Homozygous C3 deficiency: Detection of C3 by radioimmunoassay

A 5 10 12-year-old girl with recurrent infections was found to have homozygous C3 deficiency. Family studies demonstrated that the pattern of inheritance was consistent with that of an autosomal codominant trait. C3 levels have ranged from 5 mg/100 ml (electroimmunoassay) to 1.7 μg/100 ml (radioimmunoassay) 2 years later. C3 was also detected in two previous homozygous-deficient patients by radioimmunoassay. These findings suggest that an intact structural gene for C3 is present in these patients. In samples of the patient's serum with a C3 level less than 3 mg/100 ml, properdin factor B conversion did not occur upon incubation with zymosan. Immune adherence was normal. The vasopermeability response following intradermal injection of C1s was normal. The patient's serum incubated with zymosan did not produce a chemotactic response of normal leukocytes. Phagocytosis of endotoxin-paraffin oil-oil red O particles by normal leukocytes was not enhanced following incubation with the patient's serum. Humoral antibody response and lymphocyte number and function were normal. © 1977.