AS/A-level Biology - Pathogens and Immunology (2)

• 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 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.

• 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)

• 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.

• Antibodies are ready-made.
• Mother to child (in the placenta and milk)
• Artificially (injected)
• Temporary (they only last until they leave the body)

• Individuals make their own antibodies.
• Long-term
• A vaccination

• 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.

• If enough people are vaccinated, those who are not will be protected as they are fewer with the disease to come in contact with.

• 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 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:

1. Monoclonal antibodies are made to bind to the tumour markers.
2. Anti-cancer drugs are attached to the antibodies.
3. 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!

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