depot for efficient and potentially safer systemic delivery of nonsecreted proteins by ex vivo HSC gene transfer.

ATP-binding cassette transporter hallmarks tissue macrophages and modulates cytokine-triggered polarization programs

Macrophages are central players in both lipid metabolism and innate immunity. Their determinant role in the pathogenesis of atherosclerosis is under the control of the ATP-binding cassette transporter (ABCA1), which by minimizing cellular lipid content, limits development of pro-inflammatory foam cells. Considering the differential contribution of monocyte subsets to the generation of vascular lesions we analyzed the immunophenotype of ABCA1-expressing cells in the myeloid lineage, by the combined use of flow cytometry and real-time quantitative RT-PCR. ABCA1 expression is limited to "non-inflammatory" Ly6C(lo) circulating monocytes and tissue-resident macrophages expressing markers of alternative activation. In ABCA1(-/-) peritoneal macrophages the transcriptional programs induced by LPS/IFN-gamma or IL-4 cytokines are altered and deviated phosphorylation patterns of STAT transcriptional regulators in response to stimuli are observed.

In utero transplantation of monocytic cells in cats with alpha-mannosidosis

BACKGROUND

Lysosomal storage diseases are devastating illnesses, in large part because of their neurologic consequences. Because significant morbidity occurs prenatally, in utero (IU) therapy is an attractive therapeutic approach.

METHODS

We studied the feasibility and efficacy of IU injections of monocytic cells (derived from normal marrow) in feline alpha-mannosidosis. Heterozygous cats were interbred to produce affected (homozygous) and control (heterozygous and wild-type) offspring. Thirty-seven pregnancies were studied in which fetuses were transplanted intraperitoneally (1x10 cells/kg recipient) at gestational days 27 to 33 and then each week for 2 weeks (term=63 days). After birth, affected kittens were evaluated clinically and pathologically, tissue alpha-mannosidase levels were assayed, and in many studies, the numbers of alpha-mannosidase-containing cells were enumerated. When male donor cells were transplanted into female recipients, engraftment was also quantified using polymerase chain reaction to amplify a Y chromosome-specific sequence.

RESULTS

We establish methods to transplant cats intraperitoneally while IU using ultrasound guidance, thus, describing a new large animal model for prenatal therapy. We show that the donor monocytic cells engraft and persist (for up to 125 days) in the brain, liver, and spleen, albeit at levels below those needed to alter the clinical or pathological progression of the alpha-mannosidosis.

CONCLUSIONS

This is the first study of monocyte transplantation in a large animal model of a lysosomal storage disorder and demonstrates its feasibility, safety, and promise. Delivering cells IU may be a useful strategy to prevent morbidities before a definitive therapy, such as hematopoietic stem-cell transplantation, can be administered after birth.

Blood monocytes: development, heterogeneity, and relationship with dendritic cells

Monocytes are circulating blood leukocytes that play important roles in the inflammatory response, which is essential for the innate response to pathogens. But inflammation and monocytes are also involved in the pathogenesis of inflammatory diseases, including atherosclerosis. In adult mice, monocytes originate in the bone marrow in a Csf-1R (MCSF-R, CD115)-dependent manner from a hematopoietic precursor common for monocytes and several subsets of macrophages and dendritic cells (DCs). Monocyte heterogeneity has long been recognized, but in recent years investigators have identified three functional subsets of human monocytes and two subsets of mouse monocytes that exert specific roles in homeostasis and inflammation in vivo, reminiscent of those of the previously described classically and alternatively activated macrophages. Functional characterization of monocytes is in progress in humans and rodents and will provide a better understanding of the pathophysiology of inflammation.

CX3CR1+ CD115+ CD135+ common macrophage/DC precursors and the role of CX3CR1 in their response to inflammation

CX₃CR1 expression is associated with the commitment of CSF-1R⁺ myeloid precursors to the macrophage/dendritic cell (DC) lineage. However, the relationship of the CSF-1R⁺ CX₃CR1⁺ macrophage/DC precursor (MDP) with other DC precursors and the role of CX₃CR1 in macrophage and DC development remain unclear. We show that MDPs give rise to conventional DCs (cDCs), plasmacytoid DCs (PDCs), and monocytes, including Gr1⁺ inflammatory monocytes that differentiate into TipDCs during infection. CX₃CR1 deficiency selectively impairs the recruitment of blood Gr1⁺ monocytes in the spleen after transfer and during acute Listeria monocytogenes infection but does not affect the development of monocytes, cDCs, and PDCs.

