2.3 Macrophages/dendritic cells
  • Macrophage:    A monocyte that has left the circulation and settled and matured in a tissue. Macrophages are found in large quantities in the spleen, lymph nodes, alveoli, and tonsils. About 50% of all macrophages are found in the liver as Kupffer cells. They are also present in the brain as microglia, in the skin as Langerhans cells, in bone as osteoclasts, as well as in serous cavities and breast and placental tissue. Along with neutrophils, macrophages are the major phagocytic cells of the immune system. They have the ability to recognize and ingest foreign antigens through receptors on the surface of their cell membranes; these antigens are then destroyed by lysosomes. Their placement in the peripheral lymphoid tissues enables macrophages to serve as the major scavengers of the blood, clearing it of abnormal or old cells and cellular debris as well as pathogenic organisms.
  • Macrophages also serve a vital role by processing antigens and presenting them to T cells, activating the specific immune response. They also release many substances that participate in inflammation, including chemokines and cytokines, lytic enzymes, oxygen radicals, coagulation factors, and growth factors.
    • macrophage activating factor ABBR: MAF. A lymphokine that stimulates macrophages to become more effective killers of certain microbial cells. Macrophages stimulated by MAF can kill tumor cells.
    • macrophage chemotactic factor ABBR: MCF. A lymphokine released by T and B cell lymphocytes in response to an antigen. It attracts macrophages to the site of the invading antigen.
    • macrophage colony stimulating factorABBR: M- CSF. A hematopoietic growth factor that stimulates monocytes to form colonies.
    • macrophage inhibitory factor A cytokine that blocks the movement and activity of macrophages during inflammation.
    • macrophage migration inhibiting factor ABBR: MIF. A lymphokine that blocks the migration of macrophages in culture.
    • macrophage processing The mechanism by which foreign antigens are taken into the macrophage by phagocytosis and broken up.
      Part of the antigen is then displayed on the surface of the macrophage next to a histocompatibility or “self”antigen activating T lymphocytes and the specific immune response. T lymphocytes are unable to recognize or respond to most antigens without macrophage assistance.
  • dendritic cell One type of macrophage or antigen- presenting cell that helps T cells respond to foreign antigens. They are found in epithelial tissues and include the Langerhans' cells of the skin and interdigitating cells in lymph nodes; they also circulate in the blood.
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