The heterocytotoxicity of human serum. III. Studies of the serum levels and distribution of activity in human populations.

A metabolic inhibition assay has been employed to investigate the distribution of serum heterocytotoxicity mediated by natural antibody activating the classical complement pathway and by antibody-independent activation of the alternative complement pathway in human serum samples derived from various groups of individuals. Levels in female cancer patients and in women taking oral contraceptives were significantly elevated over normal controls. Newborn infants exhibited approximately half of the average adult levels. Levels were maximally elevated in patients with visceral cancer, particularly in individuals with adenocarcinomas, while patients with sarcomas exhibited reduced levels. These and other data derived from the literature suggest that the metabolic inhibition assay may provide a useful measure of natural antibody and activation of the alternate complement pathway representative of mechanisms of natural immunity vs tumours.