Table I.
Structure, Function, and Distribution of Antibody Isotypes
| IgM | IgD | IgG1 | IgG2 | IgG3 | IgG4 | IgA1 | IgA2 | IgE | |
|---|---|---|---|---|---|---|---|---|---|
| Subunit Form1 |
5 | 1 | 1 | 1 | 1 | 1 | 1,2 | 1,2 | 1 |
| Molecular Weight, kDa |
950 | 175 | 150 | 150 | 150 | 150 | 160,400 | 160,400 | 190 |
| Concentration In Serum, mg/ml |
2 | 0.03 | 10 | 4 | 1 | 0.5 | 2 | 0.5 | 0.003 |
| Complement Activating C/A2 |
+/− | −/+ | ++/+ | +/+ | ++/+ | −/+ | −/+ | −/+ | −/− |
| Macrophage FcR Binding |
+ | − | ++ | ++ | ++ | − | ++ | ++ | − |
| Mast Cell Sensitizing |
− | − | − | − | + | − | − | − | +++ |
| Placental Transport |
− | − | ++ | + | ++ | +/− | − | − | − |
| Mucosal Transport3 |
− | − | − | − | − | − | +++ | +++ | − |
1
5=pentamer, 2=dimer, 1=monomer
2
C=Classical pathway, A=Alternative pathway
3
Dimer only