1.1 Made of glycoproteins (proteins and carbohydrates) found in serum and tissue fluids.
1.1.1 We can make an antibody to match a foreighn molecule.
1.2 They bind specifically to the antigen that induced their formation.
2 There are 5 classes
2.1.1 4 subclasses of ɣ1-ɣ4 H chains
126.96.36.199.1 70% of normal IgG serum in humans
188.8.131.52.1 20% of normal IgG serum in humans
184.108.40.206.1 8% of normal IgG serum in humans
220.127.116.11.1 2% of normal IgG serum in humans
18.104.22.168 In a mouse these are IgG1, IgG2a, IgG2b and IgG3
2.1.2 75% of normal serum. Ig 12mg/ml
2.1.3 Basic monomer structure
2.1.4 Mr 150,000 - Can get
out of the serum more
easily than IgM. Can get
to the tissues and so
provides immunity for
most of the body.
22.214.171.124 Predominant Ab of secondary immune response
126.96.36.199 Extravascular - good at giving protection throughout your tissues.
188.8.131.52 Fixes complement IgG3>1>2>4 (IgG2 and 4 very weak at fixing complement)
184.108.40.206 Good opsonin
220.127.116.11 Placetal transfer IgG1, 3 and 4. Immunity for an unborn child
2.1.6 Where do they bind?
18.104.22.168 IgG binds to special Fc receptors on lymphocytes, monocytes and macrophages.
2.2.1 µ Heavy chain
2.2.2 Makes up 10% of normal
human serum Ig
2.2.3 Pentamer composed of 5 basic Ig monomers
22.214.171.124 There it has 10 antigen binding sites.
126.96.36.199 Mr 970,000
188.8.131.52 10 L chains (identical), 10
H chains (identical), means there are 10 identical antigen binding sites. There is 1 J chain.
184.108.40.206 monomers are joined by disulphide bonds.
220.127.116.11 Predominant Ab of the
primary immune response
(on first encounter, you
18.104.22.168 Most efficient complement fixing antibody
22.214.171.124.1 makes holes in cell/pathogen membranes
126.96.36.199.2 Sticks things to the pathogen
surface to be detected and
engulfed by macrophages.
188.8.131.52 Good opsonin
184.108.40.206.1 coats the pathogen so they can be phagocytosed
220.127.116.11 Half life 5 days
18.104.22.168 not found extravascularly
22.214.171.124.1 Cannot really get out of the serum because of its size. This is a
limitation as it can't reach the tissues.
126.96.36.199 Found at B lymphocyte cell surface as
a membrane bound monomer. Here it
acts as a cell surface receptor in
antigen recognition. Consists of 2 L and
H chains. This property is shared with
2.3.1 2 subclasses: α1 and α2 heavy chains.
2.3.2 10% of normal serum
2.3.3 it is mainly monomeric in normal serum
2.3.4 Mr 160,000
2.3.5 Predominant Ig in secretions eg
saliva and colostrum and in the gut
where it is present as a dimer (of
two Ig monomers, one J chain and
one secretory component
188.8.131.52 also found in the lungs, eyes and on our skin.
184.108.40.206 Secretory component wrapped
around the molecule to protect
220.127.116.11.1 J chain links and holds the chains together
2.4.1 δ heavy chain
2.4.2 Very low levels in serum
(at least 1000 fold lower
2.4.3 Basic monomer structure
2.4.4 Mr 175-185,000
2.4.5 often co-expressed with IgM
2.4.6 Acts in signal
leading to B cell
2.5.1 ε heavy chain
2.5.2 Lowest serum concentrations
of any immunoglobulin 0.0003
2.5.3 Basic monomer structure
2.5.4 Mr 190,000
18.104.22.168 However heavy chain consists of 5 domains
2.5.5 Binds to Fc receptors (specific to IgE) on mast cells and
basophils. Contact with antigens subsequently leads to the
release of pro-inflammatory agents
2.5.6 Major player in allergy responses and worm infections
3 Basic Structure
3.1 Y shaped molecule
3.1.1 2 identical light chains either λ
or K (never one of each) ~ 220AA
3.1.2 Two identical heavy chains ~ 450AA
3.1.3 Covalent and non covalent forces hold it together
3.1.4 There are two identical antigen binding sites (labelled Ag in the picture).
22.214.171.124 will bind to
exactly the same
3.2 How did
first study this
3.2.1 Broke down the
structure into its
126.96.36.199 Cleaving using...
188.8.131.52.1.1 Cleaves polypeptide to the left of the disulphide bond
(this bond holds the two heavy chains together). Splits
the antibody into two fragments, Fab and Fc.
184.108.40.206.2.1 Cleaves polypeptide to the right of the disulphide bond, antibody arms still
bound together which is called F(ab')2 fragment and has the Fc fragment left
over. The Fc fragment is the carboxy half and is called the Fc region because it
3.3 Where are they different?
3.3.1 there are 3 regions of variability and these
are called HVR. They are positioned at 30,
50 and 90 AA
220.127.116.11 The CDR makes up the shape of the antigen binding site
18.104.22.168.1 The FDR holds the domains together.
22.214.171.124.1.1 β regions are the FDRs.
At the ends of these are
the CDRs. There are 3
CDRs in the light chain
and three in the heavy
3.3.2 They need to have the correct forces in order to have high affinity
3.4 Not all antibodies of different species have two binding sites.