Thymic abnormalities and autoimmune diseases

Autoimmune diseases such as ulcerative colitis (UC) and myasthenia gravis (MG) are frequently associated with thymic abnormalities. Thymus hyperplasia and/or thymoma have been demonstrated in all cases with both of these two diseases by pneumomediastinography (PMG). In the diseases of digestive organs from which we can easily obtain the local information through the endoscopic observation and biopsy specimens, lots of immunological abnormalities have been accumulated. Antibody-dependent cell-mediated cytotoxicity mechanism has been demonstrated to play an important role in the mucosal destruction in UC. In the peripheral blood level of this disease, immunological abnormalities have been demonstrated such as the presence of lymphocytes sensitized by certain antigens, autoantibodies and disturbances of lymphocyte subpopulations. In the level of the thymus, the retrovirus has been detected in the thymus epithelial cells. The supernatant of thymus epithelial cell culture (STEC) has the capability of differentiating human bone marrow cells and of facilitating disease-specific immune abnormalities. Moreover, the serum factors (thymus growth factor) discovered in the patients with UC and MG, have been demonstrated to alter the thymic environments. Therefore, it is postulated that thymectomy is beneficial to exclude these abnormalities and it has been evaluated to be very effective in UC and MG clinically. From these observations, it is thought to be important to investigate the immunological abnormalities of autoimmune diseases from the viewpoints of three immunological levels, the level of disease-specific organ, the peripheral blood level and the level of the thymus. And it is important that the therapeutic plans should be decided in the consideration of the abnormalities in each immunological level.