IgG is particularly important in the body's long-term defence against infection as it presents a slower but more sustained response than IgM to primary antigenic stimulus; however, the levels of IgG rise rapidly and early on re-exposure to the same antigenic stimulus. IgG promotes phagocytosis and activates complement. IgG is the only immunoglobulin that crosses the placenta and is therefore of special importance in the infant’s defence against infection. Changes in serum immunoglobulin concentrations can be classified as follows:
Hypogammaglobulinemias: IgG deficiency may be genetic as in severe combined immunodeficiency or acquired as in AIDS. Definitive diagnosis requires extensive evaluation in the immune response. A decrease in IgG also occurs as a result of thermal burns, nephrotic syndrome, protein losing enteropathies and non-IgG myelomas.
Polyclonal gammopathies: Increased levels of IgG in autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, Sjögren's syndrome), sarcoidosis, chronic liver disease, some parasitic diseases and chronic or recurrent infections.
Monoclonal gammopathies: e.g. in IgG type multiple myeloma, lymphomas, leukemia, and other malignancies.
Immunoturbidimetric test for the quantitative determination of immunoglobulin G (IgG) in human serum.
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