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Chapter: Microbiology and Immunology: Antibodies

Metabolism of Immunoglobulins

Half-life (T 1/2) of immunoglobulin is one of the most com-monly used parameters to assess the catabolic rate of immunoglobulins.

Metabolism of Immunoglobulins

Half-life (T 1/2) of immunoglobulin is one of the most com-monly used parameters to assess the catabolic rate of immunoglobulins. The half-life corresponds to the time elapsed for a reduction to half of a circulating immunoglobulin concentration after equilibrium has been reached. This is usu-ally determined by injecting an immunoglobulin labeled with a radioisotope (131I).

The IgG is the immunoglobulin class with the longest half-life (average of 21 days), with the exception of IgG3. The IgG3 has a considerably shorter half-life (average of 7 days) that is nearer to that of IgA (5–6 days) and IgM (5 days).

The synthesis rate of IgA1 (24 mg/kg/day) is not very different from that of IgG1 (25 mg/kg/day), but the serum concentra-tion of IgA1 is about one-third of the IgG1 concentration. This is explained by a fractional turnover rate three-times greater for IgA1 (24%/day). The highest fractional turnover rate and shorter half-life are those of IgE (74%/day and 2.4 days, respec-tively). The lowest synthesis rate is that of IgE (0.002 mg/kg/day, compared to 20–60 mg/kg/day for IgG).


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