Table 1.
Properties of Immunoglobulin Isotypes/Subclasses
| Serum (%) | Structure | Complement Fixation |
Opsonizing | Cross Placenta |
Other Functions |
FcR | |
|---|---|---|---|---|---|---|---|
| IgG | 75 | Monomer | + | +++ | + | For all IgG subclasses: |
FcγR |
| IgG1 | 67% IgG | Monomer | Yes | Yes | + | Secondary response |
I,II,III |
| IgG2 | 22% IgG | Monomer | Yes | Yes | + | Neutralize toxins and |
II |
| IgG3 | 7% IgG | Monomer | Yes | Yes | + | virus | I,II,III |
| IgG4 | 4% IgG | Monomer | No | No | + | I,II | |
| IgM | 10 | Pentamer | +++ | + | − | Primary response |
|
| IgA | 15 | Monomer, Dimer | − | − | − | Mucosal response |
FcαR (CD89) |
| IgA1 | Monomer, Dimer | − | − | − | |||
| IgA2 | Monomer, Dimer | − | − | − | |||
| IgD | <0.5 | Monomer |
− | − | − | homeostasis | FcδR |
| IgE | <0.01 | Monomer | − | − | − | Allergy | FcεR I,II |