GRAVES AUTOIMMUNE SERUM INHIBITS GONADAL STEROIDOGENESIS - DEVELOPMENT OF A LEYDIG-CELL BIOASSAY TO IDENTIFY BROAD-SPECTRUM ANTI-ENDOCRINE AUTOANTIBODIES

In order to establish an assay for the detection of autoimmune sera wi th broad spectrum activity, we have investigated the effect of unselec ted normal and Graves' disease sera upon steroidogenesis by gonadal ce lls. Steroidogenesis was enhanced by the addition of normal serum in a 3-h primary Leydig cell bioassay, but was inhibited by the majority o f Graves' sera. The inhibition was not related to clinical thyroid par ameters, such as the severity of the TSH-binding inhibition index, and was not overcome by other agonists or second messenger supplements. A lthough pituitary TSH preparations bound to and stimulated Leydig cell s, TSH receptor mRNA was not detectable and pure recombinant TSH faile d to bind or stimulate, indicating contamination of pituitary TSH with LH. The binding of hCG to the Leydig cell luteinizing hormone recepto r was not perturbed by the Graves' autoimmune sera, indicating that cr oss-reactive anti-TSH receptor antibodies were not responsible for the inhibition. By use of intermediates in the stimulatory pathway, the s ite of Graves' serum inhibition was identified to be distal to hormone receptor/adenylate cyclase coupled responses and proximal to supply o f cholesterol for steroidogenesis.