2c (immune system)

Question 1

What is an antigen?

Answer 1

A foreign protein found on the surface of cells that can generate an immune response when detected by the body.

Question 2

4 examples of antigen presenting cells

Answer 2

• phagocyte that engulfed a pathogen
• body cell invaded by a virus
• cancerous cell
• foreign transplanted material

Question 3

What is a pathogen?

Answer 3

A microrganism that causes disease

Question 4

What are the four main stages of the immune response?

Answer 4

Phagocytes engulf pathogens
phagocytes activate T cells
T cells activate B cells which divide into plasma cells
Plasma cells make more antibodies to a specific antigen

Question 5

What is the first cell in the immune system to respond to antigens?

Answer 5

Phagocytes

Question 6

Describe phagocytosis

Answer 6

• Phagocyte recognises foreign antigen
• Cytoplasm of phagocyte moves round pathogen engulfing it
• Pathogen is now contained in phagocytic vacuole in the cytoplasm of the phagocyte
• A lysosome fuses with the phagocytic vacuole and lysozymes digest (hydrolyse) pathogen
• Phagocyte presents pathogen’s antigens by sticking them on its cell surface membrane to activate other immune system cells

Question 7

What is a T cell/ T lymphocyte? where are they produced/ matured?

Answer 7

Type of white blood cell with receptor proteins on surface which bind to complimentary antigens presented to it by phagocytes which activate it
produced in bone marrow and matured in thymus gland

cell mediated response

Question 8

What is a T helper cell

Answer 8

T cell that releases chemical signals (cytokines) that activate and stimulate phagocytes and cytotoxic T cells. Also activate B cells which secrete antibodies

Question 9

What is a cytotoxic T cell?
what happens when theyre activated?

Answer 9

T cell that kills abnormal and foreign cells
once activated, proliferate to make clones specific to 1 antigen, some differentiate into long lived memory t cells
most mature to attack and destroy infected cells

Question 10

how do cytotoxic t cells destroy cells?

Answer 10

secrete perforin which forms pore in membrane of target cell
secret granzyme which enters cell through pores and activates enzymes in cell to cause cell death
pores also mean contents of cell leaks out causing death

Question 11

What is the role of B cells? where are they produced/ matured?

Answer 11

Antibody on its surface binds to complimentary antigen
This and substances released from helper T cells activated B cells (clonal selection)
Activated B cell divides into plasma cells
produced in bone marrow and matured in lymph nodes

humoral response

Question 12

What are plasma cells?

Answer 12

Clones of B cells that secrete antibodies specific to antigen
Monoclonal antibodies
Bind to antigens on surface of pathogen

Question 13

Structure of antibodies

Answer 13

Proteins
Specificity of antibody depends on variable regions which form antigen binding sites
Variable region with unique tertiary structure complimentary to specific antigen
Same constant region

Question 14

function of antibodies

Answer 14

coat pathogen so easier for phagocytes to engulf
coat pathogen to prevent entering host
bind to and neutralise toxins produced by pathogens

Question 15

What is agglutination?

Answer 15

antibodies have 2 binding sites so can bind to 2 antigens at a time. results in the clumping together of cells or particles which assists phagocytosis

Question 16

What is cellular immune response?

Answer 16

T cells and other immune system cells they interact with
Eg phagocytes

Question 17

What is humoral response?

Answer 17

B cells, clonal selection and production of monoclonal antibodies from the humoral response

Question 18

What is a primary immune response?

Answer 18

Antigen first activates immune system
Slow as not many b cells to make antibodies
Eventually enough antibody made to overcome infection but person shows symptoms
T and b cells produce memory cells which stay in body. Memory t recognise specific antigen and memory b record specific antibodies needed
Person now immune

Question 19

What does it mean to be immune?

Answer 19

have memory B cells which can divide and differentiate into plasma cells and quickly destroy pathogens before you get symptoms

Question 20

What is the secondary immune response

Answer 20

Same pathogen enters second time and immune system can produce quicker stronger immune response
Clonal selection happens quicker
Memory b cells activated and divide into plasma cells that produce antibodies
Memory t cells activated and divide into correct T cell to kill cell carrying antigen
Gets rid of pathogen before show symptoms (immune)

Question 21

what is a vaccine?
what does it contain?

