Section 2 - Cells: 5. Cell recognition and the immune system Flashcards
What is an infection
The interaction between pathogens and the bodies defence systems
What are the two types of defence mechanisms
- Non-specific (immediate)
- Specific (longer lasting)
What is the non-specific defence system
- Physical barriers
eg. Skin, HCl in the stomach, mucus on epithelial cells, etc. - Phagocytosis (white blood cells engulf pathogens)
What is the process of Phagocytosis
- Phagocyte is attracted to the pathogen and moves towards it
- Antigen of the pathogen binds to the cell-surface receptors on the phagocyte
- Phagosome begins to form as the pathogen is engulfed
- lysosomes move towards the phagosome, containing lysozymes (digestive enzymes)
- Lysosomes release lysosomes into the phagosome, hydrolysing the pathogen to break it down.
- Non-self antigen is presented on the surface of the phagocyte, triggering a specific immune response
Why do phagocytes have a lobed nucleus
To allow the cell to pass through blood vessels more quickly
What is a phagosome
The vesical that contains the engulfed pathogen
What enzymes hydrolyse the pathogens in phagocytosis
lysozymes, stored in the lysosomes
What happens to the products of the breakdown of pathogens in phagocytosis
- Can be absorbed by the phagocyte
- Leave by exocytosis
- Non-self antigens are presented on the cell-surface membrane
What are the two stages of the specific immune response
- Cell mediated response
- Humoral response
What are the two lymphocytes associated with the specific immune response
- T-Lymphocytes: Mature in the thymus gland
(cell-mediated response) - B-Lymphocytes: Mature in the bone marrow
(humoral response)
What is the process of the cell mediated response
- Phagocyte presents non-self antigen on it’s surface
- T-helper cell binds to the antigen
- T cell is activated and cloned by mitosis to…
- Become memory cells that circulate the blood/tissue until a future infection
- Activate cytotoxic T cells that produced perforin (protein that makes holes in the cell membrane of infected cells, killing them)
- Stimulate phagocytosis by phagocytes
- Bind to B cells to stimulate the humoral response
What is the process of the humoral response
- B cells take in foreign antigens and present them on their surface
- Activated T-Helper cells bind to these non-self antigens, stimulating the B cells to clone by mitosis to become…
- Plasma cells, producing antibodies as a primary response
- Memory cells, to produce antibodies in a future infection as a secondary response
How do the lymphocytes recognise Non-self cells as foreign
- In a foetus, around 10 million lymphocytes are constantly colliding with other cells, each with receptors complementary to different antigens
- Any lymphocytes that recognise self antigens die, or are suppressed
- In adults, lymphocytes released from the bone marrow that recognise self cells also undergo programmed cell death (apoptosis), so no clones are made
What is an antibody
Protein with a specifically shaped binding site, complementary to a specific antigen
When are antibodies produced in the immune response
Synthesised by the B Cells as part of the humoral response
How many polypeptide chains make up an amino acid
4
- 2 heavy chains
- 2 Light chains
Where is the variable region of an antibody located
At the end of the light polypeptide chains
How are the polypeptide chains joined in an antibody
Disulphide bridges, acting as hinges
How many antigen binding sites are located on each antibody
2, one at the end of each variable region
Where is the protein receptor binding site located in an antibody
At the base, on the opposite end to the antigen binding sites
How can antibodies lead to the destruction of a pathogen
- Agglutination
- Stimulate phagocytosis
What is Agglutination
When 2 pathogens bind to one antibody, and multiple antibodies can bind to one pathogen.
This causes the pathogens to clump together, preventing them from spreading throughout the body, and making them easier for phagocytes to locate
What are monoclonal antibodies
A single type of antibody that can be isolated and cloned for many uses
How are monoclonal antibodies produced
- Mouse is injected with a pathogen, triggering an immune response
- Pancreas removed and antibody producing plasma cells are harvested
- B cells are fused with Tumour cell (can replicate by binary fission), to give an hybridoma cell.
- Hybridoma is cloned, giving an endless supply of monoclonal antibodies
What are the 3 main uses of monoclonal antibodies
- Targeting medication (Direct/Indirect monoclonal antibody therapy)
- Medical diagnosis
- Pregnancy tests
What is the process of direct monoclonal antibody therapy
Antibodies specific to cancer cells are given to the patient, so bind to them an block chemical signals, preventing growth and replication
What is the process of indirect monoclonal antibody therapy
Drugs to kill cancer cells are attached to the specific antibody, and are then injected into the patient, so the when the antibodies bind to the cancer cells, they are killed
How are monoclonal antibodies used for medical diagnosis
Antibodies react with the non-self antigens to give a measure of the level of antigens in the blood
How are monoclonal antibodies used in pregnancy tests
- Human chorionic gonadotrophin (HCG) is found in the urine of pregnant women
- In the test, antibodies specific to this HCG have coloured particles attached to them, and bind to the HCG is it is present
- The ‘HCG-Antibody-colour’ complexes move along the strip until trapped in a coloured line.
