Evidence that thyroid growth promoting activity of immunoglobulin preparations is due to contamination with EGF.

Immunoglobulin (IG) preparations may be contaminated with growth factors. Therefore, we investigated whether the growth promoting activity in IG preparations (thyroid growth stimulating immunoglobulins = TGI) from patients with sporadic goitre may be caused by contaminating EGF (epidermal growth factor). EGF in sera as well as in indifferently prepared IG of patients with recurrent goitre (n = 23), Graves' disease (n = 19) and normals (n = 17) was determined by EGF receptor assay. Comparatively, the ability for stimulating thyroid cell growth was determined in these IG preparations (2 mg/ml). EGF in ammoniumsulphate (AS) precipitates was about 2-fold higher than serum EGF. The growth promoting activity of indifferent IG preparations correlated with the EGF content. After additional purification on protein A-sepharose, neither EGF, nor a growth promoting activity was found in these IG preparations. We therefore conclude, that the growth promoting activity of crude IG preparations may be due to a contamination with EGF.