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Biomedical subjects

M Ludgate

Publications and source records attributed to M Ludgate.

86 records · Page 5Linked to original sources
PubMed1987

Thyroperoxidase, an auto-antigen with a mosaic structure made of nuclear and mitochondrial gene modules.

A lambda gt11 cDNA library was constructed from a normal human thyroid and screened with a rabbit anti-porcine thyroperoxidase antibody. A series of thyroperoxidase (TPO) clones were obtained which allowed determination of the complete primary structure of the protein. The library was also screened with serum from a patient with Hashimoto's thyroiditis, an autoimmune disease characterized by the presence in the serum of high titers of autoantibodies directed against the 'microsomal antigen' (McAg). Comparison of the cDNA sequences from TPO clones and McAg clones provides definite proof that the McAg is TPO. A short segment of TPO was characterized as bearing a major epitope involved in autoimmunity. The primary structure of TPO was 42% homologous to myeloperoxidase (MPO). It contains, in addition, a C-terminal extension with a membrane anchor region contiguous to two domains encoded by modules belonging to the EGF and C4b gene families. The existence in TPO of still another domain presenting a significant homology with a putative heme-binding region of cytochrome C oxidase polypeptide I raises the possibility that a mitochondrial gene module has contributed a piece to the evolution of a typical nuclear mosaic gene.

Amino Acid Sequence↗
PubMed1987

Normal and defective expression of the thyroglobulin gene.

Molecular studies of the thyroglobulin (Tg) gene have progressed significantly in recent years. Cloning and sequencing the complete bovine Tg cDNA led to the knowledge of the primary structure of the Tg subunit. This large polypeptidic chain displays a repetitive structure, especially in its amino-terminal half, and bears a striking homology with the acetylcholinesterase molecule of Torpedo californica in its carboxy-terminal portion. The four specific domains known to be involved in the formation of the thyroid hormones have been assigned to both terminal parts of the polypeptide, a location which could play a role in the process leading to hormone release. The very large (greater than 250 kb) Tg gene has been localized on the long arm of chromosome 8 in man, in close linkage with the c-myc oncogene. The study of its structure allowed the characterization of the molecular defect responsible for a congenital flaw in Tg gene expression in a herd of South-African cattle. This work led to the unexpected finding that the Tg pre-mRNA undergoes alternative splicing in normal animals, too. A DNA segment involved in the transcriptional control of Tg gene expression by cAMP has been identified by transfecting primary cultured thyrocytes with recombinant genes.

Animals↗
PubMed1986

Analysis of sequence and structure homologies between thyroglobulin and acetylcholinesterase: possible functional and clinical significance.

The homology between thyroglobulin and acetylcholinesterase (1) has been analyzed in detail. It contains 28.3% identical amino acids and extends over 544 residues, involving more than 90% of the acetylcholinesterase molecule and the C-terminal portion of thyroglobulin. The hydropathy profiles of the homologous regions have been determined and compared. Their striking resemblance suggests that both proteins adopt a similar three dimensional structure and militates for some common property. As thyroglobulin and acetylcholinesterase are known to interact with cell membranes, we suggest that the acetylcholinesterase-like domain of thyroglobulin is involved in the binding. These observations demonstrate that thyroglobulin has evolved from the condensation of a duplicated copy of the acetylcholinesterase gene with an archaic thyroglobulin gene encoding the major hormonogenic domain. The extensive homology in hydropathy profiles suggests that the two proteins may share antigenic determinants. If this were the case, it would provide a rationale for the demonstration of immunoreactive thyroglobulin in neurons (2) and the pathogenesis of Grave's ophthalmopathy.

Acetylcholinesterase↗
PubMed1986

Complement component C9 in Graves' disease.

