Instruct: Given a scientific claim, retrieve documents that support or refute the claim.
Query: Adult tissue-resident macrophages are seeded before birth.
Mononuclear phagocytes, including monocytes, macrophages, and dendritic cells, contribute to tissue integrity as well as to innate and adaptive immune defense. Emerging evidence for labor division indicates that manipulation of these cells could bear therapeutic potential. However, specific ontogenies of individual populations and the overall functional organization of this cellular network are not well defined. Here we report a fate-mapping study of the murine monocyte and macrophage compartment taking advantage of constitutive and conditional CX(3)CR1 promoter-driven Cre recombinase expression. We have demonstrated that major tissue-resident macrophage populations, including liver Kupffer cells and lung alveolar, splenic, and peritoneal macrophages, are established prior to birth and maintain themselves subsequently during adulthood independent of replenishment by blood monocytes. Furthermore, we have established that short-lived Ly6C(+) monocytes constitute obligatory steady-state precursors of blood-resident Ly6C(-) cells and that the abundance of Ly6C(+) blood monocytes dynamically controls the circulation lifespan of their progeny.
Antigen-presenting, major histocompatibility complex (MHC) class II-rich dendritic cells are known to arise from bone marrow. However, marrow lacks mature dendritic cells, and substantial numbers of proliferating less-mature cells have yet to be identified. The methodology for inducing dendritic cell growth that was recently described for mouse blood now has been modified to MHC class II-negative precursors in marrow. A key step is to remove the majority of nonadherent, newly formed granulocytes by gentle washes during the first 2-4 d of culture. This leaves behind proliferating clusters that are loosely attached to a more firmly adherent "stroma. " At days 4-6 the clusters can be dislodged, isolated by 1-g sedimentation, and upon reculture, large numbers of dendritic cells are released. The latter are readily identified on the basis of their distinct cell shape, ultrastructure, and repertoire of antigens, as detected with a panel of monoclonal antibodies. The dendritic cells express high levels of MHC class II products and act as powerful accessory cells for initiating the mixed leukocyte reaction. Neither the clusters nor mature dendritic cells are generated if macrophage colony-stimulating factor rather than granulocyte/macrophage colony-stimulating factor (GM-CSF) is applied. Therefore, GM-CSF generates all three lineages of myeloid cells (granulocytes, macrophages, and dendritic cells). Since > 5 x 10(6) dendritic cells develop in 1 wk from precursors within the large hind limb bones of a single animal, marrow progenitors can act as a major source of dendritic cells. This feature should prove useful for future molecular and clinical studies of this otherwise trace cell type.
As the immune system develops, T cells are selected or regulated to become tolerant of self antigens and reactive against foreign antigens. In mice, the induction of such tolerance is thought to be attributable to the deletion of self-reactive cells. Here, we show that the human fetal immune system takes advantage of an additional mechanism: the generation of regulatory T cells (Tregs) that suppress fetal immune responses. We find that substantial numbers of maternal cells cross the placenta to reside in fetal lymph nodes, inducing the development of CD4+CD25highFoxP3+ Tregs that suppress fetal antimaternal immunity and persist at least until early adulthood. These findings reveal a form of antigen-specific tolerance in humans, induced in utero and probably active in regulating immune responses after birth.
Mesenchymal stem cells (MSCs) and osteolineage cells contribute to the hematopoietic stem cell (HSC) niche in the bone marrow of long bones. However, their developmental relationships remain unclear. In this study, we demonstrate that different MSC populations in the developing marrow of long bones have distinct functions. Proliferative mesoderm-derived nestin(-) MSCs participate in fetal skeletogenesis and lose MSC activity soon after birth. In contrast, quiescent neural crest-derived nestin(+) cells preserve MSC activity, but do not generate fetal chondrocytes. Instead, they differentiate into HSC niche-forming MSCs, helping to establish the HSC niche by secreting Cxcl12. Perineural migration of these cells to the bone marrow requires the ErbB3 receptor. The neonatal Nestin-GFP(+) Pdgfrα(-) cell population also contains Schwann cell precursors, but does not comprise mature Schwann cells. Thus, in the developing bone marrow HSC niche-forming MSCs share a common origin with sympathetic peripheral neurons and glial cells, and ontogenically distinct MSCs have non-overlapping functions in endochondrogenesis and HSC niche formation.
