Chlorpyrifos (CPF) is a widely used organophosphorus insecticide throughout the world in
agriculture and anti-termites around homes. Silymarin is a naturally occurring substance and has
antioxidant effects. For decades, it has been used clinically in Europe for the treatment of
alcoholic liver disease and as anti-hepatotoxic agent. Therefore, the present study aimed to
assess the protective and curative effect of silymarin in attenuating the CPF-induced
immunotoxicity in rats, by measuring the level of immunoglobulin G (IgG), lymphocyte
viability, neutrophil phagocytic function assay, total white blood cells count (WBC) and relative
differential white blood cells count, as well as nitric oxide (NO) level and catalase activity. The
treatment with CPF decreased lymphocyte viability, neutrophil phagocytic index, total white
blood cells count, relative lymphocyte count, IgG concentration and catalase activity. On the
other hand, a high level of NO was detected upon animal treatment with CPF. Interestingly,
pre- and post-treatment with silymarin to CPF-treated group improved the lymphocyte viability,
total white blood cells count, relative lymphocyte count, catalase activity and the NO level. Preand
post-treatment with silymarin recovered phagocytic activity of neutrophils and restored IgG
level. In conclusion, silymarin has both protective and curative effects against CPF-induced
immunotoxicity may be through its anti-oxidant effects.