Analysis The Effect Of Thymoma In The Mobidity Of Myasthenia Gravis

PART 1EXPRESSION OF α-AchR AND α-AchR-LIKE ANTIGEN IN THYMOMA TISSUESObjective: Acetylcholine receptor α-subunit (α-AchR) is the key in the morbidity of myasthenia gravis(MG). To examine the expression of α-AchR in the tissues of normal thymus and thymoma , in order to analysis the effect of thymoma in the morbidity of myasthenia gravis and whether there are defference between the general MG pathogenic theory and the thymoma leading to MG . Midsize neurofilament (NF-M) is the marker of the neuro-endocrine capacity of tumour cells. It has the same structure as part of α-AchR and skeletal muscle. Investigate the expression of NF-M in thymoma , to analysis the effect of thymoma in the pathogenic of myasthenia gravis.Methods: We investigated the expression of α-AchRmRNA by PCR-restriction fragment polymorphism length (RT-PCR) in the tissues of 10 normal thymuses,5 hyperplasia thymuses and 30 thymomas (these patients with thymoma were operated in Qilu and Shandong province hospital during 2002-2003 ) . In the patients ,there are 12 cases with myasthenia gravis. Immunohistochemistry was carried out to investigate NF-M expression in 45 patients with thymoma(these patients were operated in Qilu hospital during1996-2003). In the cases, 21 patients with myasthenia gravis. 10 normals thymus tissues as contrast, the donor without autoimmune disease.Results:a-AchRmRNA has two isoforms(P3A- and P3A+), P3A- and P3A+ isoforms were present in all normal thymus tissues and thymus hyperplasia tissues; only P3A- isoform was present in thymoma, P3A+ isoform was absent. NF-M expressed in the epithelial cells of thymoma. In the normal thymus tissues it shows very low expression in the cells nearby the Hassal's body, maybe diagnose negative.In all the types thymoma, the rate of NF-M positive expression was higher in cortical thymomas than the other types ,p<0.05, and the cortical thymoma has a higher morbidity of MG. Correlation was found between MG status and NF-M expression p<0.005.Conclutions : Difference of the a-AchR in thymoma at the level of the expression ofa-AchR and the phase of DNA-mRNA may indicate that thymoma play other role in the immune pathogenesis of myasthenia gravis. There is correlation between the expression of NF-M in the thymoma with MG > NF-M may be important in leading to MG in patients with thymoma. PART 2ABNORMAL CHANGE OF T AND B LYMPHOCYTE SUBSETS IN THYMOMA AND THE RELATION OF THE PROLIFERATION OF THYMOCYTE TO a-AchR anda-AchR LIKE ANTIGENObjective: To study whether there were sensitive thymocytes in thymoma or not. First, to examine the change of T lymphocyte subsets in thymoma and the expression of major histocompatibility , analysis the reason why T lymphocyte subsets abnormally development and the correlation between thymoma and myasthenia gravis. B lymphocyte has the capacity of secreting antibody in autoimmune disease. Investigate the B lymphocyte in thymoma tissue and to analysis the relation of B lymphocyte number and thymoma with myasthenia gravis. Second, to study the proliferation of thymocyte in thymoma and peripheral blood lymphocytes given the acetylcholine receptor a-subunit (a-AchR) and the midsize neurofilament (NF-M) . In order to analysis the condition that thymoma leads to myasthenia gravis.Methods: T and B lymphocytes were investigated by flow cytometry (FCM); the expression of major histocompatibility complex(MHC) molecules (MHC-I,MHC-II) by immunohistochemical. Thymocytes and peripheral blood lymphocytes were cultured witha-AchR and NF-M, their proliferation rate was calculated as stimulation index, examined by MTT methods. According whether with myasthenia gravis or not, the patients were taken apart into two groups, thymoma with myasthenia gravis (MG+),the other (MG-). In the 30 cases , 12 patients associated with myasthenia gravis. 10 cases normal thymus tissues as contrast, the donor without autoimmune disease.Result: The precentages of T lymphocyte subsets were different in thymomacompared with the normal thymus tissue (CD4+CD8- subsets increased,CD3+CD4+ subsets reduced) p<0.01 , and difference was also presence between the two groups(CD4+CD8+ subsets increased in MG+ group, CD3+CD8+ subsets reduced in MG+),p<0.001. The expression of MHC-I was fonud in the normal thymus tissue and thymoma , no difference was found. No expression of MHC-II was found in thymoma . The amount of B lymphocyte was decreased in MG+ group, was increased in MG- group compared with the normal, P<0.01. a-AchR and NF-M can stimulate the thymocytes proliferation in the MG+ group, the stimulation index was higher than the contrast group, p<0.01, there are no difference betweena-AchR group and NF-M group. a-AchR and NF-M can not stimulation the thymocytes proliferation in the MG- group, and no to peripheral blood lymphocytes of MG+ , MG- patients and contrast .Conclutions.- The subsets of T cell and the expression of MHC-II are abnormal in thymoma tissues, the impaired expression of the MHC-II molecules may lead to the elect of thymus abnormal and affect the maturation of T cell subsets. The B cell were abnormal in thymoma tissues, which maybe not important for the pathogenesis of thymoma with myasthenia gravis. There are sensitive thymocytes to AchR and NF-M in thymoma tissues of patients with MG. That is the key condition if the thymoma can lead to MG.