cell recognition and the immune system

• Antigens


  Molecules that can generate an immune response when detected by the body
• Types of antigens


  • Foreign antigens
  • Pathogens
  • Abnormal body cells
  • Toxins
  • Cells from other individuals of the same species
• Phagocytosis


  1. Phagocyte recognises foreign antigens

  2. Cytoplasm engulfs pathogen

  3. Pathogen contained in phagocytic vacuole

  4. Lysosome fuses, breaks down pathogen

  5. Phagocyte presents pathogen's antigen
• 1. cells


  White blood cells with receptor proteins that bond to complementary antigens presented by phagocytes
• Types of T-cells


  • Helper T-cells
  • Cytotoxic T-cells
• 1. cells


  White blood cells covered with antibodies that bind to antigens
• Clonal selection


  1. Antigen binds to B-cell antibody

  2. Substances from helper T-cells activate B-cell

  3. Activated B-cells divide into plasma cells
• Monoclonal antibodies


  Antibodies secreted by plasma cells that are specific to one antigen
• Antibodies


  • Proteins made up of chains of amino acids
  • Specificity depends on variable regions forming antigen binding sites
• Types of immune response

  • Cellular response (T-cell mediated)
  • Humoral response (B-cell mediated)
• Cellular immune response


  1. Clonal selection

  2. Antigen presenting cell binds to T-cell

  3. T-cell undergoes clonal expansion

  4. Produces killer, helper, supporter and memory T-cells
• Humoral immune response


  1. Helper T-cells produce cytokines

  2. Bind to immature B-cell membrane

  3. Stimulates B-cell maturation

  4. Mature B-cells produce plasma cells

  5. Plasma cells produce antibodies
• Primary immune response


  Antigen enters body for first time, initially slow as few B-cells, eventually produces enough antibody
• Secondary immune response


  Memory cells remain in body, react much faster when exposed to pathogen again