Hyperplasia of the thymus in progressive systemic sclerosis

Abstract

Aerobacter aerogenes incubated in a medium containing all factors necessary for exponential growth except Mg(++) continued to synthesize nucleic acids and proteins for more than 70 hr, provided the major carbon source was in excess at all times. After 24 hr of Mg(++) starvation, deoxyribonucleic acid content in the culture had increased 10-fold. In contrast, the viable-cell count increased only about threefold during the first few hours and then remained approximately constant for the subsequent 70 hr. After specified intervals of Mg(++) starvation, extracts of the bacteria, or ribonucleic acid (RNA) purified from them, was centrifuged through gradients of sucrose to separate transfer RNA from ribosomal components. After correcting for losses, we obtained the following results. (i) There was a progressive rise in the content of transfer RNA competent to accept amino acids and during starvation it remained completely stable. (ii) In contrast, the contents of normally sedimenting ribosomal RNA and ribosomal subunits (30 and 50S) remained approximately constant for more than 24 hr. This did not result from stability of ribosomes made prior to starvation together with an inhibition of synthesis of new particles. Rather, ribosomes were continually breaking down and being replaced by an equivalent number of new ones. (iii) The breakdown of ribosomes appeared to be sequentially ordered; polysomes yielded 70S monomers, which then gave 30 and 50S particles, and these disintegrated to smaller units and finally to acid-soluble products. (iv) Furthermore, the particles derived from breakdown do not appear to exchange with subparticles on the path of assembly. Thus, ribosome decay was age-dependent and ribosomal RNA molecules had a minimal life expectancy of 90 min; however, some survived much longer.

Thymus alterations and systemic sclerosis

“…Immunological abnormalities may represent the underlying disorder of SSc, as suggested by T-lymphocyte alterations and production of various autoantibodies [1,2]. The thymus plays a crucial role in immune system homeostasis [3,4]; several anecdotal reports suggest a possible pathogenic role for thymus alterations in some immune-mediated rheumatic diseases, including SSc [5][6][7][8][9][10][11][12]. In these patients the presence of pathological thymus alterations can be occasionally suspected on the basis of radiological investigations.…”

Progressive systemic sclerosis and autoimmune haemolytic anaemia

“…Thymic changes have also been noted in PSS. Biggert and Nevin (1967) described the thymus in PSS as hyperplastic with numerous Hassall's corpuscles, medullary lymphoid follicles and plasma cells, features interpreted as evidence of disturbed immunological function. Lymphocyte toxicity to muscle, fibroblasts and epithelial cells has been described in PSS (Currie, Saunders and Knowles, 1971) and, using the leucocyte migration tests, Hughes, Holt and Rowell (1974) have demonstrated widespread cell-mediated hypersensitivity in PSS to human tissue antigens.…”

The thymus in systemic sclerosis

“…It is interesting to compare these findings with those reported by other authors. Biggart and Nevin (1967) noted cortical atrophy, but described the gland (presumably the medulla) as hyperplastic, with numerous Hassall's corpuscles, many of which were cystic, embedded in solid columns of epithelial cells. They also noted many medullary lymphoid follicles and numerous plasma cells, features that they interpreted as evidence of disturbed immunological function.…”

“…One case of a thymoma in a patient with scleroderma was reported by Lattes (1962) and we have been able to trace reports on the histology of the thymus in only six other patients with this condition. Biggart and Nevin (1967) described one patient in whom the thymus was hyperplastic, with medullary lymphoid follicles and abnormal Hassall's corpuscles, and Goldstein and Mackay (1969) studied the thymus in five patients, noting medullary lymphoid follicles in one and the features of stress involution in the other four.…”