2.4 Cell Recognition and the Immune System Flashcards
what is an antigen
-a foreign molecule/protein
-that stimulates an immune response
-leading to the production of antibodies
how are cells identified by the immune system
-each cell has specific molecules on its surface that identify it
-these molecules are often proteins with a specific tertiary structure
what types of cells and molecules can the immune system identify
-pathogens
-cells from other organisms of the same species
-abnormal body cells
-toxins released by some bacteria
what is a pathogen
-a disease causing microorganism
describe phagocytosis of pathogens (non specific immune response)
-phagocyte is attracted to chemoattractants from pathogen/ recognises antigens on pathogen
-phagocyte engulfs pathogen by surrounding it with its cell membrane
-pathogen contained in vesicle/phagosome in cytoplasm of phagocyte
-lysosome fuses with phagosome and releases lysozymes
-lysozymes hydrolyse pathogen
-phagocytes absorb products of hydrolysis
what does phagocytosis lead to
-presentation of antigens on the phagocyte cell surface membrane
-stimulating the specific immune response
describe the response of t lymphocytes to a foreign antigen (the cellular response)
-t lymphocytes recognise antigen presenting cells
-specific helper T cells with complementary receptors bind to antigen on the antigen presenting cell
-the antigen presenting cell is activated and divides by mitosis to form clones
what do the clones produced in the t lymphocyte response stimulate
-cytotoxic cells which kill infected cells
-specific b cells
-phagocytes
describe the response of b lymphocytes to a foreign antigen (humoral response)
-specific b lymphocyte with complementary receptor binds to antigen
-this is stimulated by helper T cells which releases cytokines
-so divides rapidly by mitosis to form clones (clonal selection)
-differentiate into b plasma or b memory cells
what can b lymphocytes recognise
-free antigens, not just antigen presenting cels
what do b plasma cells do
-secrete large amounts of antibodies
what do b memory cells do
-remain in the blood for the secondary immune response
what are antibodies
-quaternary structure proteins
-secreted by b lymphocytes in response to specific antigens
-bind specifically to antigens forming antigen-antibody complexes
describe the structure of an antibody
-variable region
-constant region
-heavy polypeptide chain
-light polypeptide chain
-antigen binding site
-hinge region
-disulfide bridge
explain how antibodies lead to the destruction of pathogens
-antibodies bind to antigens on pathogens forming an antigen-antibody complex
-as they have a specific tertiary structure so the binding site is complementary to the antigen
-each antibody binds to 2 pathogens at a time causing agglutination of pathogens
-antibodies attract phagocytes
-phagocytes bind to the antibodies and phagocytose many pathogens at once
describe the primary immune response
-first exposure to antigen
-antibodies produced slowly and at a lower concentration
-takes time for specific b plasma cells to be stimulated to produce specific antibodies
-memory cells are produced
describe the secondary immune response
-second exposure to antigen
-antibodies produced faster and 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 antigens from attenuated pathogens
-stimulating formation of memory cells
explain how vaccines provide protection to individuals against disease
-specific b lymphocyte with complementary receptor binds to antigen
-specific t helper cell binds to antigen presenting cell and stimulates b cell
-b lymphocyte divides by mitosis to form clones
-some differentiate into b plasma cells which release antibodies
-some differentiate into b memory cells
-on second exposure to antigen, b memory cells divide rapidly by mitosis to produce b plasma cells
-these release antibodies faster and at a higher concentration
explain how vaccines provide protections for populations against disease
-herd immunity
as
-large proportion of population immune so don’t become ill from infection
-fewer infected people pass pathogen on/unvaccinated people less likely to come into contact with someone with the disease
what is herd immunity
-large proportion of population vaccinated, reducing spread of pathogen
describe active immunity
-initial exposure to antigen
-memory cells involved
-antibody produced and secreted by b plasma cells
-slow, takes longer to develop
-long term immunity as antibody can be produced in response to a specific antigen again
describe passive immunity
-no exposure to antigen
-no memory cells involved
-antibody introduced from another organism eg breast milk/placenta
-faster acting
-short term immunity as antibody hydrolysed
explain the effect of antigen variability on disease and disease prevention
-antigens on pathogens change shape/tertiary structure due to gene mutations (creating new strains)
-so no longer immune
-b memory cell receptors cannot bind to changed antigen on secondary exposure
-specific antibodies not complementary to changed antigen
examples of antigen variability affecting diseases
