8 Immunotoxicity of Permethrin
The immune system is the first line of defense to protect animals and humans from disease. Suppression of the immune response can result in an increase in susceptibility to infectious and carcinogenic agents, and an increased response can provoke allergies and autoimmunity. In some instances, the immune system can be the primary target organ of toxic chemicals.
No data are available in the literature on the immunotoxic potential of permethrin in humans.
Two immunotoxicity studies have been conducted with permethrin. In an in vitro study (Stelzer and Gordon, 1984), permethrin at a concentration of approximately 10−5 to 10−6 M inhibited the mitogenic response of murine immune lymphocytes. Although permethrin inhibited the mitogenic response of murine lymphocytes in vitro, mitogenic responses in in vitro exposures do not represent functional immunity, nor do they simulate in vivo reactions.
McCorkle et al. (1980) fed 1-day-old chicks permethrin at 0.01, 0.1, or 1 ppm for 6 weeks. The antibody titers to a T-cell-dependent antigen (sheep red blood cells) were elevated, and titers to a T-cell-independent antigen (Brucella abortus) were depressed. The contrasting, elevated and suppressed, antibody responses to antigen do not reflect a consistent immunotoxicological effect. Immunotoxicological data for most chemicals have been acquired in laboratory mice and rats; therefore, additional studies need to be performed in those species to determine the immuno-
toxic potential of permethrin. Few immunotoxicological data from laboratory animal exposures are available for permethrin or other pyrethroids.
No human data are available to evaluate the immunotoxic potential of permethrin in humans. The two laboratory studies (an in vitro study with lymphocytes and a study in chicks) are inconclusive to assess the immunotoxicological effects of permethrin.
Little immunotoxicological information is available for permethrin. Immunotoxicological investigations need to be performed in laboratory animals to ascertain the immunotoxic properties, if any, of permethrin in mammalian species. These studies should follow the guidelines presented in the National Research Council's report Biologic Markers inImmunotoxicology (NRC, 1992).