Effect of Age on Immune Function in Terms of Chemically Induced Cancers

Abstract

Neonatal, fetal, and very old animals are particularly sensitive to chemical carcinogenesis. Reasons for this increased sensitivity could be due to increased susceptibility of "target" organs or cells, peculiar hormonal levels at these age groups, relatively deficient immune functions, or combinations of these and/or other factors. During the late fetal and first three weeks of neonatal life, the immune system is rapidly maturing, is relatively incompetent, and its diverse components are developing at different rates. Gonadotrophic hormones of the pituitary or placenta are high during pregnancy, the early neonatal period, after the menopause, and in a large fraction of men over 60 years of age. These and other hormones are immunosuppressive and could theoretically facilitate carcinogenesis. The particular immune cell type, if any, responsible for resistance to chemically induced tumors has not been determined. One can only state that susceptibility to chemical carcinogenesis is associated with a relative dysfunction of the immune system and that age is an important factor.

Metabolic activation/deactivation reactions during perinatal development.

“…If, these repair processes are present in fetal tissues they could modify the expression of transplacental toxicity. Immunological defenses are also operative in perinatal tissues (2) and might function to stop the progression of toxicity at various developmental stages.…”