2.4-Immunology Flashcards
Define these Keywords:
Pathogen
Antigen
Antibody
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
- Some white blood cells are phagocytic. 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 enzymes which are released into the phagosome
- The enzymes hydrolyse the pathogen
- 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 (TC) - 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. Stimulate phagocytosis by phagocytes
c. Stimulate B-cells
- Describe how B-lymphocytes respond when they are stimulated by antigens
• A specific B-cell has 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 APC
• 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’s on the pathogen. Ultimately resulting in the pathogens being killed (e.g. phagocytosis by a macrophage)
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 faster
What is Clonal selection =
- There are many B cells that all have different antibodies on their surface.
- Only the B cell with an antibody complementary to a specific antigen is SELECTED and activated
- So only this B cell divides by mitosis (is CLONED) to produce loads of B cells with the same antibodies
Why might one type of pathogen cause the activation of more than one type of B cell and more than one type of T cell?
- All cells (including pathogens) have more than 1 type of antigen on their surface.
- B cells can also be activated by toxins (act as antigens) produced by pathogens.
Define Antibody
A protein produced by B-plasma cells which have a variable region with a shape that is complementary to a specific antigen.
What is a primary immune response?
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? And what are the consequences for an organism who encounters a pathogen with 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
The organism will not have B-memory cells with antibodies complementary to the antigens
Therefore the organism will have a new primary immune response and will experience symptoms of the disease
Why do we only get chicken pox once but we can get the flu many times?
Chicken pox
Chicken pox
1. The antigens are conserved from one generation to the next
2. Second infection is recognised by complimentary antibodies on memory B-cells
3. The secondary immune response is fast/destroys the pathogen before symptoms are felt
Flu
1. Has antigenic variability/antigens mutate from one generation to the next
2. Second infection is NOT recognised by complimentary antibodies on memory B-cells
3. The primary immune response is slow/symptoms are felt/the person contracts the disease
What is a vaccination?
- A vaccination contains dead or weakened pathogens, or antigens from them.
- The vaccination stimulates the production of plasma cells, antibodies and memory cells
Describe and explain how vaccination can lead to protection or people against bacterially caused diseases.
- 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)
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