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909 MOLECULAR BASIS OF A GENETIC DEFICIENCY OF THE SECOND COMPLEMENT COMPONENT (C2)

C2 deficiency is the most prevalent human genetic disorder of the complement proteins. We reported that monocytes from C2 deficient humans failed to secrete functional C2. Availability of a strain of C2 deficient (C2D) guinea pigs permitted a study of the molecular basis of this defect. Production of C2,factor B,and C4 by peritoneal macrophages from normal,heterozygous and homozygous C2D animals was monitored functionally and immunochemically. Homozygous C2D macrophages failed to secrete functional C2. C2 protein with an apparent molecular weight less than normal was found intracellularly. Extracellular C2 antigen secreted by the C2D cells was present primarily as apparent catabolic fragments on SDS-PAGE. Mixtures of normal radiolabeled C2 with conditioned medium from C2D cells suggested that this finding was not due to increased proteolytic activity in the C2D medium. Cells from each animal produced comparable amounts of C4 and factor B, and were similar in morphology,phagocytosis,nonspecific esterase staining,and C3b and Fc receptor function. These data indicate that C2D guinea pig macrophages synthesize a defective,unstable C2 protein.