Cell recognition & the immune system (5) Flashcards
What is an antigen?
cell-surface molecule which stimulates immune response
What are antigens usually?
glycoproteins, sometimes glycolipids or polysaccharides
What is the advantage of the immune system recognising ‘self’ and ‘non-self’?
enables identification of cells from other organisms of same species, pathogens, toxins and abnormal body cells
How can organisms identify cells, pathogens, toxins and abnormal cells?
immune system recognises ‘self’ and non-self’
What are the 5 steps on how phagocytosis destroys pathogens?
1) phagocyte moves towards pathogen via chemotaxis
2) phagocyte engulfs pathogen via endocytosis to form a phagosome
3) phagosome fuses with lysosome (phagolysosome)
4) lysozymes digest pathogen
5) phagocyte absorbs products from pathogen hydrolysis
What are the 2 roles of antigen-presenting cells?
- macrophage displays antigen from pathogen on its surface after hydrolysis in phagocytosis
- enhances recognition by T helper cells, which cannot directly interact with pathogens/antigens in body fluid
What are the 2 types of immune response?
nonspecific
specific
What does the non-specifc response involve?
inflammation
phagocytosis
What does the specific response involve?
B and T lymphocytes
What are 2 differences between the non-specific and specific responses?
- non is same for all pathogens, specific is complementary to pathogen
- non is immediate, specific has a time lag
What are the 2 types of specific response?
cell-mediated
humoral
What are the cell-mediated and humoral responses?
types of specific immune responses
What are the 2 steps of the cell-mediated response?
1) complementary T helper lymphocytes bind to foreign antigen on antigen-presenting cells
2) release cytokines that stimulate 2 things
What 2 things do cytokines stimulate in the cell-mediated response?
- clonal expansion of complementary T helper cells (rapid mitosis) so they become memory cells or trigger the humoral response
- clonal expansion of cytotoxic T cells which secretes the enzyme perforin to destroy infected cells
What are the 3 steps of the humoral response?
1) complementary T helper lymphocytes bind to foreign antigen on antigen-presenting T cells
2) release cytokines that stimulate clonal expansion of complementary B lymphocytes
3) B cells differentiate into plasma cells which secrete antibodies with complementary variable region to antigen
What are antibodies?
proteins secreted by plasma cells
How does the quaternary structure relate to antigens?
The quaternary structure has 2 light chains which have binding sites on variable regions that have a specific tertiary structure complementary to an antigen. The rest of the molecule is known as the constant region.
How do antibodies lead to the destruction of a pathogen?
form antigen-antibody complex which results in agglutination, which enhances phagocytosis
What are monoclonal antibodies?
antibodies produced from a single clone of B cells
What are memory cells?
specialised T helper and B cells produced from the primary immune response
Where are memory cells found?
remain in low levels in the blood
What is the function of memory cells?
can divide rapidly by mitosis if organism encounters the same pathogen again
What are 5 differences between the primary and secondary responses?
Secondary response:
- faster rate of antibody production
- shorter time lag between exposure and antibody production
- high concentration of antibodies
- antibody level remains high after secondary response
- pathogen usually destroyed before any symptoms
What 4 factors cause antigen variability?
1) random genetic mutation changes DNA base sequence
2) results in different sequence of codons on mRNA
3) different primary structure of antigen means H-bonds, ionic bonds and disulfide bridges form in different places in tertiary structure
4) different shape of antigen
What 2 ways does antigen variability affect incidence of disease?
- memory cells no longer complementary to antigen so individual is not immune so can catch the disease more than once
- many varieties of a pathogen so difficult to develop vaccine containing all antigen types
What are 2 similarities between passive and active immunity?
- both involve antibodies
- both can be natural or artificial
What are the 4 types of immunity?
passive natural
passive artificial
active natural
active artificial
What is an example of passive natural immunity?
breast milk
What is an example of passive artificial immunity?
anti-venom
What is an example of active natural immunity?
humoral response to infection
What is an example of active artificial immunity?
vaccination
What are 5 features of passive immunity?
- no memory cells as it is a short-term response
- antibodies not replaced when broken down as it is a short-term response
- immediate
- antibodies from external source
- direct contact with antigen not necessary
What are 4 features of active immunity?
- memory cells produced as it is a long-term response
- time lag
- lymphocytes produced antibodies
- direct contact with antigen necessary
What are vaccinations made from?
contains dead/inactive form of pathogen or antigen
What 3 things do vaccinations do?
1) trigger primary immune response
2) cause memory cells to be produced and remain in bloodstream so secondary response is rapid and produces higher concentration of antibodies
3) ensures pathogen is destroyed before it causes symptoms
What is herd immunity?
when large proportion of population is vaccinated to reduce the available carriers of the pathogen
What is the benefit of herd immunity?
protects individuals who have not been vaccinated e.g. those with a weak immune system
What are 3 ethical issues of vaccinations?
- production may involve use of animals
- potentially dangerous side-effects
- clinical tests may be fatal
What is the structure of HIV?
- genetic material (x2 RNA) and viral enzymes (integrase and reverse transcriptase) surrounded by capsid
- surrounded by viral envelope derived from host cell membrane
- GP120 attachment proteins on surface
What are 2 reasons why antibiotics are ineffective against viruses?
1) antibiotics often work by damaging murein cell walls to cause osmotic lysis, however viruses have no cell wall
2) viruses replicate inside host cells so it is difficult to destroy them without damaging normal body cells
What are the 4 steps in how HIV results in symptoms of AIDS?
1) attachment proteins bind to complementary CD4 receptor in T helper cells
2) HIV particles replicate inside T helper cells, killing or damaging them
3) AIDS develops when there are too few T helper cells for immune system to function
4) individuals cannot destroy other pathogens and suffer from secondary diseases/infections
What are 3 clinical applications of monoclonal antibodies?
1) pregnancy tests by detecting HCG hormones in urine
2) diagnostic procedures e.g. ELISA test
3) targeted treatment by attaching drug to antibody so it only binds to cells with abnormal antigen e.g. cancer cells due to specificity of tertiary structure of binding site
What does the direct ELISA test do?
detects presence of a specific antigen
What are the 4 steps of a direct ELISA test?
1) monoclonal antibodies bind to bottom of test plate
2) antigen molecules in sample bind to antibody (rinse excess)
3) mobile antibody with reporter enzymes attached, binds to antigens that are fixed on the monoclonal antibodies (rinse excess)
4) add substrate for reporter enzyme, a positive result will cause a colour change
What are the 2 types of ELISA test?
direct
indirect
What does the indirect ELISA test do?
detects presence of antibody against specific antigen
What are the 4 steps of the indirect ELISA test?
1) antigens bind to bottom of test plate
2) antibodies in sample bind to antigen (rinse excess)
3) secondary antibody with receptor enzyme attacked, binds to primary antibodies from the sample
4) add substrate for reporter enzyme, a positive result will cause a colour change
What are 2 ethical issues of monoclonal antibodies?
- production involves animals
- drug trials against arthritis and leukaemia resulted in multiple organ failures
