Macrophage polarization in health and disease

Macrophages are terminally differentiated cells of the mononuclear phagocyte system that also encompasses dendritic cells, circulating blood monocytes, and committed myeloid progenitor cells in the bone marrow. Both macrophages and their monocytic precursors can change their functional state in response to microenvironmental cues exhibiting a marked heterogeneity. However, there are still uncertainties regarding distinct expression patterns of surface markers that clearly define macrophage subsets, particularly in the case of human macrophages. In addition to their tissue distribution, macrophages can be functionally polarized into M1 (proinflammatory) and M2 (alternatively activated) as well as regulatory cells in response to both exogenous infections and solid tumors as well as by systems biology approaches. KEYWORDS: Macrophage, polarization, M1/M2, HIV, tumors, TAMs (tumor-associated macrophages), regulatory macrophages Correspondence should be addressed to Guido Poli, [email protected] Copyright © 2011 Luca Cassetta et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Published by TheScientificWorldJOURNAL; http://www.tswj.com/ TheScientificWorldJOURNAL (2011) 11, 2391-2402 MACROPHAGE POLARIZATION: DOGMA OR REALITY? Proinflammatory, "classical Activation" of macrophages, which was delineated in early studies from the 1960s Indeed, "classically" and "alternatively" activated macrophages have been designated as "M1" and "M2" macrophages, respectively, by analogy to the Th1/Th2 division of labor of CD4 helper T cells A more flexible classification has been suggested recently by mouse studies in which macrophages are considered as part of a continuum having a range of overlapping functions and in which classically activated, wound-healing, and regulatory macrophages occupy different points of the spectrum MACROPHAGE PLASTICITY: AN OBSTACLE TO STUDY MACROPHAGE POLARIZATION? Unlike lymphocytes where phenotypic changes are largely "fixed" by chromatin modifications after exposure to polarizing cytokines, macrophages have a plastic gene expression profile that is influenced by the type, concentration, and longevity of exposure to the stimulating agents, as documented extensively There is a high number of factors contributing to diversity of macrophage function, including the synergistic or antagonistic effects of different cytokines and related signals on their differential expression, chemokines, hormones (including adrenergic and cholinergic agonists), TLR ligands, and other endogenous ligands (e.g., histamine, integrin ligands, peroxisome proliferator-activated receptor ligands, apoptotic cells); this plethora of signals underlines the fact that macrophages can display a large number of distinct, functional patterns that have not yet been completely defined. Furthermore, identical macrophages placed in different microenvironments display different functions in response to a common stimulus. Stimulation of macrophages with functionally opposite cytokines, such as IFN-γ and IL-4, initiates signal cascades that results in differential modulation (enhancement or inhibition) of different genes at the transcriptional or posttranscriptional level (e.g., stabilization or destabilization of mRNA). Unless the signal cascade triggered an apoptotic cascade, macrophages will eventually revert to their original, functional status after the cytokine signaling ceases. In vivo or in vitro treatment of macrophages with cytokines alters their functional response pattern to LPS. However, if the cytokines are washed away after incubation and macrophages are then maintained in the absence of cytokines for 1-2 days before LPS stimulation, the functional response pattern is usually identical to that of macrophages that had not been prestimulated with the cytokine. A similar reversion to basal macrophage phenotype is observed when IL-4 and granulocyte macrophage-colony-stimulating factor (GM-CSF) are removed from human monocyte-derived, immature dendritic cells (iDCs) and the cells are resuspended in a neutral environment Therefore, most Th1 and Th2 cytokines do not seem to induce a stable differentiation of macrophages into distinct subsets, but they rather promote a transient functional pattern of responses that return to basal levels in a few (3-7) days. MARKERS OF MACROPHAGE POLARIZATION: STILL AN OPEN CHASE One of the most debated issues in the context of human macrophage polarization is the identification of unique or restricted markers to be used for research and clinical purposes. Innovative approaches, including intravital imaging and other in vivo techniques, will be of great help in the identification of "real" subsets of macrophages in addition to more static antigens expressed on their cellular surface following cell polarization. An example of this broader approach is summarized by the identification of at least 6 different subsets of mouse tumor-associated macrophages (TAMs) based on their distinct functional features CONTRIBUTION OF MACROPHAGE POLARIZATION TO INNATE IMMUNE RESPONSES REGULATORY MACROPHAGES (RMs) As mentioned, diversity is a key feature of macrophage activation. In addition to M1 and M2 macrophages, RMs have recently emerged as an important population of cells that play a pivotal role in limiting inflammation during innate and adaptive immune responses Interestingly, a recent study has identified a subpopulation of Foxp3 + macrophages in the mouse 2394 TheScientificWorldJOURNAL (2011TheScientificWorldJOURNAL ( ) 11, 2391TheScientificWorldJOURNAL ( -2402 Manrique et al. reported that F4/80 + Foxp3 − cells could be converted into FoxP3 + cells by stimulation with TGF-β, Vascular Endothelial Growth Factor (VEGF), or TLR ligands Although cell activation is critical for the induction of an effective immune response to pathogens or tumors, inappropriate and sustained activation/polarization of macrophages leads to tissue damage, immune dysfunction, and disease. As with exacerbated M1 and M2 responses, dysfunctional regulatory responses contribute to tumor progression and growth (as discussed below) and can predispose the host to infection. Several pathogens including Staphylococcus aureus MACROPHAGE DIVERSITY IN SYSTEMS BIOLOGY Systems biology approaches have provided important insights into the heterogeneity of mononuclear phagocyte populations, the plasticity of macrophage activation, and the molecular pathways associated with polarization. Transcriptome profiling has been commonly used to examine networks of molecules and transcription factors linked to activation. Using this approach, Martinez et al. obtained a comprehensive global view of human macrophage polarization Epigenetic studies have begun to unravel how polarized macrophages acquire and maintain their activation phenotype. M2 genes in mice, including Chi3l3, Retnla, and Arg-1, were shown to be epigenetically regulated as a result of signal transducer and activator of transcription 6-(STAT6-) dependent induction of the H3K27 demethylase Jmjd3 Thus, systems biology will keep providing a constantly updated global view of the networks regulating or involved in macrophage polarization, allowing us to evaluate key issues related to macrophage heterogeneity and plasticity. 2395 TheScientificWorldJOURNAL (2011TheScientificWorldJOURNAL ( ) 11, 2391TheScientificWorldJOURNAL ( -2402 MACROPHAGE POLARIZATION IN CANCER BIOLOGY: A MATTER OF GOOD OR BAD EDUCATION All solid tumors recruit monocytes and local macrophages into their microenvironment making them TAM; it is being increasingly clear that TAMs play several, sometimes opposite, roles during tumor development. Originally it was believed that these cells were attempting to reject the immunologically non-self entity made of transformed cells (that frequently lose or modify their MHC profile). Indeed, macrophages can effectively kill tumor cells in vitro In conclusion, tumors can affect macrophages playing with their impressive plastic nature in order to modify the microenvironment and consequently alter the function and the strength of the cellular and innate immune response. These studies together provide useful models to investigate how cancer cells (and viruses, as discussed later on) crosstalk with macrophages; the potential application of this information will be the identification of soluble factors or inhibitors that will "reeducate" macrophages against pathogens and neoplastic lesions

