topic 2C: cells and the immune system

Question 1

antigen definition

Answer 1

antigens are specific molecules (proteins, glycoprotien or glycolipid) found on the surface of all cells, where these molecules are recognised as foreign by the immune system, they stimulate an immune response leading to the production of antibodies

Question 2

how are cells identified by the immune system?

Answer 2

each type of cell has specific molecules on its surface (cell surface membrane/ cell wall), which are often proteins that have a specific tertiary structure, or glycoproteins/ glycolipids

Question 3

what types of cells and molecules can the immune system identify?

Answer 3

-pathogens (organisms causing disease) e.g. bacteria, viruses, fungi - all pathogens have a specific antigen on their surface, identified as foreign by immune system cells, which then respond to destroy the pathogen

-cells from other organisms of the same species (e.g. organ transplant, blood transfusion) - cells have antigens different to your own triggering an immune response leading to rejection of transplanted organs

-abnormal body cells e.g. tumour cells or cancer/ virus-infected cells - abnormal antigens on surface, triggers immune response

-toxins (poisonous molecules) - produced by bacteria, immune system respond to toxins as well as the pathogens that release them

Question 4

antigenic variation

Answer 4

-some pathogens have many different strains and antigens on the surface of each strain are different, as they change frequently due to genetic mutations

-the DNA in a PATHOGEN may MUTATE frequently - if a mutation occurs in a gene that leads to a difference sequence of DNA, that codes for the antigen (protein)

-a DIFFERENT SEQUENCE OF AMINO ACIDS is coded for, which changes the PRIMARY STRUCTURE of the antigen (protein)

-this alters the TERTIARY STRUCTURE of the antigen (protein) as bonds form in different places - causing it to change, resulting antigens having different 3D shapes

-as the antigens are a new shape, the previous natural immunity to this pathogen is no longer effective, as memory cells are specific to only one type of antigen

Question 5

antigenic variability in a vaccine

Answer 5

-the antigens on pathogens may MUTATE frequently and change shape due to gene mutations, so that it’s ANTIGENS CHANGE SUDDENLY rather than gradually this creates new strains

-this means vaccines suddenly become INEFFECTIVE because the new antigens on the pathogen are no long recognised by the immune system

-therefore the B MEMORY CELL receptors cannot bind to the new antigen on the secondary exposure

-therefore the immune system does not produce antibodies (the specific antibodies are not complementary and cant bind to new antigen) and to destroy the pathogen

Question 6

pathogens definition, example + cause of disease

Answer 6

• a microorganism that causes disease e.g. bacteria, viruses and fungi

-damaging host cells and releasing toxins

Question 7

describe the two different parts of the immune system

Answer 7

white blood have specific and non specific responses:
NON SPECIFIC immune response: phagocytosis

SPECIFIC immune response: lymphocytes

Question 8

phagocyte

Answer 8

a phagocyte (e.g. macrophage) is a type of white blood cell that carries out phagocytosis (engulfment of pathogens). They are found in the blood and in tissues and the first cells to respond to an immune system trigger inside the body - they carry out a non specific immune response.

Question 9

1. describe phagocytosis of pathogens

Answer 9

-the phagocyte (e.g. macrophage) recognises and binds to the foreign antigens on a pathogen
-the phagocyte ENGULFS the pathogen by surrounding it with its cell membrane
-the pathogen is contained within a PHAGOSOME VESICLE in the cytoplasm of the phagocyte
-a lysosome (contains enzymes called lyzozomes) fuses with the phagosome vesicle and releases lyzozymes (hydrolytic enzymes)
-the lyzozymes hydrolyse the pathogen
-the phagocyte then presents the pathogen’s antigen (Sticks on it’s surface to activate other immune system cells) - antigen presenting cells

Question 10

antigen presenting cells + examples

Answer 10

-phagocytosis leads to presentation of antigens where antigens are displayed on the phagocytes cell surface membrane, stimulating the SPECIFIC immune response - either cellular and humoral response

