Increased Susceptibility to Infection Associated with Abnormalities of Complement-Mediated Functions and of the Third Component of Complement (C3)

Abstract

In a patient with Klinefelter's syndrome and lifelong increased susceptibility to infection, no abnormalities were found in humoral antibody production, cellular immunity or leukocyte function. In contrast, the patient's serum complement-mediated functions were grossly deficient. The concentrations of serum complement components were normal except for that of C3 (β_1C-globulin), which was less than one-third normal. The bulk of this was in the form of the inactive conversion product, C3b, at all times that the patient's serum or plasma was examined over a two-year period. Addition of small amounts of normal serum, but not purified C3, to the patient's serum improved all complement-mediated functions in vitro. This disorder, which may represent an inborn deficiency of a protein necessary for C3 stability in vivo and in vitro, is detected by the lowered serum C3 concentration and a positive non-gamma (C3) Coombs antiglobulin test.