Differentiation and heterogeneity in the mononuclear phagocyte system

Cells of the mononuclear phagocyte system (MPS) are found in large numbers in every organ of the body, where they contribute to innate and acquired immunity and homeostasis. This review considers the locations of MPS cells, surface markers that distinguish subsets of monocytes and macrophages, the pathways of MPS differentiation, and the growth factors and transcription factors that guide them. Although the number of MPS sub-populations that can be defined is infinite, the features that unite the MPS remain compelling. Those features clearly include antigen-presenting dendritic cells within the MPS and argue against any basis for separating them from macrophages.

Cerebral and peripheral amyloid phagocytes--an old liaison with a new twist

In this month's issue of Nature Medicine, Town et al. suggest that peripheral macrophages invading the brain reduce cerebral amyloidosis and thus may play a key role in the pathogenesis of Alzheimer's disease (AD). This observation intensifies the longstanding controversy of whether mononuclear cells such as macrophages and/or microglial cells are beneficial or detrimental in AD.

Detecting prostate cancer by intracellular macrophage prostate-specific antigen (PSA): a more specific and sensitive marker than conventional serum total PSA

BACKGROUND

Serum prostate-specific antigen (PSA) is a standard method and a widely used marker for prostate cancer, but it has a poor specificity for early detection. Herein we demonstrate that intracellular macrophage PSA (imPSA) enables screening and differentiation between benign and malignant prostate disease.

MATERIALS AND METHODS

The efficacy of intracellular macrophage PSA in circulating and tissue macrophages was therefore investigated in a double-centre study of 38 prostate cancer patients and 36 healthy controls by fluorescent-activated cell sorting analysis and immunohistology.

RESULTS

Both methods uncovered the existence of PSA-positive macrophages specific for patients with prostate cancer. In addition, we demonstrate the superiority of our new test over standard serum total PSA in a blinded double-centre trial. ImPSA had a marked higher sensitivity and specificity than serum total PSA (imPSA: sensitivity 92%, specificity 92%, positive predictive value 92%; serum total PSA: sensitivity 79.5%, specificity 87.5%, positive predictive value 26.8%).

CONCLUSION

In this study, we demonstrate that imPSA is a new prostate cancer screening method that is highly sensitive and more specific than standard PSA testing.

From bone marrow to microglia: barriers and avenues

Microglia form a unique population of brain-resident macrophages. Although microglia have been involved in multiple disorders of the central nervous system (CNS), the issue of microglial renewal, under normal or pathological conditions, has been controversial. In mice, results from bone marrow chimera studies indicated that microglia are slowly but continuously replenished by bone marrow-derived cells. Moreover, such a microglial turnover was found to be greatly accelerated under multiple neurological conditions. However, recent works questioned the use of irradiation/reconstitution experiments to assess microglial turnover. Based on these different studies, we propose here a re-evaluation of microglia origin(s) in the inflamed CNS. We also discuss the therapeutic perspectives offered by the demonstration of an adult microglial lineage, from bone marrow to brain.

Differentiation of C2D macrophage cells after adoptive transfer

C2D macrophage cells protect immunocompromised mice from experimentally induced pneumonias after intraperitoneal (i.p.) adoptive transfer. These macrophage cells are immature and display minimal activity in vitro. Therefore, we wanted to understand how adoptive transfer affected these cells. We believe that the in vivo environment affects the phenotypic and functional characteristics of macrophages that help maintain the physiological integrity of the host. To test this hypothesis, we characterized the trafficking patterns and cellular changes of the established macrophage C2D cell line after adoptive transfer. We examined phenotypic changes of the C2D macrophage cells in vivo with and without stimulation with gamma interferon (IFN-gamma). After in vivo i.p. adoptive transfer, C2D macrophage cells trafficked to the lungs, spleen, lymph nodes, and bone marrow of recipient mice. The cells were detected for as long as 2 months, and the cells expressed increased levels of CD11b, c-fms, and F4/80 on their surface, becoming more differentiated macrophages compared to cells maintained in vitro. Upon in vivo stimulation with IFN-gamma, c-fms levels decreased while Gr-1 levels increased compared to in vivo, unstimulated, phosphate-buffered saline-injected controls. These responses were independent of the genetic backgrounds of the recipient mice. These data support the hypothesis and indicate that C2D macrophage cells respond to in vivo signals that are absent during in vitro culture.