-e.g. abnormal cell (Cancerous), cells infected by virus, a macrophage which has already engulfed and destroyed a pathogen

Question 11

two types of specific immune response

Answer 11

cellular
humoral

Question 12

cellular response

Answer 12

-the cellular response is specific because t-cells respond to antigens on the surface of the ce;;s

Question 13

humoral response

Question 14

lymphocytes

Answer 14

-lymphocyte are another type of white blood cell
-important role in the specific immune response: slower in action at first, but they can provide long term immunity
-produced in the bone marrow by stem cells

TWO TYPES OF LYMPHOCYTES
-T-lymphocytes (T cells) - involved in cellular response
-B-lymphocytes (B cells) - involved in humoral response

Question 15

2. describe the response of T lymphocytes (T-cells) to a foreign antigen (cellular response) + types of different cells produced

Answer 15

-a specific HELPER T-CELLS have a complementary receptor protein on the cell surface which binds to an antigen on an antigen presenting cell
-this ACTIVATES the helper t-cell to divided rapidly by mitosis to replicate and form clones

-the cloned helper t-cells differentiate into different cells:

-remain as helper t-cells and activates B-LYMPHOCYTES which secrete antibodies and carry out humoral response

-stimulate PHAGOCYTES (macrophages) to perform more phagocytosis (engulf pathogens)

-produce CYTOTOXIC CELLS which destroys abnormal (tumour) or infected cells by releasing perforin which destroys virus infected cells

-produce more MEMORY CELLS

Question 16

3. describe the response of B lymphocytes to a foreign antigen (the humoral response) + what is clonal selection? UPTO MOCK

Answer 16

-10 million different B-cells which have antibodies on their surface complementary to 10 million different antigens - each B-cell has a different shaped antibody on its surface, so different ones bind to different shaped antigens

-b-cells recognise any free antigens, not just antigen presenting cells

CLONAL SELECTION:

-a specific B lymphocyte with a complementary receptor (antibody on surface) binds to an antigen (helper T-cell receptor), to form an antigen-antibody complex
-The B cell is ACTIVATED by the cytokines released by a specific helper T-cell
-the B cell divides by mitosis to form clones which differentiate into plasma cells and memory B cells

Question 17

4. role of B plasma cells + B memory cells UPTO MOCK

Answer 17

B PLASMA CELLS (slower + short lived - primary immune response)
-plasma cells produces and secretes large amounts of monoclonal antibodies, which are specific to the antigen

B MEMORY CELLS (faster + long lasting - secondary immune response)
-remain in the body (blood) for secondary immune response
-memory B cells divide by mitosis and produces plasma cells which release more antibodies more rapidly after the second exposure to the same antigen

Question 18

antibody definition

Answer 18

-antibodies are quaternary structure PROTEINS (4 polypeptide chains), secreted by B lymphocytes (e.g. plasma cells in response to specific antigens), they bind specifically to antigens forming antigen-antibody complexes

Question 19

antibody structure

Answer 19

-Quaternary structure proteins (4 polypeptide chains)
-the specificity of an antibody depends on its VARIABLE REGIONS, which form the antigen binding sites

-each antibody has a VARIABLE REGION with a unique tertiary structure (due to different sequence of amino acids) that’s complementary to one specific antigen
-all antibodies have the same CONSTANT REGION (doesn’t change)
-2 SHORT (light) CHAINS + 2 LONG (heavy) CHAINS

Question 20

explain how antibodies lead to the destruction of pathogens

Answer 20

-(monoclonal) antibodies bind to the antigens on the surface on the surface of the pathogen to form lots of ANTIGEN-ANTIBODY COMPLEXES (antibodies have a specific tertiary structure so binding site binds to the complementary antigen)
-an antibody has TWO BINDING SITES so can bind to TWO PATHOGENS at a time causing AGGLUTINATION, which is where pathogens become clumped together
-antibodies attract phagocytes, so phagocytes bind to the antibodies and phagocytose (engulfs) many pathogens at once
-this process leads to the DESTRUCTION of pathogens carrying this antigen in the body

