Macrophage-activating factor

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A macrophage-activating factor (MAF) is a lymphokine or other receptor based signal that primes macrophages towards cytotoxicity to tumors, cytokine secretion, or clearance of pathogens. Similar molecules may cause development of an inhibitory, regulatory phenotype. A MAF can also alter the ability of macrophages to present MHC I antigen, participate in Th responses, and/or affect other immune responses. [1] [2]

Contents

MAFs act typically in combination to produce a specific phenotype. [2]

Macrophage activated phenotypes

Macrophages inherently display tissue and environment-dependent plasticity. [3] In addition, the phenotypes of the macrophages in a certain environment play a fundamental role in determining the immune activity and response within the tissue.

Depending on the combination of MAFs signaling to the macrophage, the macrophage’s activated phenotype becomes one of three major categories: classically activated, wound healing, or regulatory. Regulatory-phenotype macrophages have only recently been recognized as an important contributor to tissue microenvironments.

Tumor-associated macrophages may be any of these types, and they have been found to be important players in the tumor microenvironment. Analysis of the macrophage population and signaling in a tumor may provide useful clinical data. [2]

Clarifications on terminology

Classically activated macrophages

After receiving signaling from both IFNγ and TNF, macrophages acquire a phenotype with higher activity against both pathogens and tumor cells. They also secrete inflammatory cytokines. IFNγ signaling can initially originate from Natural Killer (NK) cells, but adaptive immune cells are required to sustain a population of classically activated macrophages.

Toll-like receptor agonists may also cause macrophage activation. [2]

Wound healing macrophages

Interleukin 4, secreted by granulocytes after tissue damage or by adaptive immune cells within a Th2 response, causes macrophages to secrete minimal amounts of pro-inflammatory cytokines and to have lower activity against intracellular pathogens. They also promote extracellular matrix synthesis via production of ornithine, via arginase; this is used as a precursor for extracellular matrix components. The overall result is a macrophage population that promotes wound healing. [2]

The specific roles macrophages play in the Th2 response are still under investigation. [2]

Regulatory macrophages

Glucocorticoids can contribute to the development of regulatory macrophages. These macrophages produce Interleukin 10 and inhibit immune system response (See below for Effect on cancer). Tumor-associated macrophages may contain a large population of regulatory macrophages. [2]

Effect on cancer

Initially, MAFs were thought to increase a macrophage’s cytotoxic response, allowing enhanced clearance of the tumor cells. However, they also have wider ranging effects. Chronic inflammation associated with activated macrophages may lead to the development of neoplasia, such as those found surrounding tuberculosis scars.

Dysregulation of macrophage activation may cause increased inflammation and eventual neoplasia. [2]

Moreover, macrophages infiltrating the tumor microenvironment can transition towards a regulatory phenotype. Regulatory macrophages produce Interleukin 10, which can inhibit cytotoxic responses of other lymphocytes to cancer cell antigens. The stromal reaction surrounding a tumor, as well as prostaglandins and hypoxia may play a role in this transition. [2]

Epithelial-mesenchymal transition has been found to be influenced by all types of macrophages, which cause both pro and anti-inflammatory responses that can promote EMT. [7]

Non-cytokine examples of macrophage-activating factors

Pathogenic antigens can bind to toll-like receptors that stimulate macrophage activation and response. Examples include heat shock proteins released during apoptosis, and bacterial lipopolysaccharide. [2]

Examples

Miscellaneous

It has been suggested that MAF can be formed by probiotic bacteria in a yoghurt medium. This probiotic mixture has been found to be helpful in various immune disturbances including ME/CFS. [1]

Related Research Articles

<span class="mw-page-title-main">Macrophage</span> Type of white blood cell

Macrophages are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris, and foreign substances, which do not have proteins that are specific to healthy body cells on their surface. This process is called phagocytosis, which acts to defend the host against infection and injury.

<span class="mw-page-title-main">T helper cell</span> Type of immune cell

The T helper cells (Th cells), also known as CD4+ cells or CD4-positive cells, are a type of T cell that play an important role in the adaptive immune system. They aid the activity of other immune cells by releasing cytokines. They are considered essential in B cell antibody class switching, breaking cross-tolerance in dendritic cells, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages and neutrophils. CD4+ cells are mature Th cells that express the surface protein CD4. Genetic variation in regulatory elements expressed by CD4+ cells determines susceptibility to a broad class of autoimmune diseases.

