3.2.4 Cell recognition and the immune system 2 Flashcards
The humoral response
-the antibodies involved are soluble in the blood and tissue fluid of the body
The humoral response
Role of B cells/lymphocytes
The humoral response
-produced in primary immune response
-B cell / lymphocyte
└has antibodies on its surface
└which are specific and complementary to only one antigen
-clonal selection
└is the selection and activation of the specific B cell
└by macrophages / antigen presenting cells /T helper cells / cytokines
-clonal expansion
└is where the selected cell divides by mitosis to form clones
-B cells differentiate and specialise
-B cells form plasma cells
└which produce antibodies
└which are, specific and complementary to the antigen
-B cells form memory cells
└memory cells are long-lived and remain in body
└they provide a secondary response
└which is a faster and stronger response to subsequent exposure of same antigen
B cells
- type of white blood cell
- covered with antibodies which are specific and complimentary to different antigens
Clonal selection
-the selection and activation of the specific B cell
└by macrophages / antigen presenting cells /T helper cells / cytokines
Clonal expansion
-where the selected cell divides by mitosis to form clones
Antibody
Definition
-large Y-shaped protein produced by B-cells/plasma cells with antigen-specific receptors
Antibody
Role in immune response (to bacterium/viruses)
-variable region binds to antigen on the surface of the pathogen
└as the variable region specific and complimentary to the antigen
-they agglutinate pathogens
-then immobilise pathogens
-they combine with pathogen to stop entry to cell
-they break wall of bacterium open (lysis)
-the constant region, attracts phagocytes and makes it easier to engulf bacterium
Antibody specificity
–why the antibody will only detect this antigen
- the antibody has a specific primary structure
- and the specific shape of the binding site
- is complimentary to and binds with the antigens (on the pathogen)
- and forms a complex between antibody and antigen
Antibody
Structure
List
Antigen-binding site Light chain Heavy chain Receptor binding site Variable region (different in different antibodies) Constant region
Antibody
Structure
-four polypeptide chains
└one long pair of chains: heavy chains
└one shorted pair of chains: light chains
-each antibody has a specific binding site which fits precisely onto a specific antigen → antigen-antibody complex
└binding site is different on different antibodies so is called a variable region
└sequence of amino acids at binding site form specific 3d shape → binds directly to specific antigen
-the rest of the antibody is known as the constant region which binds to receptors of cells such as b cells
Antibody
Structure to function
-variable region
└= antigen binding site
└the shape of the variable region is specific and complimentary to the antigen= bind to antigen
-hinge region
└allows flexibility
└so it can bind with more than one pathogen
-constant region
└to hold tertiary structure of molecule
└for binding to receptors on cells / phagocytes
-disulphide bonds
└hold polypeptide chains together
How does the antibody lead to the destruction of the antigen?
-don’t destroy them directly
└prepare antigen for destruction
What happens when the antigen is a bacterial cell?
