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T F Davies

Publications and source records attributed to T F Davies.

At least 19 recordsLinked to original sources
PubMed1992

Cloning and sequencing of a 1.3 KB variant of human thyrotropin receptor mRNA lacking the transmembrane domain.

We amplified human thyroidal cDNA using oligonucleotide primers designed to reveal putative human thyrotropin receptor (hTSHR) mRNA variants encoding the extracellular, ligand-binding domain but lacking the transmembrane domain. Whereas the major 4.3 kb hTSHR mRNA species was not amplified to detectable levels, several shorter products were detected. A strongly amplified 1 kb product was cloned and sequenced. It contained coding sequences at the 5' end which were colinear with exons 1-8 of the hTSHR gene, encoding most of the extracellular domain. This was followed at the 3' end by additional coding and noncoding information not present in the 4.3 kb transcript. A probe specific for the 5' end recognized polyadenylated thyroidal transcripts of 4.3, 1.7, and 1.3 kb, indicating the presence of several hTSHR mRNA variants. A probe specific for the 3' end recognized only the 1.3 kb transcript. The level of the 1.3 kb variant (hTSHR-v 1.3 mRNA) was about half that of the 4.3 kb hTSHR mRNA and twice that of the 1.7 kb variant. The presence of a thyroidal mRNA encoding both the signal peptide and ligand-binding region of the hTSHR, but not the seven transmembrane helices, provides the potential to produce soluble receptors which could play important roles in thyroid physiology and/or autoimmune thyroid disease.

Amino Acid Sequence↗
PubMed1992

T cells and human autoimmune thyroid disease: emerging data show lack of need to invoke suppressor T cell problems.

Human T cells recognize self and foreign antigens when such antigens are processed into small peptides and bound to molecules coded for by genes of the HLA region on chromosome 6. The part of the T-cell surface which is responsible for such recognition is a set of molecules coded for by a variety of genes and known as the T-cell-receptor complex. In animal models, T cells are able to transfer autoimmune thyroiditis and T cells have, therefore, long been implicated in the etiology of human autoimmune thyroid disease (AITD). Information gained from the study of intrathyroidal T cells and thyroid antigen-specific T-cell clones has shown that in patients with Graves' disease, mainly helper T-cell clones have been obtained, whereas in autoimmune (Hashimoto's) thyroiditis cytolytic T-cell clones may be predominant. Such thyroid antigen-specific T cells have now been shown to recognize one or other of the three major thyroid-specific antigens; thyroglobulin, thyroid peroxidase, or the TSH receptor and efforts are currently in progress to characterize the T-cell epitopes of these major thyroid autoantigens. Recent findings of restricted T-cell receptor V gene use amongst intrathyroidal T cells confirm the primary role of T cells in human thyroid autoimmune processes leading to AITD. However, the mechanisms whereby such autoreactive T cells escape deletion and anergy, and how they become activated, remain uncertain. There is compelling evidence that the thyroid cell itself, by expressing HLA molecules, and presenting antigen directly to the T cells, may initiate disease, perhaps after an external insult.

Amino Acid Sequence↗
PubMed1992

Characteristics of long-term human thyroid peroxidase autoantibody secretion in scid mice transplanted with lymphocytes from patients with autoimmune thyroiditis.

We have explored scid mice as an in vivo model to study lymphocyte function and autoantibody production in patients with autoimmune thyroiditis and thyroid peroxidase (hTPO) autoantibodies. Patient's peripheral blood mononuclear cells (PBMC) were transplanted into scid mice via intraperitoneal injections and human immunoglobulin G (hIgG) and thyroid autoantibody levels in the murine sera were monitored for a minimum of 3 months after transplantation. Human IgG reached maximum serum levels of > 3,000 micrograms/ml (mean +/- SEM = 1,199 +/- 354 micrograms/ml) after an average of 6.5 weeks. In reconstituted mice (hereafter named At-Scid-hu) substantial titers of anti-hTPO of up to 0.51 (ELISA index, normal range < 0.02) were observed over a period of 1-2 months, followed by a gradual decline. Immunization of AT-Scid-hu mice with immunogenic, recombinant human hTPO (rec-hTPO) failed to enhance hTPO-Ab levels. Furthermore, there was no correlation between the magnitude of human IgG in the murine serum and concomitant levels of anti-hTPO. Murine thyroid function was unaffected by the transplantation of PBMC, as evidenced by normal serum thyroxine (T4) levels, and lack of specific pathologic changes in the thyroid. These data indicate, for the first time, the potential for longer-term human thyroid autoantibody secretion in the scid mouse reconstitution model allowing for further investigation of the regulatory factors inpinging on the human B cells surviving in the murine environment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Evidence for selective accumulation of intrathyroidal T lymphocytes in human autoimmune thyroid disease based on T cell receptor V gene usage.

