The immune system Flashcards
(42 cards)
What are antigens?
Molecules - usually proteins - found on the cell surface membrane which stimulate an immune response
What do antigens allow the immune system to identify?
Pathogens
Cells from other individuals
Abnormal body cells
Toxins
What is antigenic variability?
Where the antigens on viruses change
So you could be infected with the same virus again but this would produce a primary response rather than a secondary response because the antigens have changed
What type of immunity are B lymphocytes associated with?
Humoral immunity
e.g. immunity involving antibodies that are present in body fluids (‘humour’)
What type of immunity are T lymphocytes associated with?
Cell-mediated immunity
e.g. immunity involving body cells
What is a secondary response?
When the right antibodies to fight a particular pathogen are produced rapidly and in high numbers because you’ve been infected with the same pathogen before
Where are both B and T lymphocytes formed?
Stem cells found in the bone marrow
Where do T lymphocytes mature?
In the thymus gland
Where do B lymphocytes mature?
In the bone marrow
What is the process of phagocytosis?
1) The phagocyte is attracted to the pathogen by chemoattractants (released by the pathogen)
2) The phagocyte binds to the pathogen
3) They engulf the pathogen to form a vesicle known as a phagosome
4) The lysosomes release their lyctics enzymes into the phagosome where they break down (hydrolyse) the pathogen
5) The breakdown products of the pathogen are absorbed by the phagocyte
Why does phagocytosis happen?
Large particles, such as bacteria, are too big to cross surface membranes by diffusion or active transport. Instead they have to be engulfed by cells in the form of vesicles formed from the cell surface membrane
What are some non specific responses?
Physical barriers e.g. skin and scabs
Phagocytosis
Non specific responses are immediate and the same for all pathogens
What are some examples of specific defence systems?
Cell mediated response - T lymphocytes
Humoral response - B lymphocytes
Specific responses are slower and specific to each pathogen
What do helper T cells stimulate?
- Production of memory cells
- B cells to divide
- Phagocytosis
- Production of cytotoxic T lymphocytes
What do cytotoxic (TC cells) do?
Kill abnormal and foreign cells by making holes in the cell surface membrane
Why do we need antigen presenting cells (e.g. phagocytes) for T lymphocytes to respond?
Because T lymphocytes will only respond to antigens that are attached to a body cell
What is the process of B lymphocytes dealing with a pathogen?
1) The surface antigens are taken up by B cells
2) B cells then present antigens on their surface
3) T helper cells attach to processed antigens and activate the B cells
4) They are activated to divide by mitosis to give clones of plasma cells
5) These clones plasma cells produce antibodies that are complementary to the pathogen
6) These antibodies attach to antigens and destroy the pathogen
7) Some B cells develop into memory cells instead of plasma cells to respond to future infection
What is an antibody?
Proteins synthesised by B cells when the body is invaded by non self material
What are the two pairs of polypeptide chains in an antibody called?
Long pair - heavy chains
Short pair - lighter chains
What is the variable region on an antibody?
The binding site on the antibody
What is the constant region of an antibody?
The area that’s the same in all antibodies
What is clonal selection?
When the antibody on the surface of a B cell meets a complementary shaped antigen, it binds to it. This, together with substances released from helper T cells activated the B cell
What is agglutination?
When two pathogens bind to the two binding sites on an antibody and become clumped together
What is the difference between monoclonal antibodies and polyclonal antibodies?
Monoclonal antibodies are made by one type of B cell and are all clones of a unique parent cell, while polyclonal antibodies are made from several different types of B cells
