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

TLDR

The patient’s susceptibility to gram‑negative bacteria suggests that C5 dysfunction may impair in vivo bacterial clearance. A familial deficiency of serum phagocytosis‑enhancing activity caused by C5 dysfunction was demonstrated, with restoration of activity upon addition of purified C5 in both human and mouse samples.

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. In view of the patient's clinical susceptibility to primarily gram-negative bacteria, the in vitro dysfunction of C5 may be related to impaired in vivo inactivation of such organisms.