Hematopoietic progenitor cells (HPC) from mobilized peripheral blood display enhanced migration and marrow homing compared to steady-state bone marrow HPC

OBJECTIVE

Faster engraftment of G-CSF-mobilized peripheral blood (MPB) transplants compared to steady-state bone marrow (ssBM) is well documented and clinically relevant. A number of different factors likely contribute to this outcome. In the present study we explored whether independent of cell number there are intrinsic differences in the efficiency of progenitor cell homing to marrow between MPB and ssBM.

METHODS

Mobilization was achieved by continuous infusion of G-CSF alone or in combination with other mobilizing agents. In vivo homing assays, in vitro migration assays, gene expression analysis, and flow cytometry were utilized to compare homing-related in vivo and in vitro properties of MPB and ssBM HPC.

RESULTS

Marrow homing of murine MPB HPC, generated by different mobilizing schemes, was reproducibly significantly superior to that of ssBM, in lethally irradiated as well as in nonirradiated hosts. This phenotype was independent of MMP9, selectins, and beta2- and alpha4-integrins. Superior homing was also observed for human MPB HPC transplanted into NOD/SCIDbeta2microglobulin(-/-) recipients. Inhibition of HPC migration abrogated the homing advantage of MPB but did not affect homing of ssBM HPC, whereas enhancement of motility by CD26 inhibition improved marrow homing only of ssBM HPC. Enhanced SDF-1-dependent chemotaxis and low CD26 expression on MPB HPC were identified as potential contributing factors. Significant contributions of the putative alternative SDF-1 receptor, RDC1, were unlikely based on gene expression data.

CONCLUSION

The data suggest increased motility as a converging endpoint of complex changes seen in MPB HPC which is likely responsible for their favorable homing.

Characterization of monocyte-macrophage-lineage cells induced from CD34+ bone marrow cells in vitro

We characterized the expression of cell surface antigens and cytokine-secreting ability of monocyte-macrophage-lineage cells induced in vitro from CD34+ bone marrow cells. After cultivation for 3 weeks, we observed 2 distinct cell fractions: a floating small, round cell fraction and an adherent large, protruding cell fraction. Both cell fractions expressed myelocyte-monocyte-lineage antigens, but mature-macrophage markers such as CD206 were expressed only by the adherent cells. An assessment of cells cultured for 5 weeks revealed spontaneous secretion of interleukin 8 (IL-8) and IL-6, and lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF-alpha) secretion in both fractions, but only the adherent cell fraction secreted IL-10 after LPS stimulation. In contrast, both fractions of cells cultured for 3 weeks spontaneously secreted low levels of IL-8, but none of the other cytokines. Upon LPS stimulation, the cells secreted IL-6 and TNF-alpha, but not IL-10. We also assessed the effect of granulocyte colony-stimulating factor (G-CSF) pretreatment on TNF-alpha secretion by each cell fraction and found that G-CSF reduced TNF-alpha secretion only in the adherent fraction of cells cultured for 3 weeks. Monocyte-macrophage-lineage cells induced in vitro should provide an ideal model for functional analysis of monocyte-macrophage cells.

Kupffer cell heterogeneity: functional properties of bone marrow derived and sessile hepatic macrophages

Kupffer cells form a large intravascular macrophage bed in the liver sinusoids. The differentiation history and diversity of Kupffer cells is disputed; some studies argue that they are derived from blood monocytes, whereas others support a local origin from intrahepatic precursor cells. In the present study, we used both flow cytometry and immunohistochemistry to distinguish 2 subsets of Kupffer cells that were revealed in the context both of bone marrow transplantation and of orthotopic liver transplantation. One subset was radiosensitive and rapidly replaced from hematogenous precursors, whereas the other was relatively radioresistant and long-lived. Both were phagocytic but only the former population was recruited into inflammatory foci in response to CD8(+) T-cell activation. We propose the name "sessile" for the radioresistant Kupffer cells that do not participate in immunoinflammatory reactions. However, we found no evidence that these sessile Kupffer cells arise from immature intrahepatic precursors. Our conclusions resolve a long-standing controversy and explain how different experimental approaches may reveal one or both of these subsets.

