To investigate the effects of kinetin (Kn) on thymus and immune function in a rat model of D-galactose (D-gal)-induced aging, fifty SD rats were randomly divided into five groups: young control group, aging model group, low-dose Kn-treated group, middle-dose Kn-treated group and a high-dose Kn-treated group. Rats in the aging model group were subcutaneously injected with D-gal (125 mg/kg BW/day) in the back of the neck. Rats in the Kn-treated groups were intraperitoneally injected with 5, 10 or 20 mg/kg BW/day Kn solution. Changes in the thymus index, activity of antioxidant enzymes such as superoxide dismutase (SOD), the content of metabolic products such as malondialdehyde (MDA), the content of serum immunoglobulins and Interleukin–2 (IL-2), as well as histological changes in the thymus were recorded and analyzed. Results showed that the thymus index, antioxidant enzyme activity and the immunoglobulin contents of experimental animals in the aging model group decreased significantly compared with the young control group. The contents of metabolic products increased significantly compared with the young control group. The thymus index, content of immunoglobulin and IL-2, as well as antioxidant enzyme activity of the rats in the Kn-treatment groups significantly increased compared with the aging model control group, while the contents of Interleukin–6 (IL-6) and MDA decreased significantly. The structure and substructure of thymus cells were protected by Kn treatment. Therefore, we conclude that Kn can protect the tissue structure of the thymus and effectively antagonize oxidative damage in the thymus of aging rats induced by D-gal, and thereby improve the body's immune ability and delay aging of the thymus.

Key words: Aging, Immune, Kinetin, Thymus