Peripheral blood monocytes are a heterogeneous population of circulating leukocytes. Using a murine adoptive transfer system to probe monocyte homing and differentiation in vivo, we identified two functional subsets among murine blood monocytes: a short-lived CX(3)CR1(lo)CCR2(+)Gr1(+) subset that is actively recruited to inflamed tissues and a CX(3)CR1(hi)CCR2(-)Gr1(-) subset characterized by CX(3)CR1-dependent recruitment to noninflamed tissues. Both subsets have the potential to differentiate into dendritic cells in vivo. The level of CX(3)CR1 expression also defines the two major human monocyte subsets, the CD14(+)CD16(-) and CD14(lo)CD16(+) monocytes, which share phenotype and homing potential with the mouse subsets. These findings raise the potential for novel therapeutic strategies in inflammatory diseases.
Inflammasomes are multiprotein complexes that link pathogen recognition and cellular stress to the processing of the proinflammatory cytokine interleukin-1β (IL-1β). Whereas inflammasome-mediated activation is heavily studied in hematopoietic macrophages and dendritic cells, much less is known about microglia, resident tissue macrophages of the brain that originate from a distinct progenitor. To directly compare inflammasome-mediated activation in different types of macrophages, we isolated primary microglia and hematopoietic macrophages from adult, healthy rhesus macaques. We analyzed the expression profile of NOD (nucleotide-binding oligomerization domain)-like receptors, adaptor proteins, and caspases and characterized inflammasome activation and regulation in detail. We here demonstrate that primary microglia can respond to the same innate stimuli as hematopoietic macrophages. However, microglial responses are more persistent due to lack of negative regulation on pro-IL-1β expression. In addition, we show that while caspase 1, 4, and 5 activation is pivotal for inflammasome-induced IL-1β secretion by hematopoietic macrophages, microglial secretion of IL-1β is only partially dependent on these inflammatory caspases. These results identify key cell type-specific differences that may aid the development of strategies to modulate innate immune responses in the brain.
T cells have crucial roles in protection against infection and cancer. Although the trafficking of memory T cells around the body is integral to their capacity to provide immune protection, studies have shown that specialization of some memory T cells into unique tissue-resident subsets gives the host enhanced regional immunity. In recent years, there has been considerable progress in our understanding of tissue-resident T cell development and function, revealing mechanisms for enhanced protective immunity that have the potential to influence rational vaccine design. This Review discusses the major advances and the emerging concepts in this field, summarizes what is known about the differentiation and the protective functions of tissue-resident memory T cells in different tissues in the body and highlights key unanswered questions.
Adipocytes are part of hematopoietic microenvironment, even though up to now in humans, their role in hematopoiesis is still questioned. We have previously shown that accumulation of fat cells in femoral bone marrow (BM) coincides with increased expression of neuropilin-1 (NP-1), while it is weakly expressed in hematopoietic iliac crest BM. Starting from this observation, we postulated that adipocytes might exert a negative effect on hematopoiesis mediated through NP-1. To test this hypothesis, we set up BM adipocytes differentiated into fibroblast-like fat cells (FLFC), which share the major characteristics of primitive unilocular fat cells, as an experimental model. As expected, FLFCs constitutively produced macrophage colony stimulating factor and induced CD34(+) differentiation into macrophages independently of cell-to-cell contact. By contrast, granulopoiesis was hampered by cell-to-cell contact but could be restored in transwell culture conditions, together with granulocyte colony stimulating factor production. Both functions were also recovered when FLFCs cultured in contact with CD34(+) cells were treated with an antibody neutralizing NP-1, which proved its critical implication in contact inhibition. An inflammatory cytokine such as interleukin-1 beta or dexamethasone modulates FLFC properties to restore granulopoiesis. Our data provide the first evidence that primary adipocytes exert regulatory functions during hematopoiesis that might be implicated in some pathological processes. Disclosure of potential conflicts of interest is found at the end of this article.
