Topic 2.4 - Immune response Flashcards
Pathogen
A disease causing agent.
Antigen
A foreign protein or glycoprotein which stimulates an immune response
Antibody
A protein produced by B plasma cells which binds to a specific, complementary antigen
Describe how these phagocytic white blood cells destroy bacteria
Pathogen produces chemo-attractants which attract the phagocyte towards it
The phagocyte engulfs the pathogen and holds it in a vesicle called a phagosome
The phagosome membrane fuses with the membrane of lysosomes
Lysosomes contain hydrolytic enzymes called lysozymes which are released into the phagosome
The lysozymes hydrolyse the molecules the pathogen is made of
How do T-cells stimulate an immune response?
Phagocyte engulfs pathogen and presents the antigens on its cell surface membrane. It is now an Antigen Presenting Cell (APC)
Helper T-cells (TH cells) with specific shape receptors complementary to the specific antigen bind to the APC. The T-helper cells become activated.
T-helper cells secrete chemicals which activate other T-cells which have the same receptors.
T helper cells divide by mitosis.
T-helper cells:
i. Activate Cytotoxic T-cells - Produce chemicals which make the APC membrane permeable which kills the infected cell. The holes also allow toxins to get in, which will definitely kill the cell and everything in it (e.g. viruses which have invaded)
ii. Become T-memory cells - Enable rapid response to future infections by the same pathogen
b. Activate B-cells
c. Stimulate more phagocytosis by phagocytes
Describe how B-lymphocytes respond when they are stimulated by antigens
A specific B-cell has protein receptors on its surface that are complementary to a specific antigen
This specific B cell encounters the antigen on the surface of a pathogen or on the surface of an Antigen Presenting Cell
This specific B-cell engulfs and presents the antigens on its own cell surface membrane
The receptor of the activated T-helper cell binds to the complementary antigen presented on the cell surface membrane of the SPECIFIC B-cell
This activates B cell to divide by mitosis forming…
a. B plasma cells - Produce antibodies which circulate the blood and bind to the complementary antigen on the pathogen. Ultimately resulting in the pathogens being killed by agglutination.
b. B memory cells - remain in the blood so if the pathogen re-invades, these cells divide by mitosis to make B plasma cells à secondary response is much faste
What is Clonal selection
The activation of a B cell that has a specific protein receptor, which is complementary to a specific antigen.
The activated B cell divides by mitosis to produce genetically identical clones.
They then differentiate into B plasma cells and B memory cells.
What is a primary immune response?
A primary immune response occurs the first time an organism comes in contact with a specific pathogen (or antigen).
It is a relatively slow response because it takes time for;
o Clonal selection to occur to identify the T-cells with the receptors complementary to the specific antigens present
o Clonal selection to occur to identify the B-cells with the antibodies complementary to the specific antigens present
o B-cells to be activated (by TH cells) and divide by mitosis to produce plasma cells
o Plasma cells to produce antibodies
What is a secondary immune response?
A secondary immune response occurs when an organism comes into contact with a specific pathogen which it has come into contact with previously
It is faster than the primary immune response because
There are already lots of B-memory cells in the blood
The B-memory cells divide by mitosis to make plasma cells (without needing to be activated by TH cells)
So MORE antibodies are produced MORE QUICKLY
What is antigenic variability?
If a pathogen has antigenic variability it means that the genes which code for the antigen proteins mutate from one generation to the next thus the antigens change from one generation to the next
What is Herd Immunity?
Herd Immunity is when a large enough proportion of the population is vaccinated so that those who are not vaccinated are protected from the disease
What is a vaccination?
A vaccine is made from dead or weakened bacteria or antigens from them.
- B cells with complementary receptors bind to the antigen
- Specific activated T helper cells, active these B cells.
- B cells divide by mitosis to produce B-plasma cells.
- The B plasma cells release antibodies, which are complementary to the bacterial antigens
- Some B plasma cells become B memory cells
- If the person is exposed again to the antigen or pathogen, the B memory cells become active and divide by mitosis to produce B plasma cells , which produce more antibodies more quickly.
- These antibodies lead to the destruction of the pathogen before symptoms appear
- Vaccinating a large proportion of the population results in the herd effect (which means that there are fewer people to pass on the disease, so unvaccinated people are protected)
Why is Herd Immunity useful/important?
Herd immunity protects people in the population who cannot be vaccinated
What is active immunity?
Active immunity is when the antigens enter the body and the body produces its own T-cells, B-cells and antibodies
