Objective To investigate the influence of pinealectomy(Px)and melatonin (MLT) supplementation on CD4~+CD25~+Treg cells development and Foxp3 expression in rat thymus. Methods One hundred and twenty clean-grade male SD rats were divided into five groups: normal control group, sham pinealectomized group, pinealectomized group, Px +7.5 mg/(kg·d) MLT group, Px +15 mg/(kg·d) MLT group, and the thymus were taken out at the 4th week and the 8th week;Flow cytometric analysis was used to analyse the number of double positive cells in the thymus and peripheral blood;Semiquantitative RT-PCR and immunohistochemistry were applied to analyse Foxp3 expression of rat thymus. Results There was no difference of the number of CD4~+CD25~+ Treg cells in rat thymus between Px and normal/sham group, and the number increased dependently on time and dose after MLT supplementation. In rat peripheral blood the double positive cells significantly increased in models of Px at the 4th week, and then backed to normal level after MLT supplementation. The results showed no significant changes in all groups at the 8th weeek;At the 4th weeks, Foxp3 expression increased in the thymus of Px rats compared to nomal/sham group, which returned to normal level after MLT supplementation. On the other hand, Foxp3 expression showed no significant difference in all groups at the 8th weeek.Conclusion Px made no difference between the development of CD4~+CD25~+Treg cells in rat thymus, but resulted in significant increase of thymic output and Foxp3 expression. All the effects disappeared at the 8th week. MLT supplementation could reverse the abnormity.

Objective To study the effect of pinealctomy and melatonin on the cell cycle distribution during T cell development in thymus. Methods SD rats were divided into 5 groups:normal controls,sham-operated controls,pinealectomy,pinealectomy+melatonin injection 7.5 mg/kg; and pinealectomy+melatonin injection 15 mg/kg.The animals were sacrificed at 4 or 8 weeks after operation.cycilnA +and cyclinE +T cells in thymus were dyed with immunocytochemical ABC methods, measured by computer image analysis.Cell cycle analysis was performed by flow cytometry.The expression of cyclin-dependent kinase inhibitor 1? was tested by RT-PCR method. Results The effect of pinealectomy on the expression of cyclinE was stronger than that of cycilnA. Pinealectomy promotes the synthesis of cyclinE in thymus.The percentage of G-0/G-1 phase cells was decreased and G-2/M phase cells was increased.These would be convalescente by supplement with melatonin,but the reaction to melatonin was differencet in thymus cortex and in medulla.Melatonin enhanced the expression of cyclin-dependent kinase inhibitor 1? in thymus.Conclusion Pinealectomy influences notably the T cells development in thymus.Rejuvenation of degenerative thymus could be observed by melatonin administration.