5.3 T lymphocytes and cell mediated immunity

• an antigen is any part of an organism that is recognised as non-self by the immune system and stimulates an immune response
• lymphocytes are produced by stem cells in the bone marrow
• B lymphocytes mature in the bone marrow
• T lymphocytes mature in the thymus gland
• cell-mediated immunity involves body cells
• humoral immunity involves antibodies
• cells that display foreign antigens on their surface are called antigen-presenting cells
• T lymphocytes will only respond to antigens that are presented on a body cell
• cell-mediated response:

  1. pathogen invade body cells
  2. cell places antigens from the pathogen on its surface membrane
  3. receptors on a specific helper T cell fit onto these antigens
  4. this attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
• the cloned T cells can:

  1. develop into memory cells which enable a rapid response to future infections by the same pathogen
  2. stimulate phagocytes to engulf pathogens by phagocytosis
  3. stimulates B cells to divide and secrete their antibodies
  4. activate cytotoxic T cells
• cytotoxic T cells kill abnormal cells and infected body cells by producing a protein that makes holes in the surface membrane