Antibody-Independent Activation of Human C1 after Interaction with Heart Subcellular Membranes

A 19S, complement-fixing, heat-labile factor reactive with human heart mitochondria and microsomes has been detected in all normal human serum. This serum factor reacted with autologous and homologous heart mitochondria but did not react with mitochondria derived from cardiac tissue from other species. Subsequent characterization has indicated that this heat-labile factor was the first component of human complement. The C1 reacted with the mitochondrial membrane, was activated, and resulted in an apparent antibody-independent activation of the complement system.