Physiological responses to a natural antioxidant flavonoid mixture, silymarin, in BALB/c mice: II. alterations in thymic differentiation correlate with changes in c-myc gene expression.

Silymarin is a mixture of bioactive flavonoids isolated from the seeds and fruits of Milk Thistle [ Silybum marianum (L.) Gaertner]. We tested the hypothesis that exposure to silymarin will modulate differentiation and cell selection in the thymus via alterations in gene expression. Male BALB/c mice were treated intraperitoneally once daily for five days with 0, 10, 50 or 250 mg/kg of silymarin. Flow cytometric examination of thymic lymphocyte populations showed that the absolute numbers of CD4 + and CD8 + positive T-lymphocytes were increased by silymarin. The c- myc proto-oncogene is important in controlling differentiation and functions of thymocytes. Treatment with silymarin resulted in increased c- myc expression in the thymus. In contrast, the expressions of IL-2 and IL-4 were decreased by silymarin, while MHC II expression did not change. These results indicate that in vivo exposure to silymarin influences phenotypic selection processes in the thymus at doses that may be encountered in natural medicinal use. Further studies investigating the effects of silymarin on the immune system are warranted.