Controversy surrounds neutrophil function in cancer because neutrophils were shown to provide both pro- and antitumor functions. We identified a heterogeneous subset of low-density neutrophils (LDNs) that appear transiently in self-resolving inflammation but accumulate continuously with cancer progression. LDNs display impaired neutrophil function and immunosuppressive properties, characteristics that are in stark contrast to those of mature, high-density neutrophils (HDNs). LDNs consist of both immature myeloid-derived suppressor cells (MDSCs) and mature cells that are derived from HDNs in a TGF-β-dependent mechanism. Our findings identify three distinct populations of circulating neutrophils and challenge the concept that mature neutrophils have limited plasticity. Furthermore, our findings provide a mechanistic explanation to mitigate the controversy surrounding neutrophil function in cancer.

The cellular events underlying the resolution of acute inflammation are not known in molecular terms. To identify anti-inflammatory and proresolving circuits, we investigated the temporal and differential changes in self-resolving murine exudates using mass spectrometry-based proteomics and lipidomics. Key resolution components were defined as resolution indices including Ψmax, the maximal neutrophil numbers that are present during the inflammatory response; Tmax, the time when Ψmax occurs; and the resolution interval (Ri) from Tmax to T50 when neutrophil numbers reach half Ψmax. The onset of resolution was at ∼12 h with proteomic analysis showing both haptoglobin and S100A9 levels were maximal and other exudate proteins were dynamically regulated. Eicosanoids and polyunsaturated fatty acids first appeared within 4 h. Interestingly, the docosahexaenoic acid-derived anti-inflammatory lipid mediator 10,17S-docosatriene was generated during the Ri. Administration of aspirin-triggered lipoxin A4 analog, resolvin E1, or 10,17S-docosatriene each either activated and/or accelerated resolution. For example, aspirin-triggered lipoxin A4 analog reduced Ψmax, resolvin E1 decreased both Ψmax and Tmax, whereas 10,17S-docosatriene reduced Ψmax, Tmax, and shortened Ri. Also, aspirin-triggered lipoxin A4 analog markedly inhibited proinflammatory cytokines and chemokines at 4 h (20–50% inhibition), whereas resolvin E1 and 10,17S-docosatriene’s inhibitory actions were maximal at 12 h (30–80% inhibition). Moreover, aspirin-triggered lipoxin A4 analog evoked release of the antiphlogistic cytokine TGF-β. These results characterize the first molecular resolution circuits and their major components activated by specific novel lipid mediators (i.e., resolvin E1 and 10,17S-docosatriene) to promote resolution.

No abstract

Summary During the resolution phase of inflammation apoptotic leukocytes are efferocytosed by macrophages in a nonphlogistic fashion that results in diminished responses to bacterial moieties and production of anti-inflammatory cytokines. Complement receptor 3 (CR3) and pro-resolving lipid mediators promote the engulfment of apoptotic leukocytes by macrophages. Here, we present evidence for the emergence of pro-resolving, CD11blow macrophages in vivo during the resolution of murine peritonitis. These macrophages are distinct from the majority of peritoneal macrophages in terms of their functional protein expression profile, as well as pro-resolving properties, such as apoptotic leukocyte engulfment, indifference to TLR ligands, and emigration to lymphoid organs. Notably, we also found macrophages convert from the CD11bhigh to the CD11blow phenotype upon interaction with apoptotic cells ex vivo. In addition, we found that the pro-resolving lipid mediators resolvin (Rv) E1 and RvD1, and the glucocorticoid dexamethasone (Dex) regulated pro-resolving macrophage functions in vivo. This regulation culminated in a novel pro-resolving function, namely reducing the apoptotic leukocyte ingestion requirement for CD11blow macrophage generation. These new phenotype and molecular pathway markers define the new satiated-macrophage. Thus, we suggest that satisfying-efferocytosis generates CD11blow macrophages that are essential for complete non-phlogistic containment of inflammatory agents and the termination of acute inflammation.

