Transcript Specific Immunity - Truro School Moodle

Exam question: Self mark it
(a)
(i)
A disease-causing organism / bacterium;
1
(b) (i) Attracted by chemicals/antigens
Formation 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
Defence mechanisms
Non-Specific
(Response is immediate
and the same for all
pathogens)
Physical
Barrier
Phagocytosis
Specific
Response is slower and
specific to each pathogen
Cell mediated
response
T lymphocytes
Humoral
response
B lymphocytes
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 Immunity
Response:
targets specific antigens
is slower
provide 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
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.
2.
3.
4.
Cytotoxic T cells release proteins (cytokines) eg perforin
Perforin attach to membranes of infected cells
Makes holes in the cell membrane
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 pathogen
a 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 fit
to antigen on APC surface
(2 marks)
Defence mechanisms
Non-Specific
(Response is immediate
and the same for all
pathogens)
Physical
Barrier
Phagocytosis
Specific
Response is slower and
specific to each pathogen
Cell mediated
response
T lymphocytes
Humoral
response
B lymphocytes
Specific Immunity
Response:
targets specific antigens
is slower
provide 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
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?
Antibodies are proteins with specific binding sites
produced in the presence of a specific antigen
• They are made up of 4
polypeptide chains (2x light 2x
heavy)
• 2x antigen binding sites
• Variable region/constant region
• Disulphide bond
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
Agglutination
• Antibodies neutralise toxins and can stick pathogens
together making it easier for phagocytes to engulf and
destroy – act as labels
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.
Produce more
antibodies
Faster production of
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)