Primary rat monocytes migrate through a BCEC-monolayer and express microglia-markers at the basolateral side

Monocytes are pluripotent cells of the immune system, circulate in the blood and cross the blood-brain barrier continuously through life. The aim of this study was to explore if primary rat monocytes can adhere and transmigrate at a monolayer of brain capillary endothelial cells (BCEC) and if the monocytes undergo differentiation toward a microglial phenotype at the basolateral side. Monocytes and as a control primary microglia were immunohistochemically stained with markers for CD68 (clone ED-1), CD11b (clone OX-42) or CD11c (clone 8A2). The primary rat monocytes (100,000 cells added) adhered at the BCEC-monolayer (approx. 1200 cells/well) within 30 min and migrated to the basolateral side within 18 h (approx. 40,000 cells/well). The transmigrated monocytes partly differentiated and expressed microglia-markers at the basolateral side. Tumor necrosis factor-alpha as well as conditioned medium derived from BCEC stimulated the differentiation of monocytes in culture. In conclusion, monocytes adhere and migrate through a BCEC-monolayer and express microglia-markers at the basolateral side.

Newly recruited human monocytes have a preserved responsiveness towards bacterial peptides in terms of CD11b up-regulation and intracellular hydrogen peroxide production

The transmigration of peripheral human monocytes to the interstitium is a fundamental step in the host-defence mechanism against infections. Little is known about the state of function of in vivo transmigrated interstitial monocytes prior to differentiation into macrophages and dendritic cells. We hypothesized that newly recruited interstitial monocytes have a preserved responsiveness against bacterial-related peptides, giving them a specific role in the immediate defence against invading pathogens. In order to test this hypothesis, we explored the responsiveness of in vivo transmigrated as well as peripheral monocytes, in terms of CD11b expression and H(2)O(2) production towards the bacterial-related peptide formylmethionylleucylphenylalanine (fMLP) by the use of a skin chamber technique. In addition, we analysed the concentration of interleukin (IL)-8, monocyte chemotactic protein-1 (MCP-1) and tumour necrosis factor (TNF)-alpha in the skin blister exudates and in the circulation. We demonstrate that in vivo-transmigrated monocytes had a fivefold higher CD11b expression compared to monocytes obtained from the peripheral circulation. fMLP exposure induced a significantly higher CD11b expression on transmigrated cells compared to peripheral monocytes. In addition, newly recruited monocytes had a preserved H(2)O(2) production. The interstitial concentration of IL-8, MCP-1 and TNF-alpha was significantly higher in blister exudates compared to that in the peripheral circulation. Thus, in vivo transmigrated human monocytes preserve their capacity to respond towards bacterial peptides in terms of CD11b up-regulation and H(2)O(2) generation. These data strengthen a role for newly recruited interstitial human monocytes in the immediate defence against invading pathogens.

Murine hematopoietic stem cells and progenitors express adrenergic receptors

Association between the nervous and immune system is well documented. Immune cells originate within the bone marrow that is innervated. Thermal injury induces adrenergic stimulation, augments monocytopoiesis and alters the beta-adrenergic receptor (AR) profile of bone marrow monocyte committed progenitors. This provides an impetus to study AR expression in hematopoietic progenitors along myeloid lineage. Using FACS analysis and confocal microscopy, we report the expression of alpha1-, alpha2- and beta(2)-AR in enriched populations of ER-MP209(+) and ER-MP12(+) myeloid progenitors, CD117(+) and CD34(+) multi-potential progenitors and more importantly pluripotent stem cells suggesting a plausible role for catecholamine in hematopoietic development.

Microglia activation in retinal degeneration

Microglia cells are phagocytic sentinels in the CNS and in the retina required for neuronal homeostasis and innate immune defense. Accumulating experimental evidence suggests that chronic microglia activation is associated with various neurodegenerative diseases including retinal dystrophies. Endogenous triggers alert microglia cells rapidly in the degenerating retina, leading to local proliferation, migration, enhanced phagocytosis, and secretion of cytokines, chemokines, and neurotoxins. This amplified, immunological cascade and the loss of limiting control mechanisms may contribute significantly to retinal tissue damage and proapoptotic events. This review summarizes the developmental and immune surveillance functions of microglia in the healthy retina and discusses early signaling events and transcriptional networks of microglia activation in retinal degeneration. The characterization of activation pathways at the molecular level may lead to innovative, therapeutic options in degenerative retinal diseases based on a selective, pharmacological interference with the neurotoxic activities of microglia cells, without compromising their homeostastic functions.

