| Myasthenia Gravis(MG) is a prototypical CD4+ T cell-dependent autoimmune disease mediated by anti-acetylcholine receptor(AChR) autoantibodies affecting the neuromuscular transmission.Though characterized well,the mechanism of the autoimmune reaction is still unclear.The thymus is assumed to be the initiative site for the occurring of autoimmunity.Regulatory T cells(Treg),coming from thymus and characterized by expression of CD4+CD25+,is found to play a central role in dominant immune tolerance by inhibiting the immune response of CD4+ effective T cells.In a recent study,the CD4+CD25+Treg,which function is critically dependent on the expression of Foxp3,was found been dysfunction in myasthenic thymus.Aim to explore the role of Foxp3 in the thymus of MG,the HE and immunohistochemistry staining(HIS) was used to detect the expression and location of Foxp3 in myasthenic thymus and thymoma tissues;Western Blot and RT-PCR were also carried out to examine the level of Foxp3 protein and mRNA.And we also checked the frequency of Foxp3+ cells in the CD4+ or CD8+ single positive(SP) and CD4+CD8+ double positive(DP) thymocytes,as well as the expression of CTLA-4,TGF-βand IL-10, which were thought to be mediators in the suppression of immune response.At last,we explored the expressions of some cytokines such as TGF-β,IFN-γ,IL-4 and IL-10,which function as inducers of Foxp3 in the myasthenic thymus.The results from out study were described:1.Hyperplasic thymus(HT) from MG patients is characterized by the expansion of medullar area,lymphoid follicular and per vascular space(PVS),while some similar histological changes were found in atrophic thymus(AT) and the thymus near thymoma(Tnt).The ratio of CD25+ cell in HT and Tnt was significant higher than that in normal thymus,and Foxp3+ cell ratio was much lower in HT and AT compared with normal thymus.There was no significant difference of Foxp3 protein or mRNA expression level among HT,AT and Tnt tissues,while which was much lower than that in normal thymus but higher than that in thymoma.Moreover,significant differences of the expression was also found among different MGFA classification.2. Thymoma was characterized with hyperplastic epithelial cells with variant amount of lymphocytes.The ratio of CD25 positive cell and Foxp3 positive cell,as well as the expression of Foxp3 protein and mRNA,was much lower than that in HT and normal thymus.3.The expression of Foxp3 can be found both in CD4+,CD8+ SP and CD4+CD8+ DP thymocytes,CD4+ SP thymocytes had a higher percentage of Foxp3 expression than CD8+ SP and DP thymocyte.However,the ratio of Foxp3 in CD4+ SP thymocytes was much decreased compared with normal thymus,while no change of CD8+ SP and CD4+CD8+ DP thymocyte was found.Despite CD4 and CD8,more than half of CD25+ thymocyte was Foxp3 positive,with a sharp decreased ratio in the myasthenic thymus.4.The expression of CTLA-4 in the Foxp3 positive cell was significantly decreased in myasthenic thymus compared with normal thymus,while no change was found for the expression of TGF-β,IL-10.5.The level of TGF-βmRNA was significantly lower in myasthenic thymus than normal thymus,as well as the ratio Smad3/Smad7.Moreover, the expression of TGF-βwas significantly correlated with the expression of Foxp3 positively.We also found that the level of IFN-γmRNA,which was correlated with the expression of TGF-βand Foxp3 negatively,was much higher in HT than normal thymus or AT,Tnt and thymoma.Moreover,no significant changes was found of the expression of IL-10 and IL-4 mRNA.The conclusions of our study can be drawn as follows:ⅰ.There were similar pathologic changes at the medullar area of HT,AT and Tnt thymus,and the same location can also be found for Foxp3,CD25 positive cells.Moreover,there were no significant changes for the level of Foxp3 protein and mRNA among the three type of myasthenic thymus,while the expressions were much higher than that of thymoma.These kinds of changes indicated that there were some common basis for HT,AT and Tnt myasthenic thymus in the mechanisms of MG autoimmunity,which might be different from thymoma, the thymus tissue itself of MG patients combined with thymoma maybe play a similar role as HT in the autoimmune disease,ⅱ.The percentage of Foxp3 positive cells in CD4+ SP thymocytes or CD25+ thymocytes,as well as the expression of Foxp3 protein and mRNA of myasthenic thymus were significant decreased than that of normal thymus,and were significantly correlated with the MGFA clinical classification,which meant an important role of Foxp3 for the autoimmunity,ⅲ.Compared with normal thymus,the expression of CTLA-4 of Foxp3 positive cells in myasthenic hyperplasia thymus was significant decreased,which suggested that abnormal intercellular contact mediated by CTLA-4/B7 might account for the autoimmunity,ⅳ.The significant lower expression of TGF-βmRNA,as well as the ratio of Smad3/Smad7,was relevant to the expression of Foxp3.It suggested that the down-regulation of TGF might be account for the decreasing of Foxp3 expression in myasthenic thymus.In our study,an up-regulated IFN-γmRNA in myasthenic thymus suggested a important role for the occurrence of the disease.
|
PDF Full Text Request