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BIOC2004 CH > 5. Antibodies > Flashcards

5. Antibodies Flashcards

1
Q

What type of immune response are antibodies part of?

A

Adaptive immune response

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2
Q

What are the four roles of antibodies? What are names of the forms?

A
  • Cell surface receptors - IgM/IgD
  • Blood plasma - IgG/IgM
  • Inflammation - IgE
  • Lining intestines/mucosal tract - IgA
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3
Q

Which antigens are expressed on the surface of B cells?

A

IgM and IgB

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4
Q

Describe what roughly happens when the adaptive immune system is activated

A
  1. Surface IgM/IgD of B Cell binds antigen by chance (weak interaction)
  2. Antigen gets chewed up into little fragments which are expressed on surface
  3. Interacts with T cell via TCR
  4. Cytokines released causing B cell to copy itself
  5. Clonal expansion, antibody maturation, optimisation of binding and cats switching to IgG occur
  6. IgG then binds to antigen undergoing blocking, opsonisation and triggers complement
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5
Q

What is antibodies maturation?

A

Mutation of antibodies in order to optimise binding

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6
Q

What is class switching?

A

Switching of IgM/IgB to a different type of antibody (IgG) which is soluble and can enter blood plasma

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7
Q

What is opsonisation?

A

Binding of antibody to pathogen epitope which attracts phagocytes (which bind using Fc receptor)

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8
Q

Describe the antibody composition

A

Light chain - 220 AA long - 2 domains -VL and CL (constant and variable regions)

Heavy chain - 440AA long - 4 domains - VH, CH1, CH2, CH3

Variable Hinge region

2 heavy and 2 light chains in each antibody

Fc region, Fab arm, CDRs

Each domain has disulphide bonds - 2 between 2 heavy chains and 1 linking each heavy chain to a light chain

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9
Q

What are polyclonal antibodies? Do they crystallise?

A

Polyclonal antibodies are a mix of antibodies which bind the same antigen.

These do not crystallise as they are all different.

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10
Q

What are monoclonal antibodies? Do they crystallise?

A

Identical antibodies

No, they are flexible which prevents the formation of a regular lattice

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11
Q

How is it possible to crystallise antibodies?

A
  • Cleave antibodies into 2 fragments using Papain
  • FAB (fragment antigen binding) regions do not crystallise because they vary highly
  • BUT Fc regions do! This is the stem bit and remains constant
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12
Q

How do papain and pepsin cleave antibodies in different ways?

A

Papain cleaves antibody above the disulphide bond into 2 FAB fragments and 1 Fc region

Pepsin cleaves antibody below the disulphide bond into 1 FAB’ fragment and 1 Fc region

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13
Q

Which domain of the antibody contains sugars?

A

The CH2 domain (bit before the hinge region)

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14
Q

How do IgG and IgM/IgE vary?

A

IgM/IgE have an extra CH4 domain

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15
Q

How many loci are in the antibody genome? What are their names?

A

Lambda light chains, Kappa light chains and Heavy chains

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16
Q

Describe the structure of the lambda light chain loci. How is variation generated?

A
  • 30 variable gene (V) segments with leader sequence in front
  • 4 constant gene (C) segments
  • Joining (J) segment in front of each C segment
  • Splicing occurs at DNA level, taking V segment and splicing to J segment and then splicing VJ to a C segment
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17
Q

What is the difference between kappa and lambda light chains?

A

No functional difference but gene loci are arranged differently

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18
Q

How many different variation of the lambda light chain are there?

A

30x4 = 120

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19
Q

Describe the loci of the kappa light chain. How many variations are there of it?

A

40 Variable genes (V), 5 J segments, 1 constant region

200 variations!!

20
Q

Describe the loci of the heavy chain. How many variations are there of it?

A

65 Variable (V) segments, 26 diversity (D) segments, 8 joining (J) segments, 1 constant (C-mu) domain

4,212,000 variations

21
Q

What is the total amount of different antibodies producible?

A

1.3billion

22
Q

What are the 5 antibody classes? Describe each one.

A

IgM - early response antibody - 2 forms due to alternative splicing at mRNA, one w/ tail which sticks into membrane and produce surface receptor

IgD - Receptor

IgG - Late response, antibody the goes round killing shit

IGA - found in tears/mucus

IgE - degranulation of histidine release, insect bites - IgE goes to bite creates MAST cell which causes blood vessels to open up

23
Q

How do the different antibody classes vary?

A

By their heavy chain.

IgM - mu 
IgD - delta
IgG - gamma
IgA - alpha
IgE - epsilon

The greek stuff is the name of their heavy chains

24
Q

How does class switching occur?

