exam question: self mark it (a)(i)a disease-causing organism / bacterium;1 (b)(i) attracted by...
DESCRIPTION
Non-Specific (Response is immediate and the same for all pathogens) Specific Response is slower and specific to each pathogen Physical Barrier Phagocytosis Cell mediated response T lymphocytes Humoral response B lymphocytes Defence mechanismsTRANSCRIPT
Exam question: Self mark it
(a) (i) A disease-causing organism / bacterium; 1
(b)(i) Attracted by chemicals/antigensFormation of vesicle / phagosome;
lysosome fuse/hydrolytic enzymes digest Present Antigens on surface (APC) 2
(c) (i) Lysosome; 1
(ii) Contain hydrolytic enzymes;To break down / digest bacterium; 2
Specific Immunity
Non-Specific(Response is immediate
and the same for all pathogens)
SpecificResponse is slower and
specific to each pathogen
Physical Barrier
Phagocytosis Cell mediated response
T lymphocytes
Humoral response
B lymphocytes
Defence mechanisms
What are Anitgens?
An antigen is any part of an organism that is recognised as being non-self. By the immune system and stimulates the immune response.
(anti –antibody, gen-generator)
– Usually proteins or glycoproteins on the cell plasma membrane or cell wall of invading pathogen.
Specific ImmunityResponse: targets specific antigens
is slowerprovide long term immunity
•Involves lymphocytes which are WBC which circulate the body in blood and lymph.
•There are two types of lymphocyte both of which develop in bone marrow
- T cells – (Cell mediated response) - mature in thymus gland- B cells (humoral immune system) – mature in bone marrow
Both are produced in the stem cells of the bone marrow
Cell-mediated response
T lymphocytes (T cells)
T cells can distinguish and respond to foreign cells or APC by the antigens on their surfaces.
Receptors on T cells are specific to certain antigens
Cell mediated – acts inresponse to infected cells
1. Pathogens invade body cells or are taken in by phagocytosis
2. The phagocyte places antigens from the pathogen on its cell surface membrane becoming an Antigen Presenting Cell (APC)
3. Receptors on a specific helper T cell (TH cell) fit exactly onto these antigens
4. This attachment activates the T cells to divide rapidly by mitosis and form a clone of genetically identical cells (clonal expansion)
5. The cloned T cells:
a) develop into memory cells (T helper clones) 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 antibodies
d) activate cytotoxic T cells (TC cells) also known as killer T cells
Also produces cytokines (interleukins) that alert other T helper cells
How cytotoxic T cells kill infected cells
1. Cytotoxic T cells release proteins (cytokines) eg perforin2. Perforin attach to membranes of infected cells3. Makes holes in the cell membrane4. Cell lysis
Consolidation Define a pathogen
…………………………………………………………………….…………………....
(1 mark)
Explain the role of Antigen Presenting Cells (APC’s) in cell mediated immunity. ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
(3 marks)
What feature of the T helper cell allows it to identify specific foreign antigens?………………………………………………………………………………………….
(2 marks)
Consolidation – self assess Define a pathogena disease causing microorganism;
…………………………………………………………………….…………………....
(1 mark)Explain the role of Antigen Presenting Cells (APC’s) in cell mediated immunity. APC’s are phagocytic cells/cells that perform phagocytosis;…………………………………………………………………………………………lytic enzymes break down pathogen/pathogen invades the APC;…………………………………………………………………………………………Presents specific antigen on cell surface;…………………………………………………………………………………………
(3 marks)What feature of the T helper cell allows it to identify specific foreign antigens?Specific receptors that are complementary/same fit/ exact fitto antigen on APC surface(2 marks)
Non-Specific(Response is immediate
and the same for all pathogens)
SpecificResponse is slower and
specific to each pathogen
Physical Barrier
Phagocytosis Cell mediated response
T lymphocytes
Humoral response
B lymphocytes
Defence mechanisms
Specific ImmunityResponse: targets specific antigens
is slowerprovide long term immunity
•Involves lymphocytes which are WBC which circulate the body in blood and lymph.
•There are two types of lymphocyte both of which develop in bone marrow
- T cells – (Cell mediated response) - mature in thymus gland- B cells (humoral immune system) – mature in bone marrow
Both are produced in the stem cells of the bone marrow
Humoral response
Humoral involves B cells that produce antibodies in response to antigens in the plasma
Antibodies are specific to complementary antigens
Each type of antibody is produced by a different type of B cell
What is an antibody?
• They are made up of 4 polypeptide chains (2x light 2x heavy)
• 2x antigen binding sites• Variable region/constant region• Disulphide bond
Antibodies are proteins with specific binding sites produced in the presence of a specific antigen
1) The antigens of an invading pathogen are taken up by the complementary B cell.
2) The B cell processes the antigens (via endocytosis) and presents them on its surface
3) T Helper Cells (already activated by cell mediated response) attaches to the processed antigen thereby activating the B cell
4) The B cell is now activated to divide by mitosis to give clones (clonal selection):•Plasma cell•Memory cells
5) The cloned plasma cells produce and secrete the specific antibodies (monoclonal antibodies) that exactly fit the antigen on the pathogen’s surface.These are:
Short lived but make up to 200 antibodies per second
6) The antibody attaches to antigens on the pathogen and destroys them by agglutination. This is the primary immune response
• Antibodies neutralise toxins and can stick pathogens together making it easier for phagocytes to engulf and destroy – act as labels
Agglutination
7) Some B cells develop onto memory cells . These can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies . This is the secondary immune response
Memory Cells• Live longer than plasma cells – often for decades.• They do not directly produce antibodies but circulate in
the plama and tissue fluid. • When they encounter the same antigen later they can
divide rapidly and clone to produce more plasma and memory cells.
• Plasma cells then produce lots of anti bodies very quickly.
• Provide long term immunity
• Primary immune response: The first time a B cell comes into contact with a non-self antigen that is complementary to its cell receptors the production of sufficient antibody producing cells takes between 10-17 days – thus the person is likely to feel some symptoms.
• Secondary immune response: Memory cells which recognise the antigen produce plasma cells which release antibodies to fight the antigen. This takes 3-7 days – creating immunity.
Faster production of antibodies
Produce more antibodies
Symptoms may not be experienced
Consolidation – self assess Describe the function of a cytotoxic T cell
…………………………………………………………………….…………………....
(1 mark)Explain the importance of the memory B cells in immunity.………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
(2 marks)Use knowledge of antigen-variability to explain why people can still become infected with a flu virus even though they have had this virus before. ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
(3 marks)
Consolidation – self assess Describe the function of a cytotoxic T cell
Releases toxic chemical/perforin/substance/ into pathogenic cells (1 mark)
Explain the importance of the memory B cells in immunity.Produce antibodies when reinfection;Of the same antigen;
(2 marks)Use knowledge of antigen-variability to explain why people can still become infected with a flu virus even though they have had this virus before. Memory cells recognise the same antigens;Flu virus has many strains with many different antigens;Primary immune response is required;
(3 marks)