Acta endocrinologica. Supplementum最新文献

Spontaneous LT and elevated serum anti-Tg occur in the diabetes prone BB/W rat, but thyroid function is essentially normal in the rats with LT. Prolonged low dose MMI decreases the incidence of LT in BB/W rats. The administration of excess iodine beginning at 30 days of age markedly accelerates the occurrence of LT and anti-Tg at 90 days of age. Low iodine intake decreases the incidence of LT. Excess iodine intake did not induce LT in W-line, Wistar-Furth, and Sprague-Dawley rats. This suggests that iodine induced LT occurs only in genetically susceptible rats. Despite the increased incidence of LT during iodine administration, thyroid function remains essentially normal. This is in contrast to the frequent induction of hypothyroidism following iodine administration to euthyroid patients with Hashimoto's thyroiditis. In order to decrease thyroid reserve, rats were hemi-TX at 30 days of age. The administration of iodine markedly increased the incidence of LT and serum anti-Tg, increased the weight of the remaining lobe, and induced hypothyroidism as determined by significantly lower serum T4 and T3 concentrations and elevated serum TSH concentrations. Excess iodine administration to hemi-TX W-line rats (genetically equivalent, non-diabetes, non-LT prone BB/W rats) did not induce LT but did induce hypothyroidism, suggesting that BB/W and W-line rats are susceptible to iodine induced hypothyroidism, perhaps unrelated to the induction of LT. Excess iodine did not induce LT or affect thyroid function in hemi-TX Wistar-Furth and Sprague-Dawley rats.

The occurrence of HLA Class II expression by thyroid (and other endocrine) epithelia in autoimmune diseases suggests that these cells may facilitate their own destruction by immunogenically presenting autoantigens. This is supported by the findings that Class II+ thyrocytes can specifically stimulate virus-specific and autoreactive T cell clones, and that Class II expression by thyrocytes correlates with the occurrence of thyroid autoantibodies. A variety of factors may contribute to the regulation of Class II expression by thyrocytes: this is induced by interferon (IFN-gamma), and is enhanced by thyroid stimulating hormone (TSH) and by tumour necrosis factor (TNF). Conversely, epidermal growth factor (EGF) suppresses the induction of Class II in thyrocytes. This complex regulation is reflected in differences in HLA-D subregion expression between patients (DR greater than DP greater than DQ). The immune-based mechanisms of thyrocyte Class II regulation are clearly applicable to the on-going disease in an infiltrated thyroid, but the possibility of nonimmune Class II induction deserves attention, particularly in identifying factors which might contribute to the initial autoimmune attack. The possible involvement of such mechanisms in autoimmunity is supported by findings in Type I diabetes in which Class II+ islet beta cells can be found in the absence of infiltration. Further evidence is provided by the observation that a proportion of thyrocytes transformed with SV40 DNA constitutively express Class II molecules. Finally, the 'activated' state of capillary endothelial cells in organs subject to autoimmune attack suggests that they may play an important role in facilitating the autoreactive infiltration of the tissues.

Localization of PTH-binding sites has been examined in intact kidney sections and cultured cells derived from bovine kidney cortex. Tissue sections were incubated with 10(-7) M bovine PTH (1-84) for 2 h, cells for 15 min, at 37 degrees C. Visualization of PTH-binding was achieved by immunocytochemistry using a carboxy-terminal specific anti-PTH antiserum (S 478). For control, cell culture incubations were performed applying competitively 10(-7) bovine PTH (1-84) and a 10-fold excess of synthetic 1-34 PTH fragment, not antigenic for S 478. This resulted in a lack of staining. PTH-binding was found in all cells of the proximal and the distal tubule, and with less intensity in the thick ascending limb of Henle's loop. In collecting ducts a PTH specific staining was also present, which was confined to single cells localized between others without PTH binding sites. No staining was seen in glomerula, the thin limb of Henle's loop, in blood vessels, and in connective tissue. The data suggest that large parts of the nephron contain PTH-binding sites, although in different amounts. This is in agreement with the numerous actions of PTH in the kidney. In the collecting segment a distinct cell-to-cell difference was disclosed indicative for different functional states or cellular heterogeneity.