We have investigated the T cell receptor V alpha and V beta gene family usage by T lymphocytes infiltrating affected thyroids in patients with autoimmune thyroid disease. We show that the intrathyroidal T lymphocytes from patients (n = 6) with autoimmune thyroid disease display a widespread usage of V beta gene families with an average of 14.4/19 V beta gene families similar to the peripheral T lymphocytes of the same patients. Because we recently reported that the utilization of V alpha gene families is markedly reduced within these mitogen-stimulated intrathyroidal T cell populations, as well as within intact tissue from similar patients (n = 4) (overall mean of 4.0/18 families detected), these results indicate that in thyroids of patients with autoimmune thyroid disease the lymphocytes are selectively accumulating based on their V alpha rather than V beta elements. This preferential hTcR V alpha and widespread V beta gene usage was not mimicked in most 7-d autologous mixed lymphocyte reactions using non-T cell stimulators (n = 6) or EB-virus immortalized autologous B cell lines (n = 3). Hence, the selective V gene utilization by intrathyroidal T cells is likely to be secondary to multiepitopic thyroidal autoantigens activating thyroid infiltrating T cells or to the presence of a superantigenlike thyroidal self-antigen, capable of determining a selective infiltration or activation of a variety of T lymphocytes on the basis of their V alpha gene usage.

Autoantibodies↗
PubMed1992

The positive regulation of human thyrotropin (TSH) receptor messenger ribonucleic acid by recombinant human TSH is at the intranuclear level.

We have assessed the regulatory influence of human recombinant TSH (rec-hTSH) on its homologous receptor (TSHR) using a well characterized human fetal thyroid monolayer cell culture technique. Under the culture conditions employed, fetal human thyroid cells showed basal expression of TSHR-specific mRNA transcripts, and the addition of rec-hTSH (1 U/L) induced up to an 8-fold increase in specific mRNA over a 48-h observation period. This induction was simulated by bromo-cAMP in a dose-dependent manner, indicating that the stimulatory effect of rec-hTSH was active at the postreceptor level. Furthermore, there was no detectable increase in the transcription rate of the TSHR gene after stimulation with rec-hTSH for 12-36 h, although a marked increase in thyroglobulin-specific mRNA was observed. Rec-hTSH also had no influence on the half-life of TSHR-specific mRNA, which remained at approximately 16 h in the presence or absence of rec-hTSH. These data indicate that rec-hTSH induced up-regulation in human thyroid cell TSHR-specific mRNA and that the mechanism of this regulation was likely to be secondary to a posttranscriptional nuclear event involving changes in the regulation of primary unspliced mRNA for the TSHR.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1992

Human chorionic gonadotropin (hCG) interacts directly with recombinant human TSH receptors.

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.

Animals↗
PubMed1992

Preferential use of T-cell receptor V genes in human autoimmune thyroid disease.

We review here our analyses of hTcR V gene activity within the thyroid glands of patients with autoimmune thyroid disease. Our data, based on thyroid aspiration specimens, indicate that early in the onset of Graves' disease there is a marked restriction in both hTcR V alpha and V beta gene families utilized by intrathyroidal T-cells. Later, however, and as seen in surgical thyroid specimens from patients with long term disease, there appears to be a loss of V beta restriction for unclear reasons. In contrast, patients with Hashimoto's thyroiditis are usually diagnosed later in the natural history of the disease and appear to show much less hTcR V gene family restriction. The mechanisms driving the use of few and many hTcR V genes within the thyroid gland are likely to be complex and may reveal important insights into disease pathogenesis.

Autoimmune Diseases↗
PubMed1992

Graves' disease and its retroorbital aspects.