Subcapsular sinus (SCS) macrophages capture antigens from lymph and present them intact for B cell encounter and follicular delivery. However, the properties of SCS macrophages are poorly defined. Here we show SCS macrophage development depended on lymphotoxin-alpha1beta2, and the cells had low lysosomal enzyme expression and retained opsonized antigens on their surface. Intravital imaging revealed immune complexes moving along macrophage processes into the follicle. Moreover, noncognate B cells relayed antigen opsonized by newly produced antibodies from the subcapsular region to the germinal center, and affinity maturation was impaired when this transport process was disrupted. Thus, we characterize SCS macrophages as specialized antigen-presenting cells functioning at the apex of an antigen transport chain that promotes humoral immunity.
Invariant natural killer T cells (iNKT cells) are involved in the host defense against microbial infection. Although it is known that iNKT cells recognize glycolipids presented by CD1d, how and where they encounter antigen in vivo remains unclear. Here we used multiphoton microscopy to visualize the dynamics and activation of iNKT cells in lymph nodes. After antigen administration, iNKT cells became confined in a CD1d-dependent manner in close proximity to subcapsular sinus CD169(+) macrophages. These macrophages retained, internalized and presented lipid antigen and were required for iNKT cell activation, cytokine production and population expansion. Thus, CD169(+) macrophages can act as true antigen-presenting cells controlling early iNKT cell activation and favoring the fast initiation of immune responses.
Cells derived from blood vessels of human skeletal muscle can regenerate skeletal muscle, similarly to embryonic mesoangioblasts. However, adult cells do not express endothelial markers, but instead express markers of pericytes, such as NG2 proteoglycan and alkaline phosphatase (ALP), and can be prospectively isolated from freshly dissociated ALP+ cells. Unlike canonical myogenic precursors (satellite cells), pericyte-derived cells express myogenic markers only in differentiated myotubes, which they form spontaneously with high efficiency. When transplanted into severe combined immune deficient–X-linked, mouse muscular dystrophy (scid–mdx) mice, pericyte-derived cells colonize host muscle and generate numerous fibres expressing human dystrophin. Similar cells isolated from Duchenne patients, and engineered to express human mini-dystrophin, also give rise to many dystrophin-positive fibres in vivo. These data show that myogenic precursors, distinct from satellite cells, are associated with microvascular walls in the human skeletal muscle, may represent a correlate of embryonic 'mesoangioblasts' present after birth and may be a promising candidate for future cell-therapy protocols in patients.
In metazoan organisms, terminal differentiation is generally tightly linked to cell cycle exit, whereas the undifferentiated state of pluripotent stem cells is associated with unlimited self-renewal. Here, we report that combined deficiency for the transcription factors MafB and c-Maf enables extended expansion of mature monocytes and macrophages in culture without loss of differentiated phenotype and function. Upon transplantation, the expanded cells are nontumorigenic and contribute to functional macrophage populations in vivo. Small hairpin RNA inactivation shows that continuous proliferation of MafB/c-Maf deficient macrophages requires concomitant up-regulation of two pluripotent stem cell-inducing factors, KLF4 and c-Myc. Our results indicate that MafB/c-MafB deficiency renders self-renewal compatible with terminal differentiation. It thus appears possible to amplify functional differentiated cells without malignant transformation or stem cell intermediates.