Human toxic diffuse goitre tissue was xenotransplanted to athymic mice. Transplant function was analyzed as 18 h [125I]thyroid transplant uptake at day 21 and at 10 weeks after transplantation. Graves' IgG or normal IgG was given ip daily day 22-35. Epithelial cell proliferation in the thyroid transplants was analyzed by continuous [3H]thymidine administration for 12 days between day 28 and 39 in a separate series given Graves' or normal IgG daily during the same period. The 18 h transplant uptake increased 12.8 times from 3 to 10 weeks in the Graves' IgG group but only 3.6 times in the controls (P less than 0.05). The fraction of labelled cells after [3H]thymidine incorporation was 51% +/- (SEM) after parallel Graves' IgG administration but only 2 +/- 0.3% (P less than 0.002) in the controls. The increased 10 weeks iodide uptake after Graves' IgG may be explained by an increased vascularisation or capillary maturation, by an increased individual cell sensitivity to stimulation or by an increased number of cells. Our results indicate that serum from patients with toxic diffuse goitre, i.e. Graves' IgG, contains a factor which promotes thyroid epithelial cell proliferation. Whether this is identical to TSI or is another IgG fraction remains to be shown.

Dendritic cells form a morphologically distinct class of cells characterized by shape, reniform nucleus, absent to weak acid-phosphatase activity and strong Class II MHC determinant positivity. Functionally they are the most efficient cells in antigen presentation to T-lymphocytes which indicates their role in the initiation of an immune response. Using immunehistochemical techniques we studied the presence of dendritic cells in normal Wistar rat and human thyroids, in thyroids of BBW rats developing thyroid autoimmunity and in Graves' goitres. Dendritic cells could be identified in all thyroids studied and were positioned underneath the thyrocytes in between the follicles. Skin dendritic cells travel via lymphatics to draining lymph nodes, thus forming an antigen presenting cell system. It is likely that a similar cell system exists on the level of the thyroid for dendritic cells have also been detected in thyroid draining lymph nodes. In normal thyroid tissue of both human and rat dendritic cells were relatively scarce. During the initial phases of the thyroid autoimmune response in the BBW rat (before the appearance of Tg-antibodies in the circulation) numbers of thyroid dendritic cells increased. Intrathyroidal T-helper cells, B-cells or plasma cells could not be found. The thyroid draining lymph node contained large numbers of plasma cells. During the later stages of the thyroid autoimmune response in the BB/W rat (after the appearance of Tg-antibodies in the circulation) and in Graves' goitres dendritic cells were not only present in high number, but 20-30% were seen in contact with now-present intrathyroidal T-helper lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell free supernatants (conditioned medium) of isolated porcine thyroid follicles, stimulated with EGF (5 ng/ml) or TSH (1-1000 microU/ml), were tested for a mitogenic activity for fibroblasts. Whereas TSH-conditioned medium dose-dependently stimulated [3H]thymidine incorporation into DNA of fibroblasts, only a weak stimulation was found with EGF. However, when the changes in cell number were determined, a significant increase was only found with EGF-conditioned medium from thyroid follicles. The cause of this discrepancy is a dose-dependent stimulation of [3H]thymidine incorporation into fibroblasts by cAMP and thyroid hormones. Cyclic AMP, however, does not stimulate growth of fibroblasts. IGF I production is stimulated in fibroblasts by basal as well as EGF stimulated conditioned medium of thyroid follicles. In contrast, TSH-conditioned medium inhibited IGF I production in fibroblasts. Conditioned medium itself is free of detectable IGF I. As IGF I stimulates not only growth of fibroblasts, but also of thyrocytes, we conclude, that conditioned medium from thyrocytes stimulates IGF I production in fibroblasts, which itself stimulates fibroblast and thyrocyte growth.