Clinical relevance of IgG subclass deficiencies.

Patients with primary or secondary IgG subclass deficiencies suffer from infections due to encapsulated microorganisms such as H influenzae and pneumococci. In addition to relapsing infections, some patients with primary subclass deficiencies may have autoimmune disorders. The best characterized defect in IgG2 deficiency, either isolated or combined with IgG4 deficiency. It is frequently associated with IgA deficiency or with ataxia telangiectasia. IgG1 deficiency occurs mostly in combination with disturbances of other immunoglobulin isotypes, and probably represents a form of common variable immune deficiency. Decreased IgG3 levels were reported in association with lung dysfunction and viral diseases. Except in IgG1 deficiency, total IgG serum levels in primary as well as secondary IgG subclass deficiency states may be normal or even increased. It is assumed that IgG subclass deficiencies represent an indicator of more basic immunologic abnormalities. There is evidence that antibody defects correlate better with the clinical symptoms than the total serum IgG subclass concentrations. In patients with severe recurrent infections and IgG subclass deficiency, intravenous immunoglobulin treatment at dosages of 0.3 to 0.4 g/kg body weight every 3-4 weeks is indicated.