C9, the terminal component of complement, is the key part of the membrane attack complex formed as a result of complement activation; it has also been reported to be an acute phase protein. Its potential role in Graves' disease has been studied by measuring plasma C9 concentrations using an automated two-site immunoradiometric assay employing monoclonal antibodies, whose binding to thyroid tissue has also been investigated. The plasma C9 concentration in patients with hyperthyroid Graves' disease (86.3 +/- 21.6 mg/l, mean +/- SD; n = 49) was significantly increased (P less than 0.001) compared with normal subjects (60.4 +/- 13.4 mg/l; n = 48). In contrast, the plasma concentration of C-reactive protein, a marker of the acute phase response, was not significantly different between the two groups. The plasma C9 concentration in patients with hyperthyroid Graves' disease decreased significantly (P less than 0.01) after treatment with antithyroid drugs (carbimazole or methimazole; n = 14), but not after radioactive iodine (131I) treatment (n = 18). Immunohistochemical staining demonstrated that monoclonal antibody to C9 bound to the basement membranes of thyroid follicular cells of Graves' thyroid tissue but not to normal thyroid tissue. Radiolabelled monoclonal antibody to C9 bound to membrane fragments prepared from thyroid glands from two patients with Graves' disease. We conclude that C9, and by implication the membrane attack complex, may be involved in the pathogenesis of Graves' disease.

Adult↗
PubMed1984

The prevalence and progression of autoimmune thyroid disease in the elderly.

Thyroid antibodies were measured by an enzyme-linked assay system (ELISA) on a random sample of 414 asymptomatic elderly people aged 70 years or more in a South Wales town in 1977. The prevalence of elevated titres of microsomal antibodies was 15.4% and of thyroglobulin antibodies 13.3%; 8.5% had an elevation of both antibodies. Five years later thyroid function was evaluated in 51 (66.6%) of those people with raised antibody titres in 1977 and compared with a control group of 46 old people drawn from the original population. Significant fluctuations of microsomal and thyroglobulin antibody titres were observed in two thirds of the antibody positive group. Three people in the control group developed positive thyroid antibodies during this period. Only 1 person in the antibody positive group became hypothyroid. The prognostic significance of raised thyroid antibodies with or without elevated TSH levels is less in the elderly than in middle aged or younger people. The significance of the fluctuating antibody levels as measured by a more sensitive method remains to be determined.

Age Factors↗
PubMed1984

Effect of tri-iodothyronine on normal human lymphocyte function.

The effect of excessive tri-iodothyronine (T3) in vivo was assessed using normal human lymphocytes. Cells from normal subjects were frozen in liquid nitrogen before and after oral administration of T3 for 1 week to permit a direct comparison under identical culture conditions. Within the group of individuals studied, some subjects did show changes in B or T cell function but hypertri-iodothyroninaemia produced no consistent effect for the whole group on circulating T cell subsets or T and B cell activation measured by short-term culture or stimulation of lymphocyte cultures with phytohaemagglutinin or pokeweed mitogen. Tri-iodothyronine supplementation of cultures in vitro did not affect pokeweed mitogen stimulation. These findings suggest that the immunological abnormalities in Graves' disease are not the result of increased circulating thyroid hormone levels and that remission following medical treatment is due to an immuno-suppressive effect of the drug rather than the restoration of euthyroidism.

Adult↗
PubMed1983

Cyclosporin improves Graves' ophthalmopathy.

Cyclosporin given to two patients with Graves' ophthalmopathy produced a rapid objective improvement in both, including restoration of ocular-muscle function and visual acuity, improvement in exophthalmos, and reduction in orbital muscle swelling judged by computed tomographic scan. Thyroid autoantibody levels fell with treatment, and T-cell subset abnormalities returned towards normal. In one patient an absent thyrotropin response to thyrotropin-releasing hormone became normal after treatment. These results suggest that cyclospirin treatment should be considered in patients with the congestive ophthalmopathy of Graves' disease.

Acute Disease↗
PubMedDate not supplied

Measurement of cAMP accumulation in Chinese hamster ovary cells transfected with the recombinant human TSH receptor (CHO-R): a new bioassay for human thyrotropin.

