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PHAR20400 > HOST DEFENCE 2 > Flashcards

HOST DEFENCE 2 Flashcards

1
Q

What’s the role of TH / CD4+ cells?

A

Recognise antigens presented on Class II MHC (Major Hisrocompatibilty Complex)

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2
Q

What are the three antigen presenting cells?

A
  • Dendritic cells
  • B cells
  • Macrophages
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3
Q

What are the different types of TH/ CD4+ T cells and what are their functions?

A
  1. TH1 - stimulates cell mediated immunity (CDI)
  2. TH2 - stimulate the growth of specific plasma cell and antibody secretion
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4
Q

What’s the role of Tc or CD8+ T cells?

A
  • Recognise Antigen presented on class I MHC.
  • Trigger cytotoxicity (Cell Mediated Immunity)
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5
Q

All nucleated cells in the body produce MHC Class I molecules. True or false?

A

True

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6
Q

What’s the function of B lymphocyes?

A

Differentiate to plasma cells which produce antibodies (stimulated by cytokines)

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7
Q

Describe the structure of antibodies/ immunoglobulins? (6)

A
  • Tetramer of two light chains and two heavy chains
  • Light chains are two types - the lambda and kappa families 
  • Heavy chains form a single family
  • Each chain has an N-terminal variable region (V) and a C-terminal constant region (C)
  • The V domain recognizes antigen
  • The C domain binds to specific receptors present in cells of the immune system such as macrophages
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8
Q

What’s the function of antibodies? (4)

A
  • Opsonisation - antibodies bind to the pathogen, this attracts phagocytes
    • N terminal binds to the antigen
    • Fc portion of the antibody binds to an Fc receptor on the phagocyte, facilitating phagocytosis
  • Neutralisation - ability of the antibody to prevent the interaction between the pathogen and the cell
  • Complement Activation
  • Antibody dependent Cytotoxicity - antibody bound to pathogen interacts with Fc receptors on the NK cell = leads to release of cytoplasmic granules containing perforin and granzymes.
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9
Q

Where are dendritic cells found?

A

Found in thymus, lymph nodes and spleen (lymphoid organs)

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10
Q

What’s the function of dendritic cells?

A

Present the antigen or bring it to the lymphoid organs where an immune response is initiated = informing T cells that there is an infected cells

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11
Q

What are the different types of specific acquired immunity and what microbes do eliminate?

A
  • Humoral immunity - extracellular microbe
  • Cell-mediated immunity - intracellular microbe (phagocytosed microbes or microbes replicating within infected cells)
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12
Q

What lymphocytes are involved in humoral immunity?

A

B lymphocyte

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13
Q

What lymphocytes are involved in cell-mediated immunity? (2)

A
  • Helper T lymphocytes - phagocytosed microbes
  • Cyotoxic lymphocytes - microbes replicating within infected cell
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14
Q

How are infected cells killed by Tc lymphocytes?

A
  • CTL precursors are activated
  • TCR-MHC mediated recognition of target cells and re-orientation of the killing machinery on target cell through polarisation (lytic granules are orientated where MHC class I engages with TCR)
  • lytic granules within T cell fuse with cell membrane releasing contents into small gap between T cell and target cell = cytotoxins + pores created on the cell membrane
  • CTL then dissociates from the target = not affected
  • the release of perforin pokes holes in cell = allows entry of Granzyme B = pathogen is killed by apoptosis
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15
Q

What are the three characteristics of vaccinations?

A
  • Vaccine immunogenicity
  • Vaccine efficacy
  • Vaccine effectiveness
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16
Q

What is meant by vaccine immunogenicity?

A

The ability to induce antibodies

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17
Q

What is meant by vaccine efficacy?

A

Reduction in incidence between those who have been vaccinated and those who haven’t

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18
Q

What is meant by vaccine effectiveness?