During the resolution phase of inflammation, the 'corpses' of apoptotic leukocytes are gradually cleared by macrophages. Here we report that during the resolution of peritonitis, the CCR5 chemokine receptor ligands CCL3 and CCL5 persisted in CCR5-deficient mice. CCR5 expression on apoptotic neutrophils and activated apoptotic T cells sequestered and effectively cleared CCL3 and CCL5 from sites of inflammation. CCR5 expression on late apoptotic human polymorphonuclear cells was downregulated by proinflammatory stimuli, including tumor necrosis factor, and was upregulated by 'proresolution' lipid mediators, including lipoxin A 4 , resolvin E1 and protectin D1. Our results suggest that CCR5 + apoptotic leukocytes act as 'terminators' of chemokine signaling during the resolution of inflammation.The resolution of inflammation requires the elimination of local chemical mediators 1,2 . Resolution is an active rather than a passive process 3,4 . Therefore, massive apoptosis of the leukocytes that elicit this response is one of the hallmarks of resolution 5-7 . Those apoptotic cells are gradually cleared by macrophages and other phagocytic cells 8-10 . Apoptotic cell engulfment by phagocytes is mediated by the interaction between molecules on the surfaces of apoptotic cells and their corresponding receptors on the surfaces of phagocytes, including thrombospondin and CD36 (ref. 11), milk fat globule-epidermal growth factor 8 and α v β 3 integrin 9 , and others 6 . Apoptotic cells also serve as 'resolution cues' for macrophages, as their engulfment is not accompanied by the release of proinflammatory mediators characteristic of Correspondence should be addressed to C.N.S. (cnserhan@zeus.bwh.harvard.edu).. Note: Supplementary information is available on the Nature Immunology website.AUTHOR CONTRIBUTIONS All authors were involved in experimental planning and data analysis and contributed to manuscript preparation. A.A. carried out FACS analysis, binding, chemotaxis, human cell isolation and cell culture; G.F. carried out experiments, FACS analysis, human cell isolation and culture; Y.-P.S. carried out peritonitis experiments and related analyses; A.K. and T.E.V.D. carried out Luminex analyses and related experimental design; A.D.L. carried out experiments with CCR5-deficient mice. COMPETING INTERESTS STATEMENTThe authors declare competing financial interests (see the Nature Immunology website for details).Reprints and permissions information is available online at http://npg.nature.com/reprintsandpermissions/ NIH Public Access During the course of acute inflammation, a temporal switch in the profile of inflammatory lipid-derived mediators occurs; although proinflammatory prostaglandins and leukotrienes dominate in the initial phase, they give way to the 'proresolution' lipoxins in the resolution phase 3,4,17 . In addition to lipoxins, resolvins and protectins are families of lipid mediators derived from ω-3-polyunsaturated fatty acids that are generated during resolution and exert potent antiinflammatory actions 4,18...

No abstract

Docosahexaenoic acid, a major -3 fatty acid in human brain, synapses, retina, and other neural tissues, displays beneficial actions in neuronal development, cancer, and inflammatory diseases by mechanisms that remain to be elucidated. In this study we found, using lipid mediator informatics employing liquid chromatography-tandem mass spectrometry, that (10,17S)-docosatriene/neuroprotectin D1, now termed protectin D1 (PD1), is generated from docosahexaenoic acid by T helper type 2-skewed peripheral blood mononuclear cells in a lipoxygenase-dependent manner. PD1 blocked T cell migration in vivo, inhibited tumor necrosis factor ␣ and interferon-␥ secretion, and promoted apoptosis mediated by raft clustering. These results demonstrated novel anti-inflammatory roles for PD1 in regulating events associated with inflammation and resolution.

Monocytes that migrate into tissues during inflammatory episodes and differentiate to macrophages were previously classified as classically (M1) or alternatively (M2) activated macrophages, based on their exposure to different fate-determining mediators. These macrophage subsets display distinct molecular markers and differential functions. At the same time, studies from recent years found that the encounter of apoptotic leukocytes with macrophages leads to the clearance of this cellular “debris” by the macrophages, while concomitantly reprogramming/immune-silencing the macrophages. While some of the features of M2 differentiation, such as arginase-1 (murine) and 15-lipoxygenases (human and murine) expression, were also displayed by macrophages following the engulfment of apoptotic cells, it was not clear whether apoptotic cells can be regarded as an M2-like differentiating signal. In this manuscript we review the recent information regarding the impact of apoptotic cells on macrophage phenotype changes in molecular terms. We will focus on recent evidence for the in vivo existence of distinct pro-resolving macrophages and the role of apoptotic cells, specialized lipid mediators, and glucocorticoids in their generation. Consequently, we will suggest that these pro-resolving CD11blow macrophages have metamorphed from M2-like macrophages, and modulated their protein profile to accommodate the changes in their function.