Objective      To explore the changes of Foxp3 expression in myasthenic thymus and thymoma.        Methods      Thymic specimens and clinical data of 50 myasthenia gravis (MG) patients who underwent thymectomy from January 2003 to June 2006 were collected

classified into three types according to MGFA clinical classification: hyperplastic thymus

atrophic thymus and thymoma. The thymic tissues collected near the thymoma served as thymic specimens near thymoma. The normal thymic tissues excised in cardiac surgery were used as control. The levels of Foxp3 mRNA and protein

as well as their relationship with clinical characteristics

were examined by immunohistochemistry

Western blotting and RT-PCR.        Results      Foxp3 positive cells mainly located in the medulla of myasthenic thymus and mesenchyma around blood vessels

less in cortical area. The levels of Foxp3 mRNA and protein were significantly lower in myasthenic thymus than that of non-myasthenic control specimens

much less in the specimens of thymoma with a significant difference between them and that of hyperplastic thymus. The levels of Foxp3 mRNA and protein were negatively associated with MGFA clinical classification.        Conclusion      Foxp3 expression decreased in myasthenic thymus and thymoma

indicating a role of Foxp3 in etiology of MG.