the immune system

• phagocytosis:

  1. Detection of antigens

  • Foreign antigens bind to specific receptors on the cell surface of phagocytes.
• phagocytosis:

  2) Engulfing the pathogen

  • The phagocyte moves towards the pathogen.
  • The phagocyte cytoplasm surrounds the pathogen and the pathogen is engulfed.
  • When the pathogen is engulfed, it is sealed into a phagosome (a vacuole) inside the cytoplasm.
• phagocytosis:

  3) Digestion of the pathogen

  • Phagocytes have many organelles called lysosomes that contain proteolytic enzymes.
  • A lysosome fuses with the phagosome and releases the proteolytic enzymes into the phagosome.
  • The enzymes break down the pathogen.
• phagocytosis:

  4) Presenting the antigens

  • The pathogen antigens are transported to the phagocyte cell membrane and presented on the cell surface.
  • The antigens can activate the other cells in the immune response.
• Phagocytosis is the first stage in the immune response that takes place in white blood cells called phagocytes.

  
• what is a phagosome?

  A phagosome is a membrane-bound compartment formed when a cell engulfs and internalizes a pathogen through phagocytosis.
• T lymphocytes:

  1. Detection of antigens

  • The foreign antigens presented by phagocytes bind to specific receptors on the cell surface of T lymphocyte cells.
  • Binding of the antigens activates the T helper cells.
• T lymphocytes:

  2) T helper cells

  • T helper (TH) cells are a specific type of T cell that activates several cells including:
  • Phagocytes.
  • T cytotoxic (TC) cells.
  • B cells.
• T lymphocytes:

  3) T cytotoxic cells

  • TC cells are activated by TH cells.
  • TC cells release toxins that bind to and kill foreign cells and abnormal cells in the body.
• B lymphocytes:

  1. Activation of B cells

  • TH cells activates B cells.
  • Activation of the B cells causes the B cells to divide into identical cells called plasma cells.
  • The selection of the correct B cell with a complementary receptor to a pathogen's antigen is called clonal selection.
  • Once the correct B cell has been selected, it divides multiple times to produce many identical plasma cells. Plasma cells make antibodies against specific antigens. This process is called clonal expansion.
• B lymphocytes

  2) Detection of antigens

  • B cells have specific proteins called antibodies on their cell surface membranes.
  • Each antibody is complementary (specific) to a specific antigen.
  • When an antigen binds to an antibody, an antigen-antibody complex is formed.
  • Binding of antigens to B cells also causes clonal selection.
• B lymphocytes:

  3) Plasma cells

  • Clonal selection leads to clonal expansion, which is the production of many plasma cells that have the specific antibodies for the antigens present in the body.
  • The antibodies are called monoclonal antibodies.
  • Monoclonal antibodies bind to the antigens of the pathogens.
• B lymphocytes:

  4) Agglutination

  • Agglutination 'clumps' the pathogens together.
  • The pathogens are engulfed by phagocytes via phagocytosis.
  • The pathogens are destroyed.