2.4 Cell recognition and the immune system Flashcards
What is an antigen?
Cell-surface molecule which stimulate immune response.
Usually (glyco)protein, sometime (glyco)lipds or polysaccharide
Immmune system recognises as “self” or “non-self” enabling identification of cells from other organisms of same species, pathogen, toxins and abnormal body cells
How does phagocytosis destroy pathogens?
- Phagocyte moves towards pathogen via chemotaxis
2.phagocyte engulfs the pathogen via endocytosis to form a phagosome
3.phagosome fuses with lysosome (phagolysome)
4.lysozymes digest pathogen
5.phagocyte absorbs the products from pathogen hydrolysis
Explain the role of antigen-presenting cells (APCs)
Macrophage displays antigens from pathogen on its surface (after hydrolysis in phagocytosis)
Enhancing recognition by T helper cells which cannot directly interface with pathogens/antigens in body fluid
Give 2 differences between specific and nonspecific immune responses
Nonspecific (inflammation, phagocytosis) = same for all pathogens and an immediate response
Specific (B and T lymphocytes) = complementary pathogen and has a time lag
Name the two types of specific immune response
Cell mediated
Humoral
Outline the process of the cell-mediated response
In cell mediated response Complementary T helper lymphocytes bind to foreign antigen on APC. Releasing cytokines that stimulate the clonal expansion of complementary T helper cells by rapid mitosis which become memory cells or trigger humoral response or the clonal expansion of cytotoxic T cells which secrete enzyme perforin to destroy infected cells
Outline the process 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(rapid mitosis) of complementary B lymphocytes
3.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, Contains a 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 the constant region
How do antibodies 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/B cells produced from primary immune response,remaining in low levels in the blood. They are able to divide very rapidly by mitosis if organism encounters the same pathogen again
Contrast the primary and secondary immune response
Secondary response
Faster rate of antibody production
Shorter time lag between exposed 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?
Antigen variability is caused by
1.Random genetic mutation changes DNA base sequence
2.Results in different sequence of codons on mRNA
3.Different primary structure of antigens formed as H-bonds, ionic bonds and disulfide bridges form in different places in tertiary structure
4.Different shape of antigen
Explain how antigen variability affects the incidence of disease
Memory cells no longer complementary to antigen so the individual not immune meaning that they can catch the disease more than once
Many varieties of a pathogen so difficult to develop vaccine containing all antigen types
Compare passive and active immunity.
Give examples of both types
Both involve antibodies
Can both be natural or artificial
Passive natural: antibodies in breast milk/ across placenta
Passive artificial: needle stick injections
Active natural: humoral response to infection
Active artificial: vaccination
Contrast passive and active immunity
Explain the principle of vaccination
1.Vaccine contains dead/inactive form of a pathogen or antigen
2.Triggers primary immune response
- Memory cells are produced and remain in the bloodstream, so secondary response is rapid and produces higher concentration of antibodies
4.pathogen is destroyed before it causes symptoms
What is heard Immunity
Vaccinating large proportion of population reduces available carriers of the pathogen
Protects individuals who have not been vaccinated e.g. those with weak immune systems
Suggest some ethical issues surrounding the use of vaccines
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 (2XRNA) and viral enzymes (integrase and reverse transcriptase) surrounded by capsid
Surrounded by viral envelope derived from host cell membrane
GP120 attachment proteins on surface
How does HIV result in the symptoms of AIDS?
1, attachment proteins bind to complementary CD4 receptors on T helper cells
- HIV particles replicate inside T helper cells, killing or damaging them
- AIDS developes 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
Targeted treatment by attaching drug to antibody so that it only binds to cells with abnormal antigen e.g. cancer cells due to specificity of tertiary structure of binding site
Explain the principle of a direct ELISA test
Detects presence of a specific antigen
1.Monoclonal antibodies bind to bottom of test plate
- Antigen molecules in sample bind to antibody. Rinse excess
- Mobile antibody with ‘reporter enzyme’ attached binds to antigen that are ‘fixed’ on the monoclonal antibodies. Rinse excess.
- Add substrate for reporter enzyme. Positive result: colour change
Explain the principle of an indirect ELISA test
Detects presence of an antibody against a specific antigen
1.antigen binds to bottom of test plate.
2.Antibodies in sample bind to antigen. Wash away excess.
3. Secondary antibody with ‘reporter enzyme’ attached binds to primary antibodies from the sample
4.add substrate for reporter enzyme. Positive result: colour change
Suggest some ethical issues surrounding the use of monoclonal antibodies
Production involves animals
Drug trials against arthritis and leukaemia resulted in multiple organ failure
