Stromal enlargement plays a key role in the development of benign prostatic hypertrophy in humans. Human prostatic fibroblasts were obtained from fetal and adult prostates and characterized as to their androgen and estrogen receptor status and growth in response to dihydrotestosterone (DHT), estradiol (E2), hydroxyflutamide (OH-FLU), hydrocortisone, basic fibroblast growth factor (bFGF), and epidermal growth factor (EGF). In addition, the ability of hormones and growth factors to induce the messenger RNA (mRNA) for the c-fos protooncogene was assessed as a measure of the early, direct effects of these compounds on cellular proliferation. Nuclear androgen receptors were demonstrable by immunocytochemistry in both fetal and adult cells. Nuclear estrogen receptor staining was negative. Neither E2 nor hydrocortisone increased cellular proliferation. Both EGF and bFGF did increase cellular growth. DHT (10(-8)-10(-7) M) had a significant stimulatory effect on cell growth only in serum-free media. OH-FLU addition enhanced DHT induced proliferation. Changing the media during the course of the experiment obliterated the stimulatory effect of DHT. Both EGF (10 ng/ml) and bFGF (20 ng/ml) increased the mRNA for the c-fos protooncogene. DHT (10(-7) M) did not induce the mRNA for c-fos. We conclude that EGF, bFGF, and DHT (especially in combination with OH-FLU) increase the proliferation of human prostatic fetal and adult fibroblasts in vitro. E2 has no effect on fibroblast proliferation. The stimulatory effects of EGF and bFGF are direct, whereas the effect of DHT appears to be indirect, possibly mediated via the increased production and/or secretion of growth factors.

To further understand the mechanism of lymphocyte accumulation within the thyroid gland in autoimmune thyroid disease we have examined the expression, regulation, and functional significance of the intercellular adhesion molecule-1 (ICAM-1, CD54) in human thyroid monolayer cells and immortalized thyroid cell clones. Human thyroid monolayer cells derived from both normal and abnormal human thyroid tissue showed low basal expression of the ICAM-1 antigen by flow cytometric assessment (mean % +/- SD positive cells = 13.7 +/- 6.1) compatible with the presence of ICAM-1 positive nonthyroid cells within the monolayer cultures. However, thyroid cell ICAM-1 antigen expression was further induced by exposure to recombinant human interferon-gamma (IF-gamma). At 100 U/ml, IF-gamma induced ICAM-1 expression in 56.0 +/- 19.0% of thyroid monolayer cells. Even greater expression of ICAM-1 antigen was induced by IF-gamma in human fetal thyroid cell monolayers of high purity (up to 80% of ICAM-1 positivity) thyroid monolayers established from a patient with Graves' disease (up to 84%), and in two immortalized human thyroid cell clones, 12S and TAD-2 (up to 61%). Furthermore, dose-response curves for ICAM-1 and HLA-DR antigen induction by increasing concentrations of IF-gamma showed that ICAM-1 antigen gene induction was 10-fold more responsive to IF-gamma than the HLA-DR antigen gene. In order to explore the functional consequence of ICAM-1 antigen expression by thyroid epithelial cells we examined the binding of peripheral blood mononuclear cells to thyroid monolayer cells and immortalized thyroid cells. These studies revealed a preferential adhesion of human PBMC to IF-gamma-treated thyroid monolayers compared to untreated control monolayer cells. Furthermore, this IF-gamma-induced cell adhesion was specifically inhibited by monoclonal anti-ICAM-1. These experiments demonstrate not only the capacity of human thyroid epithelial cells to express ICAM-1 antigen in the presence of a cytokine but, in addition, identify ICAM-1 antigen as responsible for enhanced T cell binding to thyroid epithelial cells. ICAM-1 antigen may, therefore, play an important role in T cell targeting and accumulation within the thyroid gland in autoimmune thyroid disease.

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We have studied primary human fetal thyroid cell monolayers as an in vitro model for thyroid cell growth and function. Fetal thyroid cells grew slowly in a serum-free medium under basal conditions (i.e. without insulin and TSH), with a doubling time of 112 +/- 7 h (mean +/- SEM), indicating autonomous growth capacity. Addition of insulin (10 micrograms/ml) lead to increased growth, with a doubling time of 43.0 +/- 2.5 h, and TSH further reduced the doubling time in a dose-dependent manner, with the highest growth rate at 1-10 mU/ml (doubling time, 27 +/- 0.5 h). These growth rates were only observed when cells were subjected to a short culture time (12 h) before investigation, whereas after 96 h of culture the fetal thyroid cell growth rate was reduced by up to 50%. Addition of more than 5% serum completely inhibited the growth stimulation initiated by insulin and TSH. The accumulation of extracellular cAMP by the fetal cell monolayer was induced by TSH in a dose-dependent manner and reached a maximum effect at 10 mU/ml (4.8 +/- 0.6 pmol cAMP). Basal thyroglobulin (Tg) release was 26.9 +/- 0.5 ng/10(5) cells.day. Insulin decreased Tg release to 16.7 +/- 0.5 ng/10(5) cells,day, whereas TSH increased it up to 52.5 +/- 1.0 ng/10(5) cells.day. The T cell cytokine gamma-interferon, a product of the lymphocytic infiltrate in autoimmune thyroid disease, significantly reduced both insulin and TSH-stimulated cellular growth as well as accumulation of Tg. In conclusion, human fetal thyroid cell monolayers grew at high velocity under defined experimental conditions in vitro. These conditions included a low serum concentration, short culture time before investigation, and insulin/TSH supplementation. Furthermore, this human thyroid model confirms our earlier observations on the influence of cytokines in thyroid cell growth regulation.

We have previously shown that highly purified urinary hCG has the potential to both stimulate the intracellular accumulation of cyclic AMP and induce growth of immortalized rat thyroid cells. We have now compared the ability of recombinant human TSH and purified urinary hCG preparations to stimulate Chinese hamster ovary (CHO) cells which have been transfected with the human TSH receptor. Only transfected CHO cells expressing recombinant TSH receptors, but not control CHO cells, were stimulated by hCG to release cyclic AMP in a dose-related manner and the effect of 100 IU of HCG was equivalent to approximately 9.2 uU of rec-hTSH. These data demonstrate that hCG interacts directly with the human TSH receptor.