Lecture 29 - B Cells. Flashcards

1
Q

What is the basic structure of an immunoglobulin (Ig)?

A
  • Y-shaped glycoprotein made up of:
    -> 2 identical disulfide-linked heavy (H) chains.
    -> 2 identical light (L) chains.
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2
Q

What protein family do antibodies and B-cell receptors belong to?

A

Immunoglobulin (Ig) family (Ig-like domains)

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3
Q

How many chains are in an immunoglobulin?

A
  • 4 chains
    2 heavy (H) chains
    2 light (L) chains
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4
Q

What are the two main regions in both the heavy and light chains of an Ig?

A

Variable region and constant region

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5
Q

What are the specific names for the variable and constant regions in the light chain?

A

VL – Variable region in light chain

CL – Constant region in light chain

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6
Q

What are the specific names for the variable and constant regions in the heavy chain?

A

VH – Variable region in heavy chain

CH – Constant region in heavy chain

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7
Q

What forms the antigen-binding site in an Ig?

A

VL + VH (2 identical antigen-binding sites per antibody)

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8
Q

What is the function of the variable regions (VL and VH)?

A

Antigen binding → leads to neutralization and other immune functions

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9
Q

What is the function of the constant region (CH)?

A
  1. Complement activation (C1q → classical pathway)
  2. Fc region can bind to Fc receptors on phagocytes and other cells (e.g., mast cells, eosinophils)
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10
Q

Fab fragments

A
  • Two Fab fragments per antibody
  • Each has antigen-binding domain AND part of the
    constant H and L chains
  • Fab = fragment antigen binding
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11
Q

Fc fragment

A
  • One Fc fragment
  • Fc = fragment crystallizable
  • Constant region of the heavy chain
  • Receptors that bind antibodies recognize the Fc region
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12
Q

What is the three-dimensional structure of an immunoglobulin (Ig)?

A
  • Two heavy chains (variable and constant regions)
  • Two light chains (variable and constant regions)
  • Held together by intra-/interchain disulfide bonds
  • Constant and variable regions are folded into complex 3D structures with β strands
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13
Q

What is the complementarity determining region (CDR) in an antibody?

A
  • Part of the variable region → forms the antigen-binding site
  • Direct contact with antigen (Ag)
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14
Q

What are hypervariable loops in the CDR?

A
  • 3 loops per variable domain
  • Not part of the β strands
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15
Q

Where is the greatest variability in the antibody sequence?

A

In the CDRs

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16
Q

Where are the CDRs located on the antibody structure?

A

At the extremities of the antibody

17
Q

How does antigen binding occur in immunoglobulins?

A
  • Through non-covalent bonding between the Ig and the antigen (Ag) epitope:
    1. Hydrogen bonds
    2. Van der waals
    3. Hydrophobic
    4. Ionic
18
Q

What principle describes the specificity of antigen binding?

A

Lock and key specificity

19
Q

Which part of the antibody is responsible for antigen binding?

A

The extremities of the antibody

20
Q

What factors influence the recognition of an antigen by an antibody?

A
  1. Size variability of the antigen being recognized
  2. Variation in the antibody itself, with CDR varying in length
21
Q

Where can epitopes be located on an antigen?

A

Epitopes can be located anywhere on the antigen

22
Q

What are the five major classes of antibody?

A

IgM
IgD
IgG
IgE
IgA

23
Q

What are some key differences you observed between the different antibody
classes?

A
  • Different number of Ig-like domains – differences in the length of the constant
    region of the heavy chain.
  • Differentiated by amino acid sequence
    of heavy chain (constant region)
    -> Heavy chain is what differentiates
    the different antibodies
    -> Fc fragment of each Ig is different
  • Each class performs different functions during immune responses.
24
Q

IgM

A
  • Pentameric
  • 5 antibodies linked together via disulphide bonds
  • Heavy chain: one variable region and 4 constant
    regions
  • Mature naïve B cells express transmembrane IgM
  • IgM is part of first wave of secreted antibodies
  • Most effective initiator of complement cascade
25
Q

IgD

A

Heavy chain: one variable region and 3 constant regions

IgD is part of first wave of secreted antibodies.

26
Q

IgG

A
  • Heavy chain: one variable region and 3 constant regions
  • The most abundant in plasma
  • 4 subclasses in humans – IgG1, 2, 3, 4
  • Produced following differentiation in the Germinal Center
27
Q

IgE

A
  • Heavy chain: one variable region and 4 constant regions
  • Produced in response to Helminth infections
  • Recall role of IgE in TH2 response
28
Q

IgA

A
  • Heavy chain: one variable region and 3 constant regions
  • Monomer in plasma
  • Dimer in mucous secretions through the J chain
  • Important for mucosal immunity
  • Two subclasses: IgA1 and IgA2
29
Q

Experimental & clinical use of antibodies

A
  1. Antibodies can be made to bind virtually any epitope
    (Ex. antibody against TNF-a for the treatment of rheumatoid arthritis)
  2. Make an antibody to bind to another antibody (an ab against the Fc region of IgG)

ELISA
Western Blot

30
Q

is it possible for our immune system to mount an immune response against a therapeutic drug, including monoclonal antibodies?