Table 1.
Properties of major serum immunoglobulin classes and subclasses.
| Ig type | % of serum IgG | Half‐life (days) | Complement classical activation pathway | Binding to FcRn | Binding to myeloid FcRs |
|---|---|---|---|---|---|
| IgA | (0.60–3.50)* | 4–6 | − | − | (FcαRs) |
| IgM | (0.40–2.30)* | 5–6 | ++++ | − | − |
| IgG1 | 67–75% | 23–28 | +++ | ++++ | +++ |
| IgG2 | 22–25% | 23–28 | + | ++ | ++ |
| IgG3 | 7–10% | 5–10 | +++ | ++ | +++ |
| IgG4 | 3–5% | 23–28 | − | +++ | + |
IgA, immunoglobulin A; IgG, immunoglobulin G; IgM, immunoglobulin M; FcαR, IgA Fc receptor; FcR, receptors specific for the Fc region of immunoglobulins; FcRn, neonatal Fc receptor.
*
For IgA and IgM, serum concentration in g/l is given. For IgG subclasses, % of total IgG is given. Normal total IgG concentrations are 7.25–12.50 g/l in most laboratories.