Immunosuppressive property of bromocriptine on human B lymphocyte function in vitro

Bromocriptine (BRC), a dopamine ergot alkaloid, inhibits the release of pituitary prolactin (PRL). Hypoprolactinaemia induced in rat by treatment with BRC produces a similar immunosuppressive effect as observed in hypophysectomized rats. The effect of immunosuppression by the administration of BRC has been interpreted as the result of hypoprolactinaemia produced by BRC. However, the direct effect of BRC on lymphocyte function has never been evaluated. The purpose of this study was to investigate the in vitro effect of BRC on human B cell functions. Highly purified B cells from tonsil samples were isolated by Percoll density gradient from non-rosetted cells, and were used as target cells. BRC significantly suppressed the proliferative response of resting and activated B cells in vitro. It suppressed immunoglobulin generation of activated B cells. The inhibition of BRC was manifested in the early stage of the proliferation and differentiation of B cells. The conditioned medium from the polyclonal B cell mitogen-stimulated B cell cultures did not contain PRL as detected by immunoradiometric assay. Treatment with low-dose cyclosporin A or FK506 in conjunction with BRC has proved more effective than either drug alone in suppression of B cell proliferation. Thus, the combined therapy of BRC and immunosuppressants may be effective with decreased toxicity for clinical use.