Bone marrow CD34+/B220+ progenitors target the inflamed brain and display in vitro differentiation potential toward microglia

Recent evidence indicates that microglial cells may not derive from blood circulating mature monocytes as they express features of myeloid progenitors. Here, we observed that a subpopulation of microglial cells expressed CD34 and B220 antigens during brain development. We thus hypothesized that microglia, or a subset of microglial cells, originate from blood circulating CD34+/B220+ myeloid progenitors, which could target the brain under developmental or neuroinflammatory conditions. Using experimental allergic encephalomyelitis (EAE) as a model of chronic neuroinflammation, we found that a discrete population of CD34+/B220+ cells expands in both blood and brain of diseased animals. In EAE mice, intravenous transfer experiments showed that macrophage-colony stimulating factor (M-CSF) -expanded CD34+ myeloid progenitors target the inflamed central nervous system (CNS) while keeping their immature phenotype. Based on these results, we then assessed whether CD34+/B220+ cells display in vitro differentiation potential toward microglia. For this purpose, CD34+/B220+ cells were sorted from M-CSF-stimulated bone marrow (BM) cultures and exposed to a glial cell conditioned medium. Under these experimental conditions, CD34+/B220+ cells were able to differentiate into microglial-like cells showing the morphological and phenotypic features of native microglia. Overall, our data suggest that under developmental or neuroinflammatory conditions, a subpopulation of microglial cells derive from CNS-invading CD34+/B220+ myeloid progenitors.

Quantitative magnetic resonance and SPECT imaging for macrophage tissue migration and nanoformulated drug delivery

We posit that the same mononuclear phagocytes (MP) [bone marrow (BM) and blood monocytes, tissue macrophages, microglia, and dendritic cells] which serve as targets, reservoirs, and vehicles for HIV dissemination, can be used as vehicles for antiretroviral therapy (ART). Toward this end, BM macrophages (BMM) were used as carriers for nanoparticle-formulated indinavir (NP-IDV), and the cell distribution was monitored by single photon emission computed tomography (SPECT), transverse relation time (T2)* weighted magnetic resonance imaging (MRI), histology, and gamma-scintillation spectrometry. BMM labeled with super paramagnetic iron oxide and/or 111indium oxine were infused i.v. into naïve mice. During the first 7 h, greater than 86% of cell label was recorded within the lungs. On Days 1, 3, 5, and 7, less than 10% of BMM were in lungs, and 74-81% and 13-18% were in liver and spleen, respectively. On a tissue volume basis, as determined by SPECT and MRI, BMM densities in spleen and liver were significantly greater than other tissues. Migration into the lymph nodes on Days 1 and 7 accounted for 1.5-2% of the total BMM. Adoptive transfer of BMM loaded with NP-IDV produced drug levels in lymphoid and nonlymphoid tissues that exceeded reported therapeutic concentrations by 200- to 350-fold on Day 1 and remained in excess of 100- to 300-fold on Day 14. These data show real-time kinetics and destinations of macrophage trafficking and demonstrate the feasibility of monitoring macrophage-based, nanoformulated ART.

The origin and in vivo significance of murine and human culture-expanded endothelial progenitor cells

In adults highly purified populations of early hematopoietic progenitors or cells derived from ex vivo expanded unmobilized human peripheral blood mononuclear cells contribute to new blood vessel formation. However, the source of these culture-expanded endothelial progenitor cells (CE-EPCs) remains controversial. We demonstrate that ex vivo expansion of unmobilized human peripheral blood generated CE-EPCs with similar numbers, kinetics, and antigen expression profile as compared to plating unfractionated CD34(+)/lin(-)-enriched bone marrow mononuclear cells. Both CE-EPC populations uniformly co-expressed myeloid and endothelial markers, suggesting that peripheral blood progenitor enumeration does not correlate with the numbers of early outgrowth CE-EPCs. Using purified myeloid subpopulations obtained from mice harboring the lacZ transgene driven by an endothelial-specific promoter, we showed that the immature myeloid lineage marker CD31(+) cells generated CE-EPCs with fourfold greater frequency than mature myeloid populations. Biphenotypic cells co-expressing myeloid/endothelial antigens were not detected in circulating human or murine peripheral blood or bone marrow but were associated with murine tumors. Unlike CE-EPCs, CD14(+) leukocytes admixed within tumors did not generate vWF-positive blood vessels during a similarly defined period of tumor growth, but some leukocytes up-regulated the endothelial marker VE-cadherin. Taken together, the data suggest that the local neovascular microenvironment may facilitate vasculogenesis by promoting endothelial differentiation and that CE-EPCs may accelerate such vasculo-genesis.

