Inherited deficiency of properdin and C2 in a patient with recurrent bacteremia.

A nine-year-old white boy with recurrent pneumococcal bacteremia is described. His serum had no hemolytic activity in either the classic or alternative complement pathways. Absence of classic pathway activity was secondary to a homozygous deficiency of C2. The parents had half-normal levels of C2, compatible with an autosomal recessive mode of inheritance. Measurement of serum properdin levels by radial immunodiffusion and enzyme-linked immunoabsorbent assay revealed a profound deficiency in the patient, normal levels in the father, and half-normal levels in the mother, suggesting X-linked inheritance of the deficiency. Addition of purified properdin to the patient's serum fully reconstituted the alternative pathway function. This patient's unique combination of inherited deficiencies of properdin and C2 is a likely explanation for his susceptibility to bacterial infection.