Molecular biological and clinocopathological study on the thymuses and lymph nodes of patients with myasthenia gravis

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Several distinct immunohistochemical and molecular biological characeristics were shown using the thymic and lymph node tissues of patients with myasthenia gravis.1. Thymic lymphoid follicles were surrounded by a fine matrix fiber tenascin, but these charcteisti compartmentalized structure was not found in the corresponding lymph nodes. In these thymic lymphoid follicles, immunohistochemically, expression of Fas antigen and p53 protein (apoptosis reacted factors) were less frequent than that in the other region of the thymus. Furthermore, Several densely but scatterd stained bc1-2 (apoptosis-depressing factor) positive B cells were observed in the thymic lymphoid follicles, although there were mostly no positive B cells in the lymph nodes. Expression of the antigen and protein were also confirmed at mRNA level through analysis using RT-PCR method.2. Patients, who had several highly developed thymic lymphoid hyperplasia, have preoperatively maintained higher level of serum anti-Ach-R an … More tibody titer than that of patients with poorly developed hyperplasia or without it.3. Population of memory and non-memory B cells of expression of adhesion molecules (LFA,ICAM) of the lymphoid follicles were similary recognized in both the thymus and lymph node.4. Epitheital cells from the thymuses and thymomas were immunochemically shown using anti-CK-17mAB among several anti-cytokeratin mAB Series. In the thymus, only medullary epithelium was positively stained. In thymomas, about half of the cases possessed positive cells. CK-17 mRNA expression in these cases were also confirmed by RT-PCR method. Patients with thymomas possessing CK-17-positive cessl showed higher level of seurm anti-Ach-R antibody titer and more developing lymphoid follicles in the residual thymuses than those lacking positive cells.CK-17-positive cell thymomas were both polygonal and polygonal-spindle shaped epithelial cell thypes, but contrary to out expection, spindle shaped epithelial cell type thymoma contained no positve cells.These results indicate that some antibody producing B cells in the thymic lymphold follicles associated with myasthenia gravis could escape the entry of apoptosis. Thus, they might survive to produce auto-antibody. Thymomas containing CK-17-positive epithelial cells seem to have a promoting ability of thymic B cells to make auto-antibodies. Regarding epithelial cell differentiation toward subtype of thymomas, there were a discrepancy in the morphological and immunohistochemical observations. Less