Thymus abnormalities in ulcerative colitis- comparative study with other autoimmune diseases

Sulfhydryl blocker-induced colitis in the rat: immunological changes in thymus gland and colonic mucosa

The study was designed to examine the changes of thymus in sulfhydryl blocker-induced colitis. We used N-ethylmaleimide (NEM) as sulfhydryl blockers. Fasted male Sprague-Dawley rats were given 3% NEM in 1% methyl cellulose into the colon. N-ethylmaleimide treatment caused severe diarrhoea with bleeding for the first 7 days. At autopsy, adhesions, colon dilatation, and single or multiple erosions and ulcers were observed. Time-course studies revealed that the lesions were most extensive and severe 3 or 7 days after the administration of NEM. Histological examination of colon on the 3rd day after NEM treatment demonstrated mucosal erosion, oedema and extensive infiltration of neutrophils. The mucosal lesions extended into the submucosa and muscle on the 7th day after NEM treatment. Immunohistochemical studies showed that T cells and macrophages were markedly increased in the lamina propria of colonic mucosa. After 3 weeks, the infiltration of chronic inflammatory cells was observed and regeneration of the mucosa was noticed. The thymus gland was significantly decreased in weight and size on the 3rd day after NEM treatment, but the weight loss of thymus gland was regained in 3 weeks. Transient atrophy of thymus gland was noticed in this colitis model. The phenotypes of thymocytes were not influenced by NEM treatment. It is concluded that the thymus abnormalities in human ulcerative colitis are not induced in this animal model and that other chronic models are necessary for the elucidation of the immunological abnormalities, including thymus abnormalities.

RNA tumor virus in human thymomas and thymus hyperplasias

Human thymomas and thymus hyperplasias were examined for retroviruses. Most of these patients were complicated by systemic immunological diseases such as myasthenia gravis and pure red cell aplasia. The thymus cells were co-cultured with allogenic B cells or peripheral blood lymphocytes (PBL) pretreated with mitomycin C. Retrovirus-like particles were demonstrated in cultured thymus cells in all cases of thymomas and thymus hyperplasias examined by electron microscopy. In most cases, these particles were detected in thymus epithelial cells. Reverse transcriptase activity sedimenting at a density of 1.15-1.17 gm/cm3 in sucrose density gradients was eluted in the culture fluids. Retrovirus-like particles were demonstrated in human T cells infected with these particles. Antibodies to virus-infected T cells were detected in sera of the patients with thymoma and thymus hyperplasia. These results suggest that in thymomas and thymus hyperplasias, retroviruses that can be induced, following a proliferative stimulus, may be involved in the genesis of thymic disorders and in the pathogenesis of systemic immunological diseases.

Thymectomy in myasthenia gravis. A review

The role of thymectomy in the management of myasthenia gravis is reviewed in the light of the published data and of a personal series. The patients in whom the operation is most successful are non thymomatous patients aged between 10 and 40 years with an MG history of less than 3 years. There is no sex prevalence. Lasting improvement may be expected. There are no proven correlations between biological indices like the germinal centers in the thymus and/or AChR antibody titers and the postoperative course of the disease. Complete removal of the thymus seems to be crucial and hence the transsternal approach is preferred. The operation, less effective in patients with thymoma than in those with an active thymus, is nonetheless necessary to in these patients prevent putative damage to surrounding organs from thymoma infiltration. Why thymectomy should be effective in patients with an active thymus and not in those with a thymoma may be revealed by in vitro studies of the interactions between thymic cells and peripheral B cells, now in progress.

Myasthenia gravis. A survey

Myasthenia gravis is a chronic disease characterized by a fluctuating weakness of voluntary muscle, with a preference for the muscles innervated by cranial nerves. The pathophysiological mechanism is a loss of postsynaptic acetylcholine receptors to less than 20-30% so that the safety margin of neuromuscular transmission is lost. It is probable that the function of the remaining acetylcholine receptors is impaired by antibodies against receptor proteïn, which can be demonstrated in the serum in 80-90% of the patients, and which are highly specific for the disease. An experimental autoimmune myasthenia can be induced in many animal species by immunization with purified receptor proteïn and this disease is remarkably similar to the human myasthenia with exception of the fluctuating course. The human disease has to be considered as an autoimmune disease, although the initiating mechanism is unknown. The occurrence of tumors of the thymus in 10-15% and the presence of germinal centres in about 70% of the thymus glands removed by operation are highly suggestive of the importance of the thymus in the pathogenesis, but the definite mechanism (harbouring of an abnormal antigen in myoid cells, or/and false instruction of thymocytes with lack of suppressor cells) is essentially unknown. In most patients the disease tends ot have a favourable course from 5-10 years after onset and complete remission occur in about 20% after 10-20 years. Therapy with anticholinesterases, providing an increase in acetylcholine, is of partial benefit in most patients. Thymectomy has an excellent effect in about 30% of the patients without thymoma under the age of 40 during the first three years of the disease, and is of benefit in still another 30-40%. The use of prednisone and immuno-suppressive drugs has improved the prognosis of the 20% of the patients with severe life threatening symptoms, half of whom have a thymoma.