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OPHTH Immunology > Antibodies > Flashcards

Antibodies Flashcards

1
Q

What type of molecule is an antibody/immunoglobulin?

A

glycoprotein

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2
Q

What are 3 functions of antibodies?

A
  1. complement activation (IgM + IgG)
  2. Opsonisation
  3. Cell activation via specific antibody binding receptors - Fc receptors
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3
Q

What is the basic structure of immunoglobulins?

A
  • 2 light (25kDa) chains, 2 heavy (50kDa) chains
  • each chain has amino and carboxyl terminal
  • chains held together by disulphide bridges
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4
Q

What type of bonds hold immunoglobulin chains together?

A

disulphide bonds

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5
Q

What is the order of amounts of the globulins found in serum in decreasing order?

A

A, γ, α, β

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6
Q

What allows flexibility of immunoglobulins?

A

there is a hinge in the antibody which allows flexibility between the two Fab

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7
Q

What is the benefit of immunoglobulins having flexibility?

A
  • allows angle between the two antigen binding sites to change angle depending on the proximity of cell surface determinants (how cloes together the antigens are)
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8
Q

Label the antigen binding sites + variable + constant regions of the light and heavy chains on the diagram.

A
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9
Q

How are the variable and light chains divided in immunoglobulins?

A

both light and heavy chains can be divided into variable (where the sequences are different) and constant (same sequence) regions

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10
Q

Where are the disulphide bonds located within the immunoglobulins?

A

each domain e.g. variable light, has intramolecular disulphide bonds to maintain their specific 3D structure required for antigen binding

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11
Q

Which region of immunoglobulins binds to cells and what does this result in?

A
  • constant region binds to Fc receptors
  • can lead to cell activation e.g. NK cells (secondary effector functions in immune response)
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12
Q

How many hypervariable regions exist on each antibody binding site of each immunoglobulins?

A

3 hypervariable regions

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13
Q

What is another name for the 3 hypervariable regions?

A

complementarity determining regions (CDRs)

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14
Q

What is the role of the hypervariable regions at each antigen binding site?

A

highly specific region, significant number of interactinos between the antibody and antigen surface

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15
Q

What are 4 forces involved with antibody binding?

A
  1. hydrogen bonds
  2. ionic bonds
  3. hydrophobic interactions
  4. van der Waals interactions
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15
Q

What are 4 forces involved with antibody binding?

A
  1. hydrogen bonds
  2. ionic bonds
  3. hydrophobic interactions
  4. van der Waals interactions
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16
Q

What creates high affinity bonding between antigen and antibody?

A

non-covalent bonds are relatively weak - to have hihg affinity must only be short distance between antigen + antibody, highly complimentary, and significant number of interactinos

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16
Q

What creates high affinity bonding between antigen and antibody?

A

non-covalent bonds are relatively weak - to have hihg affinity must only be short distance between antigen + antibody, highly complimentary, and significant number of interactinos

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17
Q

What is the calaculation used to work out antibody affinity for a single antigen binding site and a single epitope on the antigen?

A
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18
Q

What is antibody affinity avidity?

A
  • Affinity = The strength of the total non-covalent interactions between a single antigen binding site and a single epitope on the antigen.
  • Avidity = The overall strength of multiple interactions between an antibody with multiple binding sites and a complex antigen with multiple epitopes
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19
Q

What are 2 examples of cross-reactivity with antibodies?

A
  1. vaccination with cowpox induced abs to smallpox
  2. antibodies against microbial agents can cross react with ABO blood group antigens
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20
Q

What are antibody isotypes vs allotypes?

A
  • isotypes = antibodies present in everybody with a constant region
  • allotypes = antibodies that contain single amino acid mutations, giving allelic polymorphisms which vary in the population
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21
Q

How many heavy chain domains are there in each of the antibody classes?

A
  • IgG: 3
  • IgA: 3
  • IgM: 4
  • IgD: 3
  • IgE: 4
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22
Q

What is the heavy chain globulin class for each of the antibody classes?

