50 kD prolactin binding protein in schizophrenics on neuroleptic medication

Serum samples from 15 age-matched normal male subjects and 15 male schizophrenic patients on neuroleptic medication were subjected to immunoprecipitation with anti-human prolactin (PRL) and analysis of the immunoprecipitate by two-dimensional gel electrophoresis. We report the unexpected immunoprecipitation of large amounts of an approximately 50 kD protein in 12/15 of the schizophrenic patients. Preliminary analyses suggest that this 50 kD protein may be an IgG heavy chain. Since total levels of IgG and each of the IgG subclasses are the same in the normal and schizophrenic group, the increased amount of the 50 kD protein in the schizophrenics is clearly specific to anti PRL precipitation. Since the anti-PRL does not directly recognize either the 50 kD protein or any immunoglobulin light chains in the precipitate, we suggest that the 50 kD protein is precipitated because it is bound to PRL. Perhaps immunoglobulin binding of PRL is a mechanism used to compensate for chronically elevated PRL levels during neuroleptic treatment.