The immune system

• Describe how HIV is replicated.

  1. Attachment proteins attach to receptors on helper T cell;

  2. RNA enters cell;

  3. Reverse transcriptase converts RNA to DNA;

  4. Viral protein produced;

  5. Virus particles assembled and released from cell;
• ADCs are molecules made of a monoclonal antibody linked to a cancer drug. The process of entering the cell and the breakdown of the antibody to release the drug is very similar to phagocytosis.

  Use your knowledge of phagocytosis to describe how an ADC enters and kills the tumour cell.

  1. Cell engulfs ADC

  2. Lysosomes fuse with phagosome containing ADC;

  3. Lysozymes breakdown ADC to release the drug;
• Some of the antigens found on the surface of tumour cells are also found on the surface of healthy human cells. Use this information to explain why treatment with an ADC often causes side effects.

  1. ADC will bind to non-tumour cells;

  2. Cause death of healthy cells
• Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells).

  1. RNA converted into DNA using reverse transcriptase;

  2. DNA inserted into helper T cell DNA;

  3. DNA transcribed into HIV mRNA;

  4. HIV mRNA translated into new viral proteins for assembly into viral particles;
• Describe how a phagocyte destroys a pathogen present in the blood.

  1. Engulfs;

  2. Forming phagosome and fuses with lysosome;

  3. Enzymes hydrolyse;
• Give types of cell, other than pathogens, that can stimulate an immune response.

  1. Cells from other organisms;

  2. Cancer/tumour cells;

  3. Cells infected by virus;
• What is the role of the disulfide bridge in forming the quaternary structure of an antibody?

  Joins two different polypeptides;
• Explain how HIV affects the production of antibodies when AIDS develops in a person.

  1. No antibody produced;

  2. Because HIV destroys helper T cells;

  3. So no B cells stimulated
• In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group. Previously, the viruses infected only one species of frog.

  Suggest and explain how the viruses became able to infect other species of frog.

  1. Mutation in the viral RNA;

  2. Altered tertiary structure of the viral attachment protein;

  3. Allows attachment protein of virus to bind to receptors of other species;
• In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group. Previously, the viruses infected only one species of frog.

  Determining the genome of the viruses could allow scientists to develop a vaccine. Explain how.

  1. The scientists could identify proteins that derive from the genetic code which is the proteome

  2. They could then identify potential antigens to use in the vaccine;
• In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group. Previously, the viruses infected only one species of frog.

  Describe how the B lymphocytes of a frog would respond to vaccination against Ranavirus. You can assume that the B lymphocytes of a frog respond in the same way as B lymphocytes of a human. Do not include details of the cellular response in your answer.

  1. B cell antibody binds to viral complementary antigen;

  2. B cell clones by divides by mitosis;

  3. Plasma cells produce and release monoclonal antibodies against the virus;

  4. B cells produce memory cells;
• What is a monoclonal antibody?

  Antibodies with the same tertiary structure produced from identical B lymphocytes;
• After a disease is diagnosed, monoclonal antibodies are used in some medical treatments. Give examples of using monoclonal antibodies in a medical treatment.

  1. Carries drug to specific antigens

  2. Block antigens/receptors on cells
• Describe the role of antibodies in producing a positive result in an ELISA test.

  1. First antibody that is complementary in shape to the antigen binds to antigen forming an antibody antigen complex

  2. Second antibody with enzyme attached is added;

  3. Second antibody attaches to antigen;

  4. Substrate/solution added and colour changes;
• Describe and explain the role of antibodies in stimulating phagocytosis. Do not include details about the process of phagocytosis.

  1. Bind to antigen which causes them to become markers

  2. Antibodies cause agglutination and attract phagocytes;
• When a person is bitten by a venomous snake, the snake injects a toxin into the person. Antivenom is injected as treatment. Antivenom contains antibodies against the snake toxin. This treatment is an example of passive immunity. Explain how the treatment with antivenom works and why it is essential to use passive immunity, rather than active immunity.

  1. Passive immunity antibodies bind to the antigen and causes its destruction;

  2. Active immunity would be slower;
• Horses or rabbits can be used to produce antivenoms. When taking blood to extract antibody, 13 cm3 of blood is collected per kg of the animal's body mass. The mean mass of the horses used is 350 kg and the mean mass of the rabbits used is 2 kg Using only this information, suggest which animal would be better for the production of antivenoms. Use a calculation to support your answer.

  1. Horses because more antivenom could be collected as more blood collected;

  2. 4550 cm3 v 26 cm3 blood collected;
• During vaccination, each animal is initially injected with a small volume of venom. Two weeks later, it is injected with a larger volume of venom.

  Use your knowledge of the humoral immune response to explain this vaccination programme.

  1. B cells specific to the venom reproduce by mitosis;

  2. B cells produce plasma cells and memory cells;

  3. The first does must be small so that animals are not killed

  4. The second dose produces antibodies in secondary immune response in higher concentration and quickly
• Describe how phagocytosis of a virus leads to presentation of its antigens.

  1. Phagosome fuses with lysosome;

  2. Virus destroyed by lysozymes;

  3. Antigen from virus are displayed on the cell membrane;
• Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen.

  1. Helper T cell binds to the antigen on the antigenpresenting cell / phagocyte;

  2. This helper T cell stimulates a specific B cell;

  3. B cell clones by dividing by mitosis;

  4. Forms plasma cells that release antibodies;
• Collagen is a protein produced by cells in joints, such as the knee. Rheumatoid arthritis (RA) is an auto-immune disease. In an auto-immune disease, a person's immune system attacks their own cells. RA causes pain, swelling and stiffness in the joints. Scientists have found a virus that produces a protein very similar to human collagen.

  Suggest how the immune response to this viral protein can result in the development of RA.

  1. The antibody against virus antigen will bind to collagen;

  2. This results in the destruction of the collagen;
• What is an antigen?


  1. Foreign protein;

  2. that stimulates an immune response and the production of antibody;
• What is an antibody?

  1. A protein or immunoglobulin specific to an antigen;

  2. Produced by B cells and secreted by plasma cells;
• Bacterial meningitis is a potentially fatal disease affecting the membranes around the brain. Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis. (a) In the UK, children are vaccinated against this disease.

  Describe how vaccination can lead to protection against bacterial meningitis.

  1. Antigen on surface of N. meninigitidis binds to surface receptor on a specific B cell.

  2. Activated B cell divides by mitosis and produces clone;

  3. Division stimulated by T cells;

  4. B cells and plasma cells release antibodies;

  5. Some B cells become memory cells;

  6. Memory cells produce plasma cells which results in antibodies being produced faster
• When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how.

  1. Vaccine contains antigen from pathogen;

  2. Macrophage presents antigen on its surface;

  3. T cell with complementary receptor protein binds to antigen;

  4. T cell stimulates B cell;

  5. With complementary antibody on its surface;

  6. B cell secretes large amounts of antibody;

  7. B cell divides to form clone all secreting same antibody
• Describe the difference between active and passive immunity.

  1. Active involves memory cells, passive does not;

  2. Active involves production of antibody by plasma cells and memory cells;

  3. Passive involves antibody introduced into body from outside

  4. Active long term, because antibody produced in response to antigen;

  5. Passive short term, because antibody given is broken down;

  6. Active can take time to develop and work, passive fast acting.