Autoantibody to human prolactin in patients with idiopathic hyperprolactinemia.

We have demonstrated the presence of anti-PRL autoantibody in 5 patients with idiopathic hyperprolactinemia. The clinical features were suggestive of a weak biological activity of PRL, such as regular menses and no galactorrhea. Total PRL levels were markedly elevated (685 +/- 386 micrograms/L) (mean +/- SD) and the proportion of the bound form was 90.7 +/- 7.1%. Scatchard analysis revealed a low-affinity, high-capacity antibody: the association constant was 0.73 +/- 0.56 x 10(7) mol-1 and the maximal binding capacity was 2139 +/- 1792 micrograms/L. Gel filtration study showed that a substantial amount of PRL (64.6 +/- 19.5%) was eluted at the position of 150,000-170,000 mol wt PRL (big-big PRL). Immunoprecipitation study using the chain-specific antibodies showed that the anti-PRL autoantibody belonged to kappa-type immunoglobulin G. These results may indicate that there exists autoantibody-related hyperprolactinemia, especially in those with particularly high serum PRL levels, who had previously been diagnosed as "idiopathic" hyperprolactinemia.