A
  • Heavy chain locus contains a series of alternative constant domains
  • Switch sites are present in front of every constant domain
  • Switch sites come together in DNA in middle is looped out and removed
  • this process is uni-directional
25
Q

What are the three types of Fc receptors? What cells are they present on?What do they do?

A

FcgR - binds IgG, present on neutrophils/macrophages/monocytes and triggers phagocytosis (of the IgG coated pathogens)

FceR- binds IgE, present on eosinophils/basophils/mast cells & triggers histamine release

FcaR- binds IgA, present on neutrophils/monocytes/macrophages/ eosinophils and responsible for phagocytosis, antibody-dependent cell-mediated cytotoxicity (ADCC), release of superoxide and inflammatory mediators

26
Q

How do IgM and IgA form multimers?

A

IgM forms a pentamer with 4 other IgM molecules attached via a J chain (not related to J segment).

IgA forms a dimer in the same way

27
Q

What does C1q do?

A
  • c1q binds to IgM and IgG
  • binds to at least two Fc’s to become active
  • c1q then drills hole in the cell like a big pneumatic drill!!!

woah steve that’s sick

28
Q

Describe the protein structure of the Fab fragment arm

A
  • each domain has immunoglobulin fold
  • Ig fold consists of a beta sandwich of 110AA with the beta sheets inclined at 30deg. to each other (superfold - stable
  • disulphide bridges link the 2 sheets and stabilise the beta sandwich - stable framework to retain shape when constantly changing CDRs
  • VH/VL chains can move with respect to one another (by 60deg.) - this means the binding site at the end can change considerably
29
Q

Between which domains of the antibody do interactions occur?

A

VL and VH
CH1 and CL
CH3 and CH3

CH2 DOES NOT INTERACT

30
Q

How may you imagine an antibody with the aid of a few LSD tabs?

A

AS A BODY - SHOULDERS AND ELBOWS AND HANDS THEY ALL CAN MOVE HALP

31
Q

How do the VL and VH domains interact?

A

Vie 5 strand sheets to form a barrel shape

32
Q

What molecules sit between the CH2 fragments? What do they do?

A

Sugars - dis is odd

dunno

33
Q

What are the elbow angles of an antibody?

A

The angle between the variable and constant domains

34
Q

What molecules may antibodies interact with?

A

Proteins, peptides, carbs, lipids, small molecules

35
Q

What did Wu and Kabat do?

A

undertook sequence analysis, Invented the variability plot (plot each position in a sequence and how variable it is), found hyper variable regions (CDRs) of antibodies

Also found that framework regions of antibodies are well conserved (even between humans/mice)

36
Q

Something about CDRH3 and CDRL3 sitting in middle of binding site

A

:)

37
Q

What was Chothias analysis?

A

Collected antibody structures and found that the structures of the hyper variable loops were actually well conserved in shape - all the loops would be similar shape (even if had different AA)

Found the difference to be in CDR length and difference in certain key residues

38
Q

What are the key residues in CDR-L1?

A

I, A, VIL, LM, YF

39
Q

What may antibodies be used for in vitro?

A
  • on immunoaffinity chromatography columns
  • diagnostic agents (measure presence of stuff in blood e.g. ELIZA assay for testing HIV presence
  • therapeutic agents
  • ## protein purification/labelling - western blots
40
Q

What may antibodies be used for in vivo?

A
  • magic bullets (targeted drugs - paul ehrlich)
  • imaging - gamma-imaging, PET, guiding surgery
  • therapeutic - immune activation, direct effects
  • targeting - radio, direct, indirect (ADEPT)
  • catalytic -
41
Q

What is ADEPT?

A

Antibody directed enzyme pro-drug therapy

Prodrug is a drug which is activated by metabolism

basically pro-drug injected into body directed by antibodies and then activated

42
Q

What are the various treatments offered by antibodies? What do they treat?

A

Herceptin - cancer
Reopro - binds to platelet fibrinogen receptors to stop platelet clumping and artery clogging
Synagis - introduces passive immunity by binding to respiratory syncytial virus (stops REV infections)

43
Q

How does Radioimmuno guided surgery work?

A

Patient injected with radio-labelled antibody before surgery

44
Q

What is radioimmuno-scintography?

A

Radio labelled Fab fragments can be imaged used to detect bowel cancer (anti-CEA antibodies used)

45
Q

What are abzymes?

A

An antibody which has enzymatic activity

46
Q

What are abzymes used for?

A

f

BIOC2004 CH (11 decks)

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