What is an antigen?
a molecule that can generate an immune response when detected by the body. - They’re usually proteins found on the surface of cells.
What is a phagocyte? e.g.?
a phagocyte is a white blood cell that engulfs pathogens (phagocytosis)
What is the first stage of immune response?
Phagoctes engulf pathogens:
- a phagocyte recorgnises the foreign antigens on a pathogen.
- the cytoplasm of the phagocte moves round the pathogen engulfing it - the phaocyte is contained in the phagocytic vacuole.
- a lysosome (organelle containing the enzymes lysozomes) fuses with the pahgocytic vacuole and the lysozomes break down (hydrolyse) the pathogen.
- the phagocyte presents the pathogens antigens on its surface to activate other immune system cells.
What is the second stage of phagocytosis?
Phagoctes activate T-cells:
- a T- lymphocyte (another white blood cell) has receptor proteins on its surface that bind with the complementary antigens presented to it by the phagocytes - this activates the T-cell
- Diff. types of T-cells respond in diff. ways:
- T Helper cells (TH cells) release chemical signals that activate and stimulate phagocytes and cytotoxic cells (TC cells), which kill abnormal foreign cells.
- TH cells also activate B-cells which secrete antibodies.
What is the third stage of immune response?
T-cells activate B-cells which divide into plasma cells:
- When an antibody on the surface of a B-lymphocyte meets a complementary shaped antigen, it binds to it, forming an antigen-antibody complex.
- This, together with the substances released from T-Helper cells, activates the b-cell. this process (when the antibody on the surface of a B-cell meets a complementary antigen) is called clonal selection.
- the activated b-cell ÷s into plasma cells.
What are the diff. types of white blood cell?
- Phagocyte
- T-lymphocte (÷ed further into T helper cellscytotoxic cells)
- B-cells
What is the fourth stage of the immune response?
Plasma calls make more antibodies to a specific antigen:
- Plasma cells are identical to the B-cells (they’re clones). They secrete loads of antibodies specific to the antigen: monoclonal antodies. They form many antigen antibody complexes.
- An antibody has two binding sites so they can bind to two pathogens at the same time- this means pathogens become clumped together (agglutination)
- Phagocytes then bind to the antibodies and phagcocytose many pathogens at once, until all cells carrying this antigen are destroyed.
Labelled diagram of an antibody
What are the different types of immune response?
- Cellular- The T-cells and other immune system cells that they interact with e.g. phagocytes.
- Humoral - B-cells, clonal selection and the production of monoclonal antibodies.
Mums is an infection caused by the mumps virus. explainn why a paerson who has already had the infection is said to be ‘immune’ to mumps.
- After being exposed to the mumps virus antigens, the persons T-cells and B-cells have produced memory cells, which will remain in the body for a long time.
- If the person is infected for a second time, the memory T-cells will recornise the specific antigen and the memory B-cells will divide to form plamsa cells, which produce specific antibodies needed to bind the antigen.
- The person is ∴ said to be immune because the immune system has the ability to respond quickly to a second infection.
Influenza is an infectious disease caused by the influenza virus. Why might the same person may catch influenza multiple times in their lifetime.
The surface antigens of the influenza virus exhibit large variability. Because the antigens change regularly, the memory cells produced from the initial infection might not recorgnise the antigens of subsequent influenza infections. These memory cells therefore do not provide immunity and the person will suffer from subsequent infections of influenza.
Give 4 types of things that the immune system can identify via the antigens found on their surface.
- pathogen
- abnormal body cells
- toxins
- cells from other indivduals of the same species (transplants)
5) Describe how the humoral and cellular immune responses interact.
E.g. T-cells (CR) are involved in the activation of B-cells (HR) and antibodies coat pathogens making it easier for phagocytes (CR) to engulf them.
7) The graph shows the concentration of the antibody to a disease in two patients infected with the disease at the same time. Patient B didn’t showany visible symptoms of the disease whilst patient A did. Explain why.
