The Immune System Flashcards
What are antigens?
Molecules (usually proteins or polysaccharides) found on cells’ surface.
What are the 2 types of immune response and what is the difference between them?
Specific and non-specific.
Non-specific is the same process for every microorganism, a specific response is antigen-specific and involved white blood cells called T and B lymphocytes.
What are four main stages in the immune response?
1) Phagocyte engulfs pathogen
2) Phagocytes activate T lymphocytes
3) T lymphocytes activate B lymphocytes, which then divide into plasma cells
4) Plasma cells make more specific antibodies for the specific antigen
Explain stage 1 of the immune response.
`-Phagocyte recognises antigens on pathogen
- Cytoplasm of phagocyte engulfs pathogen.
- Pathogen is now contained in a phagosome in the phagocyte cytoplasm
- A lysosome fuses with phagosome, enzymes in lysosome breaks down the pathogen
- Phagocyte then presents the pathogen’s antigens which activates other immune system cells. It is now an APC (antigen-presenting cell).
Explain stage 2 of the immune response.
- A T lymphocyte is another type of white blood cell
-Surface receptors bind to antigens presented by APCs
-Each T lymph has a different receptor, when it meets a complimentary antigen it binds to it and the lymph is activated
This process is CLONAL SELECTION.
-T lymph then undergoes CLONAL EXPANSION, it divides to produce clones of itself.
Explain stage 3 of the immune response.
- B lymphocytes are another type of white blood cell which is covered in antibodies
- Antibodies bind to antigens to form an antigen-antibody complex
- When each B lymph meets a complimentary shaped antigen that fits its specific antigen, it binds to it.
- This and substances released from T helpers, activated the B lymph. This is also CLONAL SELECTION.
- The B lymph then undergoes CLONAL EXPANSION and divides by mitosis into plasma cells and memory cells.
Explain stage 4 of the immune response.
- Plasma cells are clones of the B lymph and secrete a lot of the specific antibody into the blood.
- These antibodies will bind to the antigens on the surface of the pathogen to form a gen-body complex.
What are neutrophils?
A type of phagocyte that are the first WBC to respond to a pathogen. They move towards a wound in response to signals from cytokines released by cells at the site of the wound.
What are cytokines?
Messenger molecules released by cells around a wound.
Explain the three types of T lymphocyte and what they each do.
T helper cells- release substances to activate B lymphocytes and T killer cells.
T killer cells- attach to and kill cells infected by a virus.
T regulatory cells- suppress the immune response from other white blood cells. This helps to prevent the immune system from mistakenly attacking the host’s own body cells.
What is cell signalling?
How cells communicate.
Cells may release a substance that binds to the receptors on another cell which causes a response from that cell.
Helps to activate all typed of WBC needed.
E.g. T helper cells release interleukins that bind to receptors on B lymphocytes and activate it.
Describe the structure of antibodies.
Variable region- form antigen binding sites, shape is complementary to a particular antigen.
Hinge region- allows flexibility when antibody binds to antigen
Constant regions- allow binding to receptors on immune system cells, eg phagocytes. Same (same sequence of amino acids) in all antibodies.
Disulphide bridges- holds polypeptides chains of the protein together.
Describe the ways in which an antibody helps to clear an infection.
Agglutinating proteins- antibodies can bind to two pathogens at the same time and so the pathogens become clumped together which makes if easier for a phagocyte to phagocytose a lot of pathogens at once.
Neutralising toxins- antibodies called anti-toxins bind to toxins released by pathogens and render them harmless to human cells.
Preventing the pathogen from binding to human cells- when antibodies bind to the antigen on pathogens they may block the cell surface receptors that the pathogens need to bind to the host cells which prevents the pathogen from attaching to or infecting the host cell.
Is the primary or secondary response fastest?
Secondary.
Describe the primary response.
- When a pathogen enters the body for the first time, the antigens on its surface activate the immune system.
- When exposed to an antigen, both T and B lymphs produce memory cells which remain in the body for a long period of time.
- T memory cells remember the specific antigen and will recognise it, B memory cells remember the specific antibodies needed to bind to it.