Answer 21

dead or inactive part of a pathogen that stimulates an immune response
contains antigens that cause body to produce memory cells wo causing disease so immune wo symptoms

Question 22

what is herd immunity?

Answer 22

more people with vaccine means less people with disease.
vaccinated people mean it is hard to spread even to those not vaccinated so helps people who cant get vaccine

Question 23

different types of antigen in a vaccine?

Answer 23

free or attached, dead (cant replicate) or attenuated (cant cause disease but still replicate and give strongest immune response cant give to people who are immunosuppressed)

Question 24

disadvantage of taking vaccine orally

Answer 24

could be broken down by enzymes in gut or molecules may be too large to be absorbed into blood

Question 25

why may a booster vaccine be needed?

Answer 25

antigen variation and to make sure memory cells are produced or if dead antigen was used in the vaccine (produces weaker immune response)

Question 26

what is antigenic variation?

Answer 26

different antigens formed due to changes in the pathogens genes immune system cant recognise even if already been infected w that pathogen so have to start from scratch hard to develop vaccines and have to keep getting new ones

Question 27

how does antigenic variation cause people to keep getting the flu

Answer 27

antigens on surface change forming new strains memory cells from old vaccine dont recognise- immunologically distinct new vaccines have to be created

Question 28

antigenic drift vs antigenic shift

Answer 28

**antigenic drift** - small changes as virus replicates - similar so immune system may still recognise it **antigenic shift** - abrupt, major change - results in subtypes of the virus - no protection

Question 29

how vaccines make us immune 5 marks

Answer 29

vaccines contain antigens which bind to complimentary surface protein receptor of T cells T cells activate B cells which divide by mitosis producing plasma cells these release antibodies some b cells become memory cells these produce antibodies faster

Question 30

what is active immunity? What are the 2 types?

Answer 30

immune system makes own antibodies after stimulated by antigen natural- immune after catching disease artificial- immune after vaccine

Question 31

what is passive immunity? what are the 2 types?

Answer 31

immune after being given antibodies by different organism natural- from antibodies in breast milk/ from placenta artificial- injected with someone else's eg from blood donations

Question 32

contrast active and passive immunity

Answer 32

active- exposure to antigen passive- not active- takes time to be immune passive- immediate active- memory cells produced passive-not active- long term protection passive- short term as antibodies given are broken down

Question 33

what is the difference between HIV and AIDS?

Answer 33

HIV is a virus affecting immune system that leads to AIDS AIDS is a condition where immune system deteriorates and fails making someone more vulnerable to other infections

Question 34

How does HIV lead to AIDS?

Answer 34

HIV kills T helper cells (the host cells for HIV) T helper cells send chem signals that activate phagocytes, cytotoxic t cells and cells so without them, body cant produce effective immune response AIDS is developed when t cells decrease to a critically low level

Question 35

what to HIV and AIDS stand for?

Answer 35

human immunodeficiency virus acquired immune deficiency syndrome

Question 36

what is the structure of HIV?

Answer 36

core of RNA and some proteins eg reverse transcriptase capsid envelope made of membrane of host cell attachment proteins that help HIV attach to host

Question 37

how does HIV replicate?

Answer 37

attachment protein attaches to receptor molecule on cell membrane of t helper cell capsid released into cell where is uncoats and releases RNA into cells cytoplasm inside cell, reverse transcriptase is used to make complimentary strand of DNA from viral RNA template from this, double straded DNA is inserted into human DNA host cell enzymes used to make viral proteins from viral DNA in humans DNA viral proteins assembled into new viruses which bud from cell and go on to infect other cells

Question 38

3 stages of HIV

Answer 38

active infection- lots of replication and flu like symptoms clinical latency- reproduces at low levels, may be asymptomatic, with treatment, lasts decades, wo, 10 years AIDS- CD4 cells fall below 200 cells/mm2 wo treatment, survive around 3 years

Question 39

3 stages of AIDS

Answer 39

initial symptoms- minor infections of mucous membranes and recurring respiratory infections progressive- immune system cells decrease further, more susceptible to serious infections eg severe bacterial infections and tb late- very low no of immune system cells, can develop toxoplasmosis of the brain, candidiasis of the respiratory system and meningitis it is these that kill AIDS patients not HIV itself

Question 40

why cant antibiotics be used for AIDS?

