2.6 Immune System Flashcards
(24 cards)
What is an antigen?
• Foreign protein
• That stimulates an immune response if detected
What types of cells/molecules stimulate an immune response?
• Pathogens
• Cells from other organisms of the same species
• Abnormal body cells
• Toxins
How does phagocytosis occur?
• Phagocyte recognises foreign antigens on pathogen
• Phagocyte engulfs pathogen into a phagosome
• Lysosome fuses with phagosome and releases lysozymes
• Lysozymes hydrolyse pathogen
• Phagocyte presents pathogens antigens on its cell-surface membrane
What happens in the cellular immune response?
• T cells recognise foreign antigens on surface of antigen presenting cells
• Specific helper T cell with complementary receptor binds to antigen
• Activating the T cell to divide by mitosis into clones
• Stimulating cytotoxic T cells / B cells / phagocytes
What happens in the humoural response?
• B cells recognise foreign antigens on surface of antigen presenting cells
• Specific B cell with complementary receptor binds to antigen
• Activating the B cell to divide by mitosis into clones
• Which differentiate into plasma cells which secrete antibodies / MEMORY B CELLS for secondary immune response
What are antibodies?
• Quaternary structure proteins
• Secreted by B cells / plasma cells in response to specific antigens
How do antibodies lead to the destruction of pathogens?
• Specific antibodies bind to complementary antigens on pathogen forming an antigen-antibody complex
• Each antibody binds to two pathogens at once causing agglutination
• Antibodies attract phagocytes
• Phagocytosis of many pathogens at once
Primary immune response
Antibodies produced slowly and at lower concentration
Takes time for specific B cells to undergo clonal selection and expansion and memory B cells to be produced
Secondary immune response
Antibodies produced faster and at higher concentration
Memory B cells rapidly divide by mitosis to produce many plasma cells which secrete specific antibodies
What is a vaccine?
• Injection of antigens from dead/weakened pathogen
• Stimulating primary immune response and thus production of memory B cells
What is herd immunity?
• Large proportion of population is vaccinated/immune so do not become ill
• Unvaccinated people less likely to come in contact with someone with the disease
• Reducing spread of pathogen
Active immunity
Initial exposure to antigen
Memory cells involved
Antibody produced and secreted by plasma cells
Slower acting
Long term immunity as antibody can be produced by memory B cells
Passive immunity
No exposure to antigen
No memory cells involved
Antibody introduced from another organism
Faster acting
Short term immunity as antibody hydrolysed
What is antigen variability?
• Antigens on pathogens change tertiary structure due to gene mutations
• No longer immune as specific antibodies not complementary to antigen
How are viruses structured?
• Nucleic acids surrounded by a protein capsid
• Attachment proteins
• No cytoplasm or organelles
• (HIV) reverse transcriptase
• (HIV) surrounded by a lipid envelope
Why are viruses described as acellular and non-living?
• Acellular as not made of cells
• Non-living as have no metabolism / cannot independently replicate
How does HIV replicate?
• Attachment proteins attach to complementary receptor proteins on host cell (helper T cell)
• Injects viral RNA and reverse transcriptase into host cell
• Reverse transcriptase converts viral RNA to DNA
• Viral DNA inserted into host cell DNA
• DNA transcribed into mRNA and translated into viral proteins
• Viral particles assemble and are released
How does HIV cause symptoms of AIDS?
• HIV infects and kills helper T cells
• Immune system deteriorates so more susceptible to minor infections
Why are antibiotics ineffective against viruses?
• Viruses do not have metabolic processes
• Viruses do not have bacterial enzymes
What is a monoclonal antibody?
• Antibody produced from cloned B cells / plasma cells
• So have the same tertiary structure
How can monoclonal antibodies be used in medical treatments?
• Monoclonal antibody has specific tertiary structure
• Complementary to receptor/antigen on specific cell type
• Drug attached to antibody
• Antibody binds to specific antigen forming an antigen-antibody complex
How is the ELISA test used to detect antigens?
• Specific antibodies fixed to well
• Add sample, if complementary antigen present it binds to antibody
• Wash well to remove unbound antigens
• Add complementary antibodies with enzyme attached, binds to antigen if present
• Wash to remove unbound antibodies
• Add substrate, colour change if positive
How is the ELISA test used to detect antibodies?
• Specific antigens fixed to well
• Add sample, if complementary antibody present it binds to antigen
• Wash well to remove unbound antibodies
• Add complementary antibodies with enzyme attached, binds to antibody if present
• Wash to remove unbound antibodies
• Add substrate, colour change if positive
What are some issues associated with vaccines / monoclonal antibodies?
• Animal testing causing potential harm
• Potential harmful side effects
• May pass on pathogen
• Cost of production and distribution
