Croton Oil Induced Suppression of the Immune Response of Guinea-pigs

ALTHOUGH the promoter or cocarcinogenic activity of croton oil 1 and its active principle, the phorbol esters 2,3 , have been studied for many years, the precise mechanisms by which they exert this effect have not been established. Various tumours, whether induced by chemical, viral or mechanical carcinogens, have been shown to possess “tumour-specific” antigens which render them immunogenic in their host of origin 4,5 . Furthermore, immunosuppression of animals treated with these agents results in an increased incidence of tumours and a shorter latent period for their development 6 . It has been demonstrated that several carcinogens are themselves immunosuppressive 7 and also that the susceptibility of an inbred strain of mice to the carcinogenicity of an agent is positively correlated with its capacity to suppress an immune response in that strain 8 . It has been proposed that the immune system, especially cell-mediated immunity, is part of a homoeostatic mechanism for the control of carcinogenesis 9 .