Immunoglobulin G subclasses in immunodeficiency.

Immunodeficiencies have been described ranging from stem cell dysfunction to low levels of isolated IgG subclasses. Subclass deficiencies seem in most cases to depend on regulatory defects rather than absence of genes encoding Ig heavy chains. It is, thus, not surprising that low levels of IgG subclasses can be seen in various immunodeficiency syndromes, where regulatory defects of the immune response may be present. Isolated IgG subclass deficiencies, however, are often found among patients with increased susceptibility to e.g. infections. The frequent B and/or T cell abnormalities observed in IgG subclass deficient individuals may explain the increased susceptibility to infections, suggesting that low subclass levels may function as an indicator of a clinically important immunodeficiency.