Immunology Flashcards
What does the immune system identify
- pathogens
- cells from other organisms of the same species
- abnormal body cells
- cells infected with viruses
- toxins
Define antigen
An antigen is a foreign protein ( glycoprotein) that stimulates the production of antibodies
What are the 4 main stages of the immune response
- Phagocytes engulf pathogens
- Phagocytes activate T cells
- T cells activate B cells which divide into plasma cells
- Plasma cells make more antibodies to a specific antigen
What is a phagocyte
A type of white blood cell that carries out phagocytosis. They are found in the blood and I’m the tissues and are the first cells to respond to an immune system trigger inside the body. It only targets cells dependant on the antigen it has - these cells are complimentary to the receptor on the cell surface membrane of phagocytes.
What happens during phagocytosis
- A phagocytes recognises the foreign antigens on a pathogen and engulfs the pathogen,as the cytoplasm moves round the pathogen, forming a vehicle called a phagosome, which then fuses with a lysosome
- The bacteria/ virus is destroyed by lysozymes ( from the lysosome ) and releases other hydrolytic enzymes
- Phagocytosis can result in the production of antigen presenting cells ( e.g. macrophages ) where antigens from the bacteria/virus are displayed on the cell surface membrane
What is the cellular immune response
The T cells and other immune system cells they interact with ( phagocytes ) form the cellular response
What is the humoral immune response
B-cells, clonal selection and the production of monoclonal antibodies form the humoral response
What is clonal selection
When a specific lymphocyte binds to the presented antigen ( on an antigen presenting cell ) and so it is selected to be cloned
What is clonal expansion
The T cell is activated, dividing many times rapidly by mitosis, to produce many clones. These cells then differentiate into multiple cells types
What happens during the cellular response
- An antigen presenting cell is presented to a specific t lymphocyte/cell that has a receptor complimentary to this antigen ( clonal selection )
- The T cell is activated and goes through clonal expansion
- It differentiates into multiple different cell types including helper T cells
- Upon infection with the antigen the helper T cell binds to the antigen on the antigen presenting cell
- Helper T cells then stimulate cytotoxic killer cells, specific b cells and phagocytes
What does a cytoxic T cell do
Cytoxic t lymphocytes kill infected cells
What do B lymphocytes do
The B cell divides many times by mitosis producing many clones, these can differentiate into plasma cells that release antibodies or memory cells that can respond and release antibodies more rapidly on re infection with the same antigen
What do phagocytes do
Helper T cells release chemicals called cytokines that attract phagocytes and B cells to the area of infection
What happens during the humoral response
- An antigen is presented by a phagocyte/macrophage to a Helper T lymphocyte
- The helper T cell binds to and activates a specific B lymphocyte with a complementary antibody, by binding to the antigen ( clonal selection )
- The B lymphocyte is activated and goes through clonal expansion
- These clones differentiate into plasma cells and memory cells
What is a plasma cell
Secretes specific antibodies to the antigen ( short lived - 5 days )
What is a memory cell
Remain in the body to give rapid response to the pathogen should there be a future re infection ( can give lifelong immunity )
What is an antibody
A protein ( immunoglobulin ) specific to an antigen, secreted by plasma cells
Made from 4 polypeptide chains - 2 long and 2 short with 2 variable binding site regions at the top and a constant region at the bottom
They are proteins that have a specific tertiary structure each with a different binding site that is complementary to one specific antigen, forming and antigen-antibody complex.
What does the formation of an antigen-antibody complex lead to
An antigen-antibody complex that leads to the destruction of the antigen. One method is via agglutination, where antibodies bind to an antigen acting as markers for phagocytosis, they cause clumping ( agglutination ) of the pathogen, attracting phagocytes to engulf and hydrolyse bacterial cells
What is the primary immune response
- Occurs when you are infected with the pathogen for the first time
- slow as it takes time for the correct B cells to be activated and divide the differentiate into lots of plasma cells to produce antibodies with a complementary shape to the antigen
- the T cells and the B cells produce memory cells
What is the secondary response
If you are infected with the same pathogen in the future, t and b memory cells will recognise the antigen and start dividing
T memory cells will divide into the correct type of t killer cell
B memory cells will divide into plasma cells to produce many antibodies which are complimentary to the antigen on the pathogen
This happens so quickly that the pathogen is suppressed before you experience symptoms
What are vaccines used for
To increase heard immunity and to reduce the spread of disease through a population
What is a vaccine
An antigen taken from the pathogen that stimulates an immune response
How do you make a vaccine
- Vaccines contain antigens from the pathogen
- This antigen is displayed on the surface of the antigen presenting cells ( macrophages in the ceullar response or B cells in the humoral response )
- A specific helper T cell with a complimentary receptor protein binds to the antigen and activates a specific B cell using cytokines
- The B cell divides by mitosis to form many clones which differentiate into plasma cells
- The plasma cells produce large amount of antibodies against that specific antigen
- Some B cells become memory cells that can produce plasma cells and antibodies more rapidly upon future infection with the same antigen
What is active immunity
Involves the production of antibodies and memory cells by the patients own immune system