A

The ability of a vaccine to protect a community

19
Q

Describe the 5 different types of vaccines

A
  • Killed Virulent Organism: Pathogen killed but antigen intact
    • e.g. Whooping cough
  • Live Attenuated: Strain doesn’t cause disease but still elicits an immune response
    • e.g. Rubella
  • Modified Toxins: Toxin treated with heat/chemicals, no symptoms experienced but immune response is triggered
    • Diphtheria
  • Isolated Antigens: Antigen injected to elicit immune response
    • Influenza
  • Genetically Engineered Antigens: Antigen is isolated and genetically engineered
    • Hepatitis B
20
Q

What affects the response to a vaccine? (7)

A
  • Antigen content (e.g. live vaccines have higher content)
  • Protein content (results in increased antibody content)
  • Adjuvants present
  • Type of antigen
  • Dosage intervals - Longer intervals = more MHC interaction
  • Genetics
  • Age
21
Q

How do viruses replicate? (8)

A
  • Adsorption: the attachment of the extracellular virus particle to the surface of the host cell
  • Penetration: virus fuse their envelope with the plasma membrane of the host cell and move into the cystol (endocytosis)
  • Uncoating: is broken down and viral genome is released into the cytoplasm.
  • Transcription: the production of viral mRNA (enzymes that are required are in the nucleocapsid)
  • Translation: the production of viral polypeptides from viral mRNA
  • Replication
  • Assembly: the newly replicated viral genes are encapsidated.
  • Egress: the release of virus from the infected cell
22
Q

How does the immune system identify virally infected cells?

A
  • The proteases of the host cell break down the viral products
  • These bind to MHC class 1 (if epithelial cell) in the endoplasmic reticulum
  • They are transferred onto the surface of the epithelial cell and the viral antigen is displayed on the surface.
23
Q

What is the first response against the viral infection?

A

Non-specific.
Cytokines produced include IFN-alpha, IFN-beta, TNF-alpha and IL-12 (act on target cells to inhibit viral replication, not the virus)

24
Q

What is the second response against a viral infection? (After cytokines)

A
  • NK mediated killing of infected cells
25
Q

What is the third response against a viral infection?

A
  • Specific
  • T-cell mediated killing of infected cell
26
Q

What type of virus is Influenza?

A

Single stranded RNA virus

27
Q

Which types of influenza virus can infect humans?

A
  • Type A
  • Type B
  • Type C

(so, all types of influenza virus can infect humans)

28
Q

Which types of influenza virus cannot infect birds/animals?

A

Type B
Type C

29
Q

Which antigenic surface proteins does the influenza virus have?

A

Haemagglutinin
Neuraminidase

30
Q

How many types of haemagglutinin are there?

A

15 types

31
Q

How many types of neuraminidase are there?

A

9 types

32
Q

What caused the 1918 “Spanish influenza”?

A

Bird-to-human transmission of H1N1 virus

33
Q

What type of haemagglutinin/ neuraminidase caused the 1957 “Asian Influenza”?

A

H2N2

34
Q

What type of haemagglutinin/ neuraminidase caused the 1968 “Hong Kong Influenza”?

A

H3N2

35
Q

What is the function of haemagglutinin?

A
  • Binds to sialic acid-containing receptors expressed on the host cells (this allows the endocytosis of the virion)
36
Q

What is the function of neuraminidase?

A
  • Cleaves the bond between the host cell and the newly produced viruses (this allows the viruses release into the body and spread the infection)
37
Q

What protein does the virus use to produce a new capsid?

A

M1 protein

38
Q

What is the function of M2 proteins?

A
  • Proton pump (buffers the pH of the environment where the virus is = more virions produced)
39
Q

What is the problem with trying to target haemagglutinin receptors by making antibodies against them?

A

Every year, a different type of haemagglutinin is in circulation = new vaccine needed because the antibodies are different

40
Q

What are the 2 types of epidemics that can occur?

A

Antigenic drift and Antigenic shift

41
Q

What is antigenic drift?

A
  • minor changes to the surface of the influenza virus (small changes in haemagglutinin)
42
Q

What is a antigenic shift?

A
  • two or more different strains of a virus combine to form a new subtype = different type of neuraminidase and haemaggluttin
    (RNA exchanged)
  • The virus is not recognized
43
Q

How can viruses evade the B and T cell immune response?

A
  • Inhibition of the function of cytokines
  • Inhibition of antigen presentation
  • Reduction of the MHC class I expression 
  • Reduce the levels of class II MHC molecules (HIV and measles do this)
  • Evade complement mediated destruction 
  • Constantly changing their antigens (influenza virus) = cannot be recognised

PHAR20400 (20 decks)

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