The immune response

• Humoral Immunity = body responds to antigens found outside of the cell (e.g. bacteria or fungi)
• Humoral Immunity:

  • B cell with complementary antibody binds to pathogen, engulfs it and processes its antigens becoming an APC
  • activated T helper cell binds to B cell APC (clonal selection)
  • T helper cell produces interleukins to activate B cell
  • B cell divides into plasma cells and B memory cells (clonal expansion)
  • plasma cells produce antibodies that fit the antigens on the pathogens surface
• Cell-mediated Immunity = responds to cells that have been changed (e.g. by a virus or mutation)
• Cell-mediated Immunity:

  • macrophages engulf pathogens, process the antigens and become APCs
  • receptors on some T helper cells will fit the antigens
  • these T helper cells become activated and release interleukins to stimulate more T cells to divide
  • these cloned T cells may develop into T memory cells, produce interleukins to stimulate phagocytosis or to stimulate B cells to divide or develop into T killer cells and destroy infected cells
• How antibodies defend the body:

  • act as opsonins (tag pathogens so the complex is engulfed by phagocytosis)
  • act as agglutinins (clump together pathogens preventing them from spreading + allowing multiple to be engulfed at once)
  • act as anti-toxins (bind to toxins produced by pathogens and make them harmless)
• T helper cells = receptors bind to antigens, produce interleukins, interleukins stimulate B cells (increases antibody production, stimulates production of other types of T cells and attracts macrophages to engulf pathogens)
• T killer cell = produce perforin which kills pathogens by creating holes in their cell membrane
• T memory cells = live for a long time, rapidly divide into T killer cells if a pathogen is encountered again
• T regulatory cells = suppress the immune system once a pathogen has been destroyed and makes sure the body recognises self antigens
• Plasma cells = produce antibodies to a particular antigen
• B effector cells = divide to form plasma cell clones
• B memory cells = enable a rapid response if a pathogen is encountered again
• Antibodies = Y-shaped glycoproteins called immunoglobulins
• Antibodies:

  • made up of polypeptide chains - two heavy chains and two light chains
  • Chains are held together by disulfide bridges
  • variable region - antigen binding site
  • constant region - same on every antibody