3.2.4 Cell recognition and the immune system Flashcards
What is an antigen
Cell surface molecule which stimulate immune response
Usually glycoprotein or glycolipid or polysaccharide
Immune system recognises as self or non self = enabled identification of cells from other organisms of same species, pathogens, toxins and abnormal body cells
foreign protein that stimulates an immune response
How do phagocytes destroy pathogens
Phagocytes in blood engulf pathogen to form a phagosome
Phagosome fuses with lysosome, lysozymes hydrolyse the pathogen
The phagocyte then presents the antigens on its surface to activate other immune system cells. The phagocyte acts as an antigen presenting cell
Explain the role of antigen presenting cells
Macrophage displays an antigen from pathogen on its surface
Enhances recognition by TH cells which cannot directly interface with pathogens/antigens in body fluid
2 differences between specific and nonspecific immune response
Nonspecific = immediate
Specific = time lag
Nonspecific = same for all pathogens
Specific= complementary to pathogen
2 types of specific immune response
Cell mediated
Humoral
Outline the process of cell mediated response
Complementary T helper cells bind to foreign antigen
Release cytokines that stimulate
a) clonal selection of complementary T lymphocyte cells become memory cells or trigger humoral response
b) clonal selection of cytotoxic T cells secrete enzymes to hydrolyse infected cells
Outline the process of the humoral repsonse
Complementary TH cells bind to foreign antigen in antigen presenting T cells
Release cytokines that stimulate clonal selection of B lymphocytes with complimentary antibody to foreign antigens
B cells differentiate into plasma cells
Plasma cells secrete monoclonal antibodies with complementary variable region to antigen
What is an antibody
Proteins secreted by plasma cells that is specific to an antigen
Quaternary structure
Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen
The rest of the molecule is 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 produces from a single clone of B cells
What are memory cells
Specialised TH/B cells produced from primary immune response
Remain in low levels in the blood
Can divide very rapidly by mitosis if organisms encounters the same pathogen again
Contrast the primary and secondary immune response
Secondary - 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 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 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
Give examples of both types
Both involve antibodies, both can be natural or artificial
Passive N - antibodies in breastmilk/placenta
Passive A - anti-venom, needle stick injections
Active N - humoral response to infection
Active A - vaccination
Contrast passive and active immmunity
Passive - no memory cells produces and antibodies not replaced when broken down = short term
Immediate
Antibodies from external source
Direct contact with antigen not necessary
Active - memory cells produced = long term
Time lag
Lymphocytes produce antibodies
Direct contact with antigen necessary
Explain the principles of vaccination
Vaccine contains dead/inactive form of pathogen
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 usually destroyed before it causes symptoms
What is herd immunity
Vaccinating large proportion of population reduces available carriers of the pathogen
Protects individuals who have not been vaccinated
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 (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
How does HIV result in the symptoms of AIDS?
Attachment proteins bind to complementary CD4 receptor on TH cells
HIV particles then replicate inside TH cells killing or damaging them
AIDS develops when there are too few TH 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 eg ELISA test
Targeted treatment by attaching drug to antibody so that it only binds to cells with abnormal antigen eg cancer cells due to specificity of tertiary structure of binding site
Explain the principle of a direct ELISA test (detects antigen)
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 antigens 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 antibody)
Antigens bind to bottom of 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
Suggest some ethical issues surrounding the use of monoclonal antibodies
Production involves animals
Drug trials against arthritis and leukaemia resulted in multiple organ failure
