Immunoglobulins
The table below summarises the characteristics of the 5 types of immunoglobulin found in the body:
| Type | Frequency | Shape | Notes |
|---|---|---|---|
| IgG | 75% | Monomer | • Enhance phagocytosis of bacteria and viruses • Fixes complement and passes to the fetal circulation • Most abundant isotype in blood serum |
| IgA | 15% | Monomer/ dimer | • IgA is the predominant immunoglobulin found in breast milk. It is also found in the secretions of digestive, respiratory and urogenital tracts and systems • Provides localized protection on mucous membranes • Most commonly produced immunoglobulin in the body (but blood serum concentrations lower than IgG .) • Transported across the interior of the cell via transcytosis |
| IgM | 10% | Pentamer | • First immunoglobulins to be secreted in response to an infection • Fixes complement but does not pass to the fetal circulation • Anti-A, B blood antibodies (note how they cannot pass to the fetal circulation, which could of course result in haemolysis) Pentamer when secreted |
| IgD | 1% | Monomer | • Role in immune system largely unknown • Involved in activation of B cells |
| IgE | 0.1% | Monomer | • Mediates type 1 hypersensitivity reactions • Binds to Fc receptors found on the surface of mast cells and basophils • Provides immunity to parasites such as helminths • Least abundant isotype in blood serum |