Table 2.
Properties of antibody isotypes and antibody fragments1
| Isotype | Serum level (mean adult; mg·mL−1) | Biological half-life (days) | Biological Functions | Molecular weight (kDa) |
|---|---|---|---|---|
| IgA1 | 6 | 6 | Pathogen neutralization in mucosal secretions | 160 |
| IgA2 | 6 | 6 | Pathogen neutralization in mucosal secretions | 160 |
| IgD | 3 | 3 | Membrane B-cell receptor | 184 |
| IgE | 2 | 2 | Mast cell histamine release | 188 |
| IgG1 | 21 | 21 | Pathogen neutralization in tissues | 146 |
| Classical complement activation | ||||
| Opsonization | ||||
| NK cell ADCC | ||||
| Transplacental transfer | ||||
| IgG2 | 20 | 20 | Pathogen neutralization in tissues | 146 |
| IgG3 | 7 | 7 | Pathogen neutralization in tissues | 165 |
| Classical complement activation | ||||
| Opsonization | ||||
| NK cell ADCC | ||||
| Transplacental transfer | ||||
| IgG4 | 21 | 21 | Pathogen neutralization in tissues | 146 |
| Transplacental transfer | ||||
| IgM | 10 | 10 | Classical complement activation | 970 |
| Membrane B-cell receptor (monomer) | ||||
| Fab | 0.3–0.8 | 50 | ||
| scFv | 0.1 | 27 | ||
| sdAb | <0.05 | 13 |
1
Adapted from Janeway CA, Travers P, Walport M and Shlomchick. Immunobiology. Garland publishing, NY, 2001.
ADCC, antibody-dependent, cell-mediated cytotoxicity; NK, natural killer; sdAbs, single-domain antibodies.