Targeting the Endothelin-1 Receptors Curtails Tumor Growth and Angiogenesis in Multiple Myeloma

The endothelin-1 (ET-1) receptors were recently found to mediate pro-survival functions in multiple myeloma (MM) cells in response to autocrine ET-1. This study investigated the effectiveness of macitentan, a dual ET-1 receptor antagonist, in MM treatment, and the mechanisms underlying its activities. Macitentan affected significantly MM cell (RPMI-8226, U266, KMS-12-PE) survival and pro-angiogenic cytokine release by down-modulating ET-1-activated MAPK/ERK and HIF-1 alpha pathways, respectively. HIF-1 alpha silencing abrogated the ET-1 mediated induction of genes encoding for pro-angiogenic cytokines such as VEGF-A, IL-8, Adrenomedullin, and ET-1 itself. Upon exposure to macitentan, MM cells cultured in the presence of the hypoxia-mimetic agent CoCl2, exogenous ET-1, or CoCl2 plus ET-1, down-regulated HIF-1 alpha and the transcription and release of downstream pro-angiogenic cytokines. Consistently, macitentan limited significantly the basal pro-angiogenic activity of RPMI-8226 cells in chorioallantoic membrane assay. In xenograft mouse models, established by injecting NOG mice either via intra-caudal vein with U266 or subcutaneously with RPMI-8226 cells, macitentan reduced effectively the number of MM cells infiltrating bone marrow, and the size and microvascular density of subcutaneous MM tumors. ET-1 receptors targeting by macitentan represents an effective anti-proliferative and anti-angiogenic therapeutic approach in preclinical settings of MM

