Thyroid growth stimulating immunoglobulins in sporadic and endemic colloid goitre.

Several methods have been described to measure immunoglobulins stimulating the growth of thyroid cells in vitro, the so called Thyroid Growth stimulating Immunoglobulins (TGI). The methods make use of either Ig-stimulated guinea pig thyroid (organ) cultures (the cytochemical bioassays; growth is measured via Feulgen-densitometry or pentose shunt analysis), the culture of Ig-stimulated rat or porcine thyroid follicles (growth is measured via 3H-thymidine incorporation), or of Ig-stimulated rat FRTL-5 cells (growth is measured via 3H-thymidine incorporation, or counting the number of mitoses in arrest). The various methods have now been validated: (a) the data obtained with TGI preparations in the Feulgen Cytochemical Bioassay (CBA's) correlate well with those obtained in the FRTL-5 mitosis arrest assay with the same TGI preparations, (b) the growth stimulation can not be ascribed to hormonal contaminations of the used Ig preparations, since protein A-sepharose purified IgG is active in the assays and since anti human IgG's neutralize the growth stimulating effects of the preparations. Using the assays TGI has been found positive in goitrous Graves patients, in sporadic goitre patients and in endemic goitre patients. Particularly, patients complaning of recurrent goitre after thyroidectomy or with recent goitre growth are TGI positive. TGI occurs in sporadic goitre in the absence of TSH-receptor antibodies. The autoimmune-prone animal model of the BB rat also proved to be TGI-positive; the animal shows an increased thyroid glandular weight. Both the histomorphology of human goitres as well as the goitre of the BB rat indicate that the dendritic cell plays a prominent role in initiating the thyroid autoimmune reaction.