Question 21

primary response (initial response to first exposure)

Answer 21

-occurs when a foreign antigen enter the body for the first time it activates the immune system, this is the primary response

-primary response is a SLOW (so antibodies are produced slowly and at a lower concentration) because there aren’t many B-cells and takes time for specific B plasma cells to activate and produce the specific antibody needed to bind to the antigen

-eventually the body will produce enough of the right antibody to overcome the infection, meanwhile the infected person will show SYMPTOMS of the disease

-MEMORY cells are produced by T and B cells -they remember the specific antibodies needed to bind the antigen

-person is now immune - immune system has the ability to respond quickly to a second infection

Question 22

secondary response (secondary response to second exposure to antigen)

Answer 22

-if the same pathogen enters the body again, the immune system will produce a FASTER, stronger response, this is the secondary response

-CLONAL SELECTION happens FASTER (so antibodies are produced faster and at a higher concentration): MEMORY B-CELLS are activated and divided rapidly by mitosis into plasma cells that produce MORE SPECIFIC ANTIBODIES MORE RAPIDLY to the specific antigen + MEMORY T-CELLS are activated and divided into the correct type of T-cells to kill the cell carrying the antigen

-the secondary response is quick so often destroys the pathogen before show any symptoms (immune to the pathogen)

Question 23

vaccine definition

Answer 23

-an injection of antigens from a dead pathogen, stimulating the production of memory cells

Question 24

explain how vaccines provide protection to individuals against disease

Answer 24

1. a specific B-LYMPHOCYTE with
   complementary receptor binds to ANTIGEN
2. a specific HELPER T-CELL binds to an ANTIGEN-PRESENTING CELL (antigen on surface of phagocyte) and STIMULATES the B-cell to go through CLONAL SELECTION: clonal expansion and differentiation
3. B lymphocyte divides by MITOSIS to form clones
4. Some differentiate into PLASMA B-CELLS which secrete ANTIBODIES complementary to the pathogens antigen + some differentiate into MEMORY B-CELLS which remain in the blood (primary response)
5. On SECONDARY EXPOSURE to antigen, memory B-cells rapidly divide by mitosis to produce plasma B-cells in large quantities
6. These antibodies FASTER and at a higher concentration
7. so the specific antibody can bind to the specific antigens, causing agglutination (clumping of pathogens together) which will encourage phagocytosis of the pathogen and destroy it
8. this happens rapidly to prevent experiencing symptoms (secondary response)

Question 25

herd immunity definition

Answer 25

a large proportion of population vaccinated against a specific pathogen, this is reducing the spread of the pathogen

Question 26

Explain how vaccines provide protections for populations against disease

Answer 26

-a large proportion of population are immune so do not become ill or get symptoms from the infection
-fewer infected people to pass the pathogen on / unvaccinated people less likely to come in contact with someone with disease

Question 27

active immunity

Answer 27

-immunity created by your immune system makes its own antibodies after initial exposure to an ANTIGEN and antibodies and memory cells are produced.

-natural: body creates its own ANTIBODIES produced and secreted by PLASMA B-CELLS and creates MEMORY CELLS
-artificial: VACCINATION (containing a harmless dose of antigen)

-SLOW acting, takes longer to develop protection, however LONG TERM IMMUNITY as antibody can be produced in response to a specific complementary antigen being present in the body again

Question 28

passive immunity

Answer 28

-this is the type of immunity you get from your body being introduced to ANTIBODIES made by a different organism - your immune system doesn’t produce any antibodies of its own. there is NO EXPOSURE to antigen, so plasma cells and memory cells are not made