<span class="mw-page-title-main">Cell-mediated immunity</span> Immune response that does not involve antibodies

Cellular immunity, also known as cell-mediated immunity, is an immune response that does not rely on the production of antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

<span class="mw-page-title-main">Interleukin 12</span> Interleukin

Interleukin 12 (IL-12) is an interleukin that is naturally produced by dendritic cells, macrophages, neutrophils, helper T cells and human B-lymphoblastoid cells (NC-37) in response to antigenic stimulation. IL-12 belongs to the family of interleukin-12. IL-12 family is unique in comprising the only heterodimeric cytokines, which includes IL-12, IL-23, IL-27 and IL-35. Despite sharing many structural features and molecular partners, they mediate surprisingly diverse functional effects.

<span class="mw-page-title-main">Interleukin 4</span> Mammalian protein found in Mus musculus

The interleukin 4 is a cytokine that induces differentiation of naive helper T cells (Th0 cells) to Th2 cells. Upon activation by IL-4, Th2 cells subsequently produce additional IL-4 in a positive feedback loop. IL-4 is produced primarily by mast cells, Th2 cells, eosinophils and basophils. It is closely related and has functions similar to IL-13.

Interleukin 27 (IL-27) is a member of the IL-12 cytokine family. It is a heterodimeric cytokine that is encoded by two distinct genes, Epstein-Barr virus-induced gene 3 (EBI3) and IL-27p28. IL-27 is expressed by antigen presenting cells and interacts with a specific cell-surface receptor complex known as IL-27 receptor (IL-27R). This receptor consists of two proteins, IL-27Rɑ and gp130. IL-27 induces differentiation of the diverse populations of T cells in the immune system and also upregulates IL-10.

<span class="mw-page-title-main">Interleukin 19</span> Protein-coding gene in the species Homo sapiens

Interleukin 19 (IL-19) is an immunosuppressive protein that belongs to the IL-10 cytokine subfamily.

<span class="mw-page-title-main">Alveolar macrophage</span>

An alveolar macrophage, pulmonary macrophage, is a type of macrophage, a professional phagocyte, found in the airways and at the level of the alveoli in the lungs, but separated from their walls.

Understanding of the antitumor immunity role of CD4+ T cells has grown substantially since the late 1990s. CD4+ T cells (mature T-helper cells) play an important role in modulating immune responses to pathogens and tumor cells, and are important in orchestrating overall immune responses.

T helper 17 cells (Th17) are a subset of pro-inflammatory T helper cells defined by their production of interleukin 17 (IL-17). They are related to T regulatory cells and the signals that cause Th17s to actually inhibit Treg differentiation. However, Th17s are developmentally distinct from Th1 and Th2 lineages. Th17 cells play an important role in maintaining mucosal barriers and contributing to pathogen clearance at mucosal surfaces; such protective and non-pathogenic Th17 cells have been termed as Treg17 cells.

<span class="mw-page-title-main">Interleukin-4 receptor</span> Protein-coding gene in the species Homo sapiens

The interleukin 4 receptor is a type I cytokine receptor. It is a heterodimer, that is, composed of two subunits. IL4R is the human gene coding for IL-4Rα, the subunit which combines with either common gamma chain or with IL-13Rα1.

Gamma delta T cells are T cells that have a γδ T-cell receptor (TCR) on their surface. Most T cells are αβ T cells with TCR composed of two glycoprotein chains called α (alpha) and β (beta) TCR chains. In contrast, γδ T cells have a TCR that is made up of one γ (gamma) chain and one δ (delta) chain. This group of T cells is usually less common than αβ T cells. Their highest abundance is in the gut mucosa, within a population of lymphocytes known as intraepithelial lymphocytes (IELs).

<span class="mw-page-title-main">CD200</span> Protein-coding gene in the species Homo sapiens

OX-2 membrane glycoprotein, also named CD200 is a human protein encoded by the CD200 gene. CD200 gene is in human located on chromosome 3 in proximity to genes encoding other B7 proteins CD80/CD86. In mice CD200 gene is on chromosome 16.

T helper 3 cells (Th3) are a subset of T lymphocytes with immunoregulary and immunosuppressive functions, that can be induced by administration of foreign oral antigen. Th3 cells act mainly through the secretion of anti-inflammatory cytokine transforming growth factor beta (TGF-β). Th3 have been described both in mice and human as CD4+FOXP3− regulatory T cells. Th3 cells were first described in research focusing on oral tolerance in the experimental autoimmune encephalitis (EAE) mouse model and later described as CD4+CD25−FOXP3−LAP+ cells, that can be induced in the gut by oral antigen through T cell receptor (TCR) signalling.

An inflammatory cytokine or proinflammatory cytokine is a type of signaling molecule that is secreted from immune cells like helper T cells (Th) and macrophages, and certain other cell types that promote inflammation. They include interleukin-1 (IL-1), IL-6, IL-12, and IL-18, tumor necrosis factor alpha (TNF-α), interferon gamma (IFNγ), and granulocyte-macrophage colony stimulating factor (GM-CSF) and play an important role in mediating the innate immune response. Inflammatory cytokines are predominantly produced by and involved in the upregulation of inflammatory reactions.

