Everything about Igg totally explained
Immunoglobulin G (
IgG) is a
tetrameric immunoglobulin, built of two
heavy chains and two
light chains. Each IgG has two
antigen binding sites. It is the most abundant immunoglobulin and is approximately equally distributed in
blood and in tissue liquids, constituting 75% of
serum immunoglobulins in humans. IgG molecules are synthesised and secreted by
plasma B cells.
In birds, IgG is replaced with IgY, and is found in serum and yolk.
Functions
This is the only
isotype that can pass through the human
placenta, thereby providing protection to the
fetus in utero. Along with
IgA secreted in the
breast milk, residual IgG absorbed through the
placenta provides the
neonate with
humoral immunity in its first weeks of life before its own
immune system has developed.
It can bind to many kinds of
pathogens, for example
viruses,
bacteria, and
fungi, and protects the body against them by
complement activation (classic pathway),
opsonization for
phagocytosis and
neutralization of their toxins.
IgG can cause
food allergy, and in such causes delayed-onset food allergy, in contrast to food allergy by
IgE, whose effects appear rapidly.
Structure
IgG antibodies are large molecules of about 150
kDa composed of 4
peptide. It contains 2 identical heavy chains of about 50 kDa and 2 identical light chains of about 25 kDa. The two heavy chains are linked to each other and to a light chain each by
disulphide bonds. The resulting tetramer has two identical halves which together form the Y-like shape. Each end of the fork contains an identical
antigen binding site.
Subclasses
| Name |
Percent |
Crosses placenta easily |
Complement activator |
Binds to Fc receptors on phagocytic cells |
| IgG1 |
66% |
yes |
second highest |
high affinity |
| IgG2 |
23% |
no |
third highest |
extremely low affinity |
| IgG3 |
7% |
yes |
highest |
high affinity |
| IgG4 |
4% |
yes |
no |
intermediate affinity |
Note: IgG affinity to Fc receptors on phagocytic cells is specific to individual species from which the antibody comes as well as the class.
Further Information
Get more info on 'Igg'.
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