A Familial Deficiency of the Phagocytosis-Enhancing Activity of Serum Related to a Dysfunction of the Fifth Component of Complement (C5)

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Abstract
A patient, previously described, was found to have increased susceptibility to bacterial infections related to a deficiency of serum enhancement of in vitro phagocytosis. The same deficiency affected the patient's mother and 15 other relatives. The deficiency was shown to involve a dysfunction of the fifth component of complement (C5) by the fact that the phagocytosis-enhancing activity of the mother's serum was restored to normal by the addition of highly purified C5. Also, serum from mice with a genetic deficiency of C5 indicated poor enhancement of phagocytosis, and the addition of highly purified C5 to the Co-deficient mouse serum restored phagocytosis-enhancing activity. Finally, the addition of C5-deficient mouse serum to the mother's serum failed to improve the phagocytosis-enhancing effect of the maternal serum, whereas the addition of small amounts of normal mouse serum did.