12.6 SPECIFIC IMMUNE SYSTEM

Question 1

what are antibodies?

Answer 1

• Y shaped glycoproteins called immunoglobulins
• bind to a specific antigen on the pathogen or toxin that has triggered the immune system
• there is a specific antibody for each antigen

Question 2

what is the structure of antibodies?

Answer 2

• made up of two identical long polypeptide chains (the heavy chains)
• two much shorter identical chains (the light chains)
• chains are held together by disulphide bridges within the polypeptide chains, holding them in shape

Question 3

how do antibodies bind to antigens?

Answer 3

• with a protein based ‘lock and key’ mechanism similar to the complementarity between the active site of an enzyme and its substrate
• binding site is an area of 110 amino acids on both the heavy and light chains, this is known as the variable region
• it is a different shape on each antibody and gives the antibody its specificity (the rest of the antibody is always the same, so this is called the constant region)

Question 4

what is the name given to when an antibody binds to an antigen?

Answer 4

antigen-antibody complex

Question 5

what is the point of a hinge region of an antibody?

Answer 5

• provides the molecule with flexibility
• allows it to bind two separate antigens, one of each of its antigen-binding sites

Question 6

how do antibodies defend the body?

Answer 6

1. the antibody of the antigen-antibody complex acts as an opsonin so the complex is easily engulfed and digested by phagocytes
2. most pathogens can no longer effectively invade the host cells once they are part of an antigen-antibody complex
3. antibodies act as agglutinins causing pathogens carrying antigen-antibody complexes to clump together. helps prevent them spreading through the body makes it easier for phagocytes to engulf a number of pathogens at the same time
4. antibodies can act as anti-toxins, binding to the toxins produced by pathogens and making them harmless

Question 7

what white blood cells are involved in the specific immune system?

Answer 7

• B lymphocytes
• T lymphocytes

Question 8

where are B lymphocytes found?

Answer 8

• Bone marrow (B)

Question 9

where are T lymphocytes found?

Answer 9

• Thymus gland (T)

Question 10

what are the main types of T lymphocytes?

Answer 10

• T helper cells
• T killer cells
• T memory cells
• T regulator cells

Question 11

what are T helper cells?

Answer 11

• have CD4 receptors on cell surface membranes, which bind to the surface antigens on APCs
• produce interleukins, which are a type of cytokine
• the interleukins stimulate the activity of B cells, which increases antibody production of other types of T cells and attacks and stimulates production of other types of T cells
• the interleukins attract and stimulate macrophages to ingest pathogens with antigen-antibody complexes

Question 12

what are T killer cells?

Answer 12

• destroy pathogen carrying the antigen
• produce a chemical called perforin, which kills the pathogen by making holes in the cell membrane so it is freely permeable

Question 13

what are T memory cells?

Answer 13

• live for a long time and are part of the immunological memory
• if meet an antigen a second time, they divide rapidly to form a huge number of clones of T killer cells that destroy the pathogen

Question 14

what are T regulator cells?

Answer 14

• these cells suppress the immune system, acting to control and regulate it
• stop immune response once a pathogen has been eliminated, and make sure the body recognises self antigens and does not set up an autoimmune response
• interleukins are important in this control

Question 15

what are the main types B lymphocytes?

Answer 15

• plasma cells
• B effector cells
• B memory cells

Question 16

what are plasma cells?

Answer 16

• produce antibodies to a particular antigen and release them into the circulation
• an active plasma cell only only lives for a few days but produces around 2000 antibodies per second while it is alive and active

Question 17

what are B effector cells?

Answer 17

• divide to form the plasma cell clones

Question 18

what are B memory cells?

Answer 18

• these live for a very long time and provide the immunological memory
• they are programmed to remember a specific antigen and enable the body to make a very rapid response when a pathogen carrying that antigen is encountered again

Question 19

what is cell-mediated immunity?

Answer 19

• T lymphocytes respond to the cells of an organism that have been changed in some way by antigen processing or by mutation and to cells from transplanted tissue
• particularly important against viruses and early cancers

Question 20

what happens in cell-mediated immunity?

Answer 20

1. in non-specific defence system, macrophages engulf and digest pathogens in phagocytosis. they process the antigens from the surface of the pathogen to form antigen-presenting cells (APCs)
2. receptors on some of T helper cells fit the antigens.
3. these T helper cells become activated and produce interleukins, which stimulate more T cells to divide rapidly by mitosis.
4. they form clones of identical activated T helper cells that all carry the right antigen to bind to a particular pathogen

Question 21

what may the cloned T cells do in cell-mediated immunity?

Answer 21

• develop into T memory cells
• produce interleukins that stimulate phagocytosis
• produce interleukins that stimulate B cells to divide
• stimulate the development of a clone of T killer cells that are specific for the presented antigen and then destroy infected cells

Question 22

what is humoral immunity?

Answer 22

• when the body responds to antigens found outside the cells
• produces antibodies that are soluble in the blood and tissue fluid and are not attached to cells

Question 23

what happens in humoral immunity?

Answer 23

1. activated T helper cells bind to the B cell APC. this is clonal selection - the point at which the B cell with the correct antibody is selected for cloning
2. interleukins produced by the activated T helper cells activate the B cells
3. the activated B cell divides by mitosis to give clones of plasma cells and B memory cells. this is clonal expansion
4. cloned plasma cells produce antibodies that fit the antigens on the surface of the pathogen, bind to the antigens and disable them, or act as opsonins or agglutinins. this is the primary immune response and can take days/weeks.
5. some cloned B cells develop into B memory cells. if the body is infected by the same pathogen again, the B memory cells divide rapidly to form plasma cell clones. this is the secondary immune response.

Question 24

what does the term autoimmune disease mean?

Answer 24

• when the immune system stops recognising ‘self’ cells and starts to attack healthy body tissue
• there are 80 different type
• immunosuppressant drugs may be used as treatments by preventing the immune system from working

Question 25

what are some common autoimmune diseases?

Answer 25

• Type 1 diabetes
• Rheumatoid arthritis
• lupus

Question 26

what does type 1 diabetes affect and how can it be overcome/treated?

Answer 26

• the insulin-secreting cells of the pancreas
• insulin injections, pancreas transplants, immunosuppressant drugs

Question 27

what does Rheumatoid arthritis affect and how can it be overcome/treated?

Answer 27

• joints, especially in the hands, wrists, ankles and feet
• no cure, anti-inflammatory drugs, steroids, immunosuppressants, pain relief

Question 28

what does lupus affect and how can it be overcome/treated?

Answer 28

• often affects skin and joints and causes fatigue, can attack any organ incl. liver, lungs, kidney, or brain
• no cure, anti-inflammatory drugs, steroids, immunosuppressants, pain relief