Tumor-associated macrophages (TAM) form a major component of the tumor stroma. However, important concepts such as TAM heterogeneity and the nature of the monocytic TAM precursors remain speculative. ...Here, we show for the first time that mouse mammary tumors contained functionally distinct subsets of TAMs and provide markers for their identification. Furthermore, in search of the TAM progenitors, we show that the tumor-monocyte pool almost exclusively consisted of Ly6C(hi)CX(3)CR1(low) monocytes, which continuously seeded tumors and renewed all nonproliferating TAM subsets. Interestingly, gene and protein profiling indicated that distinct TAM populations differed at the molecular level and could be classified based on the classic (M1) versus alternative (M2) macrophage activation paradigm. Importantly, the more M2-like TAMs were enriched in hypoxic tumor areas, had a superior proangiogenic activity in vivo, and increased in numbers as tumors progressed. Finally, it was shown that the TAM subsets were poor antigen presenters, but could suppress T-cell activation, albeit by using different suppressive mechanisms. Together, our data help to unravel the complexities of the tumor-infiltrating myeloid cell compartment and provide a rationale for targeting specialized TAM subsets, thereby optimally "re-educating" the TAM compartment.
The death of retinal ganglion cells (RGCs) is a hallmark of many retinal neuropathies. Neuroprotection, axonal regeneration, and cell renewal are vital for the integrity of the visual system after ...insult but are scarce in the adult mammalian retina. We hypothesized that monocyte-derived macrophages, known to promote healing in peripheral tissues, are required after an insult to the visual system, where their role has been largely overlooked. We found that after glutamate eye intoxication, monocyte-derived macrophages infiltrated the damaged retina of mice. Inhibition of this infiltration resulted in reduced survival of RGCs and diminished numbers of proliferating retinal progenitor cells (RPCs) in the ciliary body. Enhancement of the circulating monocyte pool led to increased RGC survival and RPC renewal. The infiltrating monocyte-derived macrophages skewed the milieu of the injured retina toward an antiinflammatory and neuroprotective one and down-regulated accumulation of other immune cells, thereby resolving local inflammation. The beneficial effect on RGC survival depended on expression of interleukin 10 and major histocompatibility complex class II molecules by monocyte-derived macrophages. Thus, we attribute to infiltrating monocyte-derived macrophages a novel role in neuroprotection and progenitor cell renewal in the injured retina, with far-reaching potential implications to retinal neuropathies and other neurodegenerative disorders.
Although macrophages (MPhi) are known as essential players in wound healing, their contribution to recovery from spinal cord injury (SCI) is a subject of debate. The difficulties in distinguishing ...between different MPhi subpopulations at the lesion site have further contributed to the controversy and led to the common view of MPhi as functionally homogenous. Given the massive accumulation in the injured spinal cord of activated resident microglia, which are the native immune occupants of the central nervous system (CNS), the recruitment of additional infiltrating monocytes from the peripheral blood seems puzzling. A key question that remains is whether the infiltrating monocyte-derived MPhi contribute to repair, or represent an unavoidable detrimental response. The hypothesis of the current study is that a specific population of infiltrating monocyte-derived MPhi is functionally distinct from the inflammatory resident microglia and is essential for recovery from SCI.
We inflicted SCI in adult mice, and tested the effect of infiltrating monocyte-derived MPhi on the recovery process. Adoptive transfer experiments and bone marrow chimeras were used to functionally distinguish between the resident microglia and the infiltrating monocyte-derived MPhi. We followed the infiltration of the monocyte-derived MPhi to the injured site and characterized their spatial distribution and phenotype. Increasing the naïve monocyte pool by either adoptive transfer or CNS-specific vaccination resulted in a higher number of spontaneously recruited cells and improved recovery. Selective ablation of infiltrating monocyte-derived MPhi following SCI while sparing the resident microglia, using either antibody-mediated depletion or conditional ablation by diphtheria toxin, impaired recovery. Reconstitution of the peripheral blood with monocytes resistant to ablation restored the lost motor functions. Importantly, the infiltrating monocyte-derived MPhi displayed a local anti-inflammatory beneficial role, which was critically dependent upon their expression of interleukin 10.