What are the ethical issues with using monoclonal antibodies
- Process requires cancer to be induced in mice
Saves human life, so is justified
- Treatment for multiple sclerosis lead to several deaths
There has been many successful treatment, and
patients are warned of risks
- Human trials in 2006 lead to healthy volunteers having organ failure
Problems in trials were delt with
What is immunity
The ability of an organism to resist infection
What is passive immunity
- No direct contact with the pathogen (non-self antigen)
- Antibodies are introduced from an external source
- Short term, as body can’t produce antibodies, so will run out
What is an example of passive immunity
- Foetal immunity: Mother to baby (i.e. antibodies in breast milk)
- Anti-Venom: Introduces antibodies to kill toxins
What is active immunity
- Direct contact with the pathogen (non-self antigen)
- Stimulates an immune response, so the body produces antibodies
What is natural active immunity
- Individuals are infected with the disease, leading to an immune response, producing antibodies
- Symptoms of the condition are likely during first infection
- Long term, as memory cells can produce antibodies for years after
What is artificial active immunity
- Inducing an immune response through immunisation (i.e. Vaccines)
- Dead/inactive form of the pathogen is injected
- Memory cells are produced so allows for long term protection
What is heard immunity
Arises when a large enough proportion of the population is immune, so it is difficult for the pathogen to spread, as it is unlikely for an infected person to contact a vulnerable person
What are the features of a successful vaccination program
- Economically viable
- Few side-effects
- Sufficient means of production, transport and storage
- Means of administering the vaccine
- Possible to reach heard immunity
Why might a vaccination programme fail
- Fails to induce immunity in certain individuals
- Vaccine may cause disease/infection
- Antigenic variability: (Mutating pathogens may change antigens, so antibodies no longer work)
- No vaccines available for certain infections
- Pathogens can ‘hide’ from the immune system (in cells/out of reach of antibodies)
- Patient objections
What are some ethical issues with vaccinations
- Expensive (money could be invested in cures)
Reaching heard immunity will save lives
- Individual health risks
Greater benefits for the whole population
- Ineffective vaccines may lead to spread
Potential lives saved justify risk
- To be more effective, all should be vaccinated (compulsory?)
heard immunity can be reached with most (doesn’t have to be all)
- Side effects could cause long term damage
Symptoms of disease would be worse
- Risks during testing
Tested on animals first (raises other ethical issues)
What is HIV
Human immunodeficiency virus, causes AIDS
What is AIDS
acquired immune deficiency syndrome, caused by HIV
How does HIV replicate
- HIV enters bloodstream
- Attachment proteins bind to CD4 proteins on T-helper cells
- Capsid fuses with the T-helper cell membrane
- RNA and enzymes enter the host cell
- Enzymes reverse transcriptase converts the RNA to DNA
- New DNA moves into the host’s nucleus
- HIV DNA in the host codes for mRNA that will produce new viral proteins
- New HIV particles break away from the host with a piece of the cell-surface membrane forming the lipid envelope
What cells are usually the host of HIV replication
T-helper cells
What are the protein receptors on the T-helper cells that the HIV binds to
CD4 protein receptors
What enzyme is within the capsid that enters the host during HIV replication
reverse transcriptase
How does HIV cause AIDS
- HIV interferes with the normal functioning of the T-Helper cells
- This means the T-Helper cells can’t stimulate the production of cytotoxic T-Cells/antibodies
- Leads to the inability to fight infection (causing death)
What is the ELISA test
Enzyme link immunosorbent assay, uses antibodies to detect the presence and quantity of a protein in a sample
What is the process of the ELISA test
- Apply the sample to a surface, to which all the antigens will attach
- Wash to remove the unattached antigens
- Add the antigen specific antibody and leave to bind
- Wash to remove excess antigens
- Add a second antibody with an enzyme attached to bind to the first antibody
- Add the colourless substrate of the enzyme (enzyme causes colour change)
- Quantity of antigen present is relative to the intensity of the colour
Can detect HIV, tuberculosis, hepatitis, etc.
Why are antibiotics ineffective against viruses (eg. HIV)
- Antibiotics inhibit the enzymes required to for the peptide cross-linkages in bacterial cell walls, making the cells weaker so they bust during osmosis
- Viruses rely on host cells, and don’t have their own structures to be disrupted
+ Viruses are within the bodies cells, so can’t be reached by the antibiotics.
