IgG4 immunodeficiency.

IgG4 deficiency can be an isolated phenomenon, or it can occur in combination with deficiencies of IgG2, IgA, and/or IgG1 (in order of decreasing frequency). Isolated deficiency of IgG4 is associated with symptoms and signs which are similar to those associated with other IgG subclass deficiencies. The most common manifestation is an unusual frequency of pyogenic infections, most often of the respiratory tract. There is also an increased frequency of isolated serum IgG4 deficiency in subjects who have recurrent or chronic diarrhea, asthma, adverse reactions to foods, chronic candidiasis, pediatric AIDS, and autoimmune disorders. The mean and normal ranges of serum IgG4 in 400 subjects ages four months to 17 years are given. Diagnostic studies, unique features of IgG4, illustrative case reports and possible mechanisms are discussed.