The results of this study attribute a novel anti-inflammatory role to a unique subset of infiltrating monocyte-derived MPhi in SCI recovery, which cannot be provided by the activated resident microglia. According to our results, limited recovery following SCI can be attributed in part to the inadequate, untimely, spontaneous recruitment of monocytes. This process is amenable to boosting either by active vaccination with a myelin-derived altered peptide ligand, which indicates involvement of adaptive immunity in monocyte recruitment, or by augmenting the naïve monocyte pool in the peripheral blood. Thus, our study sheds new light on the long-held debate regarding the contribution of MPhi to recovery from CNS injuries, and has potentially far-reaching therapeutic implications.
Macrophages are a source of both proinflammatory and restorative functions in damaged tissue through complex dynamic phenotypic changes. Here, we sought to determine whether monocyte-derived ...macrophages (MDMs) contribute to recovery after acute sterile brain injury. By profiling the transcriptional dynamics of MDMs in the murine brain after experimental intracerebral hemorrhage (ICH), we found robust phenotypic changes in the infiltrating MDMs over time and demonstrated that MDMs are essential for optimal hematoma clearance and neurological recovery. Next, we identified the mechanism by which the engulfment of erythrocytes with exposed phosphatidylserine directly modulated the phenotype of both murine and human MDMs. In mice, loss of receptor tyrosine kinases AXL and MERTK reduced efferocytosis of eryptotic erythrocytes and hematoma clearance, worsened neurological recovery, exacerbated iron deposition, and decreased alternative activation of macrophages after ICH. Patients with higher circulating soluble AXL had poor 1-year outcomes after ICH onset, suggesting that therapeutically augmenting efferocytosis may improve functional outcomes by both reducing tissue injury and promoting the development of reparative macrophage responses. Thus, our results identify the efferocytosis of eryptotic erythrocytes through AXL/MERTK as a critical mechanism modulating macrophage phenotype and contributing to recovery from ICH.
Aging in humans is associated with increased hyperglycemia and insulin resistance (collectively termed IR) and dysregulation of the immune system. However, the causative factors underlying their ...association remain unknown. Here, using "healthy" aged mice and macaques, we found that IR was induced by activated innate 4-1BBL
B1a cells. These cells (also known as 4BL cells) accumulated in aging in response to changes in gut commensals and a decrease in beneficial metabolites such as butyrate. We found evidence suggesting that loss of the commensal bacterium
impaired intestinal integrity, causing leakage of bacterial products such as endotoxin, which activated CCR2
monocytes when butyrate was decreased. Upon infiltration into the omentum, CCR2
monocytes converted B1a cells into 4BL cells, which, in turn, induced IR by expressing 4-1BBL, presumably to trigger 4-1BB receptor signaling as in obesity-induced metabolic disorders. This pathway and IR were reversible, as supplementation with either
or the antibiotic enrofloxacin, which increased the abundance of
, restored normal insulin response in aged mice and macaques. In addition, treatment with butyrate or antibodies that depleted CCR2
monocytes or 4BL cells had the same effect on IR. These results underscore the pathological function of B1a cells and suggest that the microbiome-monocyte-B cell axis could potentially be targeted to reverse age-associated IR.
Acute inflammation is traditionally characterized by polymorphonuclear leukocytes (PMN) influx followed by phagocytosing macrophage (Mφs) that clear injurious stimuli leading to resolution and tissue ...homeostasis. However, using the peritoneal cavity, we found that although innate immune-mediated responses to low-dose zymosan or bacteria resolve within days, these stimuli, but not hyperinflammatory stimuli, trigger a previously overlooked second wave of leukocyte influx into tissues that persists for weeks. These cells comprise distinct populations of tissue-resident Mφs (resMφs), Ly6chi monocyte-derived Mφs (moMφs), monocyte-derived dendritic cells (moDCs), and myeloid-derived suppressor cells (MDSCs). Postresolution mononuclear phagocytes were observed alongside lymph node expansion and increased numbers of blood and peritoneal memory T and B lymphocytes. The resMφs and moMφs triggered FoxP3 expression within CD4 cells, whereas moDCs drive T-cell proliferation. The resMφs preferentially clear apoptotic PMNs and migrate to lymph nodes to bring about their contraction in an inducible nitric oxide synthase-dependent manner. Finally, moMφs remain in tissues for months postresolution, alongside altered numbers of T cells collectively dictating the magnitude of subsequent acute inflammatory reactions. These data challenge the prevailing idea that resolution leads back to homeostasis and asserts that resolution acts as a bridge between innate and adaptive immunity, as well as tissue reprogramming.
•Resolving, but not hyperinflammatory stimuli create a microenvironment conducive for the optimal development of adaptive immunity.•After onset and resolution, we introduce a third phase to acute inflammatory responses dominated by macrophages and lymphocytes.