Macrophages play a pivotal role in innate and acquired immune responses to Schistosoma mansoni. Classical (M1) or alternative (M2) activation states of these cells further delineate their roles in tissue damage through innate immunity or fibrotic remodeling, respectively. In the present study, we addressed the following question: Does systemic Th2-type cytokine polarization evoked by S. mansoni affect macrophage differentiation and activation? To this end, we analyzed bone marrow-derived macrophages from mice with S. mansoni egg-induced pulmonary granulomas and unchallenged (or naïve) mice to determine their activation state and their response to specific TLR agonists, including S. mansoni egg antigens. Unlike naïve macrophages, macrophages from Th2-polarized mice constitutively expressed significantly higher "found in inflammatory zone-1" (FIZZ1) and ST2 (M2 markers) and significantly lower NO synthase 2, CCL3, MIP-2, TNF-alpha, and IL-12 (M1 markers). Also, compared with naïve macrophages, Th2-polarized macrophages exhibited enhanced responses to the presence of specific TLR agonists, which consistently induced significantly higher levels of gene and protein levels for M2 and M1 markers in these cells. Together, these data show that signals received by bone marrow precursors during S. mansoni egg-induced granuloma responses dynamically alter the development of macrophages and enhance the TLR responsiveness of these cells, which may ultimately have a significant effect on the pulmonary granulomatous response.
Adipose tissue macrophages (ATMs) infiltrate adipose tissue during obesity and contribute to insulin resistance. We hypothesized that macrophages migrating to adipose tissue upon high-fat feeding may differ from those that reside there under normal diet conditions. To this end, we found a novel F4/80(+)CD11c(+) population of ATMs in adipose tissue of obese mice that was not seen in lean mice. ATMs from lean mice expressed many genes characteristic of M2 or "alternatively activated" macrophages, including Ym1, arginase 1, and Il10. Diet-induced obesity decreased expression of these genes in ATMs while increasing expression of genes such as those encoding TNF-alpha and iNOS that are characteristic of M1 or "classically activated" macrophages. Interestingly, ATMs from obese C-C motif chemokine receptor 2-KO (Ccr2-KO) mice express M2 markers at levels similar to those from lean mice. The antiinflammatory cytokine IL-10, which was overexpressed in ATMs from lean mice, protected adipocytes from TNF-alpha-induced insulin resistance. Thus, diet-induced obesity leads to a shift in the activation state of ATMs from an M2-polarized state in lean animals that may protect adipocytes from inflammation to an M1 proinflammatory state that contributes to insulin resistance.
DEFINITIVE erythropoiesis in birds originates from stem cells that emerge in the splanchnopleural mesoderm near the embryonic aorta1–4. The yolk sac is still generally held to be the unique provider of haematopoietic stem cells during mammalian ontogeny5, although there may be an alternative intraembryonic source of stem cells in the mouse fetus6,7. Here we search for a possible non-yolk-sac source of stem cells by grafting intraembryonic splanchnopleura from 10- to 18-somite mouse embryos into adult immunodeficient SCID mice. We find significant amounts of donor-derived serum IgM, normal numbers of IgM-secreting plasma cells, and the Bla (IgMa brightB220dullCD5+) cell subset to be fully reconstituted by donor progenitors 3 to 6 months after engraftment. The haematogenic capacity revealed in our experiments is present in a previously unrecognized site, the earliest described in the embryo, 12 hours before fetal liver colonization.
Some authors claim that microglia originate from the neuroepithelium, although most now believe that microglial cells are of mesodermal origin, and probably belong to the monocyte/macrophage cell line. These cells must enter the developing central nervous system (CNS) from the blood stream, the ventricular space or the meninges. Afterward microglial cells are distributed more or less homogeneously through the entire nervous parenchyma. Stereotyped patterns of migration have been recognized during development, in which long-distance tangential migration precedes radial migration of individual cells. Microglial cells moving through the nervous parenchyma are ameboid microglia, which apparently differentiate into ramified microglia after reaching their definitive location. This is supported by the presence of cells showing intermediate features between those of ameboid and ramified microglia. The factors that control the invasion of the nervous parenchyma, migration within the developing CNS and differentiation of microglial cells are not well known. These phenomena apparently depend on environmental factors such as soluble or cell-surface bound molecules and components of the extracellular matrix. Microglial cells within the developing CNS are involved in clearing cell debris and withdrawing misdirected or transitory axons, and presumably support cell survival and neurite growth.
