Why no simple relationship between thyroid peroxidase activity-inhibiting immunoglobulins and thyroid function in autoimmune thyroid disease?

Hypothyroidism presenting as a hot pertechnetate nodule

The authors report an uncommon finding of hot nodule on Tc-99m sodium pertechnetate thyroid scan in three patients with hypothyroidism. Data indicate that hypothyroidism is secondary to Hashimoto's disease (HD). There was a concordant aspect on I-131 scan in two; a nodular discrepancy (cold nodule with I-131) was associated with the highest microsomal antibodies titer. The findings of thyroid scan and ultrasonographic findings indicate that hot nodules may be observed either on initial or advanced stages of HD. Color flow Doppler sonography, showed an absence of internal increase of vascularization. These data suggest that the observed hot nodules correspond to localized hyperplasia of the less diseased portions secondary to chronic stimulation by TSH.

Evidence for the effect of antibodies to TSH receptors on the thyroid ultrasonographic volume in patients with Graves' disease

OBJECTIVE

It has been demonstrated that antibodies (Ab) to thyroid-stimulating hormone receptors (R), which stimulate the thyroid gland, induce hyperthyroidism in patients with Graves' disease. Furthermore, it has been shown in thyroid cells in culture that thyroid-stimulating hormone receptor Ab acts through the adenosine 3', 5'-monophosphate pathway which stimulates both thyroid hormonogenesis and growth. We investigated the relations between thyroid autoimmunity expression and thyroid ultrasonographic parameters or thyroid hormonal status in patients with Graves' disease.

PATIENTS

A prospective study of 53 consecutive patients referred with untreated Graves' disease.

MEASUREMENTS

Measurements were made of serum TSH-R, peroxidase (TPO) and thyroglobulin (Tg) Ab and basal plasma free T4 (FT4), free T3 (FT3) and TSH. Thyroid morphological characteristics (number and total volume of nodule(s), total volume of lobes and total thyroid volume) were determined by ultrasonography.

RESULTS

There were significant correlations (P < 0.001) between TSH-RAb levels and FT4 values (r = 0.48) or FT3 levels (r = 0.46). Likewise, significant correlations were found between TSH-RAb levels and total lobe volume values (r = 0.56, P < 0.001), total nodular volume values (r = 0.59, P < 0.01) or total thyroid volume values (r = 0.63, P < 0.001). By contrast, no correlation was found between TSH-RAb levels and the number of nodules or between any of the ultrasonographic parameters and TPOAb levels or TgAB values.

CONCLUSIONS

This study demonstrates, in vivo, that TSH receptor antibodies modulate the thyroid ultrasonographic extranodular and nodular volumes in patients with Graves' disease.

Anti-thyroid peroxidase (anti-TPO) antibodies in thyroid diseases, non-thyroidal illness and controls. Clinical validity of a new commercial method for detection of anti-TPO (thyroid microsomal) autoantibodies

The identification of the thyroid peroxidase (TPO) as the main antigen of the thyroid microsomal fraction has enabled the development of a sensitive and specific assay for detection of the corresponding autoantibodies. We evaluated the diagnostic validity of the anti-TPO assay in 303 patients with different types of thyroid disease and in controls. Clearly elevated anti-TPO values (anti-TPO > 500 units/ml) were found in 59% of patients with thyroiditis but in none of the controls or the patients with non-thyroidal illness. The mean anti-TPO levels in these two control groups were 26 +/- 31 units/ml (mean +/- S.D.) and 39 +/- 34 units/ml, respectively. The highest frequency of positive results (88%) was obtained in patients with auto-immune hypothyroidism (clinical diagnosis: Hashimoto's thyroiditis) followed by patients with Graves' disease (53%). With a cut-off point of 200 units/ml, a sensitivity of 96% was obtained for Hashimoto's thyroiditis and of 59% for Graves' disease with a specificity of 100% (50 cases). The new method (anti-TPO, Dynotest) was compared with three conventional methods (35 samples). The results for all measurements were in general agreement. In two cases the results were clearly discordant: one sample contained high anti-thyroglobulin antibody concentrations, the other was obtained from a patient with non-thyroidal illness. In both instances the 'classical' assays yielded false-positive results. Treatment of autoimmune hyperthyroidism resulted in a median decrease in anti-TPO levels of over 50% after reaching the euthyroid state (P < 0.05), whereas in persistent hyperthyroidism no consistent changes were observed. In autoimmune hypothyroidism a marked variability in anti-TPO levels was noted. Some patients showed a clear decrease in anti-TPO levels during T4 substitution whereas in others no consistent changes were observed.

Expression of human thyroid peroxidase in insect cells using recombinant baculovirus

The baculovirus expression system was used to overexpress recombinant human thyroid peroxidase. Sf-9 cells infected with the recombinant virus AcMNPV-hTPO synthesized hTPO protein (hTPO-bac) immunogenic on Western blots when probed with either rabbit anti-TPO peptide sera or pooled human anti-TPO sera (MS12/89). hTPO-bac was a major constituent of the membrane fraction from the infected cells, constituting 14.9% and 10.1% of the 1% deoxycholate-soluble and insoluble fractions, respectively, as judged by densitometry. Recombinant hTPO-bac was extracted from cellular membranes with 1% deoxycholate and partially purified by Sepharose 6B column chromatography. Specific immunoreactivity of MS12/89 to hTPO-bac on microtiter plates was seen using ELISA. Detergent extract from wild-type virus-infected Sf-9 cells was used as background control antigen; no specific reactivity to either hTPO-bac or control antigen was seen with control sera. To determine antigenic potency, MS12/89 was incubated with increasing concentrations of various preparations of hTPO antigen and with ovalbumin as control. The capacity of the partially purified hTPO-bac to immunoneutralize human anti-hTPO standard at 50% inhibition of binding was 0.01 U/microgram hTPO-bac (NIBSC Units), compared with 0.5 U/microgram and 0.06 U/microgram for natural hTPO and CHO-hTPO, respectively. When ELISA was performed using clinical samples of human sera to detect hTPO autoantibodies, results using hTPO-bac correlated well with those using hTPO from Graves' thyroid tissue (r = 0.85, p = 0.02) and those using recombinant hTPO from Chinese hamster ovary cells (hTPO-CHO) (r = 0.85, p = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)