A
  • IgG: γ
  • IgA: α
  • IgM: µ
  • IgD: δ
  • IgE: ε
23
Q

What are the light chain globulins in each of all 5 classes of immunoglobulin?

A

κ/λ

24
Q

Which immunoglobulins have subclasses and what are they?

A
  • IgG: IgG1-4
  • IgA: IgA1 + IgA2
25
Q

In what form does IgG exist?

A

monomer

26
Q

Where does the variability resulting in subclasses of IgG arise?

A

hinge region + effector function domains

27
Q

Which IgG subclasses are the main activators of classical complement pathway?

A

IgG1 + 3

28
Q

What are the frequencies of the IgG subclasses?

A

decrease in proportion from 1-4

29
Q

What is the second most abundant monomer in blood?

A

IgA

30
Q

What are the forms in which IgA exists in a) blood and b) secretions?

A
  • a) blood = monomer
  • b) secretions = dimer
31
Q

What is the major secretory immunoglobulin?

A

IgA

32
Q

What is the function of IgA?

A

major secretory immunoglobulin - protects mucosal surfaces from bacteria, viruses and protozoa

33
Q

How is secretory form of IgA produced?

A
  • joined by J chain and secretory component.
  • Plasma cell secretes dimeric form without secretory component.
  • This bonds to poly-Ig receptor and is endocytosed and secreted into lumen.
  • The poly-Ig receptor is cleaved and becomes the secretory component
34
Q

What is the function of the IgA secretory component?

A

protects IgA from being degraded in the lumen by proteases etc.

35
Q

What is the structure of IgM?

A

pentameric - 5 monomers joined by J chain (10x Fab)

36
Q

Where does IgM exist in the body?

A

mainy in the blood

37
Q

What is the first Ig synthesised after exposure to antigen?

A

IgM - primary antibody response

38
Q

What is the first Ig synthesised after exposure to antigen?

A

IgM - primary antibody response

39
Q

What do the multiple binding sites of IgM compensate for?

A

low affinity

40
Q

Which cells express IgD?

A

only exists expressed on B cell surface

41
Q

What is the function of IgD?

A

involved in B cell development and activation

42
Q

What is the function of IgE?

A
  • produced in response to parasitic infections and in allergic diseases
  • binds to high affinity Fc receptors of mast cells and basophils
  • cross-linking by antigen triggers mast cell activation and histamine release
43
Q

Which 2 Igs are abundant in blood?

A

IgG and IgM

44
Q

Which Ig exist in extracellular fluid?

A

IgG

45
Q

Which Ig is present in secretions across epithelia including breast milk?

A

dimeric IgA

46
Q

Where does IgE exist?

A

with mast cells below epithelium

47
Q

Which are of the body is devoid of antibodies?

A

brain

48
Q

Which antibody is mainly responsible for neutralisation of toxins by inhibiting their toxicity?

A

mainly IgG

49
Q

Which Ig is mainly responsible for neutralisation of viruses?

A

IgG

50
Q

Which Ig is mainly responsible for neutralisation at body surfaces?

A

Secretory IgA

51
Q

Which 2 antibodies are involved in agglutination i.e. Ag-Ab complexes/lattice formation?

A

IgM, IgG

52
Q

Which Ig is mainly responsible for opsonisation to promote phagocytosis?

A

IgG

53
Q

Which 2 antibodies are responsible for complement activation via the classical pathway?

A

IgM and IgG

54
Q

Which Ig is responsible for mast cell sensitisation + triggering?

A

IgE

55
Q

Which Ig is responsible for NK cell cytotoxicity/ADCC?

A

IgG

56
Q

What is the first step of the classical complement pathway (same as for lectin pathway)?

A

activation fo complement C1

57
Q

Which amino acid is involved in the formation of disulfide bonds, which makes Igs durable?

A

cysteine

OPHTH Immunology (8 decks)

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