Circulating TSH bioactivity may vary in several clinical and experimental conditions. Since the reliability of the current methods for the measurement of TSH bioactivity is limited, a new bioassay based on cAMP accumulation in Chinese Hamster Ovary cells transfected with recombinant human TSH receptor (CHO-R) was set up. The sensitivity was 0.3 +/- 0.1, 0.4 +/- 0.1 and 0.01 +/- 0.01 micrograms/L for TSH IRP 80/558, recombinant human TSH and bovine TSH, respectively. Standard curves were parallel, and the intra- and inter-assay coefficients of variation were 13 +/- 1.1% and 22 +/- 1.9%, respectively. LH, FSH, CG and TSH subunits did not stimulate cAMP accumulation up to high concentrations. Circulating TSH was partially purified by immunoaffinity separation and concentrated before being bioassayed. However, plain sera with high TSH levels, such as those from primary hypothyroid patients (PH), could be directly tested in CHO-R bioassay, provided that sera were added at concentrations lower than 10%. TSH from 6 normal subjects had biological to immunological ratio (B/I) ranging from 0.6 to 2.1 (mean +/- SD = 1.4 +/- 0.5). TSH from 6 patients with PH showed bioactivity significantly lower than in normals (B/I = 0.6 +/- 0.3; p < 0.001; range = 0.3-1.1). TSH from 5 patients with central hypothyroidism of hypothalamic origin (CH) had undetectable basal bioactivity (B/I < 0.2), which normalized in only one patient after acute TRH and in all patients after chronic TRH administration. In conclusion, CHO-R cells provide an excellent tool for evaluating TSH bioactivity, owing to high sensitivity, specificity, reproducibility and feasibility of the assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Muscle autoantigens in thyroid associated ophthalmopathy: the limits of molecular genetics.

Unlike autoimmune thyroid disease (AITD) in which a number of autoantigens have been identified and characterized, the situation in thyroid associated ophthalmopathy (TAO) is far from clear. A number of candidate antigens have been identified by probing Western blots of orbital tissue (OT) with sera from TAO patients, the most frequently cited being proteins of molecular weight 23, 28, 55, 64, 78 and 120 kilodaltons. In an attempt to identify autoantigens in TAO we have produced a lambda gt11 human eye muscle expression library. This has been screened with sera from four patients with severe TAO whose antibodies bind to one or more of the aforementioned candidate antigens or to a thyroglobulin/acetylcholinesterase (Tg/Ache) shared epitope. Four clones were isolated and characterized; clone R14 encodes the carboxyl terminal 193 amino acids of an IgE binding protein, clones R10 and R13 encode unknown proteins having significant similarity with heat shock protein 27 and the U1 small nuclear ribonucleoprotein respectively. Clone R1 encodes an unknown peptide of 347 amino acids having no similarity with proteins in available data banks. R1 clone affinity purified autoantibodies bind to a protein of Mr 78 kD in a Western blot of porcine eye muscle tissue. Autoantibodies to the R1 recombinant lysogen were clearly demonstrated in 5 of 20 sera from Graves disease patients, its role merits further investigation. The possible relevance of these clones to the pathogenesis of TAO is discussed as well as the limitations of this type of approach in the identification of unknown autoantigens.

Adult↗
PubMedDate not supplied

Effect of lithium carbonate therapy on thyroid immune status in manic depressive patients: a prospective study.

Serum thyroid autoantibodies to thyroglobulin (TG) and thyroid microsomes (M) were measured by ELISA prospectively in 37 manic depressive patients prior to receiving lithium carbonate and during therapy with this drug for a mean of 16.2 months. They were also measured once in 27 normal subjects and several times in five psychiatric patients not receiving lithium. Sixteen patients (43%) had either thyroglobulin, microsomal antibodies or both before receiving lithium therapy. During therapy significant fluctuations in antibody titre, both upwards and downwards were observed in ten out of 12 patients with M antibodies and in nine out of 11 with TG antibodies. The fluctuations in antibody titre are consistent with an immunomodulatory effect of lithium as has been shown in animal studies. It is suggested that psychiatric patients should have thyroid antibodies measured routinely before and during lithium therapy.

Adult↗