Correlation of the antibody titers with serum prolactin levels and their clinical course in patients with anti-prolactin autoantibody.

Patients with anti-prolactin (PRL) autoantibody were surveyed among 208 patients with hyperprolactinemia (PRL > or = 30 micrograms/l) and 228 subjects with normal PRL levels, and the relationship of the antibody titers with serum PRL levels and their clinical course were studied. Diagnosis of possessing the anti-PRL autoantibody was based on the polyethylene glycol method, displacement of the binding of [125I]PRL with the serum by unlabeled PRL and the binding of PRL to protein G, the affinity gel for immunoglobulin G. Prolactin was measured by an immunoradiometric assay that we found was not affected by the anti-PRL autoantibody. A significantly high frequency of anti-PRL autoantibody in patients with idiopathic hyperprolactinemia (16%) and a positive correlation between titers of the autoantibody and serum PRL levels (r = 0.74, p < 0.01) may indicate that the anti-PRL autoantibody itself is another cause of hyperprolactinemia, probably owing to the delayed clearance of PRL. Most patients with anti-PRL autoantibody lacked the clinical symptoms of hyperprolactinemia, such as amenorrhea and galactorrhea, and spontaneous pregnancy occurred despite the marked hyperprolactinemic state, indicating that the biological activity of PRL was attenuated by the autoantibody. In addition, PRL levels and the titers of anti-PRL autoantibody were not changed significantly during the observation period of up to 5 years without any medical intervention. These results suggest that the anti-PRL autoantibody itself is one of the causes of hyperprolactinemia and that medical intervention is unnecessary for this type of hyperprolactinemia.