2C - The immune system Flashcards
What are antigens?
Molecules (usually proteins) that can generate an immune response when detected by the body.
Any part of an organism (often a protein of the surface of a cell) that is recognised as foreign by our immune system.
What can antigens generate?
An immune response when detected by the body.
Where are antigens found?
On the surface of cells.
What are antigens used by?
The immune system
How/why does the immune system use antigens?
To identify pathogens, abnormal body cells, toxins and cells from other individuals of the same species.
How are antigens controlled and what does this mean?
Genetically controlled - close relatives have more similar antigens.
What are the 2 immune systems?
Specific and non-specific.
Who/what has a non-specific immune system?
All animals
Who/what has a specific immune system?
Only vertebrates.
What are examples of non-specific immune systems?
Phagocytosis by phagocytes.
Physical barriers.
What is the response like for the non-specific immune system?
Immediate and the same for all pathogens.
What are examples of specific immune systems?
T and B lymphocytes.
What is the response like for the specific immune system?
Slower and specific to each pathogen.
What type of immune system (response) are physical barriers?
Non-specific
What type of immune system (response) is phagocytosis by phagocytes?
Non-specific
What type of immune system (response) are B and T lymphocytes?
Specific
What are the barriers the body has to infection?
Skin
Hydrochloric acid
Epithelial mucus
How does the skin act as a barrier to infection?
Physical barrier that pathogens find it difficult to penetrate.
How does hydrochloric acid act as a barrier to infection?
Denatures the enzymes or coat proteins of most pathogens that enter the stomach.
How does epithelial mucus act as a barrier to infection?
Epithelial layers inside the body produce mucus that pathogens stick to and become immobilised.
What is the phagosome?
Where the vesicle transports the pathogen to and where the pathogen is broken down in the phagocyte.
What are lysozymes?
The enzymes found in lysosomes that break down the pathogen when fused to the phagosome.
What are the parts to a phagocyte?
Phagosome lysosome (& lysozymes) Nucleus Cell membrane Vesicles
Why are T-lymphocytes called that?
T because they mature in the thymus gland.
What are T-lymphocytes used in?
Cell-mediated immunity.
What has to be present for cell-mediated immunity?
The pathogen.
What to T-lymphocytes have on each cell?
Receptor proteins.
What can the receptor proteins on each T-lymphocyte do?
Detect one specific antigen.
Approximately how many types of T-cell are there?
100000000
What do each different type of T-cell do?
Display different receptors.
What forms do T-cells occur in?
Helper T-cells (Th cells)
Cytotoxic T-cells (Tc cells)
What happens when a phagocyte destroys a pathogen?
It presents the pathogens antigens on its outer membrane (antigen-presenting cell).
What cells have antigens on their surface?
Cancerous cells and non-self cells.
What are non-self cells?
Not cells that normally occur in our body e.g. viruses.
What are the 2 immune responses?
Cell-mediated immunity and humoral immunity.
Explain what happens in cell-mediated immunity:
- Pathogens invade body cells or are taken in by phagocytes.
- The phagocyte places antigens from the pathogen on its cell-surface membrane.
- Receptors on the specific helper T cell (TH cell) fit exactly onto these antigens.
- This attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells.
- The cloned T cells:
a - develop into memory cells that enable a rapid
response to future infections by the same
pathogen.
b - stimulate phagocytes to engulf pathogens by
phagocytosis.
c - stimulate B cells to divide and secrete their
antibody.
d - activate cytotoxic T cells (TC cells).
How do lymphocytes recognise cells belonging to the body?
- 10 million lymphocytes in body at once capable of recognising chemical shape.
- In the fetus they are constantly colliding with each other.
- These will therefore collide more exclusively with self-cells.
- They fit the body cells and the die or become suppressed.
- Remaining lymphocytes are the ones that might fight non-self cells and therefore only respond to foreign material.
What are the 2 types of WBC?
Phagocytes and lymphocytes.
What process to phagocytes carry out?
Phagocytosis.
Where are phagocytes found?
Travel in the blood but can move out of the blood vessels and into other tissues.
Describe the process of phagocytosis:
- Chemical products of pathogen or dead/damaged cells act as attractants, causing phagocytes to move towards the pathogen.
- Phagocytes receptors recognise and attach to chemicals on the surface of the pathogen.