Functional heterogeneity of colony-stimulating factor-induced human monocyte-derived macrophages

OBJECTIVES

Macrophages (Mphis) have various functions and play a critical role in host defense and the maintenance of homeostasis. Mphis exist in every tissue in the body, but Mphis from different tissues exhibit a wide range of phenotypes with regard to their morphology, cell surface antigen expression and function, and are called by different names. However, the precise mechanism of the generation of macrophage heterogeneity is not known. In the present study, the authors examined the functional heterogeneity of Mphis generated from human monocytes under the influence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage-CSF (M-CSF).

METHODOLOGY

CD14 positive human monocytes (Mos) were incubated with M-CSF and GM-CSF for 6-7 days to stimulate the generation of M-CSF-induced monocyte-derived Mphis (M-Mphis) and GM-CSF-induced monocyte-derived Mphis (GM-Mphis), respectively. The expression of cell surface antigens and several functions such as antigen presenting cell activity, susceptibility to oxidant stress, and the susceptibility to HIV-1 and mycobacterium tuberculosis infection were examined.

RESULTS

GM-Mphis and M-Mphis are distinct in their morphology, cell surface antigen expression, and functions examined. The phenotype of GM-Mphis closely resembles that of human Alveolar-Mphis (A-Mphis), indicating that CSF-induced human monocyte-derived Mphis are useful to clarify the molecular mechanism of heterogeneity of human Mphis, and GM-Mphis will become a model of human A-Mphis.

Transplantation of NGF secreting primary monocytes counteracts NMDA-induced cell death of rat cholinergic neurons in vivo

Cholinergic neurons of the basal forebrain degenerate in Alzheimer's disease. Nerve growth factor (NGF) is so far the most potent molecule to counteract this neurodegeneration; however, the delivery of NGF into the brain is very difficult. The aim of the present study was to observe, if transplanted primary monocytes secreting NGF may counteract N-methyl-D-aspartate (NMDA)-induced cell death of cholinergic neurons of the basal nucleus of Meynert (nBM) in vivo. Monocytes were purified by indirect magnetic separation from rat blood. Recombinant NGF was introduced into cells using the novel protein-delivery reagent BioPORTERtrade mark and secretion of NGF was measured by ELISA. Monocytes secreted approximately 4000 pg NGF/day/1 x 10(6) cells. Injection of monocytes onto organotypic brain slices of the nBM in vitro protected cholinergic neurons against cell death. When monocytes were transplanted in vivo into the lateral ventricle, the cells survived for up to 7 days and counteracted the NMDA-induced cell death of cholinergic neurons. In conclusion, primary monocytes secreting recombinant NGF are useful to deliver NGF directly into the brain.

Differentiation to the CCR2+ inflammatory phenotype in vivo is a constitutive, time-limited property of blood monocytes and is independent of local inflammatory mediators

It is proposed that CCR2+ monocytes are specifically recruited to inflammatory sites, whereas CCR2- monocytes are recruited to normal tissue to become resident macrophages. Whether these subsets represent separate lineages, how differential trafficking is regulated and whether monocytes undergo further differentiation is uncertain. Using a mouse model of autoimmune uveoretinitis we examined monocyte trafficking to the inflamed retina in vivo. We show that bone marrow-derived CD11b+ F4/80- monocytes require 24 to 48 h within the circulation and lymphoid system before acquiring the CCR2+ phenotype and trafficking to the inflamed retina is enabled. This phenotype, and the capacity to traffic were lost by 72 h. Monocyte CCR2 expression followed a similar time course in normal mice indicating that differentiation to an inflammatory phenotype is a constitutive, time-limited property, independent of local inflammatory mediators. Phenotypic analysis of adoptively transferred cells indicated that circulating inflammatory monocytes also differentiate into CD11c+ and B220+ dendritic cells and F4/80+ tissue macrophages in vivo. Our data supports the hypothesis of continuous extravasation and progressive differentiation over time of inflammatory monocytes in the circulation rather than replication within the actively inflamed tissue, and supports the concept of myeloid dendritic cell differentiation from trafficking monocytes under physiological conditions in vivo.

