Macrophages

MACROPHAGES

  • Immature macrophages are produced in the bone marrow and released into blood stream as monocytes.
  • Monocytes constitute about 5% of total blood leukocytes.
  • After circulating for several days they migrate into tissues and mature into macrophages.
  • Macrophages rarely divide and are not destroyed by radiation.
  • They have life of 3-4 months but influenced by antigenic stimulation.
  • In suspension, they are round cells of 15-20µm in diameter with a bean shaped or round single nucleus.
  • Cytoplasm is rich in mitochondria, lysosomes, rough endoplasmic reticulum and Golgi apparatus.
  • Because of their various habitats they are of various shape and sizes.
  • They differentiated into microglia (CNS), kupffer cells (liver), alveolar macrophages (lung), osteoclasts (bone), splenic macrophages, peritoneal macrophages, dendritic cells in lymphoid organs, Langerhans cells in skin and mesangial cells in kidneys etc.

Functions

  • Destroy foreign particles (phagocytosis).
  • Process antigen for the immune response.
  • Secrete several biologically reactive molecules.
  • Regulate immune response.
  • Antitumor activity.
  • Helps in wound healing.
  • Phagocytosis:
    •  Phagocytosis is the process of engulfment of a foreign particle. Macrophages act as phagocytes.
  • Macrophages as secretary cells:
    •  Macrophages secrete several bio reactive molecules (over 100 products have been identified).
    • Some important factors released by macrophages include:
      • Enzymes: Lysozyme, collagenase, proteases, and elastases.
      • Immune mediators: Interleukin-1, interferon- a and complement components.
      • Inflammatory mediators: Prostaglandins, thromboplastins, plasminogen activators etc.
  • Regulate immune response:
    • Macrophages regulate immune response mainly in three different ways
      • They present antigen to lymphocytes in correct fashion. Lymphocytes recognize antigen when it is correctly presented.
      • Macrophages regulate the doses of antigen presented to lymphocytes. 
      • Macrophages also secrete monokines and that also regulates immune response.
  • Antitumor activity:
    • Activated macrophages possess increased tumoricidal activity. Secretes tumor necrosis factor (TNFα), hydrolytic enzymes, hydrogen peroxide, super oxide, singlet oxygen, hydroxyl radicals and interleukin-I which are toxic to tumor cells and microbes.
  • Tissue reorganization and Wound healing:
    • Macrophages secrete proteases that breakdown connective tissue.
    • Once the damaged tissue is removed, macrophages secrete growth factors for fibroblast and stimulate them to secrete collagen.
    • They also secrete molecules that promote the growth of new blood vessels.
Last modified: Tuesday, 17 April 2012, 8:48 AM