Innate lymphoid cells (ILCs) are the most recently discovered family of innate immune cells, derived from common lymphoid progenitors (CLPs). In response to pathogenic tissue damage, ILCs contribute to immunity via the secretion of signalling molecules, and the regulation of both innate and adaptive immune cells. ILCs are primarily tissue resident cells, found in both lymphoid, and non- lymphoid tissues, and rarely in the blood. They are particularly abundant at mucosal surfaces, playing a key role in mucosal immunity and homeostasis. Characteristics allowing their differentiation from other immune cells include the regular lymphoid morphology, absence of rearranged antigen receptors found on T cells and B cells, and phenotypic markers usually present on myeloid or dendritic cells.

Immunoediting is a dynamic process that consists of immunosurveillance and tumor progression. It describes the relation between the tumor cells and the immune system. It is made up of three phases: elimination, equilibrium, and escape.

Macrophage polarization is a process by which macrophages adopt different functional programs in response to the signals from their microenvironment. This ability is connected to their multiple roles in the organism: they are powerful effector cells of the innate immune system, but also important in removal of cellular debris, embryonic development and tissue repair.

B10 cells are a sub-class of regulatory B-cells that are involved in inhibiting immune responses in both humans and mice. B10 cells are named for their ability to produce inhibitory interleukin: Interleukin-10 (IL-10). One of their unique abilities is that they suppress the innate and adaptive immune signals, making them important for regulating the inflammatory response. Like the B cell, the B10 cell requires antigen specific binding to the surface of CD5 receptor to illicit a response from the T-cell. Once an antigen binds to the CD19 receptor, immediate downregulation in B-cell receptor (BCR) signal expression occurs and mediates the release of IL-10 cytokines. In mice and humans, B10 cells are distinguishable in their expression of measurable IL-10 due to the lack of unique cell surface markers expressed by regulatory B cells. However, IL-10 competence is not limited to any one subset of B cells. B10 cells do not possess unique phenotypic markers or transcription factors for further identification. B10 cells predominantly localize in the spleen, though they are also found in the blood, lymph nodes, Peyer's patches, intestinal tissues, central nervous system, and peritoneal cavity. B10 cells proliferate during inflammatory and disease responses.

Autoinflammatory diseases (AIDs) are a group of rare disorders caused by dysfunction of the innate immune system. These responses are characterized by periodic or chronic systemic inflammation, usually without the involvement of adaptive immunity.

References

  1. 1 2 Mosser DM (February 2003). "The many faces of macrophage activation". J. Leukoc. Biol. 73 (2): 209–12. doi: 10.1189/jlb.0602325 . PMID   12554797.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Mosser DM, Edwards JP (December 2008). "Exploring the full spectrum of macrophage activation". Nat. Rev. Immunol. 8 (12): 958–69. doi:10.1038/nri2448. PMC   2724991 . PMID   19029990.
  3. ↑ Giorgio S (September 2013). "Macrophages: plastic solutions to environmental heterogeneity". Inflamm. Res. 62 (9): 835–43. doi:10.1007/s00011-013-0647-7. PMID   23872927. S2CID   253601859.
  4. ↑ Mills CD, Kincaid K, Alt JM, Heilman MJ, Hill AM (2000). "M-1/M-2 macrophages and the Th1/Th2 paradigm". J Immunol. 164 (12): 6166–73. doi: 10.4049/jimmunol.164.12.6166 . PMID   10843666.
  5. ↑ Weisser SB, et al. (2013). Generation and characterization of murine alternatively activated macrophages. Methods in Molecular Biology. Vol. 946. pp. 225–39. doi:10.1007/978-1-62703-128-8_14. ISBN   978-1-62703-127-1. PMID   23179835.
  6. ↑ Yu WG, et al. (2013). "IFN-γ-induced iNOS Expression in Mouse Regulatory Macrophages Prolongs Allograft Survival in Fully Immunocompetent Recipients". Mol. Ther. 21 (2): 409–422. doi:10.1038/mt.2012.168. PMC   3594012 . PMID   22929659.
  7. ↑ Helm O, et al. (Jan 23, 2013). "Tumor-associated macrophages exhibit pro- and anti-inflammatory properties by which they impact on pancreatic tumorigenesis". Int. J. Cancer. 135 (4): 843–61. doi: 10.1002/ijc.28736 . PMID   24458546. S2CID   205949628.
  8. ↑ DeFilippis RA, et al. (July 2012). "CD36 repression activates a multicellular stromal program shared by high mammographic density and tumor tissues". Cancer Discov. 2 (9): 826–39. doi:10.1158/2159-8290.CD-12-0107. PMC   3457705 . PMID   22777768.
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