Synthesis of the subcomponents of C1 was detected in human cell lines derived from fetal intestine, intestine of an agammaglobulinemic fetus, colorectal adenocarcinomas, normal bladder, and transitional cell carcinomas of the bladder. Criteria for synthesis were detection of hemolytic activity in the culure medium; immunoprecipitation of specifically labeled protein after incubation of the cells with medium containing 3H- or 14C-labeled amino acids; isolation from the immunoprecipitates of labeled proteins with m.w. approximating those of the subcomponents of C1; and identification on autoradiographs of labeled precipitin bands after immunoelectrophoresis of labeled extracellular or intracellular medium and reaction with monospecific antisera.

Fetal intestine and intestine derived from an agammaglobulinemic fetus synthesized similar amounts of C1q, C1r, and C1s. Both synthesized twice as much C1s as C1r and one-half as much C1q as C1r. Hemolytically active C1̄, isolated from IgG-Sepharose, gave m.w. analogous to published reports on SDS-polyacrylamide gels.

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