A Functional Abnormality of the Fifth Component of Complement (C5) from Human Serum of Individuals with a Familial Opsonic Defect

Abstract

The nature of a familial opsonic defect of human serum was explored. Studies of the unseparated deficient serum indicated a functional abnormality of C5 despite the presence of C5 in normal amounts. Studies of the isolated C5 from opsonically deficient serum revealed a restricted, primary, functional defect analogous to the one suggested by the studies of unseparated C5 in the deficient serum: absent opsonic but normal hemolytic function. In addition a secondary, functional defect occurred in isolated deficient C5 upon prolonged handling at 4°C: hemolytic as well as -generated chemotactic activity was lost. There was no indication of an inhibitor or inactivator of C5, nor of an abnormality of C activation at levels other than that of C5 in deficient serum. These functional studies therefore verify our previous interpretation that the yeast opsonic defect reflects a functional defect or dysfunction of C5. No structural correlate for the functional abnormality of C5 has as yet been demonstrated in studies with the Ouchterlony technique, various modifications of the polyacrylamide gel electrophoretic procedure, as well as sucrose density ultracentrifugation.