Immunotoxicity and Risk Assessment: Effect of Temporal Factors

Abstract

The immune system is composed of cells collectively best known as leukocytes. They are derived from bone marrow and are widely distributed throughout the body, which they defend against infections and certain tumors. Immune cells may also react to relatively innocuous foreign substances or against “self” components resulting in allergic or autoimmune disease, respectively. There is evidence that various chemicals can act as either immunosuppressants, allergens, or inducers of autoimmunity. A number of immune function tests have been developed to identify chemicals with immunosuppressive potential. However, immune suppression only poses a hazard in the presence of infectious agents or tumor cells. Temporal relationships between exposure to a compound and exposure to these agents have an impact on the risk associated with immune suppression. Three examples from animal research are presented to illustrate how temporal factors may affect the risk of infection: (1) effects of immunosuppressants on natural killer cell activity and susceptibility to murine cytomegalovirus infection; (2) effects of phosgene on alveolar macrophage phagocytic function and susceptibility to Streptococcus zooepidemicus infection in mice and rats; and (3) effects of ultraviolet radiation on delayed-type hypersensitivity responses and susceptibility to Leishmania major and mycobacterial infections