2.4 Cell Recognition And The Immune System Flashcards
What is an antigen?
- Cell surface membrane which stimulate immune response
- Usually glycoprotein, sometimes glycolipid or polysaccharide
- Immune system recognises as ‘self’ or ‘non-self’ = enables identification of cells from other organisms of same species, pathogens, toxins and abnormal body cells
How does phagocytosis destroy pathogens?
- Phagocyte moves toward pathogen via chemotaxis
- Phagocyte engulfs pathogen via endocytosis
- Phagosome fuses with lysosome
- Lysozymes digest pathogens
- Phagocyte absorbs the products from pathogen hydrolysis
Explain the role of antigen-presenting cells
- Macrophage displays antigen from pathogen on its surface
- Enhances recognition of helper T cells, which cannot directly interface with pathogens/antigens in body fluid
Give 2 differences between specific and nonspecific immune responses
- Nonspecific - same for all pathogens, specific - complementary pathogen
- Nonspecific - immediate, specific - time lag
Name two types of specific immune response
- Cell mediated
- Humoral
Outline the process of the cell-mediated response
- Complementary helper T lymphocytes bind to foreign antigen on APC
- Release cytokines that stimulate clonal expansion of complementary helper T cells and clonal expansion of cytotoxic T cells
What is clonal expansion of complementary helper T cells?
Become memory cells or trigger humoral response
What is clonal expansion of cytotoxic T cells?
Secrete the enzyme perforin to destroy infected cells
Outline the process of the humoral response
- Complementary T helper lymphocytes bind to foreign antigen on antigen-presenting T cells
- Release cytokines that stimulate clonal expansion of complementary B lymphocytes
- B cells differentiate into plasma cells
- Plasma cells secrete antibodies with complementary variable region to antigen
What is an antibody?
- Proteins secreted by plasma cells
- Quaternary structure: 2 ‘light chains’ held together by disulfide bridges, 2 longer ‘heavy chains’
- Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen
- The rest of the molecule is known as a constant region
How do antigens lead to the destruction of a pathogen?
Formation of antigen-antibody complex 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 cells/ B cells produced from primary immune response
- Remain in low levels in the blood
- Can divide very rapidly by mitosis if organism encounters the same pathogen again
Contrast the primary and secondary immune response
- Faster rate of antibody production
- Shorter time lag between exposure and antibody production
- Higher concentration of antibodies
- Antibody level remains higher after the secondary response
- Pathogen usually destroyed before any symptoms
What causes antigen variability?
- Random genetic mutation changes in DNA base sequence
- Results in different sequence of codons on mRNA
- Different primary structure of antigen = H bonds, ionic bonds and disulfide bridges form in different places in the tertiary structure
- Different shape of antigen
Explain how antigen variability affects the incidence of disease
- Memory cells no longer complementary to antigen = individual not immune = can catch the disease more than once
- Many varieties of a pathogen = difficult to develop vaccine containing all antigen types
Compare passive and active immunity
- Both involve antibodies
- Can be both natural or artificial
Examples of passive natural immunity
Antibodies in breast milk/across placenta
Examples of passive artificial immunity
Anti-venom, needle stick injections
Examples of active natural immunity
Humoral response to infection
Examples of active artificial immunity
Vaccination
Contrast passive and active immunity
- Passive: no memory cells and antibodies not replaced when broken down = short term, active: memory cells produced = long term
- Passive: immediate, active: time lag
- Passive: antibodies from external source, active: lymphocyte produce antibodies
- Passive: direct contact with antigen not necessary, active: direct contact with antigen necessary
Explain the principles of vaccination
- Vaccine contains dead/inactive form of a pathogen or antigen
- Triggers primary immune response
- Memory cells are produced and remain in the bloodstream, so secondary response is rapid and produces higher concentration of antibodies
- Pathogen is destroyed before it causes symptoms
What is herd immunity?
- Vaccinating a large proportion of population reduces available carriers of the pathogen
- Protects individuals who have not been vaccinated e.g. those with a weak immune system
Suggest some ethical issues surrounding the use of vaccine
- Production may involve use of animals
- Potentially dangerous side effects
- Clinical tests may be fatal
- Compulsory vs opt out
Describe the structure of HIV
- Genetic material (2x RNA) and viral enzymes surrounded by capsid
- Surrounded by viral envelope derived from host cell membrane
- GP120 attachment proteins on surface
How does HIV result in symptoms of AIDs?
- Attachment proteins bind to complementary CD4 receptor on T helper cells
- HIV particles replicate inside T helper cells, killing or damaging them
- AIDS develops when there are too few T helper cells for the immune system to function
- Individuals cannot destroy other pathogens and suffer from secondary diseases/infections
Why are antibiotics ineffective against viruses?
- Antibiotics often work by damaging murein cell walls to cause osmotic lysis
- Viruses have no cell wall
- Viruses replicate inside host cells = difficult to destroy them without damaging normal body cells
Suggest the clinical applications of monoclonal antibodies
- Pregnancy tests by detecting HCG hormones in urine
- Diagnostic procedures e.g. ELISA test
- Targeted treatment by attaching drug to antibody so that it only binds to cells with abnormal antigen
Explain the principle of the direct ELISA test
- Monoclonal antibodies bind to the bottom of the test plate
- Antigen molecules in the sample bind to the antibody. Rinse excess
- Mobile antibody with ‘reporter enzyme’ attached binds to antigens that are ‘fixed’ on the monoclonal antibodies. Rinse excess
- Add substrate for reporter enzyme. Positive result: colour change
What does a direct ELISA test do?
Detect the presence of a specific antigen
Explain the principle of an indirect ELISA test
- Antigens bind to the bottom of the test plate
- Antibodies in sample bind to antigen. Wash away excess
- Secondary antibody with ‘reporter enzyme’ attached binds to primary antibodies from the sample
- Add substrate for reporter enzyme. Positive result: colour change
What does an indirect ELISA test do?
Detects the presence of an antibody against a specific antigen
Suggest some ethical issues surrounding the use of monoclonal antibodies
- Production involves animales
- Drug trials against arthritis and leukaemia resulted in multiple organ failures