During the inflammatory response that drives atherogenesis, macrophages accumulate progressively in the expanding arterial wall. The observation that circulating monocytes give rise to lesional macrophages has reinforced the concept that monocyte infiltration dictates macrophage buildup. Recent work has indicated, however, that macrophage accumulation does not depend on monocyte recruitment in some inflammatory contexts. We therefore revisited the mechanism underlying macrophage accumulation in atherosclerosis. In murine atherosclerotic lesions, we found that macrophages turn over rapidly, after 4 weeks. Replenishment of macrophages in these experimental atheromata depends predominantly on local macrophage proliferation rather than monocyte influx. The microenvironment orchestrates macrophage proliferation through the involvement of scavenger receptor A (SR-A). Our study reveals macrophage proliferation as a key event in atherosclerosis and identifies macrophage self-renewal as a therapeutic target for cardiovascular disease.
Studies of the identity and physiological function of mesenchymal stromal cells (MSCs) have been hampered by a lack of markers that permit both prospective identification and fate mapping in vivo. We found that Leptin Receptor (LepR) is a marker that highly enriches bone marrow MSCs. Approximately 0.3% of bone marrow cells were LepR(+) , 10% of which were CFU-Fs, accounting for 94% of bone marrow CFU-Fs. LepR(+) cells formed bone, cartilage, and adipocytes in culture and upon transplantation in vivo. LepR(+) cells were Scf-GFP(+), Cxcl12-DsRed(high), and Nestin-GFP(low), markers which also highly enriched CFU-Fs, but negative for Nestin-CreER and NG2-CreER, markers which were unlikely to be found in CFU-Fs. Fate-mapping showed that LepR(+) cells arose postnatally and gave rise to most bone and adipocytes formed in adult bone marrow, including bone regenerated after irradiation or fracture. LepR(+) cells were quiescent, but they proliferated after injury. Therefore, LepR(+) cells are the major source of bone and adipocytes in adult bone marrow.
The mechanism of B cell–antigen encounter in lymphoid tissues is incompletely understood. It is also unclear how immune complexes are transported to follicular dendritic cells. Here, using real-time two-photon microscopy we noted rapid delivery of immune complexes through the lymph to macrophages in the lymph node subcapsular sinus. B cells captured immune complexes by a complement receptor–dependent mechanism from macrophage processes that penetrated the follicle and transported the complexes to follicular dendritic cells. Furthermore, cognate B cells captured antigen-containing immune complexes from macrophage processes and migrated to the T zone. Our findings identify macrophages lining the subcapsular sinus as an important site of B cell encounter with immune complexes and show that intrafollicular B cell migration facilitates the transport of immune complexes as well as encounters with cognate antigen.
The rising incidence of obesity and associated metabolic diseases has increased the urgency in understanding all aspects of adipose tissue biology. This includes the function of adipocytes, how adipose tissue expands in obesity, and how expanded adipose tissues in adults can impact physiology. Here, we highlight the growing appreciation for the importance of de novo adipocyte differentiation to adipose tissue expansion in adult humans and animals. We detail recent efforts to identify adipose precursor populations that contribute to the physiological postnatal recruitment of white, brown, and beige adipocytes in mice, and summarize new data that reveal the complexity of adipose tissue development in vivo.
Bone marrow stem cells give rise to a variety of hematopoietic lineages and repopulate the blood throughout adult life. We show that, in a strain of mice incapable of developing cells of the myeloid and lymphoid lineages, transplanted adult bone marrow cells migrated into the brain and differentiated into cells that expressed neuron-specific antigens. These findings raise the possibility that bone marrow-derived cells may provide an alternative source of neurons in patients with neurodegenerative diseases or central nervous system injury.
In semisyngeneic heterotopic bone marrow transplants the donor or recipient origin of cells of osteogenic and hematopoietic tissues was identified by chromosome markers (T6) and by reverse transplantation into the initial donor line. In syngeneic and semisyngeneic grafts of bone marrow under the renal capsule bone and bone marrow are formed. In allogeneic grafts only bone is formed; this bone is subsequently resorbed. In 14-month semisyngeneic transplants the bone marrow consists of recipient cells. This is true for both the proliferating pool and the stem cells of hematopoietic tissue. At the same time, osteogenic precursor cells and bone tissue in these transplants are of donor origin. A discussion is presented of the interrelationship between determinated osteogenic precursor cells (preosteoblasts) and hematopoietic stem cells (or their descendants) in which osteogenesis is inducible.
