Topic 2C - Cells And The Immune System Flashcards
What is a pathogen?
A harmful microorganism that can cause disease
What do antigens allow the immune system to identify? (3)
Pathogens
Abnormal body cells
Toxins
What are antigens?
Molecules that can generate an immune response when detected by the body
What are the 4 main stages of the immune response?
Phagocytosis
T-cells
B-cells
Antibody production
What is a phagocyte?
A type of WBC that carries out phagocytosis
How does phagocytosis occur? (5 steps)
- Pathogen secretes chemicals which is detected by the pathogen
- Cytoplasm of the phagocyte moves around the pathogen and engulfs it
- The pathogen is now in the phagocytosis vesicle in the cytoplasm of the phagocyte
- A lysosome fuses with the vesicle and releases lysozymes. The lysozymes digest the pathogen
- Phagocyte then presents the pathogens antigens on its surface - this activates other immune cells. Phagocyte acts as an APC (antigen presenting cell)
What are T cells?
Another WBC - has receptor proteins on surface which bind to complimentary antigens presented by phagocytes. This activates the b cell.
What do helper T cells do?
Release chemical signals that activate and stimulate phagocytes, cytotoxic T cells and activate b cells
What do cytotoxic T cells do?
Kill abnormal and foreign cells
What do b cells do?
Secrete antibodies
What is on b cells?
Covered in antibodies - proteins that bind to antigens to form an antibody-antigen complex
What happens in clonal selection?
When a b cell meets a complimentary antigen it binds together
This, aswell as substances released from t helper cells activates the b cell
Activated b cells will divide into plasma cells
What are monoclonal antibodies?
Antibodies which are specific to the antigen - bind to the antigen on the surface of the pathogen to form lots of antigen-antibody complexes
What is agglutination?
An antibody has 2 binding sites, meaning 2 pathogens can bind at the same time and they become clumped together
State the different parts of an antibody? (6)
Variable regions
Light chain
Hinge region
Disulfide bridge
Heavy chain
Constant region
What are the 2 responses the immune response is split into?
Cellular
Humoural
What is the cellular response?
T cells and other immune cells that they interact with
What is the humoural response?
B cells, colonal selection and the production of monoclonal antibodies
Describe what happens in the primary response? (5)
Antigen enters the body for the first time
Response is slow as there aren’t many b-cells that can make the antibody needed to bind to it
Eventually body will make enough right antibody to overcome the infection
After exposure, t-cells and b-cells make memory cells
These remain for a long time in the body
What would memory t-cells do? What will memory b-cells do?
Remember the specific antigen for next time
Secrete the specific antibodies needed to bind to the antigen
What happens during the secondary response? (3)
If same pathogen enters again, response happens much quicker
Clonal selection happens faster
Memory b cells and T cells are activated
What are the the 2 types of active immunity? How do they work?
Natural - when you become immune after catching the disease
Artificial - when you become immune after receiving a vaccination
What are the 2 types of passive immunity? How do they work?
Natural - when a baby becomes immune due to the antibodies it receives from the mother
Artificial - when you become immune after being injected with antibodies from someone else
What are the differences between active immunity and passive immunity? (4)
Active:
Requires exposure to antigen
Takes a while for protection to be developed
Memory cells are produced
Protection is long term
Passive:
Doesn’t require exposure to antigen
Protection isn’t immediate
Memory cells aren’t produced
Protection short term as antibodies given are broken down
What is a vaccination?
Dead or weakened pathogen that are injected into a person to trigger an immune response
What is herd immunity?
Indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection
What are the ethical issues surrounding the use of vaccines? (4)
Vaccines are tested on animals beforehand - people may disagree with animal testing
Testing vaccine on humans can be risky
Some people dont take vaccine dune to fear of side effects, however they can still be protected via herd immunity - some people deem this as unfair
If there was a new epidemic then there would be conflict for who should get the vaccine first
What is antigenic variation?
When some pathogens change the antigens on the surface of their cell membrane
How does antigenic variation affect the production of vaccines?
Pathogen will change the antigens on its surface
This means the antibodies in the vaccine will be ineffective so it won’t stop the infection
This means new antibodies and vaccines will have to be created
What is the ELISA test?
ELISA allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody
How does an ELISA test work?
An antibody is used which has an enzyme attached to it
This enzyme can react with a substrate to produce a coloured product
This causes the solution in the reaction vessel to change colour
If a colour change is present, it shows the antigen or antibody is present in the sample being tested
What is the direct ELISA test?
Uses a single antibody that is complimentary to the antigen your testing for
Antigens from sample are bound to the inside of a well
A detection antibody (with an attached enzyme) that is complimentary to the antigen of interest is added
If the antigen of interest is present, it will be immobilised on the inside of the surface of the well and the detection antibody will bind to it
The well is then washed out to remove any unbound antibody and a substrate solution is added
If the detection antibody is present, the enzyme reacts with the substrate to give a colour change
This is a positive result
What is the indirect ELISA test
Uses 2 different antibodies
Antigen bound to well
Sample is added
Antibody in sample will stick to antigen
Well washed to remove unbound antibodies
Secondary antibody with enzyme attached is added
Secondary antibody binds to primary antibody
Well is washed to remove secondary antibody
Substrate added - if reacts colour change will be observed
What are the ethical issues surrounding the use of monoclonal antibodies?
Often involve animal rights issues - animals used to produce the cells from which monoclonal antibodies are produced
What is HIV?
A virus that affects the human immune system
What does HIV do?
Infect and kill helper t-cell, these act as hosts
Helper T cells send signals which activate phagocytosis, b-cells and cytotoxic T cells
Without enough T cells the immune system is unable to deliver an effective response
When helper T cells get critically low
What are the symptoms of AIDS?
Initial symptoms include minor infections of mucous membranes
As aids progresses, more serious infections occur such as chronic diarrhoea, severe bacterial infections and Tb
During late stages, parasite infections and a fungal infection
Label the structure of HIV and explain each
Capsid
Nuclear envelope - made of membrane from cell membrane of previous host cell
Attachment protein - attach to host t-helper cell
RNA
Reverse transcriptase - needed for viral replication
Explain the process of HIV replication (6)
- The attachment protein attaches to a receptor on the cell membrane on the host helper T cell
- Capsid is released into the cell, where it uncoats and releases the genetic material into the cells cytoplasm
- Inside the cell, reverse transcriptase is used to make a complimentary strand of DNA
- From this, double stranded DNA is made and inserted into human DNA
- Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
- The viral proteins are assembled into new viruses, which go and infect other cells