Renal ischemia/reperfusion injury inhibits differentiation of dendritic cells derived from bone marrow monocytes in rats

Dendritic cells (DCs) are impacted by surgical injury, exercise, and other physiological stressors. This study aims to determine whether renal I/R injury affects 1) the differentiation of myeloid DCs from bone marrow monocytes (BMMos) and the maturation and activation state of these DCs and 2) DC infiltration of kidney. Sprague-Dawley rats were subjected to I/R injury or sham-operated. Creatinine clearance was monitored daily during the 14 d of reperfusion that followed the ischemic insult. At 2 and 14 d of reperfusion, the following were assessed 1) properties of BMMo-derived DCs (i.e., the amount of generated DCs, differentiation state markers [CD11c, CD80, CD86, and Ia], and functional state [MLR and amount of IL-12 produced]), and 2) the presence of DCs in the kidney. Numbers of BMMo-derived DCs were significantly decreased in the I/R injured group (compared with the sham-operated group) at 2 d but not 14 d. A comparison of the their functionality found mixed lymphocyte response [MLR] and IL-12 production were similar in the two groups at both time points. Also, immunohistochemistry showed infiltrating DCs in the outer medulla of the I/R injured kidney at 2 d but not 14 d of reperfusion. Thus, I/R stress reduces the number of DCs differentiated from BMMos but not the functional activity of these DCs. This decrease may reflect a stress-induced downshift in the capacity of BMMos to differentiate into DCs and a parallel upshift in the capacity of DCs to infiltrate the kidney.

Blood-derived macrophages infiltrate the retina and activate Muller glial cells under experimental choroidal neovascularization

Inflammation is a major mechanism in the pathogenesis of age-related macular degeneration, the most important cause of blindness in the elderly. Previous studies have focused on the role of macrophages in regulating the growth of pathological new vessels over the retina, called choroidal neovascularization (CNV). However, no research has been done to evaluate the role of inflammation as a mechanism of vision loss and retinal degeneration in the retina underlying CNV. In other neuropathological conditions, hematogenous macrophages and/or resident microglia contribute to neurodegeneration. We have combined laser-induced CNV in mice and bone marrow transplantation with GFP-labeled bone marrow to determine the relative role of recruited blood-derived macrophages versus resident microglia in the retina associated with CNV. Using these chimeric mice, we have found that many GFP-labeled cells infiltrated the retina underlying CNV but not the retina unaffected by CNV. Immunostaining for the cell adhesion molecules VCAM 1, ICAM 1, and PECAM was strongly upregulated in retinal blood vessels under CNV. All GFP-labeled cells were immunoreactive for the macrophage marker F4/80. Most (70%) of the F4/80 immunoreactive cells were GFP-labeled under CNV. The density of resident microglia did not increase. Most GFP-labeled cells were found in close proximity to activated Muller cells. Depleting circulating macrophages with clodronic acid diminished the density of F4/80 immunoreactive cells as well as the density of pERK immunoreactive Muller cells in the retina under CNV. Thus, recruitment of blood-derived macrophages more than resident microglia seems to be associated with CNV.

Listeria monocytogenes-infected bone marrow myeloid cells promote bacterial invasion of the central nervous system

Listeria monocytogenes is a facultative intracellular pathogen that is able to invade the central nervous system causing meningoencephalitis and brain abscesses. The mechanisms allowing bacteria to cross the blood-brain barrier are poorly understood. In this work, we used an experimental model of acute listeriosis in the mouse inducing a reproducible invasion of the central nervous system. At the early phase of infection, we find that bacteria invade and rapidly grow in bone marrow cells identified as bone marrow myelomonocytic cells expressing the phenotype CD31pos:Ly-6Cpos:CD11b(pos):LY-6Glow. We demonstrate that central nervous system invasion is facilitated by injecting L. monocytogenes-infected bone marrow cells in comparison with free bacteria or infected spleen cells. In mice transplanted with bone marrow cells from transgenic donor mice expressing the green fluorescent protein (GFP), we show that infected myeloid GFP+ cells adhere to activated brain endothelial cells, accumulate in brain vessels and participate to the pathogenesis of meningoencephalitis and brain abscesses. Our results demonstrate that bone marrow, the main haematopoietic tissue, is a previously unrecognized reservoir of L. monocytogenes-infected myeloid cells, which can play a crucial role in the pathophysiology of meningoencephalitis by releasing infected cells into the circulation that ultimately invade the central nervous system.

