MONOCLONAL-ANTIBODIES SPECIFIC FOR THE FREE ALPHA-SUBUNIT OF GLYCOPROTEIN HORMONES AND THEIR USE IN THE DEVELOPMENT OF A SENSITIVE IMMUNOFLUOROMETRIC ASSAY

Glycoprotein hormone free alpha subunit has been used as a marker for some pituitary tumors and to study the reactivity of glycoprotein horm one-producing cells under different circumstances. We describe a highl y sensitive and specific immunofluorometric assay for the measurement of serum free alpha subunit levels. The assay is based on a monoclonal antibody, specific for free alpha subunit, bound to microtiter plates . As tracer antibody we employed an europium-labelled free/complexed a lpha subunit specific monoclonal antibody. Using overnight incubation and 50-mu l samples, the least detectable dose was of the order of 4 n g/l. Cross-reactivity with LH, TSH, FSH and hCG was 6.5, 1.2, 4.3 and 1.1%, respectively. Normal adult males showed values ranging from 120 to 790 ng/l, not different from normal adult premenopausal females (88 to 604 ng/l). In post-menopausal females, serum concentrations were s ignificantly higher, ranging from 341 to 4071 ng/l. In 56 patients wit h untreated pituitary tumors (18 ''non-secreting'', 25 GH-producing an d 13 prolactin-producing tumors), 10 showed high values, 3 of them fro m the first group, 3 from the second and 4- from the third. We conclud e that this highly sensitive assay can be a valuable tool for the diag nosis and followup of selected patients with pituitary tumors and in o ther circumstances in which the glycoprotein hormone-producing cells o f the pituitary require evaluation.