Immunology

Question 1

Describe the non-specific defence mechanisms the body may launch against pathogens.

Answer 1

PHAGOCYTOSIS
1) Pathogen engulfed by the phagocyte
2) Engulfed pathogen enters cytoplasm of phagocyte in a vesicle
3) Lysosomes fuse with vesicles forming a phagolysome releasing hydrolytic digestive enzymes
4) Lysosome enzymes hydrolyse the pathogen
5) Waste materials are ejected from the cell by exocytosis

Question 2

Describe how a phagocyte destroys a pathogen present in blood

Answer 2

1) Engulfs
2) Forming a vesicle/phagosome and fuses to lysosome
3) Enzymes digest

Question 3

What is the function of memory B and T cells on a reinfection

Answer 3

Activates secondary response, allowing production of antibodies to be faster

Question 4

Give two other cells (other than a pathogen) that can stimulate an immune response

Answer 4

• cancer cells
• cells infected by a virus

Question 5

When a vaccine is given to a person, it leads to the production of antibodies against a disease causing organism. describe how

Answer 5

1) Vaccine contains antigen from pathogen
2) Macrophage presents antigens on its surface
3) T helper cells with complimentary receptor protein bind to antigen
4) T cells stimulate B cell with complimentary antibody on its surface
5) B cells divide to produce same antibody
6) B cell secretes large amounts of antibody

Question 6

Explain how the humoral response leads to immunity (3)

Answer 6

1) B cells specific to the antigen reproduce by mitosis
2) B cells produce plasma and memory cells
3) Second infection produces antibodies in larger quantities and quicker

Question 7

What is the function of the T helper cell in the cellular response

Answer 7

1) Specific T helper cell binds to antigen presenting cell
2) Releases cytokines that attract phagocytes to the area of infection
3) Release cytokines that activate cytotoxic Killer T cell
4) Activates specifically complimentary B cell
5) Form memory Th cells

Question 8

What is the function of the cytotoxic Killer T cell

Answer 8

• Locate and destroys infected body cells that present the correct antigen.
• Binds to antigen-presenting-cells
• Releases perforin which creates holes in the cell surface membrane which destroys the APC (antigen presenting cells)

Question 9

How do antibodies assist in the destruction of pathogens

Answer 9

1) AGGLUTINATION - specific antibodies bind to the antigens on pathogens and clump them together, forming antigen-antibody complex.
2) OPSONISATION - marking pathogens so phagocytes recognise and destroy the pathogen more efficiently.
3) LYSIS - Bind to antigens and lead to destruction of pathogens membrane.
4) ANTI-TOXIN & ANTI-VENOM - bind to toxins or venom to prevent these molecules from binding to their complimentary target receptors.
5) PREVENT PATHOGEN REPLICATION

Question 10

What is the secondary response

Answer 10

The activation of memory cells to produce more antibodies, more rapidly

Question 11

Describe the difference between active and passive immunity

Answer 11

1) Active involves memory cells passive does not
2) Active involves production of antibody by plasma cells/memory cells whereas passive does not;
3) Passive involves antigen introduced into body from outside source whereas active does not.
4) Active is long term because antibodies are produced in response to antigen
5) Passive is short term because antibody is broken down
6) Active takes time to develop whereas passive is fast acting

Question 12

State 2 ways that pathogens cause harm / disease?

Answer 12

• Pathogens can produce toxins which can directly damage tissue
• Pathogens can sometimes replicate inside and destroy host cells

Question 13

Define antigen

Answer 13

An antigen is a molecule (usually a protein) that stimulates an immune response that results in the production of a specific antibody. (Antibody generator)

Question 14

Describe the role of antibodies in producing a positive result in an ELISA test (4 marks)

Answer 14

1. (First) antibody binds/attaches /complementary
   (in shape) to antigen;
2. (Second) antibody with enzyme attached is
   added;
3. (Second) antibody attaches to antigen;
4. (Substrate/solution added) and colour changes;

Question 15

What is a monoclonal antibody ? (1 mark)

Answer 15

1)Type of antibody which is isolated from a single clone of B cells
2) antibody with the same tertiary structure

Question 16

What is herd immunity

Answer 16

When enough individuals in the population are vaccinated (85%), then there is little chance of the disease spreading therefore even non-vaccinated individuals will be protected.

Question 17

Describe the structure of HIV ( 4 marks )

Answer 17

1) The genetic material is two strands of RNA.
2) These are contained inside a protein coat called the capsid
3) along with an enzyme called reverse transcriptase.
4) This capsid is protected by a lipid envelope in which are embedded many attachment proteins.

Question 18

Describe how a person with HIV will develop AIDS ( if untreated )and die off secondary diseases. ( 4 marks )

Answer 18

1) High viral load leads to increased destruction of helper T cell/CD4 cells;
2) Less activation of B cells/cytotoxin T cells/phagocytes;
3) Less production of plasma cells/antibodies;
4) More able to destroy other microbes/pathogens

Question 19

Describe HIV replication

Answer 19

1. Attachment proteins attach to receptors on helper T cell/lymphocyte;
2. Nucleic acid/RNA enters cell;
3. Reverse transcriptase converts RNA to DNA;
4. Viral protein/capsid/enzymes produced;
5. Virus (particles) assembled and released (from cell);