Human Innate Lymphoid Cells: Their Functional and Cellular Interactions in Decidua

Innate lymphoid cells (ILC) are developmentally related cell subsets that play a major role in innate defenses against pathogens, in lymphoid organogenesis and in tissue remodeling. The best characterized ILC are natural killer (NK) cells. They are detectable in decidua in the early phases of pregnancy. During the first trimester, NK cells represent up to 50% of decidua lymphocytes. Differently from peripheral blood (PB) NK cells, decidual NK (dNK) cells are poorly cytolytic, and, instead of IFNγ, they release cytokines/chemokines that induce neo-angiogenesis, tissue remodeling, and placentation. dNK interact with resident myeloid cells and participate in the induction of regulatory T cells that play a pivotal role in maintaining an efficient fetal–maternal tolerance. dNK cells may originate from CD34+ precursor cells present in situ and/or from immature NK cells already present in endometrial tissue and/or from PB NK cells migrated to decidua. In addition to NK cells, also ILC3 are present in human decidua during the first trimester. Decidual ILC3 include both natural cytotoxic receptor (NCR)+ and NCR− cells, producing respectively IL-8/IL-22/GM-CSF and TNF/IL-17. NCR+ILC3 have been shown to establish physical and functional interactions with neutrophils that, in turn, produce factors that are crucial for pregnancy induction/maintenance and for promoting the early inflammatory phase, a fundamental process for a successful pregnancy. While NCR+ILC3 display a stable phenotype, most of NCR−ILC3 may acquire phenotypic and functional features of NCR+ILC3. In conclusion, both NK cells and ILC3 are present in human decidua and may establish functional interactions with immune and myeloid cells playing an important role both in innate defenses and in tissue building/remodeling/placentation during the early pregnancy. It is conceivable that altered numbers or function of these cells may play a role in pregnancy failure

Addressing gaps in care of people with conditions affecting sex development and maturation

Differences of sex development are conditions with discrepancies between chromosomal, gonadal and phenotypic sex. In congenital hypogonadotropic hypogonadism, a lack of gonadotropin activity results primarily in the absence of pubertal development with prenatal sex development being (almost) unaffected in most patients. To expedite progress in the care of people affected by differences of sex development and congenital hypogonadotropic hypogonadism, the European Union has funded a number of scientific networks. Two Actions of the Cooperation of Science and Technology (COST) programmes - DSDnet (BM1303) and GnRH Network (BM1105) - provided the framework for ground-breaking research and allowed the development of position papers on diagnostic procedures and special laboratory analyses as well as clinical management. Both Actions developed educational programmes to increase expertise and promote interest in this area of science and medicine. In this Perspective article, we discuss the success of the COST Actions DSDnet and GnRH Network and the European Reference Network for Rare Endocrine Conditions (Endo-ERN), and provide recommendations for future research

Characterizing the Complexities of Neutrophils with Suppressive Properties

Several not-yet fully described neutrophil populations exerting either antitumor or suppressive/protumor functions may appear in the circulation of patients with cancer and/or infiltrate tumor tissues. In this issue, Emmons and colleagues provide new information on how complement-dependent "activation" of normal mature neutrophils renders the cells able to inhibit T-cell responsiveness in vitro. The data highlight the complexities of understanding the biology of neutrophil-mediated T-cell suppression

L33. Neutrophil in immunity: A key modulator.

No abstract availabl

Neutrophil-derived chemokines on the road to immunity

During recent years, it has become clear that polymorphonuclear neutrophils are remarkably versatilecells, whose functions go far beyond phagocytosis and killing. In fact, besides being involved in pri-mary defense against infections\u2013mainly through phagocytosis, generation of toxic molecules, releaseof toxic enzymes and formation of extracellular traps\u2013neutrophils have been shown to play a role infinely regulating the development and the evolution of inflammatory and immune responses. These lat-ter neutrophil-mediated functions occur by a variety of mechanisms, including the production of newlymanufactured cytokines.Herein, we provide a general overview of the chemotactic cytokines/chemokines that neutrophils canpotentially produce, either under inflammatory/immune reactions or during their activation in moreprolonged processes, such as in tumors. We highlight recent observations generated from studyinghuman or rodent neutrophils in vitro and in vivo models. We also discuss the biological significance ofneutrophil-derived chemokines in the context of infectious, neoplastic and immune-mediated diseases.The picture that is emerging is that, given their capacity to produce and release chemokines, neutrophilsexert essential functions in recruiting, activating and modulating the activities of different leukocytepopulations