The Immune Response

• What are the 4 mains stages of the immune response?

  1. Phagocytosis
  2. T-Cells
  3. B-Cells
  4. Antibody production
• What is a phagocyte?

  A type of white blood cell that carries out phagocytosis
• How to phagocytes work?

  • A phagocyte recognises the foreign antigen on a pathogen
  • The cytoplasm of the phagocyte engulfs the pathogen
  • The pathogen is contained in a phagocytic vacuole
  • A lysosome contains enzymes called lysozymes) fuses with the phagocytic vacuole. Lysozymes break down the pathogen and it is destroyed
  • The phagocyte sticks the antigens on its surface to activate other immune system cells and is now an antigen-presenting cell
• What is a T-Cell?

  A type of white blood cell
• How are T-cells activated?

  It has receptor proteins of its surface that bind to complementary antigens presented by phagocytosis
• What do helper T-cells do?

  • Release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells
  • And activate B-cells which secrete antibodies
• What do phagocytes and cytotoxic T-cells do?

  Kill abnormal and foreign cells
• What are B-cells also known as?

  B-lymphocytes
• What are B-Cells?

  • A type of white blood cell
  • Covered in antibodies (proteins that bind to antigens to form an antigen-antibody complex)
  • Each B-cell has a different shaped antibody on its membrane so different ones bind to different shaped antigens
• What is clonal selection?

  • When the antibody on the surface of a B-cell meets a complementary shaped antigen it binds to it
  • Clonal selection and the other substances released from helper T-cells activates the B-cell
• What do the activated B-cells do?

  Divide into plasma cells
• Antibody production:

  How are monoclonal antibodies produced?

  • Plasma cells are identical to the B-cells
  • They secrete lots of antibodies specific to the antigen
• What is agglutination?

  • Antibodies has 2 binding sites so can bind 2 pathogens at the same time
  • This means that pathogens become clumped together
• What process leads to the destruction of pathogens?

  • After agglutination
  • Phagocytes bind to antibodies and makes many pathogens undergo phagocytosis
• Structure of and antibody

  • Made up of a chain of amino acids
  • Variable region with a unique tertiary structure (due to different amino acid sequences) that is specific to one antigen
  • All antibodies have the same constant region

  
• What is a cellular response?

  • The T-cells and other immune system cells that they interact with,
  • e.g. phagocytes, form the cellular response.
• What is a Humoral response?

  B-cells, clonal selection and the production of monoclonal antibodies form the humoral response.
• Similarity between cellular and humoral responses?

  • Both are needed to remove a pathogen from the body and the responses interact with each other
  • e.g. T-cells help to activate B-cells,
  • Antibodies coat pathogens making it easier for phagocytes to engulf them.
• What is a primary response?

  • Antigen enters the body for the first time a primary response is activated
  • Slow response because there aren't any B-cells to make the antibody to bind to it
  • An infected person will show symptoms
• In the primary response what happens after being exposed to an antigen?

  • T and B cells produce memory cells
  • T cells remember specific antigens
  • B cells remember specific antibodies
  • The person is now immune
• What is a secondary response?

  If the same pathogen enters the body again the immune system will be

  • Quicker and stronger
  • Clonal selection happens faster
  • Memory B cells are activated and divide into plasma cells that produce the right antibody to the antigen
  • Memory T cells are activated and divide into the correct type of T cells to kill the cell carrying the antigen
  • An infected person will not show symptoms
• How do Cytotoxic T cells kill abnormal or infected cells?

  • Release the protein perforin
  • This embeds itself in the cell surface membrane causes pores to form
  • Any substances can enter or leave the cell
  • Causing the death of the cell
• Describe the difference between active and passive immunity (5 marks).

  • Active involves memory cells passive doesn't
  • Active involves production of antibodies by plasma cells
  • Passive involves antibody production from outside into the body
  • Active is long term because antibodies are produced
  • Passive is short term as the antibody is broken down
  • Active takes longer passive is faster