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From Monocytes to M1/M2 Macrophages: Phenotypical vs. Functional Differentiation

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      Abstract

      Studies on monocyte and macrophage biology and differentiation have revealed the pleiotropic activities of these cells. Macrophages are tissue sentinels that maintain tissue integrity by eliminating/repairing damaged cells and matrices. In this M2-like mode, they can also promote tumor growth. Conversely, M1-like macrophages are key effector cells for the elimination of pathogens, virally infected, and cancer cells. Macrophage differentiation from monocytes occurs in the tissue in concomitance with the acquisition of a functional phenotype that depends on microenvironmental signals, thereby accounting for the many and apparently opposed macrophage functions. Many questions arise. When monocytes differentiate into macrophages in a tissue (concomitantly adopting a specific functional program, M1 or M2), do they all die during the inflammatory reaction, or do some of them survive? Do those that survive become quiescent tissue macrophages, able to react as naïve cells to a new challenge? Or, do monocyte-derived tissue macrophages conserve a “memory” of their past inflammatory activation? This review will address some of these important questions under the general framework of the role of monocytes and macrophages in the initiation, development, resolution, and chronicization of inflammation.

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      Most cited references 225

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      Exploring the full spectrum of macrophage activation.

      Macrophages display remarkable plasticity and can change their physiology in response to environmental cues. These changes can give rise to different populations of cells with distinct functions. In this Review we suggest a new grouping of macrophage populations based on three different homeostatic activities - host defence, wound healing and immune regulation. We propose that similarly to primary colours, these three basic macrophage populations can blend into various other 'shades' of activation. We characterize each population and provide examples of macrophages from specific disease states that have the characteristics of one or more of these populations.
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        Alternative activation of macrophages.

         Siamon Gordon (2002)
        The classical pathway of interferon-gamma-dependent activation of macrophages by T helper 1 (T(H)1)-type responses is a well-established feature of cellular immunity to infection with intracellular pathogens, such as Mycobacterium tuberculosis and HIV. The concept of an alternative pathway of macrophage activation by the T(H)2-type cytokines interleukin-4 (IL-4) and IL-13 has gained credence in the past decade, to account for a distinctive macrophage phenotype that is consistent with a different role in humoral immunity and repair. In this review, I assess the evidence in favour of alternative macrophage activation in the light of macrophage heterogeneity, and define its limits and relevance to a range of immune and inflammatory conditions.
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          The chemokine system in diverse forms of macrophage activation and polarization.

          Plasticity and functional polarization are hallmarks of the mononuclear phagocyte system. Here we review emerging key properties of different forms of macrophage activation and polarization (M1, M2a, M2b, M2c), which represent extremes of a continuum. In particular, recent evidence suggests that differential modulation of the chemokine system integrates polarized macrophages in pathways of resistance to, or promotion of, microbial pathogens and tumors, or immunoregulation, tissue repair and remodeling.
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            Author and article information

            Affiliations
            1Laboratory of Innate Immunity and Cytokines, Institute of Protein Biochemistry, National Research Council , Napoli, Italy
            Author notes

            Edited by: Klaus Ley, La Jolla Institute for Allergy and Immunology, USA

            Reviewed by: Fulvio D’Acquisto, Queen Mary University of London, UK; Gaurav K. Gupta, Harvard Medical School, USA

            *Correspondence: Paola Italiani, Laboratory of Innate Immunity and Cytokines, Institute of Protein Biochemistry, National Research Council, Via Pietro Castellino 111, Napoli 80131, Italy e-mail: italianipaola@ 123456gmail.com

            This article was submitted to Inflammation, a section of the journal Frontiers in Immunology.

            Contributors
            Journal
            Front Immunol
            Front Immunol
            Front. Immunol.
            Frontiers in Immunology
            Frontiers Media S.A.
            1664-3224
            23 September 2014
            17 October 2014
            2014
            : 5
            4201108
            10.3389/fimmu.2014.00514
            Copyright © 2014 Italiani and Boraschi.

            This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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            Figures: 4, Tables: 3, Equations: 0, References: 226, Pages: 22, Words: 20250
            Categories
            Immunology
            Review Article

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