3.2.4 Cell recognition and the immune system Flashcards
what is an antigen
- foreign molecule
- that stimulates an immune response leading to production of an antibody
how are cells identified by the immune system
- each type of cell has specific molecules on its surface that identify it
- often proteins - have specific tertiary structure
what types of cells and molecules can the immune system identify
1) pathogens
2) cells from other organisms
3) abormal body cells
4) toxins
Describe phagocytosis of pathogens
1) phagocyte attracted by chemicals / recognises antigens on pathogen
2) phagocyte engulfs pathogen by surrounding it within its cell membrane
3) pathogen contained in phagosome in cytoplasm of phagocyte
4) Lysosome fuses with phagosome and released lysozymes
5) lysozymes hydrolyse or digest pathogen
Describe the response of T lymphocytes to a foreign antigen ( the cellular response )
Specific Helper T cells with complementary receptors bind to antigen on antigen present cell - activated and divide by mitosis to form clones which stimulate :
- cytotoxic t cells - kills infected cells by producing preforin
- specific b cells ( humoral response )
- phagocytes - engulf pathogens by phagocytosis
Describe the response of B lymphocytes to a foreign antigens ( humoral response )
1) clonal selection :
• specific B lymphocyte with complementary receptor binds to antigen
• This is then stimulated by helper T cells
• So divided by mitosis to form clones
2) some differentiate into B plasma cells - secrete large amounts of antibody’s
3) Some different into B memory cells - remain in blood for secondary immune response
what are antibodies
- quaternary structure proteins
- Secreted by B lymphocytes
- Bind specifically to antigens forming antigen - antibody complexes
describe the structure of an antibody
- Antigen
- antigen binding site
- variable region
- disulfide bridge
Explain how antibodies lead to the destruction of pathogens
- antibodies bind to antigens on pathogens forming an antigen - antibody complex
• specific tertiary structure so binding site binds to complementary antigen - Each antibody binds to 2 pathogens at a time causing agglutinations of pathogens
- Antibodies attract phagocytes
- Phagocytes bind to the antibodies and phagocytose many pathogens at once
Explain the differences between the primary and secondary immune response
Primary - first exposure to antigen :
• antibodies produced slowly and lower conc
• takes time for specific plasma cells to be stimulated to produce specific antibodies
• memory cells produced
Secondary - second exposure to antigen :
• Antibodies produced faster and a at a higher concentration
• B memory cells rapidly undergo mitosis to produce many plasma cells which produce specific antibodies
what is a vaccine
- injection of antigen from attenuated pathogens
- stimulating formation of memory cells
explain how vaccines provide protection to individuals against disease
1) specific b lymphocytes with complementary report binds to antigen
2) Specific Helper T cell binds to antigen - presenting cell and stimulated B cell
3) B lymphocytes divides by mitosis to form clones
4) Dome differentiate into B plasma cells which release antibodies
5) some differentiate into B memory cells
6) On secondary exposure to antigen , B memory cells rapidly divide by midtown’s to produce B plasma cells
7 ) these release antibodies faster and at a higher concentration
explain how vaccines provide protections for population against disease
Herd immunity - large proportion of population vaccinated , reducing spread of pathogen
• Larger proportion of population immune so do not become ill from infection
• Fewer infected people to pass pathogen on / unvaccinated people less likely to come in contact with someone with disease
Describe the difference between active and passive immunity
Active :
- initial exposure to antigen
- memory cells involved
- Antibody produced and secreted by B plasma cells
- Slow - longer to develop
- Long term immunity as antibody can be produced in response to a specific antigen again
Passive immunity
- No exposure to antigen
- No memory cells involved
- Antibody introduced from another organisms
- Faster acting
- Short term immunity as antibody hydrolysed
Explain the effect of antigen variability on disease and disease prevention
• antigen on pathogens changes shape / tertiary structure due to gene mutations
• so no longer immune
- b memory cell receptors cannot bind to do antigen on secondary exposure
- Specific antibodies not complementary to changed antigen
