Topic 2 - The immune system Flashcards
What are antigens ?
The immune system
Molecules, usually proteins, found on the surface of the cell that can generate an immune response when detected by the body.
What’s an antibody ?
The immune system
A protein that’s specific to an antigen. They’re secreted by plasma cells
What are antibodies made of ?
The immune system
- 2 light and 2 heavy polypeptide chains.
- which are joined by disulphide bridges. Each antibody has 2 identical binding sites at the variable region.
- The variable region is determined by the sequence of amino acids.
- The constant region is the binding site for receptors.
What do immune system cells identify ?
The immune system
pathogens, abnormal body cells, toxins and cells from different organisms of the same species.
What are pathogens ?
The immune system
organisms that cause disease.
What’s the four steps in an immune response ?
The immune system
1.Phagocytosis
2. T-cells
3. B-cells
4.plasma cells
What’s a phagocyte ?
The immune system
A type pf white blood cell that carries out phagocytosis
What’s the first stage of an immune response ?
The immune system
phagocytosis:
1.A phagocyte recognises the foreign antigens on a pathogen.
2. The cytoplasm of the phagocyte moves around the pathogen, engulfing it.
3. The pathogen is now contained in a phagosome.
4.A lysosome containing hydrolytic enzymes fuses with the phagosome and forms a phagolysosome.
5. The enzymes hydrolyse the pathogen.
6. The phagocyte presents the pathogens antigens - sticking them on its surface to activate other immune cells.
How is a T-cell activated ?
The immune system
It has receptor proteins on its surface that bind to the complimentary antigens presented to it by phagocytes. This activates the T-cell.
What are two types of T-cells ?
The immune system
helper T-cells (TH cells)
cytotoxic T-cells (Tc cells)
What’s the role of helper T-cells ?
The immune system
- Their cell surface receptors bind to the foreign antigen.
- They release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells
- They also help activate b-cells, which secrete antibodies.
What is the role of cytotoxic T-cells ?
The immune system
- Kill abnormal and foreign cells.
- Make holes in the cell surface membrane using perforins, this makes the cell membrane become freely permeable and the cell dies
What is the role of B-cells ?
The immune system
- When the antibody on the b-cells’ surface meets a complimentary antigen it binds.
- This and the substances released from the T-cells activates the B-cell: clonal selection.
- Activated B-cells then divide into plasma cells: clonal expansion.
What’s the role of plasma cells ?
The immune system
- They’re identical clones of B-cells
- they secrete lots of antibodies monoclonal antibodies specific to the antigen.
- They bind to the antigens on the pathogens surface and form lots of antigen-antibody complexes.
- Antibodies have 2 binding sites meaning they can bind to 2 pathogens at once, meaning that pathogens clump together - agglutination.
- Phagocytes then bind to the antibodies and phagocytose many pathogens at once, leading to the destruction of the antigen carrying pathogens.
What forms the cellular response ?
The immune system
T-cells and phagocytes
What forms the humoral response ?
The immune system
B-cells, clonal selection and the prodction of monoclonal anitbodies.
What is the primary response of the immune system ?
The immune system
- When an antibody enters the body for the first time it triggers an immune response:
- The response is slow because there are limited numbers of B-cells that produce the anitbody.
- Eventually the body will produce enough correct antibodies to overcome the infection.
- Meanwhile the infected person will develop syptoms.
- After being exosed to an anitgen, both T-cells and B-cells produce memory cells which remian in the body for a long time.
- Memory T-cells remember the specifc antigen and will recognise it a second time round.
- Memory B-cells remember the antibdoes needed to bind to the anitgen.
- The person is now immune and their immune system will reponse quicly to a second infection.
What is the secondry response of the immune system ?
The immune system
- If the same pathogen enters the body again the immune system will recognise the antigens and produce a faster and stronger reposne:
- Clonal selection happens faster, memory B-cells ( which remeber the right anitbodies that are needed to bind to the antigens) are activated and divide into plasma cells that produce the complimentary antibodies.
- T memory cells(which remember and recognise the anitgen) are activated and divide to produde the correct T-cells to kill the antigens.
- The pathogen is often killed before you show syptoms.
What are vaccines ?
The immune system
- antigens that are free or attached to a weakened pathogen that can be injected or orally taken.
- it causes the body to produce memory cells against the disease without causing the disease.
- you develop immunity without getting symptoms.
What is herd immunity
The immune system
both the unvaccinated and vaccinated are protected as the overall occurrence of the disease is reduced so the unvaccinated are less likely to catch the disease.
what is a disadvantage of taking vaccines orally
The immune system
the enzymes in the gut may break down the antigens.
the molecules may be too big to be absorbed into the bloodstream
why are booster vaccines given
The immune system
to ensure that memory cells are produced
what is antigenic variation
The immune system
pathogens change their surface antigens due to gene mutations.
why is antigenic variation a problem
The immune system
memory cells to the other strain of the virus do not recognise new strains so new vaccines have to be developed.
