3.2.5 The Defensive Functions of Mammalian Blood Flashcards
What is an antigen?
Molecules (usually proteins) that stimulates an immune response when detected by body
Describe how lymphocytes recognise self from non-self
- Each lymphocyte recognises a different chemical shape
- They collide with body’s own material (self)
- Some lymphocytes have receptors that fit body’s cells
- These either die or are suppressed
- Remaining fit only foreign material
Name the 4 main stages of immune response
- Phagocytosis
- Phagocytes Activate T-cells
- T-cells Activate B-cells, which divide into Plasma cells
- Plasma cells make more Antibodies to a Specific Antigen
Where are phagocytes found?
In blood and tissues
Describe phagocytosis (5)
- Phagocyte recognises (foreign) antigen
- Phagocyte engulfs pathogen
- Enclosed in vacuole/phagosome
- (Vacuole) fuses with lysosome
- Lysosome contains enzymes (lysozymes) that hydrolyse pathogen
Why does phagocytes moves towards pathogens?
∵ they’re attracted to pathogen’s chemical products
Phagocytes engulf pathogens by _____
endocytosis
Waste products removed by _____
exocytosis
How do lysozymes break down bacteria?
Hydrolyse the cell walls of bacteria
What do phagocytes do at the end of phagocytosis?
Phagocyte presents pathogen’s antigens on its surface to activate other immune system cells
What do T-cells only respond to?
Antigen-presenting cells
Where do T-cells (aka T-lymphocyte) mature?
In thymus gland
Describe what T-cells do
- Respond to antigens on foreign and infected cells
- Specific receptors on helper T cells bind to specific antigen presented by phagocytes (antigen-presenting cell)
- This activates T-cell: Binding triggers rapid mitosis = T cells are cloned
Name 4 things that the cloned helper T-cells do
- Activate cytotoxic T cells
- Activate B-cells to divide and secrete their antibodies
- Develop into memory cells
- Release chemical signals that activate and stimulate phagocytes
Describe how cytotoxic T-cells kill infected cells
- Produce protein called perforin that makes holes in cell-surface membrane
- Holes means cell membrane becomes freely permeable
- Control of substances no longer controls and cell dies
Why is the action of T-cells most effective against viruses?
∵ they replicate inside cells, sacrificing these body cells prevents viruses from multiplying and infecting more cells
What is the role of macrophages in stimulating B lymphocytes?
- Antigen in membrane presented to lymphocytes
- Produce cytokinins
What are B-cells (B-lymphocytes)?
White blood cell that’s covered with antibodies
What are antibodies?
- Proteins that bind antigens to form antigen-antibody complex
- Stimulate immune response
Describe how T-cells activate B-cells, which divide into plasma cells
- When antibody on surface of B-cells meets complementary shaped antigen = binds to it
- This, together with chemicals released from helper T-cells, activates B-cell = divides by mitosis
- Clonal selection: form clones/produce plasma cells
- Make antibodies
- Plasma cells produce memory cells
What do plasma cells do?
Secrete loads of antibodies specific to antigen
callled monoclonal antibodies
Describe what antibodies do to destroy pathogens
- Antibody has 2 binding sites = can bind 2 pathogens at same time
- Means pathogens & antibodies become clumped together = called agglutination
- Phagocytes bind to antibodies and phagocytose many pathogens at once
- Process leads to destruction of pathogens carrying this antigen in body
All antibodies have same _____ region
All antibodies have same constant region
What does the constant region allow antibodies to do?
To bind to receptors on B-cells
What does the hinge region allow antibodies to do?
Allows flexibility so molecules can group more than one antigens
Why are antibodies specific to one antigen? (3)
- Variable region has specific primary structure
- Tertiary structure of binding site is complementary to bind with these antigens
- Forms complex between antigen and antibody
What is the primary response?
When antigen enters body for 1st time & activates immune system
Why is the primary response slow?
∵ there aren’t many B-cells that can make antibody needed to bind to pathogen
Primary Immune Response
After being exposed to antigens, T- and B-cells produce ____ ___
memory cells
Memory cells remain in body for ____ time
long
What do memory B-cells do?
Record specific antibodies needed to bind the antigen
What do memory T-cells do?
Remember specific antigen and will recognise it 2nd time round
Explain why antigenic variability causes some people to get infected more than once
- ∵ Memory B/T cells don’t recognise new antigens
- Antibodies previously produced are not effective ∵ shape not complementary to new antigen
What is the secondary response?
When same pathogen enters body = immune system will produce quicker, stronger immune response
Why is the secondary response quicker than the primary response? Explain in terms of memory T-cells/B-cells
Clonal selection happens faster
- Memory T-cells are activated and divide into correct type of T-cells to kill cell carrying antigen
- Memory B-cells are activated and divide into plasma cells that produce right antibody to antigen
Why do you suffer from symptoms?
∵ B-cells busy dividing to increase their numbers to deal with pathogen
What are vaccinations?
- Injection of antigens
- (Antigen from) attenuated pathogen
- Stimulates the formation of memory cells
What is meant by herd immunity?
- Many vaccinated = reduces occurrence of disease ∴ those unvaccinated, less likely to catch disease
- Chance of disease spreading is reduced
Name 2 disadvantages of oral vaccines
- Could be broken down by enzymes in gut
- Molecules of vaccine = too large to be absorbed into blood
Describe how vaccination lead to immunity (7)
- Vaccine contains antigen from pathogen
- Macrophage presents antigen on its surface
- T cell with complementary receptor protein binds to antigen
- T cell stimulates B cell, with complementary antibody on its surface
- B-cells undergo mitosis/form clones
- Plasma cells produce lots of antibodies
- Memory cells produced = more antibodies produced faster in secondary response on reinfection
What is antigenic variation?
When pathogens change their surface antigens
Why do different antigens form?
∵ of changes in genes
Why does antigenic variation makes it difficult to develop vaccines against some pathogens?
- If infected, T/B memory cells produced from vaccination won’t recognise different antigens
- Antibodies previously produced not effective as shape not complementary to new antigen
Strains of Influenza are _______ ___
immunologically distinct
What is active immunity?
When your immune system makes its own antibodies after being stimulated by antigen
What is passive immunity?
Immunity gotten from being given antibodies made by different organism
(immune system doesn’t produce any antibodies of its own)
Active Immunity
What is natural immunity?
Becoming immune after catching a disease
Active Immunity
What is artificial immunity?
Becoming immune after being given vaccination
Passive Immunity
What is natural immunity?
Baby become immune due to antibodies it receives from mother, through placenta and breast milk
Passive Immunity
What is artificial immunity?
Becoming immune after being injected with antibodies from something else
Name 4 differences between active and passive immunity
A person may develop influenza twice within a short time. Explain why. (2)
- New strain of virus
- New strain not recognised by memory cells
Explain why during the secondary response, the person doesn’t show any symptoms (4)
- Memory cells produced
- Infection with same pathogen causes secondary response
- More antibodies produced
- Pathogen killed before symptoms occur
What is an antigen presenting cell?
A cell of the body infected by a virus or a phagocyte that presents the foreign antigen on its surface
What is purpose of agglutination?
- Acts as marker = makes phagocytosis easier
- Stops entry into cells
