12 - B cell Mediated Immunity Flashcards

1
Q

What do forms do antibodies exist in

A
  1. Membrane-bound antibodies on the surface of B lymphocytes function as antigen receptors
  2. Secreted antibodies neutralise toxins, prevent the entry and spread of pathogens, and eliminate microbes.
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2
Q

3 hypervariable regions

A
  • Three hypervariable regions of a Variable light domain and the three hypervariable regions of a Variable heavy domain are brought together to create an antigen-binding surface
  • Also called complementarity-determining regions (CDRs): CDR1, CDR2, CDR3 (most extensive contact is with CDR#)
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3
Q

Dissociation constant (Kd)

A

Represents affinity of antibody

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4
Q

Main antibody functions

A
  • Neutralisation of microbes and toxins
  • Opsonisation and phagocytosis of microbes
  • ADCC
  • Phagocytosis of microbes opsonised with complement fragments
  • Inflammation (through complement activation)
  • Lysis of microves (through complement activation)
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5
Q

Antibody responses in lymphoid tissues

A
  • Develop under direction of Tfh cells
  • Antigen is retained for long periods in these complexes as iccosomes
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6
Q

What do activated B cells that undergo rounds of mutation and selection for higher affinity mutants in the germinal centre result in

A

High- affinity antibody-secreting plasma cells and high-affinity memory B cells

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7
Q

Half-life of IgE

A
  • Very short (~2 days)
  • Although cell-bound IgE associated with the high-affinity IgE receptor on mast cells has a very long half-life
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8
Q

Half life of IgA

A

~ 3 days

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9
Q

Half life of IgM

A

~ 4 days

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10
Q

Half life of IgG

A

21-28 days

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11
Q

B cell proliferation and differentiation outcomes

A
  • Antibody secretion
  • Isotope switching
  • Affinity maturation
  • Memory B cell
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12
Q

Distributions and functions of immunoglobulin classes

A
  • Antibodies of different classes operate in distinct places and have distinct effector functions.
  • Transport proteins that bind to the Fc regions of antibodies carry particular isotypes across epithelial barriers.
  • Antibodies can block adherence of bacteria to host cells
  • Antibody:antigen complexes activate the classical pathway of complement by binding to C1q.
  • Complement receptors are important in the removal of immune complexes from the circulation.
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13
Q

High-affinity IgG and IgA

A
  • Can neutralise bacterial toxins.
  • Can inhibit the infectivity of viruses.
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14
Q

Structure of IgM and IgA

A
  • Can form multimers, in association with an additional polypeptide chain, the J chain
  • IgA is dimeric and IgM is pentameric
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15
Q

IgG function

A
  • Opsonisation of antigens for phagocytosis by macrophages and neutrophils
  • Activation of classical pathway
  • ADCC
  • Transfer of antibody across placenta and gut
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16
Q

IgM function

A

Activation of classical pathway and antigen receptor of naive B lymphocytes

17
Q

IgA function

A

Mucosal immunity

18
Q

IgE function

A

Mast cell degranulation (immediate hypersensitivity reactions)

19
Q

IgD function

A

Antigen receptor of naive B lymphocytes

20
Q

Secretary dimeric IgA

A

Binds to the layer of mucous overlaying the gut epithelium and acts as an antigen-specific barrier to pathogens and toxins in the gut lumen

21
Q

Poly Ig receptor

A

Facilitates transport of dimeric IgA from the lamina proprietor, across the mucosal epithelium and into the lumen

22
Q

What is the dominance of IgA production by intestinal plasma cells due to

A

Due to selective induction of IgA isotype switching in B cells in GALT and mesenteric lymph nodes

23
Q

How do antibodies neutralise microbes and microbial toxins

A
  • Blocks binding of microbe and infection of cell
  • Blocks infection of adjacent cell
  • Blocks binding of toxin to cellular receptor
24
Q

What is classical complement pathway initiated by

A

Binding of the complement protein C1 to IgG or IgM molecules that have bound antigen

25
Q

Which IgG antibodies are more efficient activators of complement

A

IgG3 and IgG1

26
Q

Form of antibodies that can initiate classical pathway activation

A

Only antibodies bound to antigens, not free circulating antibodies

27
Q

Do free Ig cross link Fc receptors

A

NOOOOOOOOOO

28
Q

Opsonisation

A
  • Bacterium is coated with complement and IgG antibody
  • When C3b binds to CR1 and antibody binds to Fc receptor, bacteria are phagocytosed
  • Phagosome is formed
  • Lysosomes fuse with these vesicles, delivering enzymes that degrade the bacteria
29
Q

Neonatal Fc recetor

A
  • Involved in the transport of IgG from the maternal circulation across the placental barrier as well as the transfer of maternal IgG across the intestine in neonates
  • Does this by recycling IgG to cell surface rather than destroying by lysosomes
30
Q

How are neonatal mammals protected from infection at birth

A
  • Maternally produced antibodies transported across placenta (IgG)
  • Antibodies in ingested breast milk (IgA and IgG)
31
Q

Mast cell activation

A

Activated by cross-linking of FcεRI molecules, which occurs by binding of multivalent antigens to the IgE molecules that are attached to the Fc receptors

32
Q

Antibody Dependent Cellular Cytotoxicity (ADCC)

A

Natural killer (NK) cells and other leukocytes bind to antibody-coated cells by Fc receptors and destroy these cells

33
Q

NK cells and ADCC

A
  • NK cells use their Fc receptor, FcγRIIIA, to bind to antibody-coated cells.
  • FcγRIIIA (CD16) is a low-affinity receptor that binds clustered IgG molecules displayed on cell surfaces but does not bind circulating monomeric IgG.
  • Therefore, ADCC occurs only when the target cell is coated with antibody molecules
34
Q

Immune complex removal

A

Immune complexes bind to CR1 on RBC, which transports them to the liver and spleen, where they are removed by macrophages expressing receptors for both Fc and bound C’

35
Q

Antibody isotope in primary vs secondary response

A
  • Primary: IgM > IgG
  • Secondary: IgG predominates, and IgA or IgE depending on type of infection