Age-related susceptibility to immunotoxicants: animal data and human parallels

There are numerous examples, of both the identical and different effects of animals exposure to toxic agents, which can be compared in both, exposed prenatal/neonatal animals and exposed adults. In some instances, although the chemical and its metabolites are stored for long periods in adipose tissue, adult exposure (short of acute poisoning) has little effect on the immune system (Johnson et al., 1986. An immunotoxicological evaluation of gamma-chlordane. Fundam. Appl. Toxicol. 6, 317-326), while exposure during gestation results in immunoteratology (Barnett, 1996. Developmental immunotoxicology. In: Smialowicz, R.J., Holsapple, M.P. (Eds.), Experimental Immunotoxicology, CRC Press, Boca Raton, FL, pp.47-62). With the heavily studied dioxins, both prenatal as well as adult exposure causes immunotoxicity, however, the effects are not always the same. Attempts to confirm these observations in humans have been hampered by a multitude of problems that are directly related to the exposure paradigm, such as lack of accurate exposure data, varying lengths of exposure, etc. as well as many variables that are simply related to differences in genetic makeup, lifestyle, socioeconomic status, etc. that are part of the human populations. A few studies have noted important trends in immune status that are correlated with levels of halogenated aromatic hydrocarbon exposures, however, even these fail to provide unequivocal answers regarding the relative risk of prenatal exposure.