Clinical significance of IgG subclass deficiency.

IgG is quantitively and functionally the major class of immunoglobulin found in serum and all extra- vascular fluids except mucosal secretions. Four structurally and functionally distinct subclasses (IgG 1 to 4) have been described in man.' Deficiencies of Recurrent or severe upper respiratory tract infec- tions, otitis media, sinusitis, and bronchopulmonary infections are the most common manifestation of IgG subclass deficiency.6 19 They occur particularly on July 16,