Deficiency of the Fourth Component of Complement in Man

A new type of complement deficiency was found in the course of mass medical examinations. The following findings were obtained in three persons with this deficiency. a) The sera showed a selective decrease in C4 hemolytic activity. b) Serum complement activity was largely restored by the addition of highly purified C4. c) On immunoelectrophoresis, a β1E precipitin line developed with the sera of all three cases and was not noticeably weaker than that observed with control serum. d) C1 inactivator activity in these sera was not reduced as compared with that in normal serum. e) The sera were shown to have potent C4 inactivating activity.