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Antigens
- An antigen is a protein or carbohydrate on the surface of a cell which can be used for identification.
- It is used in the process of specific response.
- Lymphocytes deal with specific response.
- There are two types of lymphocytes:
(1) B-cells which are made in the bone marrow
(2) T-cells which are made in the thymus
B-Cells
- B-cells destroy a pathogen breakout through clonal selection.
- When a receptor on a B-cell compliments the antigen of a pathogen, they bind.
- After this, the B-cell clones itself grossly.
- B-memory cells are stored in the bone marrow, and B-plasma cells are used to destroy the pathogen.
- The formation of an antigen-antibody complex is called a humeral response.
T-Cells
- Cell meditated response involves T-cells.
- T-cells do not make antibodies.
- They either help the B-cells divide or they attach to the pathogen. (T-helper and T-killer cells)
Primary and Secondary Response
- An antigen enters the body for the first time, it activates the immune system - primary response.
- There are not many b-cells (because the pathogen has not been encountered before) so it is slow.
- Eventually the b-cells overcome the infection.
- The plasma cells die, but T-cells and B-cells produce memory cells which remain in the body.
- The same pathogen enters again, and the immune system produces a faster response with more antibodies - secondary response.
- This makes the secondary response faster.
Passive Immunity
- Antibodies are ready-made.
- Mother to child (in the placenta and milk)
- Artificially (injected)
- Temporary (they only last until they leave the body)
Active Immunity
- Individuals make their own antibodies.
- Long-term
- A vaccination
Vaccinations
- Vaccinations stimulate primary response so that when the actual pathogen is encountered, the secondary response is strong enough to prevent the disease from developing and reducing the incubation time.
- Types of vaccine:
(1) Live vaccines
- The pathogens in the vaccine are treated so they only divide a few times and do not create the infection.
- Mumps, rebella
(2) Dead microorganisms
- They do not cause the disease but contain the antigens to stimulate an immune response.
(3) Purified antigens
- Made by genetic engineering.
- They stimulate B-cells to produce antibodies.
- The B-Cells divide by mitosis to make plasma cells.
- They also produce memory cells for secondary response.
Herd Immunity
- If enough people are vaccinated, those who are not will be protected as they are fewer with the disease to come in contact with.
Antigenic Variation
- This is when the proteins on the outer coat of a cell change.
- Each new strain of virus has different antigens, so memory cells do not work.
Do you remember the steps of creating monoclonal antibodies in AS/A-level Biology?
Monoclonal Antibodies (Passive Immunity)
- Monoclonal antibodies are made specifically for a known antigen (epitope).
- They are artificially induced.
To make monoclonal antibodies:
- Indentify the required epitope and inject it into a mouse.
- The mouse will make complimentary B-cells with antibodies.
- Extract the B-cells from the spleen.
- Fuse the B-cells with the cancerous myeloma cell to form hybridoma.
- Grow the hybridoma then extract the antibodies.
Applications
- We use monoclonal antibodies to detect antigens. These could be self-antigens.
- Monoclonal antibodies are used in pregnancy tests.
- They can be used to treat cancer:
- Monoclonal antibodies are made to bind to the tumour markers.
- Anti-cancer drugs are attached to the antibodies.
- The drug accumulates in the body where there are cancer cells.
References:
1. https://byjus.com/biology/antigens-and-immunology/
That's the end of the topic!
Drafted by Bonnie (Biology)