Immunoglobulin subclass deficiency

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Abstract
IgG subclass deficiency was first noted in 1968. Subnormal levels of one or two, occasionally three IgG subclasses may be relatively common. It has not been determined, however, at what level below the normal range the IgG subclass deficiency is of clinical relevance. It remains important to clarify this point because certain subclass deficiencies may be without relevance of their own. Because patients with decreases of various IgG subclasses often present with a number of diseases, the low immunoglobulin levels may signify the presence of other abnormalities of more biologic significance. IgG subclass deficiency has been noted in about 25% of patients with well-defined food allergy and in patients with asthma, diabetes mellitus, Henoch-Schönlein's purpura, Bechterew's disease, intractable epilepsy of childhood, Friedreich's ataxia and autoimmune cytopenias. Most commonly they have increased frequency of infections especially in the respiratory tract, including sinusitis, otitis media and bronchopneumonia, but also osteomyelitis, meningitis, septicemia and various skin infections. Low levels of various subclasses have been noted in connection with other immunodeficiencies such as ataxia-telangiectasia. In common variable immunodeficiency there is an obvious imbalance in the IgG subclasses. Furthermore IgG subclass deficiency can be seen in relatives of patients with common variable immunodeficiency and in IgA deficiency. They also occur in relatives of patients with systemic lupus erythematosus, diabetes mellitus type 1 and C2 deficiency. In a few cases of subclass deficiency gene deletions have been shown. Subnormal levels of IgG subclasses make a remarkable change in sex distribution around puberty from 3/1 in boys and girls to the reverse sex ratio among adults. Simultaneously there is a switch from a predominance of IgG2 deficiency in the children to IgG3 deficiency in adults. Vaccination with bacterial antigens of IgG subclass as well as IgA-deficient individuals show quite variable responses in both serum and secretions. The poor response to bacterial polysaccharide capsules is obvious in the IgG2-deficient patients and also in IgA-deficient individuals with frequent infections but normal serum IgG subclass levels. The background to those presumably regulatory abnormalities of the antibody response is unknown. Immunoglobulin prophylaxis has proved effective in anectodal cases and in larger open studies, including one covering 1500 patient months. In one analysis of children with intractable epilepsy a striking response to immunoglobulin prophylaxis was seen in 5 of 6 of the children who were IgG subclass-deficient. Convulsions vanished and electroencephalograms normalized in time relation to the prophylaxis.

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