NATURAL: e.g. a baby becomes immune due to the antibodies it receives from its mother through the placenta and in breast milk
ARTIFICIAL: immune after being injected with antibodies from someone else e.g. blood donations

-protection is FASTER acting but SHORT TERM IMMUNITY as antibody HYDROLYSED + no memory cells are created - as no exposure to antigen

Question 29

HIV definition + causes

Answer 29

HIV (human immunodeficiency virus) is a virus that affects the human immune system - it eventually leads to AIDS

Question 30

structure of HIV

Answer 30

-a spherical structure which contains:

-a core that contains the GENETIC MATERIAL (RNA) and some PROTEINS which are the ENZYME REVERSE TRANSCRIPTASE, which is needed for virus replication - (HIV cannot replicate itself)

-LIPID ENVELOPE - membranes stolen from the cell membrane of a previous host cell

-CAPSID - outer protein coat (enzyme reverse transcriptase)

-ATTACHMENT PROTEIN - sticking out of the envelope, helps HIV attach to the host helper T-cell

Question 31

Describe the replication of HIV in helper T cells

Answer 31

HIV can only reproduce inside the cell of the organism it has infected, HIV replicates inside the helper T-cells of the host

1. HIV attachment proteins on the virus attach to specific complementary receptors on the cell membrane of helper T cell
2. Lipid envelope fuses with cell-surface membrane, releasing capsid into helper T-cell
3. Capsid uncoats, releasing the genetic material (RNA) and enzyme reverse transcriptase
4. inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA –> makes double-stranded DNA
5. double stranded viral DNA is inserted into the helper T cell DNA
6. host cell enzymes are used Viral protein from the viral DNA enzymes are produced
   a. DNA transcribed into HIV mRNA
   b. HIV mRNA translated into new HIV proteins
7. Virus particles assembled and released from cell (via budding)

Question 32

how does HIV cause the symptoms/ development of AIDS

Answer 32

-HIV infects and kills helper T cells (host cell) by replicating rapidly insides its host helper T cells
-so T helper cells can’t stimulate cytotoxic T cells, B cells and phagocytes
-so B plasma cells can’t release as many antibodies for agglutination & destruction of pathogens
-Immune system deteriorates (worsens) as a result, the body is unable to produce an adequate immune response leading to more susceptible to (opportunistic) infections
-pathogens reproduce, release toxins and damage cells

Question 33

typical symptoms of aids?

Answer 33

-recurring respiratory disease - lung infection
-minor infections of mucous membranes (e.g. inside the nose, ears and genitals)
-weight loss
-diarrhoea

Question 34

treatment of HIV

Answer 34

-cannot be treated by antibiotics as it is a virus
-therefore antiviral drugs are used, and often changed as viruses have high mutation rate and becomes resistant to them eventually

Question 35

why antibiotics are ineffective against viruses

Answer 35

-antibiotics kills bacteria by interfering with their metabolic reactions - targetting the bacterial enzymes and ribosomes used in these reactions

viruses do not have structures which are enzymes and ribosomes they use the ones in host cells/ processes which are metabolic reactions that antibiotics inhibit:
-viruses do not have metabolic processes (eg. do not make protein) / ribosomes
-viruses do not have bacterial enzymes / murein cell wall

Question 36

What is a monoclonal antibody?

Answer 36

-Antibody produced from genetically identical / cloned B lymphocytes (plasma cells), so they have identical tertiary structure

Question 37

Explain how monoclonal antibodies can be used in medical treatments

Answer 37

Monoclonal antibody has a specific tertiary structure / binding site
-Complementary to antigen found only on a specific cell type (eg. cancer cell)
-Therapeutic drug attached to antibody
-Antibody binds to specific cell, forming antigen-antibody complex, delivering drug

Some monoclonal antibodies are also designed to block antigens / receptors on cells

