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

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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. For example, thymus-dependent (T) alloreactive cells capable of proliferating in mixed lymphocyte reactions (T helper cells) develop by 7 days of age, but precursors of T killer cells are not competent until approximately 14 days of age. Bursa equivalent-dependent (B) cells capable of generating antibody responses are present in fetal liver but are extremely sensitive to tolerance induction until 10-14 days of age when IgD cell surface receptors are detectable. Marrow-dependent (M) cells res...

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