macrophage

(noun)

A white blood cell that phagocytizes necrotic cell debris and foreign material, including viruses, bacteria, and tattoo ink. It presents foreign antigens on MHC II to lymphocytes. Part of the innate immune system.

Related Terms

Examples of macrophage in the following topics:

  • Macrophages

    • Phagocytosis is a front-line defense against pathogen attack requiring the concerted action of macrophages.
    • Macrophages are antigen presenting cells that actively phagocytose large particles .
    • Resident macrophages become adapted to perform particular functions in different organs; so that brain macrophages (microglia) are very different from alveolar macrophages of the lung, Kupffer cells of the liver, or the largest tissue macrophage population, those lining the wall of the gut.
    • The macrophage then has the task of clearing both the dead pathogens and the dead neutrophils.
    • The process of recruitment of neutrophils and macrophages involves the resident macrophages which act as sentinels.

  • Phagocyte Migration and Phagocytosis

    • Dendritic cells and macrophages, on the other hand, are not so fast, and phagocytosis can take many hours in these cells.
    • All phagocytes, and especially macrophages, exist in degrees of readiness.
    • Macrophages are usually relatively dormant in the tissues and proliferate slowly.
    • In this state, macrophages are good antigen presenters and killers.
    • When they receive signals from macrophages at the sites of inflammation, they slow down and leave the blood.

  • Superantigens

    • Parts of a bacterium or a virus are usually recognized by the macrophage cells of the immune system.
    • The macrophage ingests the foreign invaders and breaks them down.
    • Then the macrophage takes parts of the broken-down invader or other molecules that it ingested and posts the fragments on the outside of the cell using a major histocompatibility complex (MHC) to hold the fragment.
    • This excess amount of IFN-gamma is in turn what activates the macrophages.

  • Type IV (Delayed Cell-Mediated) Reactions

    • 2. activating macrophages and natural killer cells, enabling them to destroy pathogens
    • The antigen-presenting cells in this case are macrophages that secrete IL-12, which stimulates the proliferation of further CD4+ Th1 cells.
    • Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.

  • Tissue Tropism in Animal Viruses

    • T helper cells, macrophages or dendritic cells).
    • HIV has a gp120 which is precisely what the CD4 marker is on the surface of the macrophages and T cells.
    • Therefore, HIV can enter T cells and macrophages.

  • Type II (Cytotoxic) Reactions

    • These cells are recognized by macrophages or dendritic cells, which act as antigen-presenting cells.
    • These tagged cells are then recognised by natural killer (NK) cells and macrophages (recognised via IgG bound (via the Fc region) to the effector cell surface receptor, CD16 (FcγRIII)), which in turn kill these tagged cells.

  • Leishmaniasis

    • Metacyclic promastigotes that reach the puncture wound are phagocytized by macrophages and transform into amastigotes.
    • Sandflies become infected during blood meals on infected hosts when they ingest macrophages infected with amastigotes.

  • Type III (Immune Complex) Reactions

    • Large complexes can be cleared by macrophages but macrophages have difficulty in the disposal of small immune complexes.
    • The cause of damage is as a result of the action of cleaved complement anaphylotoxins C3a and C5a, which, respectively, mediate the induction of granule release from mast cells (from which histamine can cause urticaria), and recruitment of inflammatory cells into the tissue (mainly those with lysosomal action, leading to tissue damage through frustrated phagocytosis by polymorphonuclear neutrophils and macrophages).

  • The Complement System

    • The following are the basic functions of the complement: opsonization (enhancing phagocytosis of antigens); chemotaxis (attracting macrophages and neutrophils); cell lysis (rupturing membranes of foreign cells); and clumping (antigen-bearing agents).
    • But significant amounts are also produced by tissue macrophages, blood monocytes, and epithelial cells of the genitourinal tract and gastrointestinal tract.
    • Kupffer cells and other macrophage cell types help clear complement-coated pathogens.

  • Overview of the Immune System

    • Macrophages begin to fuse with, and inject its toxins into, the cancer cell.
    • As the macrophage cell becomes smooth.
    • These lumps are actually the macrophages fused within the cancer cell.