Cell recognition and the immune system Flashcards
What is the definition of an antigen?
Molecules (usually proteins) that can generate an immune response when detected by the body.
What do antigens allow the immune system to detect?
- Pathogens
- Cells from other organisms of the same species
- Abnormal body cells
- Toxins
What is a pathogen?
A disease-causing microorganism (e.g bacteria, virus, and fungi)
- Bacteria cause disease by producing toxins
- Viruses cause disease by dividing in cells causing them to burst
What is a phagocyte?
A phagocyte is a type of white blood cell which carries out phagocytosis (englufment of a pathogen)
What happens during phagocytosis?
- Phagocyte e.g macrophage recognizes foreign antigens on the pathogen and binds to the antigen
- Phagocyte engulfs pathogen by surrounding it with its cell surface membrane/cytoplasm
- Pathogen contained in phagocytic vacuole in the cytoplasm of phagocyte
- Lysosome fuses with phagocytic vacuole and releases lysozymes
- These breakdown (hydrolyse/digest) the pathogen
- Phagocyte becomes antigen-presenting and stimulates specific immune response
Descirbe The cellular response?
- Phagocytes perform phagocytosis (engulf and destroy pathogen) without destroying the antigen, they place antigens on their surface, they present antigens
- T-lymphocyte (t-cells) bind to the antigen and become stimulated
- T-helper cells release chemicals signals that activate and stimulate phagocytes and cytotoxic t-cells (which kill abnormal and foreign cells)
- T-helper cells also stimulate B-cells which secrete antibodies
What is a t-lymphocyte (t-cell)?
- A T-cell (also called t-lymphocyte) is another type of white blood cell.
- It has receptor proteins on its surface which bind to complimentary antigens presented to it by phagocytes
What is the role of t-cells in the cellular response?
- T-lymphocyte (t-cells) bind to the antigen and become stimulated
- T-helper cells release chemicals signals that activate and stimulate phagocytes and cytotoxic t-cells (which kill abnormal and foreign cells)
- T-helper cells also stimulate B-cells which secrete antibodies
What forms the cellular response?
- Phagocyte
- T-cells ( t-helper, t-cytotoxic)
What forms the humoral response
B-cells
Clonal selection
Production of monoclonal antibodies
Describe what happens in the humoral response?
- When an antibody on the surface of the b cell meets a complementary-shaped antigen, it binds to it
Stimulates B cells (clonal selection)
Stimulated B cells divide into plasma cells - Plasma cells secrete lots of antibodies specific to the antigen (monoclonal antibodies)
- Antibodies bind to the antigens on the surface of the pathogen to form antigen-antibody complexes
- An antibody has two binding sites, so can bind to two pathogens at the same time so pathogens become clumped together -agglutination
- Phagocytes then bind to the antibodies and phagocytose many pathogens at once
- This process leads to the destruction of pathogens carrying this antigen in the body
Describe the primary response?
Antigen enters body for the first time
- The primary response is slow because there aren’t many B-cells that can make the antibody needed to bind to the antigen
- Therefore, infected person will show symptoms
- T and B-cells produce memory cells which remain in the body
- The person is now immune
Describe the secondary response?
- if the same pathogen enters the body again, the immune system will produce a quicker,stronger immune response (secondary response)
- Clonal selection happens faster
- Memory b cells are activated and divide into plasma cells that produce the right antibody to the antigen
- Memory t cells are activated and divide into the correct type of t cells to kill the cell carrying the antigen
- the secondary response often gets rid of the pathogen
- The secondary response often gets rid of the pathogen before u see any symptoms
What are some difference between the primary and secondary immune response?
- Speed
- Primary response involves symptoms
- Primary response involves b and t cells, secondary response involves memory cells too
- primary= first time a pathogen invade
secondary= second time same pathogen invades
What is an antibody?
- a globular protein
- made by plasma cells
- has 3 regions: variable region, hinge region, constant region
- variable region has a different shape in each antibody, contains the antigen binding sites, these bind to complementary antigens (on a pathogen) to form an antigen-antibody complex, destroying the pathogen
- hinge region gives the antibody flexibility
- constant region the same shape in all antibodies, binds to phagocytes to help with phagocytosis
What is the difference between active and passive immunity?
Active
- Requires exposure to antigen
- It takes a while for protection to develop
- Memory cells are produced
- Protection is long term
Passive
- Doesn’t require exposure to antigen
- Protection is immediate
- Memory cells aren’t produced
- Protection is short-term (because antibodies produced are broken down)
How does a vaccine produce immunity?
involves giving an injection that contains dead/weakened pathogens that carry antigens which stimulates the immune response leading to production of antibodies & memory cells
Definition of active and passive immunity?
Active = type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen
Passive = The type of immunity you get from being given antibodies made by another organism
Definition of herd immunity?
when a large proportion of the population is vaccinated, therefore most people will be immune, only a few will not be a immune, increases chance of non-immune person coming into contact with immune person, so the pathogen has no where to go, so it dies out
Ethical issues associated with the use of vaccines and monoclonal antibodies?
- Tested on animals before tested on humans -animals have a central nervous system so feel pain
- Tested on humans -volunteers may put themselves at unnecessary risk of contracting the disease because they think they’re fully protected
- Can have side effects
- Expensive- less money spent on research and treatments of other diseases
What is antigen variability?
- Change in antigen shape due to mutation
- Not recognised by t memory cells- no plasma/antibodies
- Disease symptoms felt
- Must undergo primary response again
Why are antibiotics ineffective against viruses?
Antibodies can’t enter human cells- viruses exist in its host cell
- viruses don’t have own metabolic reactions (ribosomes) which antibiotics target
(antivirals usually target virus specific enzymes)
humoral response
B cells
- Many types of B cells - each have their own specific antibody.
- The B cell with complementary antibody forms antigen-antibody complex -activates the right B cell
- selected B-cell divides/clones itself -> plasma cell
Clonal selection: only the B-cell which forms antigen-antibody complex is selected to divide into plasma cells
- Plasma cells: clones of selected B-cell with complementary antibody to pathogens antigen
- makes monoclonal antibodies
- stick pathogens together = agglutination
- phagocytes can destroy many pathogens at once
- plasma cells remain in blood as b-memory cells
