Y12 MS - Immunity Flashcards
What is an antigen?
A molecule which triggers an immune response
What is an antibody?
A protein produced by lymphocytes in response to the presence of specific antigens
What is a pathogen?
A microorganism which causes disease
What is immunity?
When the body is resistant to a disease
What is an immune response?
The production of antibodies against specific antigens of a pathogen
What are self cells?
The body’s own cells
What are non-self cells?
Cells not from the body (may be from a pathogen, cancer or transport)
What are toxins?
The waste products released by pathogens
What kind of response is phagocytosis?
Non specific
What is the process of phagocytosis?
Phagocytes are white blood cells found in the blood and tissues
Chemical products released by abnormal cells attract them
The receptor binding points on the cell surface attach to the antigen. The phagocyte then changes shape to engulf the pathogen
Once the pathogen is engulfed it is held within a phagosome vesicle which will then fuse with a lysosome
The lysosome releases its contents and the lysozymes hydrolyse the pathogen, destroying it
Soluble products are absorbed and used by the phagocyte
Where are phagocytes produced?
The bone marrow
What types of molecules can be antigenic?
Proteins
Polysaccharides
Glycoproteins
Why does antigenic variability occur?
The shape of antigens frequently alter due to mutations which change the tertiary structure
Does the cellular response involve T lymphocytes or B lymphocytes?
T lymphocytes
Does the humoral response involve T lymphocytes or B lymphocytes?
B lymphocytes
What is exocytosis?
The release of contents from a cell
What is the process of the cell mediated response?
Pathogens which invade body cells are destroyed through phagocytosis. The phagocyte presents the antigens from the pathogen on its cell surface
T lymphocytes are activated when they bind to the specific antigen presented on the cell surface and produce cytokines to stimulate rapid cell division by mitosis
Cloned T cells can differentiate into cytotoxic cells which produce perforin, a protein which makes holes in infected cell membranes so they become permeable and die
Cloned T cells can also stimulate B cells to divide by mitosis and secrete antibodies, stimulate phagocytosis and differentiate into memory cells for a more rapid future response
What is the process of the humoral response?
A pathogen invades the body with a specific antigen. B cells recognise the antigen and small numbers with complementary antibodies bind to them
When T lymphocytes bind to the antigen of a pathogen presented on the cell surface of a phagocyte, rapid division of B cells by mitosis to form clones which produce the correct antibody
These clones of B cells can differentiate into either plasma cells which can secrete complementary antibodies to destroy the pathogen or memory cells which circulate in the blood and tissue fluid. If the pathogen invades the body again, a rapid response is made as memory cells can divide and develop into plasma cells and more memory cells
What does 1 show?
What do 2 and 3 show?
What does 5 show?
What does 4 show?
What is a vaccination?
When a dead or weakened pathogen is introduce to induce an immune response where memory cells are produced so that future infection by the same pathogen produces a more immediate immune response
What is the structure of an antibody?
An antibody has a quaternary structure with two heavy polypeptide chains bonded to two light chains by disulphide bonds
How do antibodies help destroy pathogens in the body?
When an antibody collides with a cell with non-self complementary antigens, an antigen-antibody complex is formed
As antibodies have two antigen-binding sites they can bind to more than one pathogen at a time, causing agglutination where groups of pathogens become clumped together
This attracts phagocytes to engulf and destroy the pathogens
What type of cells does the cell mediated response involve?
T cells
What type of cells does the humoral response involve?
B cells
Following cloning by mitosis, what can B cells differentiate into?
Memory cells or plasma cells
Following cloning by mitosis, what can T cells differentiate into?
Cytotoxic cells
Describe a secondary immune response
When the antigen enters the body a second time, the memory cells produced from the initial immune response quickly divide to produce more plasma cells. These plasma cells secrete antibodies complementary to the antigen
What is antigenic variation?
Where a pathogen may mutate mutate frequently so its antigens change suddenly and vaccines become ineffective against it because the antigen are no longer recognised by the immune system
What is herd immunity?
When a sufficiently large proportion of the population has been vaccinated and are therefore immune so it is more difficult for the pathogen to spread
Why may vaccinations be ineffective?
Antigenic variation
Symptoms may be hard to diagnose or trace
What is active immunity?
When an antigen enters the body and triggers a specific immune response, producing antibodies as a result
Can be naturally acquired through exposure to microbes or artificial through a vaccination
What is passive immunity?
Immunity without an immune response so no antibodies produced by the body
Can be acquired naturally by antibodies received from another organism such as via the placenta or artificially with antibodies manufactured and injected into an organism e.g monoclonal antibodies
What is the structure of HIV?
HIV is made up of two RNA strands, proteins (e.g reverse transcriptase), a capsid, attachment proteins and viral envelope consisting of a lipid bilayer and glycoproteins
HIV is a ——
Retrovirus
What is HIV transmitted by?
The direct exchange of bodily fluids such as from mother to child by breastmilk, blood donation or sharing needles
How does HIV replicate?
When HIV enters the bloodstream, it attaches its receptors onto a T cell and injects its genetic material into the cell
The HIV uses the cellular machinery to replicate itself as the viral reverse transcriptase produces DNA from the RNA of HIV so each time the cell divides, the viral genetic information is copied
After many copies are made, the host cell is destroyed by the HIV
How does HIV lead to the inability of the immune system to respond to infection
By HIV replication, T cells are destroyed meaning there is a decreased lymphocyte number. Therefore, there is reduced ability to produce antibodies against pathogens
How are monoclonal antibodies produced?
A mouse is immunised with a specific antigen and an immune response is triggered
the spleen cells are extracted from the mouse where some B cells will be producing antibodies against the antigen
B cells from the mouse and cancerous B cells which divide rapidly and indefinitely are fused with the addition of detergent to disrupt the phospholipid bilayer. This produces hybridoma cells
The cells are then placed in a culture medium where only fused cells can grow
The hybridoma cells are separated and tested for required antibody production. They are then allowed to multiply and the antibodies are collected and purified for use e.g cancer treatments, pregnancy tests
What are the uses of monoclonal antibodies?
Diagnostically
Pregnancy tests
Detecting cancer cells
Therapeutically
Targeted breast cancer treatment
Preventing blood clotting
What is an ELISA test and what are the two types?
The ELISA test is used to see whether a patient has any antibodies to a specific antigen or any antigens to a specific antibody
These can be direct (using a single antibody) or indirect (using two antibodies)
Describe an indirect ELISA test
Indirect tests for specific antibodies e.g for HIV
First the HIV antigens are bound to the bottom of a reaction vessel
A blood plasma sample is taken from the patient and added to the sample
Any HIV specific antibodies present in the sample bind to the antigens
Any other antibodies which are unbound are washed away
A second type of antibody with an enzyme attached to it is added to the reaction vessel
These secondary antibodies bind to the primary antibodies and the reaction vessel is washed again to remove any unbound antibodies
A solution containing a substrate which reacts with the enzyme attached to the secondary antibodies is added. If the secondary antibodies are present, there is a colour change indicating the patient has the HIV antibodies in their blood
Describe a direct ELISA test
A direct ELISA test can be used to test whether a patient has specific antigens in their blood plasma e.g for prostate cancer
The antibodies specific to the prostate cancer antigens are bound to the bottom of the reaction vessel
The patient blood plasma sample is added and if present, the prostate cancer antigens bind to the primary antibody. The vessel is then washed
A secondary antibody with an enzyme attached is added and will only bind if the prostate cancer antigens are present
A solution containing the substrate complementary to the enzyme attached to the secondary antibody is added and if a colour change is present, the prostate cancer antigens are present