-yearly flu vaccinations developed
-no vaccine for HIV
-can catch a cold many times
describe the structure of a HIV particle
-lipid envelope
-RNA
-reverse transcriptase
-capsid
-attachment protein
describe the replication of HIV in helper T cells
-HIV attachment proteins attach to the receptors on helper T cell
-lipid envelope fuses with cell surface membrane, releasing capsid into cell
-capsid uncoats, releasing RNA and reverse transcriptase
-reverse transcriptase converts viral RNA to DNA
-viral DNA inserted/ incorporated into helper T cell DNA (may remain latent)
-viral protein/capsid/enzymes are produced
a) DNA transcribed into HIV mRNA
b) HIV mRNA translated into new HIV proteins
-virus particles assembled and released from cell (via budding)
explain how HIV causes the symptoms of AIDS
-HIV infects and kills helper T cells (host cell) as it multiplies rapidly
-so T helper cells cant stimulate cytotoxic T cells, B cells and phagocytes
-so B plasma cells can’t release as many antibodies for agglutination and destruction of pathogens
-immune system deteriorates so more susceptible to infections
-pathogens reproduce, release toxins and damage cells
explain why antibiotics are ineffective against viruses
viruses do not have structures/ processes that antibiotics inhibit:
-viruses do not have metabolic processes eg do not make protein/ribosomes
-viruses do not have bacterial enzymes/murein cell wall
what is a monoclonal antibody
-antibody produced from genetically identical/cloned B lymphocytes/plasma cells
-so have same tertiary structure
explain how monoclonal antibodies can be used in medical treatments
-monoclonal antibody has a specific tertiary structure/variable region
-complementary to receptor/protein/antigen found only on a specific cell type
-therapeutic drug attached to antibody
-antibody binds to specific cell, forming antigen-antibody complex, delivering drug
what are some monoclonal antibodies designed to do other than being attached to a therapeutic drug
-block antigens/receptors on cells
explain how monoclonal antibodies can be used in medical diagnosis
-monoclonal antibody has a specific tertiary structure/variable region
-complementary to specific receptor/protein/antigen associated with diagnosis
-dye/stain/fluorescent marker attached to antibody
-antibody binds to receptor forming antigen-antibody complex
explain the use of antibodies in the ELISA test to detect antigens (direct)
-attach sample with potential antigens to well
-add complementary monoclonal antibodies with enzymes attached that will bind to antigens if present
-wash well to remove unbound antibodies that could cause a fake positive
-add substrate - enzymes create products that cause a colour change (positive result)
explain the use of antibodies in the ELISA test to detect antigens (sandwich)
-attach specific monoclonal antibodies to well
-add sample with potential antigens, then wash well
-add complementary monoclonal antibodies with enzymes attaches which bind to antigens if present
-wash well to remove unbound antibodies that could cause a false positive
-add substrate - enzymes create products that cause a colour change
explain the use of antibodies in the ELISA test to detect antibodies (indirect)
-attach specific antigens to well
-add sample with potential antibodies, wash well
-add complementary monoclonal antibodies with enzyme attached which bind to antibodies if present
-wash well to remove unbound antibodies
-add substrate as enzymes create products that cause a colour change
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 on the ELISA test
-antibody with enzyme remains/not washed out
-so substrate converted into colour product
discuss some general ethical issues associates with the use of vaccines and monoclonal antibodies
-pre clinical testing on/ use of animals - potential harm/stress
but animals not killed and helps produce drugs to reduce human suffering
-clinical trials on humans - potential harm/side effects
-vaccines - may continue high risk activities and still develop/pass on pathogen
-use of drug- potentially dangerous side effects
suggest some points to consider when evaluating methodology relating to the use of vaccines and monoclonal antibodies
-was the sample size large enough to be representative
-were participants diverse in terms of age, sex, ethnicity and health
-were placebo/control groups used for comparison
-was the duration of the study long enough to show long term effects
-was the trial double blind to reduce bias
what is a double blind trial
-neither doctor/patient knew who was given drug or placebo
suggest some points to consider when evaluating evidence and data relating to the use of vaccines and monoclonal antibodies
-what side effects observed and how frequently
-was a statistical test used - difference in start and final results
-was the standard deviation of final results large
-did standard deviations of start and final results overlap
-what dosage was optimum
-does increasing dose increase effectiveness enough to justify extra cost
-was the cost of production and distribution low enough
