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 |
| • Synthesised by plasma cells | |||
| • 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 |
| Disease | Associated raised immunoglobulin subtype |
|---|---|
| Alcoholic liver disease | IgA |
| Primary biliary cirrhosis | IgM |
| Autoimmune hepatitis | IgG |
Uses
Basics