Topic 5 - Immunity Flashcards
Antigens
Foreign atigens are proteins which trigger an immune response. Usually found on the surface of pathogensand toxins. Allow the immune system to detect the pathogens and toxins
4 stages to immune response
- Phagocytosis
- Phagocytes activate T cells
- T cells acitvate B cells which divide into plasma cells
- Plasma cells produce antibodies specific to antigen
Stage 1: Phagocytosis
- Phagocyte recognises foreign antigen on surface of pathogen
- Cytoplasm of phagocyte moves around the pathogen and causes phagocyte to engulf pathogen
- Phagocyte contains pathogen in a phagocytic vacuole inside cytoplasm
- Lysosomes (which contain lysozymes) fuse with phagocytic vacuole and lysozymes break down the pathogen
- Phagocyte then presents the antigens on its surface, to activate other immune system cells
Stage 2: Phagocytes activate T cells
- T cells have protein receptors on their surface which bind to complementary antigens presented to it by phagocyte
- This activates the T cells.
- Two types of T cells: Helper T cells, which release chemicals which activate more phagocyes and cytotoxic cells which kill abnormal and foreign cells
Stage 3: T cells activate B cells which divide into plasma cells
- B cells covered with antibodies on surface
- Antibodies on B cells bind with antigens with complementary shape
- Activates B cell (activates B cells)
- B cell now divides into plasma cells
Stage 4: Plasma cells produce antibodies specific to the antigen
- Plasma cells are clones of B cells
- Plasma cells produce antibodies called monoclonal antibodies
- These antibodies are specifc to the antigen
- These antibodies bind to the antigen on surface of pathogen forming antigen-antibody complexes
- Antibodies have 2 binding sites, allowing them to bind to two pathogens at once, causing pathogens to be clumbed together (“agglutination”)
- Phagocytes then bind to the antibodies and phagocytosis occurs to the pathogens
Structure of antibody
DIAGRAM
- Antigen-antibody binding site (all antibodies have 2)
- Variable region (all antibodies have different variable regions with different tertiary structures, complementary to a specific antigen)
- Constant region (all antibodies have same constanr region)
- Hinge protein]
- Light chain
- Heavy chain
- Disulfide bridge
Cellular immune response
Stage 1 and 2 of immune response
Humoral immune response
Stage 3 and 4 of immune response
Primary immune response
This is the first exposure to the foreign antigen. The immune system is activated. The response is slow due to low no. of B cells and therefore, less of the right antibodies produced to that specifc antigen.
However, after some time, enough of the right antibodies will be produced to the specific antigen to overcome infection. However, person will have developed symptoms of the disease
After first exposure, memory T cells and B cells are formed and remain in body for long period of time
Memory T cells remember the specific antigen and recognise it if it enters body again
Memory B cells remember the specific antibodies needed to bind to that antigen
The person is now immune. The immune system can produce a strong and quick response to that specific antigen, and it is unlikely that the person will developany symptoms
Secondary immune response
This is where the person is exposed to the pathogen for the second time. The immune response is stronger and quicker.
This is because clonal selection happens quicker. This is where B cells are activated and divide into plasma cells which then produce the right antibody to the specific antigen
Memory T cells then produce the right T cells to kill the cell carrying antigen (e.g. pathogen)
Secondary response destroys and removes pathogen before symtoms even show up.
Vaccines
- Provide immunity against a specific disease
- Contains antigens from a particular pathogen
- These antigens trigger a primary immune response and therefore, lead to formation of memory cells
- However, the pathogens do not cause disease and therefore, person does not show symptoms because the antigens are either free (not attached to pathogen) or attached to dead / attenuated (weakened) pathogen
- Vaccinations can be taken injected or taken orally. -ve of taking orally: enzymes in gut may break down the vaccine or molecules of vaccine too large to enter blood
- Herd immunity: This is where those who are not vaccinated are less likely to get the disease because, those who are vaccinated are fully protected and therefore, there are less people to catch the disease from
- Booster vaccines sometimes required (after few years) to ensure that enough memory cells are produced
Antigenic Variability
- This is where antigens on surface of pathogen change. 2. This is due to genes in the pathogen changing.
- This means that memory cells produced by the first infection will not recognise the antigens on surface of pathogen
- Primary immune response occurs which is slow. Low no. of B cells, therefore, less of right antobody produced to bind to the antigens. Infected person will show symptoms of disease
Why is there a new version of the influenza vaccine developed each year?
- Due to antigenic variability: The antigens on surface of virus change regularly. This is due to change in genes in the virus - new strains of virus formed
- Therefore, memory cells produced by the vaccine for the previous strain of the virus, will not recognise the antigens on surface of new strain
]3. The strains are immulogically distinct
Ethical issues surrounding vaccines
- Vaccines are tested on animals before humans. Some vaccines require animal based substances to be produced.
- Vaccines being tested on humans is risky. Volunteers are at risk of contracting disease. They may believe that they are fully protected
- Some people may not want to take the vaccine due to potential side effects. However, they are still protected due to herd immunity. This can be seen as unfair
- If there is an epidemic of a new disease, rush to get vaccine. Difficult decisions will need to be made regarding who to give the vaccine to first
