Cell Recognition and the Immune System- The Immune System Flashcards
What are antigens?
Molecules (usually proteins) that trigger an immune response when detected by the body
Where are antigens found?
Usually on surface of cells
How are antigens used by the immune system?
To identify pathogens, abnormal body cells, toxins and non-self cells
What are the four main stages in 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
How do phagocytes engulf pathogens (phagocytosis)?
- Phagocyte recognises foreign antigens on pathogen
- Cytoplasm of phagocyte moves round pathogen (engulfing it)
- Pathogen now contained in a phagosome
- Lysosome releases lysozymes which break down pathogen
- Phagocyte presents pathogen’s antigens
What is a phagocyte?
A type of white blood cell that carries out phagocytosis
Where are phagocytes found?
In blood and in tissues
What is a T cell?
A type of white blood cell
How are T cells activated?
The T cell has receptor proteins on its surface that bind to complementary antigens presented to it by the phagocytes
How can T cells respond?
TH cells (helper T cells) release chemical signals that activates and stimulates phagocytes and cytotoxic T cells (TC cells) which kill abnormal and foreign cells They can also stimulate B cells
What are B cells?
A type of white blood cell that secretes antibodies
What does it mean that antibodies are specific?
Each B cell has a different shaped antibody so different ones bind to different shaped antigens
What happens when antibodies bind to antigens?
An antigen-antibody complex is formed and B cells are activated (clonal selection) which divides into plasma cells
What do plasma cells do?
They secrete lots of antibodies specific to the antigen called monoclonal antibodies that bind to the antigen on the pathogens surface to form antigen-antibody complex
What is an antibody?
Proteins made up of chains of amino acids
What does the specificity of an antibody depend on?
Its variable regions which form antigen binding sites
What is agglutination?
Pathogens become clumped together as an antibody has two binding sites so can bind to two pathogens at the same time
What is involved in cell-mediated immunity?
T cells and other immune system cells they interact with
What is involved in humoral immunity?
B cells, clonal selection and the production of monoclonal antibodies
What is the primary immune response?
When an antigens enters the body for the first time and activates the immune system
What is the speed of the primary immune response?
Slow because there aren’t many B cells to make the antibody that is needed
What happens in the primary immune response?
Over time, enough antibodies are produced to overcome the pathogen and the individual will show symptoms of the disease
What will happen after being exposed to a pathogen?
Memory cells are produced that remain in the body for a long time and they remember the specific antigen and will recognise it when the individual is infected a second time
What is the secondary immune response?
When the pathogen enters the body a second time, the memory cells recognise the antigen and produce more antibodies quicker
What is the speed of the secondary immune response?
Quick and strong
What happens in the secondary immune response?
Clonal selection happens faster, memory B cells are activated and divide into plasma cells that produce the correct antibody to fit the antigen, memory T cells are activated and divide into the correct type of T cells to kill the cell
Does the individual show symptoms with the secondary immune response?
The secondary immune response often gets rid of the pathogen before showing any symptoms
