Approaches to the evaluation of chemical-induced immunotoxicity.

The immune system plays a crucial role in maintaining health; however, accumulating evidence indicates that this system can be the target for immunotoxic effects caused by a variety of chemicals including the environmental pollutants of polychlorinated biphenyls, chlorinated dibenzo-p-dioxins, pesticides, and heavy metals. Adverse chemical-induced immunomodulation, which is studied within the discipline of immunotoxicology, may be expressed either as immunosuppression/immunodepression or immunoenhancement. The former may be manifested either as decreased resistance to opportunistic viral, bacterial, fungal, and other infectious agents or increased susceptibility to cancer. Immunoenhancement on the other hand may either increase the risk of autoimmune reactions or result in allergic reactions. This paper attempts to integrate several aspects of the immune system that are relevant to the assessment of potentially immunotoxic chemicals.