2 Cells- Cell recognition & the immune system

Question 1

What do specialised cells in the immune system detect?

Answer 1

-Abnormal body cells
e.g. cancerous cells
-Pathogens (microorganisms that cause disease)
e.g. bacteria, viruses, fungi, protists
-Cells from other organism, same species
e.g. organ transplant
-Toxins (harmful substances produced by pathogens)

Question 2

What does every type of cell have on its surface that identifies it?

Answer 2

Specific molecules, like proteins

Question 3

What is an antigen?

Answer 3

Molecules (proteins and glycoproteins) that are present on the cell surface membrane of all cells and signal to the immune system if the cells are ‘foreign’

Question 4

How do antigens induce the immune response?

Answer 4

Every cell has specific antigens, which bind to complementary receptors on the cell surface membrane of immune cells. If the antigens are foreign, it’ll induce an immune response. Antigens can also signal if the cells are ‘self’ or they belong to the host organism

Question 5

In what ways does the immune system respond to antigens?

Answer 5

-Lysozymes break down foreign cells
-Phagocytosis of foreign cells
-Production of antibodies which bind to antigens and inhibit functioning of foreign cells

Question 6

What are the steps of the immune response?

Answer 6

1. Phagocytosis-
   Pathogens are ingested by phagocytes and destroyed inside
2. T cells activated by phagocytes-
   helper T cells or cytotoxic T cells, cellular response
3. B cells activated by T cells -
   divide into plasma cells, humoral response
4. Production of antibodies by plasma cells-
   (proteins that bind specific to antigens on the cell surface membrane of pathogens)

Question 7

What are the steps of phagocytosis?

Answer 7

1. Detection of antigens- foreign antigens bind to specific receptors on cell surface of phagocytes
2. Engulfing the pathogen- the phagocyte moves towards the pathogen and its cytoplasm surrounds the pathogen, engulfing it. It’s sealed in a phagosome (vacuole)
3. Digestion of the pathogen- pathogens contain lysosomes, which have proteolytic enzymes (lysozymes). A lysosome fuses with the phagosome, releasing the enzymes into it and breaking down the pathogen
4. Presenting the antigens- the pathogen antigens are transported to the phagocyte cell membrane and presented on the cell surface; these can activate other cells in the immune response

Question 8

What are the steps in the cellular immune response?

Answer 8

1. Detection of antigens- foreign antigens presented by phagocytes bind to specific receptors on the cell surface of T lymphocyte cells, activating T helper cells
2. T helper cells- activate phagocytes, T cytotoxic cells and B cells
3. T cytotoxic cells- release toxins that bind to and kill foreign and abnormal cells in the body

Question 9

What are the steps in the humoral immune response?

Answer 9

1.Activation of B cells by T helper cells.
2.Clonal selection- the correct B cell is selected with a complementary receptor to the pathogen’s antigen.
3.Clonal expansion- Once this happens, it divides, producing plasma cells- which make (monoclonal) antibodies against specific antigens
4. Agglutination- clumping the pathogens together, which are engulfed by phagocytosis and destroyed

Question 10

What are antibodies?

Answer 10

Proteins called immunoglobulins, produced by plasma cells during the immune response (monoclonal antibodies)

Question 11

What is the structure of antibodies?

Answer 11

-Each has 2 variable regions that are different; these bind specifically to specific antigens. So, 1 antibody can bind 2 antigens, allowing antigens to be clumped together in agglutination
-Each antibody has the same constant regions
-Made from 2 heavy chains (at constant region) and 2 light chains (at variable region), connected by disulphide bridge
-Hinge protein connects the variable and constant region

Question 12

What are the uses of monoclonal antibodies?

Answer 12

-Targeted medication; antigens of cancer cells signal them as abnormal. Monoclonal antibodies can be used to bind specifically to antigens on cancer cells, allowing the cancer treatment to only target the cancer cells and not harm other cells

-Medical diagnosis; antibodies attached to a dye/fluorescent and when they bind to complementary antigens= marker becomes visible. Used in pregnancy tests

Question 13

What are the steps involved in the ELISA test?

Answer 13

1. Fixing of the antigens- antigen for the infection being tested is immobilised to the bottom of the beaker
2. Addition of the blood- tested blood sample added. If the antibodies that are complementary to the antigens are in the blood, they will bind to the antigens at the bottom and form antigen-antibody complexes
3. Washing- the beaker is washed so any non-bound antibodies are removed
4. Secondary antibodies added- bound to an enzyme.
5. Solution added- If the secondary antibodies bind to the other antibodies from the blood, the enzyme will change the solution’s colour, indicating the sample is infected

Question 14

Describe the primary immune response?

Answer 14

-Slow; takes time for the antigens to be detected and specific plasma cells to activate
-Likely to show the symptoms of the pathogen, which has time to cause harm to the person before it is removed
-T cells and B cells produce memory cells after the infection, which stay in the body after infection is removed so if the person is reinfected the response is quicker

Question 15

Describe the secondary immune response?

Answer 15

-Fast; due to the presence of memory cells which quickly identify antigens and produce correct antibodies
-Stronger; more plasma cells produced more quickly
-Unlikely to show symptoms of the pathogen as it is removed before it has time to cause harm
-The person is immune