Deficiency of the fifth component of complement in human subjects. Clinical, genetic and immunologic studies in a large kindred.
The discovery of a large kindred with a heritable deficiency of the fifth component of complement ( C5 ) has permitted the accumulation of new clinical , genetic and immunologic data concerning the role of C5 in human subjects . The proband , who has had nine episodes of disseminated gonococcal infection , has a hemolytic C5 level of approximately 0 . 5 per cent of normal . No C5 protein was detectable , but low levels of functional C5 activity could be found using a sensitive bactericidal assay . The probands twin as well as another sister also had extremely low levels of hemolytic C5 ( approximately 0 . 5 per cent normal ) , but both these subjects have been healthy . Hemolytic complement and bacteriolytic activity could be restored by the addition of purified C5 . No chemotactic activity for polymorphonuclear leukocytes could be generated in the C5-deficient serums upon activation of either the classic or alternative pathways , again demonstrating the importance of C5 in human subjects for the production of chemotactic factors . The chemotactic responsiveness of the patients polymorphonuclear leukocytes and monocytes to preformed chemotactic factors was not depressed . Twenty-two of 32 other family members from three generations had depressed whole hemolytic complement levels . In 19 of 30 family members , levels of hemolytic C5 ranged from 13 to 64 per cent of normal . No linkage for C5 deficiency and the A or B loci of the major histocompatibility complex could be found . These data suggest an autosomal codominant mode of inheritance of C5 deficiency . Deficiency of C5 is compatible with good health , but it can be associated with repeated disseminated gonococcal infection
