Immunity Flashcards
What is an antigen
Foreign molecule / protein
• That stimulates an immune response leading to production of antibody
What types of cells and molecules can the immune system identify?
Pathogens (disease causing microorganisms) eg. viruses, fungi, bacteria
2. Cells from other organisms of the same species (eg. organ transplants)
Abnormal body cells eg. tumour cells or virus-infected cells
4. Toxins (poisons) released by some bacteria
What are antibodies?
Quaternary structure proteins (4 polypeptide chains)
Secreted by B lymphocytes eg. plasma cells in response to specific antigens Bind specifically to antigens forming antigen-antibody complexes
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 / variable region binds to complementary antigen
• Each antibody binds to 2 pathogens at a time causing agglutination (clumping) of pathogens
• Antibodies attract phagocytes
• Phagocytes bind to the antibodies and phagocytose many pathogens at once
Explain the differences between the primary & secondary immune response
Primary - first exposure to antigen
• Antibodies produced slowly & at a lower conc.
• Takes time for specific B plasma cells to be stimulated to produce specific antibodies
Memory cells produced
Secondary - second exposure to antigen
• Antibodies produced faster & at a higher conc.
• B memory cells rapidly undergo mitosis to produce many plasma cells which produce specific antibodies
What is a vaccine?
Injection of antigens from attenuated (dead or weakened) pathogens
• Stimulating formation of memory cells
Explain how vaccines provide protections for populations against disease
Herd immunity - large proportion of population vaccinated, reducing spread of pathogen
Large 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
Explain how HIV causes the symptoms of acquired immune deficiency syndrome
infects and kills helper T cells (host cell) as it multiplies rapidly
So T helper cells can’t stimulate cytotoxic T cells, B cells and phagocytes
• So B plasma cells can’t release as many antibodies for agglutination & destruction of pathogens
• Immune system deteriorates → more susceptible to (opportunistic) infections
• Pathogens reproduce, release toxins and damage cells
Suggest the purpose of a control well in the ELISA test
Compare to test to show only enzyme causes colour change
Compare to test to show all unbound antibodies have been washed away
Suggest why failure to thoroughly wash the well can result in a false positive in the ELISA test
Antibody with enzyme remains / not washed out
So substrate converted into colour product
