(5) Cell Recognition Flashcards
Describe Phagocytosis:
-Phagocyte attracted to chemicals from pathogen
-binds to pathogen
-Engulfs pathogen and puts it into phagosome
-lysosomes fuse with phagosome
-lysozymes hydrolyse the pathogen
Then Phagocyte absorb soluble products of digestion.
-Phagocyte presents the pathogen’s foreign antigens on its cell membrane.
Describe specific and non specific defense mechanisms:
Non specific:
Response is immediate and the same for all pathogens
Eg: skin acting as a physical barrier
Eg: Phagocytosis
Specific:
Response is slower and specific to each pathogen
Eg: Cell-mediated Reponse
T-Lymphocytes
Eg: Humoral Reponse
B-Lymphocytes
Explain the steps in Cell Mediated Immunity:
1: Pathogens invade body cells or are taken in by phagocytosis
2: Phagocyte places antigens from the pathogen on its cell-surface membrane
3: Receptors on a specific helper T cell fit exactly onto these antigens.
4: This attachment activates T cell to divide rapidly by mitosis and form a clone of genetically identical cells
5: The cloned T cells
a: develop into memory cells that enable a rapid response to future infection
b: Stimulate phagocytes to engulf pathogens by phagocytosis
c: Stimulate B cells to divide and secrete their antibody
D: Activate cytotoxic T cells (which have perforin) to make holes into the cell surface membrane. Membrane becomes freely permeable to all substances and dies.
Describe B cells in Humoral Immunity:
1: Surface antigens of a pathogen are taken up by B cell.
2: B cell processes the antigens and presents them on its surface
3: Helper T cells attach to the processed antigens on the B cell thereby activating the B cell.
4: B cell is now activated to divide by mitosis to give a clone of plasma cells.
5: Cloned Plasma cells produce and secrete specific antibody that exactly fits the antigen on the pathogens surface.
6: The antibody attaches to the antigens on the pathogen and destroys them.
7: Some B cells develop into 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.
Antibodies:
Define
Structure
Function
Protein with specific binding sites synthesised by B cells
Made up of 4 polypeptide chains
1 pair long, heavy chains
1 pair short, light chains
Each antibody has specific antigen it binds to: antigen-antibody complex
Binding site has different location on every antibody hence the variable region.
Antibodies cause agglutination. Clumps of pathogens are formed. So less spread out
Phagocytes can locate them easier.
Attach themselves onto pathogens, serves as markers for phagocytes to do phagocytosis.
Monoclonal Antibodies
Treatment on cancer by
Direct/Indirect Monoclonal Antibody Therapy
Direct:
Antibodies produced that specific to antigens on cancer cells.
Antibodies attach themselves to the receptors on their cancer cells
They attach to the surface of their cancer cells and block chemical signals that stimulate uncontrolled growth.
Indirect:
Attaching a radioactive/cytotoxic drug to the monoclonal antibody.
When the antibody attaches to cancer cell it kills them.
Describe the ELISA Test:
Apply sample containing the antigen to the well
Antibodies already In the well attach to antigen. (Antigens stick to well)
(Wash to remove any excess molecules)
Add antibody solution which is specific for that antigen
(Wash to remove any excess antibody molecules)
Add a second antibody solution which binds specifically to the first antibody.
The second antibody has an enzyme molecule attached to it.
Wash again to remove any unbound second antibody molecules
Add substrate molecule.
When the enzyme substrate binds. Releases colour
Passive vs Active Immunity
Passive:
Introduction of antibodies from outside source
Immediate Immunity but not long-lasting
Active:
Stimulate Production of antibodies by immune system. Immunity takes time but long-lasting
(a) Explain what is meant by herd immunity. (2 marks)
(b) Describe how a vaccination program can lead to herd immunity. (3 marks)
(c) Discuss two factors that could affect the success of a vaccination program in achieving herd immunity. (4 marks)
A: When a sufficiently large proportion of the population are vaccinated
This reduces the spread of the disease because there are fewer hosts for the pathogen
B:Vaccination introduces antigens that stimulate an immune response (1).
This leads to the production of memory cells without causing disease (1).
If enough people are immune, the transmission of the pathogen is significantly reduced (1).
C:Uptake rate: If a significant proportion of the population refuses or cannot access vaccines, herd immunity may not be achieved (1).
Pathogen mutation: Frequent mutations can result in antigenic variation, reducing vaccine effectiveness (1).
Immunocompromised individuals: Cannot receive vaccines, making it essential for others to be vaccinated (1).
