ENDOCRINE, PARACRINE AND AUTOCRINE ACTIONS OF PROLACTIN ON IMMUNE CELLS

The immune response is regulated by locally released factors, collecti vely referred to as cytokines. Data on the human immune system have co nvincingly demonstrated that the hormone prolactin (PRL), in addition to exerting its endocrine control on the immune system, acts as a cyto kine in that it is released within the immune system and regulates the lymphocyte response by paracrine and autocrine mechanisms. Both lymph ocyte and pituitary PRLs are under the control of immune factors. Synt hesis of human PRL by lymphocytes is induced by T-cell stimuli, while increased release of PRL by the pituitary, observed in vivo after immu ne challenge, may be mediated by cytokines produced by monocyte-macrop hages. Since hyperprolactinemia and hypoprolactinemia are both immunos uppressive, physiological levels of circulating PRL must be necessary to maintain basal immunocompetence. The effects of Cyclosporin (CsA) o n IL-2 and PRL gene activation and the analysis of the intracellular s ignaling events downstream IL-2 and PRL receptors suggest coordinate a ctions of these two cytokines during T cell activation.