Topic 5 - Cell Recognition And The Immune System Flashcards
What are antigens?
Proteins on the surface of cells which cause an immune response
What is a pathogen?
An organism that causes disease by destroying host cells/producing toxins etc.
What is the first line of defence in the immune response?
Phagocytosis
What are the 4 stages of phagocytosis?
1) Phagocyte identifies foreign antigen
2) Phagocyte engulfs foreign antigen into phagocytic vacuole
3) Lysosomes fuse with phagocytic vacuole and release lysozyme that hydrolyse the pathogen
4) Phagocyte presents antigens on it’s surface (antigen presenting cell)
What are the two types of t-lymphocytes?
T-helper cells and cytotoxic cells
Where do t-lymphocytes mature?
Thymus gland
How do t-lymphocytes distinguish invader cells from normal cells?
○Antigen presenting cells present the pathogens antigens on their own cell surface
○Body cells invaded by a virus present some of the viruses antigens on their cell membrane
○Transported cells from individuals of the same species have different antigens on their cell membrane
○Cancer cells are different from normal body cells and present different antigens on their cell membranes
Role of t-helper cells
1) Receptors on specific t-helper cel bind to antigens on surface of antigen presenting cell
2) This attachment activates the T cell to divide rapidly by mitosis and form genetically identical cells
3) These clones T cells then:
- Develop into memory cells
- Stimulate phagocytosis
- Stimulate B cells to divide and secrete antibodies
- Activate cytotoxic T cells
How do cytotoxic T cells kill infected cells?
They produce a protein called perforin that makes holes in the cell-surface membrane. These holes mean the cell membrane becomes freely permeable to all substances and therefore the cell dies
Role of plasma cells
They secrete antibodies usually into blood plasma. These cells survive only for a few days but can make around 2000 antibodies per second. These antibodies lead to the destruction of the antigen
Role of memory cells
These live considerably longer than plasma cells. They don’t produce antibodies directly but circulate in the blood and tissue fluid. When they meet the same antigen later on, they divide rapidly and develop into plasma cells and more memory cells
Where do B lymphocytes mature?
Bone marrow
Roles of B cells in immunity:
1) The surface of antigens of an invading pathogen are taken up by a B cell
2) B cell processes the antigens and presents them on its surface
3) T Helper cells attach to processed antigens thereby activating the B cell
4) B cell is now activated to divide by mitosis to give clone of plasma cells
5) Cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogens surface
6) The antibody attaches to antigens on the pathogen and destroys them
7) Some B cells develop into memory cells which play a role in the secondary immune response
Describe the structure of an antibody
Antibodies are proteins with specific 1º and therefore specific 3º structures. However they have a variable region which has a different shape to fit the shape of the complimentary antigen to form antigen-antibody complexes
