IgG Subclasses, Serum


Reference Range

This test is used to study patients with recurrent bacterial infections or allergy, and for the quantitation of IgG 1, IgG 2, IgG 3, IgG 4 and total IgG. See also below each IgG subclass separately: The IgG1 sub-class accounts for 40 to 80% of total IgG. The relative proportions of the different sub-classes vary with age. Adult concentrations of IgG1 are reached by the age of 2 to 3 years. In adults, IgG1 antibodies tend to be directed at proteinaceous antigens. Children, because of their isotypic immaturity, produce mainly IgG1 antibodies in response to bacteria, be the antigens proteinaceous or polysaccharide-based. Most antibodies directed against viruses are either IgG1 or IgG3.Autoantibodies can be of any of the four sub-classes. The IgG2 sub-class accounts for 10 to 40% of total IgG. Adult concentrations of IgG2 are reached after the age of 15 years. In adults, IgG2 antibodies tend to be directed at polysaccharide antigens and, by virtue of their three-dimensional structure; they tend to be the most effective sub-class against encapsulated pathogens (e.g. pneumococci). The IgG3 sub-class represents 2 to 10% of total IgG. Adult IgG3 concentrations are reached by the age of 2 to 3 years. Most antibodies directed against viruses are either IgG1 or IgG3. IgG3 deficiency can occur in isolation and it is characterized by recurrent viral infections. In autoimmune disease, the pathological antibodies are often IgG1 or IgG3 and the serum levels of these sub-classes are increased. The IgG4 sub-class represents 0 to 15% of total IgG. Adult IgG4 concentrations are sometimes not reached until after 15 years of age. The Fc portion of the IgG4 molecule can bind to basophils and this sub-class seems to be involved in the phenomenon of desensitization because these antibodies appear following effective immunotherapeutic treatment of allergic patients.

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