Question 38

Explain how monoclonal antibodies can be used in medical diagnosis

Answer 38

MEDICAL DIAGNOSIS: screen patients for specific infections

Monoclonal antibody has a specific tertiary structure (binding site / variable region) that is complementary to a specific antigen associated with diagnosis
-the use of Dye / stain / fluorescent marker which can bind to an antibody
-antibody binds to antigen, forming antigen-antibody complex

examples vary
TREATING ILLNESS:
-targeting monoclonal antibodies to cancer cells: cancer drugs can be attached to monoclonal antibodies specific for antigens on cancer cells
-drug testing: identifies a specific drug in a urine of blood sample
MEDICAL DIAGNOSIS:
-pregnancy tests: used to detect a specific pregnancy hormone
-elisa tests

Question 39

Discuss some general ethical issues associated with the use of VACCINES and MONOCLONAL ANTIBODIES

Answer 39

FOR
-provide new, successful treatments for specific conditions eg, cancer and diabetes

AGAINST
-pre-clinical testing involving on animals in the production of monoclonal antibodies - potential harm and mistreatment (e.g. by producing cancer in mice, unfair to give them a disease) -but animals may not be killed and helps produce new drugs to reduce human suffering
-clinical trials on humans - potential harm and side-effects
-vaccines - may continue high risk activities and still develop and pass on pathogen
-use of drug - potentially dangerous side effects

Question 40

what are the two types of ELISA tests?

Answer 40

DIRECT ELISA: uses a single antibody that is complementary to the antigen you’re testing for
INDIRECT ELISA: different because it uses two different antibodies

Question 41

Explain the use of antibodies in the ELISA test to detect ANTIGENS

Answer 41

direct ELISA - testing for antigens using a known antibody

-attach sample (patients blood plasma) with potential antigens to the bottom of well
-add complementary monoclonal antibodies with enzymes attached to the well → bind to antigens if present
-wash well to remove unbound antibodies (to prevent false positive)
-add substrate → enzymes create products that cause a colour change (positive result)

Question 42

Explain the use of antibodies in the ELISA test to detect ANTIBODIES

Answer 42

INDIRECT ELISA - testing for antibodies using a known antigen
-attach specific antigens to bottom of well
-add sample (patients blood plasma) with potential antibodies, these will bind to the antigen stuck to the bottom of the well, wash well to remove any unbound antigens
-add complementary monoclonal antibodies (secondary) with enzymes attached to the well, monoclonal antibodies bind to (primary) antibodies if
present
-wash well to remove any unbound secondary antibodies
-add solution containing substrate, which reacts with enzymes to create a coloured products - if solution changes colour (positive result) indicating present antibodies

Question 43

Suggest some points to consider when evaluating methodology relating to
the use of vaccines and monoclonal antibodies

Answer 43

-SAMPLE SIZE: Was the sample size large enough to be representative?
–FACTORS WITHIN VOLUNTEERS AFFECTING: Were participants diverse in terms of age, sex, ethnicity and health status?
-PLACEBO EFFECT: Were placebo / control groups used for comparison?
-LONG TERM EFFECTS: Was the duration of the study long enough to show long-term effects?
-Was the trial DOUBLE-BLIND (neither doctor / patient knew who was given drug or placebo) to reduce bias?

Question 44

Suggest some points to consider when evaluating evidence and data
relating to the use of vaccines and monoclonal antibodies

Answer 44

-SIDE EFFECTS: What side effects were observed, and how frequently did they occur?
-Was a statistical test used to see if there was a significant difference between start & final results?
-STANDARD DEVIATIONS: Was the standard deviation of final results large, showing some people did not benefit?
-Did standard deviations of start & final results OVERLAP, showing there may not be a SIGNIFICANT DIFFERENCE?
-OPTIMUM DOSAGE: What dosage was optimum? Does increasing dose increase effectiveness enough to justify extra cost?
-COST PRODUCTION + DISTRIBUTION: Was the cost of production & distribution low enough?