Complement-immunoglobulin relation: deficiency of C'1q associated with impaired immunoglobulin G synthesis.

Concentration of the complement protein C'lq was determined immunochemically in serums of individuals with a wide variety of immunoglobulin abnormalities. A significant correlation was observed between decreased concentration of C'lq and deficient synthesis of immunoglobulin G; C'lq was particularly diminished in subjects with congenital, sex-linked (Bruton) agammaglobulinemia. In contrast, two to five times the normal concentration of C'lq was found in the serum of three patients with heavy chain disease (subtype immunoglobulin G3). No significant relation was found between C'lq and concentrations of immunoglobulins A and M.