Recurrent Bacterial Infections Associated with C3 Nephritic Factor and Hypocomplementemia

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Abstract
COMPLEMENT has a pivotal role in host defense against bacterial pathogens. Most patients with primary or acquired deficiencies of the third component of complement (C3) have recurrent bacterial infections with a variety of microorganisms.1 Patients with deficiencies of the terminal components (C5 through C9) are especially prone to repeated episodes of neisserial infection.2 , 3 Recently, we encountered a patient who had recurrent Neisseria meningitidis meningitis, normal terminal complement components, and markedly diminished plasma concentrations of C3. His evaluation led to the discovery of a circulating immunoglobulin that triggered uncontrolled C3 breakdown through activation of the alternative pathway. A similar globulin, C3 . . .