Graves' disease is a common, familial, but easily treated condition caused by unique autoantibodies which act as TSH agonists. Patients with the diagnostic eye signs of Graves' disease, however, require more careful treatment than those patients with principally thyroidal involvement because destructive therapy to the thyroid gland may exacerbate the eye disease. The cause of ophthalmic eye disease appears to be "crossover specificity" by the immune system for a recurrent antigen in extraocular muscles, fibroblasts, and the thyroid gland. Treatment directed at the autoimmune response may offer the most appropriate therapy in the years to come.

Exophthalmos↗
PubMed1979

Regulation of primate testicular luteinizing hormone receptors and steroidogenesis.

The testicular luteinizing hormone (LH) receptors of the rhesus monkey and human have many features in common, including high equilibrium association constant, marked species specificity, and relatively low binding capacity. We have, therefore, used rhesus monkeys as models for human LH-receptor regulation in vivo during gonadotropin treatment. In four adult male monkeys, treated with 10,000 IU human chorionic gonadotropin (hCG), serum and testicular steroidogenic responses were monitored at 24-h intervals during the following 4 d, and LH-receptor concentrations were measured by (125)I-hCG binding to 15,000-g particles prepared from testis biopsy specimens. In treated animals, serum hCG was maximal on day 1 at 322+/-16 ng/ml and declined to 24.4+/-2.3 ng/ml by day 4. Serum testosterone was increased threefold during the subsequent 4 d (from 6.5+/-2.0 to 18.6+/-4.4 ng/ml) but serum progesterone remained unchanged. In contrast, serum 17alpha-hydroxyprogesterone increased 12-fold to 5.5+/-0.5 ng/ml at day 1 and was increased fourfold during the subsequent 3 d. The LH-receptor binding capacity of the primate testis was reduced by 18.3+/-6.0% on day 1, 51.7+/-7.4% on day 2, and 45.3+/-2.4% on day 4. Occupancy of the LH receptors by endogenously bound hCG was significant on day 1 but was negligible by day 4. These data demonstrate that gonadotropin-induced LH-receptor depletion occurs in the rhesus testis and indicate that primate gonadotropin receptors are susceptible to the regulatory processes recently described in the rat. In addition, the simultaneous and disproportionate accumulation of 17alpha-hydroxyprogesterone indicates that 17,20-desmolase was rate-limiting under these conditions in the primate testis Leydig cell.

Animals↗
PubMed1978

Thyrotropin receptors in adipose tissue, retro-orbital tissue and lymphocytes.

Thyrotropin (TSH) receptors on retro-orbital muscle and fat have been implicated in the pathogenesis of Graves' exophthalmos and it has been suggested that TSH has a direct effect on human fat metabolism. We have therefore investigated the interaction of biologically active 125I-labelled TSH with membranes prepared from human adipose, retro-orbital and thyroid tissue. Since lymphocytes contain receptors for several polypeptide hormones, TSH binding to lymphocyte membranes was also studied. We were unable to demonstrate TSH receptors in adult human adipose tissue, retro-orbital muscle and fat, or peripheral blood lymphocytes. In contrast, adult and neonatal guinea pig adipose tissue membranes showed similar TSH binding characteristics to guinea pig thyroid membranes.

Adipose Tissue↗
PubMed1978

Binding of thyroid stimulators to guinea pig testis and thyroid.

We have demonstrated TSH binding sites in membranes prepared from guinea pig testis. The binding of TSH to testicular homogenate was localized to the interstitial tissue and showed similar characteristics to the binding of TSH to thyroid membranes with high affinity (Ka = 2.5 X 10(10) M-1) but limited capacity (approximately 0.9-1.7 pg/mg equivalent testis homogenate). In addition, thyroid-stimulating antibodies inhibited the binding of TSH to both testicular and thyroid homogenate but failed to inhibit the binding of hCG to the testis preparation. These data suggested that the TSH-binding site was distinct from the hCG/LH binding site. Testicular and thyroid TSH-binding sites also appeared to demonstrate a similar degree of cross-reactivity with a crude preparation of hCG. In conclusion, our findings suggest that thyroid-stimulators may influence gonadal function. Furthermore, the ability of hCG to inhibit the binding of TSH to thyroid membranes provides a possible mechanism for the known thyroid-stimulating properties of hCG.

Animals↗