- They engulf the pathogen to form a vesicle known as phagosome.
- Lysosomes move towards the vesicle and fuse with it.
- Lysozymes destroy pathogen by hydrolysis of their cell walls.
- The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte.
How to cytotoxic T cells kill infected cells?
Produce the perforin protein which makes holes in the cell-surface membrane meaning that it becomes freely permeable to all substances and a result, the cell dies.
Why is the action of T cells most effective against viruses?
Because they replicate inside cells and this sacrifice of a body cell prevents viruses from multiplying and infecting more cells.
Is humoral immunity active or passive?
Active
Why is humoral immunity active?
Because it uses antibodies dissolved in tissue fluid or plasma.
How do antigens enter the B cell?
Endocytosis.
What is endocytosis?
The process by which antigens enter the B cell.
What is clonal selection?
When B cells it activated to divide by mitosis to produce B cell clones (plasma cells).
What is it called when B cells are activated to divide by mitosis to produce B cell clones?
Clonal selection
What is the function of plasma cells?
Secrete antibodies into blood plasma leading to the destruction of an antigen.
In what immune response are plasma cells and antibodies produced?
Primary immune response.
In what immune response are memory cells produced?
Secondary immune response.
What do memory cells do?
Don’t produce antibodies directly but circulate in the blood and tissue fluid. When they encounter the same pathogen at a later date, they divide rapidly and develop into plasma cells and more memory cells.
Do memory cells produce long term or short term immunity?
Long term
What type of immunity are B cells associated with?
Humoral immunity.
Describe the process of humoral immunity:
1- B cell with complementary antibody engulfs pathogen.
2- B cell presents antigen (antigen-presenting cell).
3- T cell binds to presented antigen using its complementary receptor protein.
4- Activates B cell to divide.
AND THEN EITHER:
5- Plasma cell clones made to secrete antibodies (primary response).
6- Attach to antigens and; agglutinate (stick cells to target), stop pathogens invading body cells or bind to free toxin proteins.
OR:
7- Memory cells made and circulate in blood for future infections (secondary response).
What are antibodies?
Proteins with specific binding sites synthesised by B cells.
What type of lymphocytes are associated with antibodies?
B-cells
Describe the structure of an antibody:
Composed of 4 polypeptide chains (2 heavy chains and 2 light chains).
Chains joined by disulphide bonds.
Form a Y shaped structure.
Stem = constant region.
Ends of the arms = variable regions that bind to the antigen.
What do the variable regions of an antibody do?
Bind to antigens.
What part of the antibody binds to the antigen?
Variable regions.
What protein structure does an antibody have?
Quaternary structure as it has multiple polypeptide chains.
What are the long chains on an antibody called?
The heavy chains.
What are the short chains on an antibody called?
The light chains.
What is formed when an antibody binds to an antigen?
An antigen-antibody complex.
What does the constant region on an antibody do?
Binds to receptors on cells such as B cells.
What do antibodies do?
Prepare antigen for destruction.
In what 2 ways to antibodies assist antigen destruction?
- Cause agglutination of bacterial cells making it easier for phagocytes to locate and engulf them.
- Serve as markers that stimulate phagocytosis to engulf the bacterial cells to which they are attached.
All antibodies have the same…
…constant region.
What is the speed like of the primary immune response?
Slow
Why is the primary immune response slow?
Because there aren’t many B-cells that can make the antibody needed to bind to the antigens.
Will a person show symptoms in a primary immune response?
Yes
What happens after being exposed to an antigen?
Both T and B cells produce memory cells which circulate in the blood for a long time. Memory T cells remember the specific antigen and will recognise it a second time round. Memory B cells record the specific antibodies needed to bind to the antigen.
What does the term immune mean?
The immune system has the ability to respond quickly to a second infection.
How fast is the secondary immune response compared to the primary immune response?
Much quicker and much stronger.
Why is the secondary immune response quicker and stronger?
Clonal selection happens faster. Memory B cells are activated and divide into plasma cells which produce the right antibody to the antigen. Memory T cells are activated and divide into the correct type of T cells to kill the cell carrying the antigen.
What will each antigen induce?
A different B cell to multiply and form a clone of itself.
What will each clone of a B cell do?
Produce a different antibody.
