cell recognition and immune system Flashcards

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1
Q

what is an antigen

A
  • cell-surface molecule which stimulate immune response
  • usually (glyco)protein, sometimes (glyco)lipid 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
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2
Q

how does phagocytosis destroy pathogens

A
  1. phagocyte moves towards pathogen via CHEMOTAXIS
  2. phagocyte engulfs pathogen via endocytosis to form a phagosome
  3. phagosome fuses with lysosome (PHAGOLYSOSOME)
  4. lysosomes digest pathogen
  5. phagocyte adsorbs the products from pathogen hydrolysis
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3
Q

explain the role of antigen-presenting cells (APCs)

A

macrophage displays antigen from pathogen on its surface (after hydrolysis)

enhances recognition by TH cells, which cannot directly interface with pathogens/antigens in body fluid

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4
Q

give 2 differences between specific and nonspecific immune responses

A

nonspecific (inflammation, phagocytosis) = same for all pathogens ; immediate

specific (B and T lymphocytes) = complementary pathogen ; time lag

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5
Q

2 types of specific immune response

A
  • cell mediated
  • humoral
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6
Q

outline process of cell-mediated response

A
  1. complementary TH lymphocytes bind to foreign antigen on APC
  2. release cytokines that stimulate:
    a) clonal expansion of complementary TH cells (rapid mitosis): become memory cells or trigger HUMORAL RESPONSE
    b) clonal expansion of cytotoxic T cells (Tc): secrete enzyme perforin to destroy infected cells
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7
Q

outline process of humoral response

A
  1. complementary TH lymphocytes bind to foreign antigen or antigen-presenting T cells
  2. release cytokines that stimulate clonal expansion (rapid mitosis) of complementary B lymphocytes
  3. B cells differentiate into plasma cells
  4. plasma cells secrete antibodies with complementary variable region to antigen
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8
Q

what is an antibody

A
  • proteins secreted by plasma cells
  • quaternary structure: 2 ‘light chains’ held together by disulfide bridge, 2 longer ‘heavier chains’
  • binding sites on variable region of light chains have specific tertiary structure complementary to an antigen
  • rest of the molecule known as constant region
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9
Q

how do antibodies lead to the destruction of pathogen

A

formation of antigen-antibody complex results in AGGLUTINATION which enhances phagocytosis

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10
Q

what are monoclonal antibodies

A

antibodies produced from a single clone of B cells

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11
Q

what are memory cells

A
  • specialised TH / 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
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12
Q

secondary immune response compared to primary immune response

A

secondary
- has 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

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13
Q

what causes antigen variability

A
  1. random genetic mutation changes DNA base sequence
  2. results in different sequence of codons on mRNA
  3. different primary structure of antigen = H-bonds, ionic bonds and disulphide bridges form in different places in tertiary structure
  4. different shape of antigen
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14
Q

explain how antigen variability affects the incidence of disease

A
  • 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
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15
Q

examples of passive natural

A

antibodies in breast milk/across placenta

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16
Q

examples of passive artificial

A

antivenom, needle stick injections

17
Q

examples of active natural

A

humoral response to infection

18
Q

examples of active artificial

A

vaccination

19
Q

passive immunity

A
  • no memory cells and the antibodies are not replaced after breaking down = short-term
  • immediate response
  • antibodies from external source
  • direct contact with antigen not necessary
20
Q

active immunity

A
  • memory cells produced = long term
  • time lag
  • lymphocytes produce antibodies
  • direct contact with antigen necessary
21
Q

explain principle of vaccination

A
  1. vaccine contains dead/inactive form of pathogen or antigen
  2. triggers primary immune response
  3. memory cells are produced and remain in the bloodstream, so secondary response is rapid and produces higher concentration of antibodies
  4. pathogen destroyed before causing symptoms
22
Q

what is herd immunity

A

vaccinating large proportion of population reduces available carriers of the pathogen
protects individuals who have not been vaccinated e.g. those with weak immune system

23
Q

suggest ethical issues surrounding use of vaccines

A
  • production may involve use of animals
  • potentially dangerous side-effects
  • clinical tests may be fatal
  • compulsory vs opt-out
24
Q

describe the structure of HIV

A
  • genetic material (2xRNA) and viral enzymes (integrase and reverse transcriptase) surrounded by capsid
  • surrounded by viral envelope derived from host cell membrane
  • GP120 attachment protein on surface
25
Q

how does HIV result in the symptoms of AIDS

A
  1. attachment proteins bind to complementary CD4 receptor on TH cells
  2. HIV particles replicate inside TH cells, killing or damaging them
  3. AIDS develops when there are too few TH cells for the immune system to function
  4. individuals cannot destroy other pathogens and suffer from secondary diseases/infections
26
Q

why are antibiotics ineffective against viruses

A

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

27
Q

suggest the clinical application of monoclonal antibodies

A
  • 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 e.g. cancer cells due to specificity of tertiary structure of binding site
28
Q

explain the principle of a direct ELISA test

A

detects presence of a specific antigen

  1. monoclonal antibodies bind to bottom of test plate
  2. antigen molecules in sample bind to antibody. rinse excess.
  3. mobile antibody with ‘reporter enzyme’ attached binds to antigens that are ‘fixed’ on the monoclonal antibodies. rinse excess
  4. add substrate for reporter enzyme. positive result: colour change
29
Q

explain the principle of an indirect ELISA test

A

detects presence of an antibody against a specific antigen

  1. antigens bind 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 sample
  4. add substrate for reporter enzyme. positive result: colour change
30
Q

suggest ethical issues around monoclonal antibodies

A
  • production involves animals
  • drug trials against arthritis and leukaemia resulted in multiple organ failure