Interstitial fibrosis is associated with chronic renal failure. In addition to fibroblasts, bone marrow-derived cells and tubular epithelial cells have the capacity to produce collagen. However, the ...amount of collagen produced by each of these cell types and the relevance of fibrosis to renal function are unclear.
We generated conditional cell type-specific collagen I knockout mice and used (reversible) unilateral ureteral obstruction and adenine-induced nephropathy to study renal fibrosis and function.
In these mouse models, hematopoietic, bone marrow-derived cells contributed to 38%-50% of the overall deposition of collagen I in the kidney. The influence of fibrosis on renal function was dependent on the type of damage. In unilateral ureteral obstruction, collagen production by resident fibroblasts was essential to preserve renal function, whereas in the chronic model of adenine-induced nephropathy, collagen production was detrimental to renal function.
Our data show that hematopoietic cells are a major source of collagen and that antifibrotic therapies need to be carefully considered depending on the type of disease and the underlying cause of fibrosis.
Monocyte recruitment to sites of inflammation is regulated by members of the chemokine family of chemotactic cytokines. However, the mechanisms that govern the migration of monocytes from bone marrow ...to blood and from blood to inflamed tissues are not well understood. Here we report that CC chemokine receptor 2 (CCR2) is highly expressed on a subpopulation of blood monocytes whose numbers are markedly decreased in CCR2(-/-) mice. In bone marrow, however, CCR2(-/-) mice had an increased number of monocytes, suggesting that CCR2 is critical for monocyte egress. Intravenous infusion of ex vivo-labeled WT or CCR2(-/-) bone marrow into WT recipient mice demonstrated that CCR2 is necessary for efficient monocyte recruitment from the blood to inflamed tissue. Analysis of mice lacking monocyte chemoattractant protein-1 (MCP-1), MCP-3, MCP-5, or MCP-2 plus MCP-5 revealed that MCP-3 and MCP-1 are the CCR2 agonists most critical for the maintenance of normal blood monocyte counts. These findings provide evidence that CCR2 and MCP-3/MCP-1 are critical for monocyte mobilization and suggest new roles for monocyte chemoattractants in leukocyte homeostasis.
The bacteria Streptomyces davawensis and Streptomyces cinnabarinus produce roseoflavin, the only known natural riboflavin (vitamin B2) analogue with antibiotic activity. Roseoflavin can be considered ...a natural antimetabolite and has been postulated to be biosynthesized from riboflavin via the key intermediate 8‐demethyl‐8‐aminoriboflavin (AF). The required site‐specific substitution of one of the methyl groups on the dimethylbenzene ring of riboflavin by an amino group (to give AF) is challenging. The pathway from riboflavin to AF has remained elusive, and the corresponding enzyme/s was/were unknown. Herein, we show by systematic gene deletion, heterologous gene expression, and biochemical studies that the enzyme specified by the gene BN159_7989 from S. davawensis is able to carry out a whole set of chemical reactions starting from riboflavin‐5′‐phosphate to give the final product 8‐demethyl‐8‐aminoriboflavin‐5′‐phosphate (AFP).
All by myself: Unexpectedly, a single enzyme (RosB) was found to catalyze several essential steps of the biosynthesis of the antibiotic roseoflavin from riboflavin (vitamin B2). RosB was identified in the bacterium Streptomyces davawensis, which was used to produce roseoflavin in a bioreactor containing a nutrient broth.
Interleukin 17-producing γδ T (γδT17) cells have unconventional trafficking characteristics, residing in mucocutaneous tissues but also homing into inflamed tissues via circulation. Despite being ...fundamental to γδT17-driven early protective immunity and exacerbation of autoimmunity and cancer, migratory cues controlling γδT17 cell positioning in barrier tissues and recruitment to inflammatory sites are still unclear. Here we show that γδT17 cells constitutively express chemokine receptors CCR6 and CCR2. While CCR6 recruits resting γδT17 cells to the dermis, CCR2 drives rapid γδT17 cell recruitment to inflamed tissues during autoimmunity, cancer and infection. Downregulation of CCR6 by IRF4 and BATF upon γδT17 activation is required for optimal recruitment of γδT17 cells to inflamed tissue by preventing their sequestration into uninflamed dermis. These findings establish a lymphocyte trafficking model whereby a hierarchy of homing signals is prioritized by dynamic receptor expression to drive both tissue surveillance and rapid recruitment of γδT17 cells to inflammatory lesions.
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