-antibodies assist destruction in 2 ways:
└cause agglutination of the bacterial cells
└=easier for the phagocytes to locate
└serve as markers
└=stimulate phagocytes to engulf bacterial cells they are attached to
Variable region
Function
= antigen binding site
└the shape of the variable region is specific and complimentary to the antigen= bind to antigen
Hinge
Function
-allows flexibility
└so it can bind with more than one pathogen
Constant
Function
-to hold tertiary structure of molecule
└for binding to receptors on cells / phagocytes
Disulphide bonds
Function
-hold polypeptide chains together
The formation of an antigen-antibody complex
-if antigen is specific and complimentary to the antibody
└forms antigen-antibody complex
Agglutination
-as antibodies have 2 binding sites, it can attach to two pathogens at the same time
└they can clump together= agglutination
└=easier for phagocyte to engulf
Agglutination
Issues
-each antibody cam bind to more than one antigen so more than one bacterium
└=agglutination
-an issue as clotting occurs if blood transfusion is not correct
Plasma cells
-secrete antibodies to destroy antigen
└usually into blood plasma
-cells survive for a few days
└make vast quantities
EQ: Suggest three cells where you might expect to find large quantities of plasma cell
Explain why
-rough endoplasmic reticulum
└makes and transport the proteins of the antibodies
-golgi apparatus
└to sort, process and compile the proteins
-mitochondria
└to release the energy needed for such massive antibody production
Memory cells
-responsible for secondary immune response
-live longer than plasma cells (often decades / rest of life)
-circulate blood and tissue fluid
-divide rapidly into plasma cells and more memory cells when they encounter the same antigen
└the plasma cells produce antibodies needed to destroy pathogen
└new memory cells circulate for future infection
-don’t produce antibodies directly
Memory cells
Function
-long-term immunity against the original infection
-increased quantity of antibodies
└produced at faster rate than primary immune response
-ensures new infection is destroyed before it can develop enough to cause harm/symptoms
└the person is often totally unaware that they have been infected
Importance of memory cells
- memory cells remain from previous infection
- when an individual comes in contact with the antigen again
- a rapid secondary response is caused and many antibodies are produced
- which destroy the antigen before it can cause harm/symptoms
Primary immune response
- when an antigen first activates the immune response
- slower
Secondary immune response
Why faster than primary immune response
Primary immune response
-antigen of the pathogen has to be ingested, processed and presented
-helper t cells link with b cells that then clone
some cells develop into plasma cells that produce antibodies
└these processes occur consecutively and therefore take time
Secondary immune response
-memory cells already present
cloning → development into plasma cells → produce antibodies
└fewer processes means quicker response
Cell-mediated vs humeral responses to a pathogen
Cell-mediated immunity // Humoral immunity
Involves T cells // Involves mostly B cells
No antibodies // Antibodies produced
First stage of immune response // Secondary
stage of immune response after cell-mediated stage
Effective through cells // Effective through body fluids
How vaccines protect people against disease
- vaccines that contain antigens are injected
- from dead/weakened pathogens
- this means memory cells are made
- and upon second exposure memory cells recognise pathogens and become active
- by rapidly producing more antibodies
- which destroy pathogens
- when vaccinated there are fewer people to pass on the disease (herd effect)
EQ: Why were 3 injections of the vaccine given
- so there are more antigens
- and more memory cells
- so more antibodies are produced
Why high mutation rate makes it difficult to develop a vaccine
- a high mutation rate leads to antigens changing (antigenic variability)
- the vaccine contains specific antigen
- and antibodies are not complementary to changed antigen, so are unable to bind
The concept of herd immunity
-more people are immune
└fewer people carry the pathogen
-so unvaccinated people are less likely to contact infected people
EQ: why vaccinating a large number of people would reduce significantly the spread of HPV through the population
- virus is not carried in vaccinated people
- so non vaccinated people more likely to come into contact with vaccinated people
Types of immunity
- active immunity
- passive immunity
Active immunity
-immune system makes its own antibodies after being stimulated by an antigen
Active immunity
Natural
Become immune after catching a disease
Active immunity
Artificial
Become immune after been given a vaccination containing a harmless dose of antigen
Describe how an effective vaccine can produce active immunity to a disease
-injection of antigen or weakened/ dead pathogen
└ causes immune response
-pathogen is engulfed by phagocytes
└antigens are presented
-selection / production of active T cells
└which divide by mitosis to produce clones
└secretion of cytokines
└activation of B cells
-B cells divide by mitosis to produce clones
└=production of plasma cells
└which produce of antibodies
└and produce of memory cells
-memory cells remain in body
└=secondary response to infection quicker and greater
└=no symptoms when infected
Passive immunity
-type of immunity you get after being given antibodies made by a different orgamism
└immune system doesn’t make own antibodies
Passive immunity
Natural
Baby becomes immune due to antibodies it receives from mother in breast milk
Passive immunity
Artificial
Become immune after beung injected with antibodies from someone else
The differences between active and passive immunity
Active immunity/passive immunity
- requires exposure to antigen/ doesn’t require exposure to antigen
- takes a while for protection to develop/protection is immediate
- memory cells are produced/memory cells aren’t produced
- protection is long term (memory cells)/protection is short term (foreign antibodies broken down)