Answer 40

antibiotics kill bacteria by interfering with their enzymes and ribosomes which are diff to human ones so human cells are not affected viruses dont have own enzymes and ribosomes to replicate so use humans so antibiotics cant inhibit them

Question 41

what are reverse transcriptase inhibitors?

Answer 41

antiviral drugs that inhibit reverse transcriptase as it is a virus specific enzyme so humans dont use it and arent affected HIV uses it to replicate

Question 42

no cure for HIV but what can we do?

Answer 42

antiviral drugs can slow down progression best to control spread spread via sharing infected bodily fluids (unprotected sex, sharing needles, and from mother to fetus) not all babies from HIV positive mothers are born with HIV and can reduce chance by taking antiviral drugs during pregnancy

Question 43

what is proliferation of t helper cells?

Answer 43

proliferate once activated, form clone of itself specific to same antigen, some become long lived memory t cells most mature to produce cytokines to help w immediate cell mediated response

Question 44

what are the 2 types of specific response?

Answer 44

**cell mediated** t cells secrete antibodies that remain on the surface of the cell **humoral** b cells release antibodies

Question 45

what are monoclonal antibodies?

Answer 45

antibodies with the same tertiary structure produced from plasma cells that have been isolated and cloned

Question 46

uses of monoclonal antibodies

Answer 46

target medication at particular cell types eg cancer drugs at cancer cells medical diagnosis eg pregnancy tests and identifying cancel cells ELISA testing

Question 47

how do monoclonal antibodies target drugs to cancer cells?

Answer 47

cancer cells antigens are tumour markers- not on normal body cells attach cancer drug to antibody and will bind to tumour markers accumulating only where the cancer cells are so, less side effects and cheaper

Question 48

how does a pregnancy test work?

Answer 48

application area contains antibodies complimentary to hCG, bound to coloured beads urine applied, any hCG binds to antibodies forming antigen- antibody complex. urine moves up carrying beads with it test strip has immobilised antibodies to hCG so is present, test strip turns blue as immobilised antibodies bind to hCG not present, beads pass through test area control window contains immobilised antibodies specific to mobile antibodies from reaction zone

Question 49

What is an ELISA test?

Answer 49

enzyme-linked immunosorbent assay allows you to see if patient has antibodies to a certain antigen or an antigen to a certain antibody

Question 50

describe a direct ELISA test

Answer 50

testing for presence of antigen in a sample antigens from patient bound to inside of a well antibody complimentary to antigen and with an enzyme attached is added the well is washed to remove unbound antibodies add substrate and if enzyme reacts, antibody has bound not washed away so antigen is present

Question 51

describe indirect ELISA test for antibodies eg HIV

Answer 51

antigens bound to bottom of reaction vessel and blood plasma sample added any antibodies in blood specific to antigen will bind- these are primary antibodies any unbound are washed out secondary antibodies with enzymes attached are added and bind to primary then wash out again (to avoid false positive) substrate added and reacts w enzyme. if secondary antibodies present, coloured product forms

Question 52

describe indirect ELISA test for antigens eg PSA (prostate specific antigens)

Answer 52

antibodies bound to bottom of reaction vessel and blood plasma sample added any antigens in blood specific to antibody will bind any unbound are washed out antibodies with enzymes attached are added and bind to antigens then wash out again (to avoid false positive) substrate added and reacts w enzyme. if secondary antibodies present, coloured product forms

Question 53

ethical issues of vaccines

Answer 53

tested on animals testing on humans can be risky eg have unprotected sex as think immune from HIV but vaccine may not work some dont want it but herd immunity so okay but could be unfair who receives vaccine first

Question 54

ethical issues of monoclonal antibodies

Answer 54

animals used to produce cells from which they are produced

Question 55

why might a mutation make no difference to the polypeptide structure

Answer 55

1. Triplets code for same amino acid 2. Occurs in introns /non-coding sequence