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Immune recognition and memory

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A vaccine stimulates the recipient's own memory response. This is...

  1. artificially acquired active immunity.
  2. artificially acquired passive immunity.
  3. naturally acquired active immunity.
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artificially acquired active immunity.

Vaccination deliberately stimulates the recipient's adaptive response.

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Which is a role of a cytotoxic T cell?

  1. Secreting antigen-specific antibodies to neutralise free virions
  2. Binding free virus particles in the blood through its T-cell receptor.
  3. Clearing extracellular bacteria mainly by phagocytosis
  4. Triggering apoptosis of an infected cell that presents the matching antigen
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Triggering apoptosis of an infected cell that presents the matching antigen

Apoptosis, programmed cell death, removes a cellular site of pathogen replication.

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Which order is correct?

  1. Matching cell activation -> clonal expansion -> effector/memory descendants
  2. Antigen instructs a new matching receptor -> expansion -> memory
  3. All receptor types expand equally -> antigen selects their antibodies
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Matching cell activation -> clonal expansion -> effector/memory descendants

Selection and proliferation generate a focused response.

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After a second exposure to antigen P, antibody to P rises within 3 days. At the same time, a first exposure to antigen Q gives antibody to Q only after 10 days. Which conclusion is best supported?

  1. The immune system was weaker during exposure to Q.
  2. Memory cells for P but not Q were present.
  3. Q is a more dangerous antigen than P.
  4. Antibodies to P also bind Q.
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Memory cells for P but not Q were present.

A fast response needs memory from an earlier exposure. Q has never been met, so it gets a slower primary response.

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Which region most directly determines antigen-binding specificity?

  1. The variable regions at the binding sites
  2. The hinge and its disulfide bridges alone
  3. Only the constant tail, regardless of the tips
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The variable regions at the binding sites

Their shape and chemistry determine recognition.

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Which statements about an IgG molecule are correct? 1: It has two identical antigen-binding sites. 2: It is made of four polypeptide chains. 3: Its Fc region binds receptors on phagocytes. 4: Its variable regions differ between its two arms.

  1. 1, 2, 3 and 4
  2. 1, 2 and 3 only
  3. 2, 3 and 4 only
  4. 1 and 2 only
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1, 2 and 3 only

IgG has two heavy and two light chains, two identical binding sites and an Fc region that phagocytes recognise. Both arms share the same variable regions.

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Which event directly underlies affinity maturation?

  1. Initial V(D)J recombination before antigen exposure
  2. Class switching with no variable-region variation or selection
  3. Variable-region hypermutation followed by selection of suitable B-cell variants
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Variable-region hypermutation followed by selection of suitable B-cell variants

Mutation supplies variants and selection can enrich higher-affinity binding.

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Question 1 of 9

Trace a response from presentation to antibodies

5 marks

A dendritic cell engulfs a bacterium in the skin. Outline how this leads to the production of antibodies against the bacterium. Name the MHC class involved, explain how a helper T cell recognises the antigen, and state the role of cytokines. [5]

Engulf, process, present on MHC class II; T-cell receptor binds the complex; cytokines activate B cells.

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