Macrophages in the murine pancreas and their involvement in fetal endocrine development in vitro

Macrophages are a heterogeneous population of cells that belong to the mononuclear phagocyte system. They play an important role in tissue homeostasis and remodeling and are also potent immune regulators. Pancreatic macrophages are critically involved in the development and pathogenesis of autoimmune diabetes. To elucidate the ontogeny of pancreatic macrophages, we characterized in this study the macrophages present in the adult and developing fetal pancreas of normal mice. We additionally examined the presence of local macrophage precursors and the involvement of macrophages in the growth of endocrine tissue in the fetal pancreas. We identified two phenotypically distinct macrophage subsets in the adult pancreas. The majority of macrophages was CD45(+)ER-MP23(+)MOMA-1(+). Under noninflammatory conditions, only a minority ( approximately 5%) of the pancreatic macrophages additionally expressed the macrophage marker F4/80. In contrast, in the fetal pancreas, phenotypically, mature macrophages were identified exclusively by their expression of F4/80 and lacked detectable staining with ER-MP23 and MOMA-1 antibodies. In fetal pancreas organ cultures, we could show that macrophages develop from pre-existing precursors, which are present in the fetal pancreas at embryonic age 12.5. Moreover, the number of macrophages increased significantly when macrophage-colony stimulating factor was added to these cultures. It is important that this increase of F4/80-positive cells was paralleled by an increase in the number of insulin-producing cells, suggesting that macrophages support the growth of these endocrine cells.

Prior injury accelerates subsequent wound closure in a mouse model of regeneration

Tissue regeneration and scarless healing involves the complete replacement and functional restoration of damaged organs and tissues. In this study of the "scarless healing" MRL mouse model, we demonstrate that 2-mm diameter through-and-through holes made in the cartilaginous part of previously injured MRL mouse ears are closed more efficiently, and that the regenerative repair response is significantly accelerated compared with unprimed MRL and control "nonhealer" strains of mice. Accelerated healing was detected both locally and distally from the original site of injury indicating the involvement of systemic components such as circulating cell types or soluble factors. Histologically, we observed early differences during the wound repair process (before Day 4 post injury) with accelerated formation of blastema-like structures, epidermal downgrowths, and enhanced epithelium thickening in wound border zones in primed MRL mice versus unprimed MRL mice. Although the mechanism of tissue regeneration remains unclear, the results from this study justify the use of the MRL model for further experimentation directed toward the identification of proteins and cell types capable of stimulating scarless tissue regeneration.

Macrophages at intermediate stage of maturation produce high levels of IL-12 p40 upon stimulation with Leishmania

IL-12 is one of the main cytokines driving the immune response to a resistant phenotype in leishmaniasis and in several other diseases involving intracellular microbes. In this study, we investigated IL-12 production by mononuclear phagocytes at several developmental stages when stimulated with Leishmania major, L. amazonensis or L. chagasi. Bone marrow cells were cultured for 4-6 days in vitro in the presence of M-CSF, GM-CSF or IL-3. After density separation, only cells banding at the 40-50% Percoll interface, but not those at 20-40% or 50-80% interfaces, produced large amounts of IL-12 p40 when stimulated with LPS or live Leishmania promastigotes. However, only low levels of IL-12 p70 were produced under these conditions. The high IL-12 p40-producing cells could be similarly derived from mouse strains with different susceptibility to Leishmania. Quantitative analysis of monocyte/macrophage lineage marker expression, in combination with positive and negative selection, led to the conclusion that the high IL-12 p40-producing cells are macrophages at an intermediate stage of maturation between immature and fully differentiated cells, expressing ER-HR3 but only low levels of the mature markers, scavenger receptor and CD11b/Mac-1. They do not express any of the precursor markers CD31/ER-MP12, Ly-6C/ER-MP20 or ER-MP58. Because recruitment of monocytes to an infection site and its draining lymph node is a general phenomenon, the notion that, developing from these monocytes, a population of mononuclear phagocytes at an intermediate maturation stage has the capacity to synthesize large amounts of IL-12 p40 has significant bearing on our understanding of immune regulation in leishmaniasis and also in infections by other pathogens.