Rho family proteins are known to regulate actin organization in fibroblasts, but their functions in cells of haematopoietic origin have not been studied in detail. Bac1.2F5 cells are a colony-stimulating factor-1 (CSF-1)-dependent murine macrophage cell line; CSF-1 stimulates their proliferation and motility, and acts as a chemoattractant. CSF-1 rapidly induced actin reorganization in Bac1 cells: it stimulated the formation of filopodia, lamellipodia and membrane ruffles at the plasma membrane, as well as the appearance of fine actin cables within the cell interior. Microinjection of constitutively activated (V12)Rac1 stimulated lamellipodium formation and membrane ruffling. The dominant inhibitory Rac mutant, N17Rac1, inhibited CSF-1-induced lamellipodium formation, and also induced cell rounding. V12Cdc42 induced the formation of long filopodia, while the dominant inhibitory mutant N17Cdc42 prevented CSF-1-induced formation of filopodia but not lamellipodia. V14RhoA stimulated actin cable assembly and cell contraction, while the Rho inhibitor, C3 transferase, induced the loss of actin cables. Bac1 cells had cell-to-substratum adhesion sites containing beta1 integrin, pp125FAK, paxillin, vinculin, and tyrosine phosphorylated proteins. These 'focal complexes' were present in growing and CSF-1-starved cells, but were disassembled in cells injected with N17Cdc42 or N17Rac1. Interestingly, beta1 integrin did not disperse until long after focal phosphotyrosine and vinculin staining had disappeared. We conclude that in Bac1 macrophages Cdc42, Rac and Rho regulate the formation of distinct actin filament-based structures, and that Cdc42 and Rac are also required for the assembly of adhesion sites to the extracellular matrix.
It has been shown by several investigators that adipocyte number is stable in mature human beings and several species of rodents. Although the number of new cells appearing in the adipose depot can be measured histometrically and by Coulter counting of osmium-fixed cells, such methods do not distinguish between "lipid filling" of preexistent adipocytes and synthesis of new adipocytes. The experiments reported here using in vivo injection of [(3)H]thymidine show that synthesis of new adipocytes in the Sprague-Dawley rat continues after birth and ceases before sexual maturity. Furthermore, during the second and third postnatal weeks, a "bed" of preadipocytes is synthesized. Preadipocytes may take as long as 30 days to appear as mature adipocytes.
Summary Neutrophils are specialized innate cells that require constant replenishment from proliferative bone marrow (BM) precursors as a result of their short half‐life. Although it is established that neutrophils are derived from the granulocyte‐macrophage progenitor (GMP), the differentiation pathways from GMP to functional mature neutrophils are poorly defined. Using mass cytometry (CyTOF) and cell‐cycle‐based analysis, we identified three neutrophil subsets within the BM: a committed proliferative neutrophil precursor (preNeu) which differentiates into non‐proliferating immature neutrophils and mature neutrophils. Transcriptomic profiling and functional analysis revealed that preNeu require the C/EBP&egr; transcription factor for their generation from the GMP, and their proliferative program is substituted by a gain of migratory and effector function as they mature. preNeus expand under microbial and tumoral stress, and immature neutrophils are recruited to the periphery of tumor‐bearing mice. In summary, our study identifies specialized BM granulocytic populations that ensure supply under homeostasis and stress responses. Graphical Abstract Figure. No Caption available. HighlightsProliferation activity identifies committed neutrophil precursor in mice and humansNeutrophil subsets possess distinct transcriptomic and functional signaturesDefect in neutrophil development leads to impaired neutrophil‐mediated responsesIncreased circulating immature neutrophils are associated with cancer progression &NA; The neutrophil differentiation pathway is poorly defined. Evrard et. al. demonstrate a workflow of characterizing bone marrow neutrophil subsets on the basis of their proliferative capacity and molecular signatures and thereby define the developmental trajectory and functional properties of neutrophils.