Prolactin and autoimmunity.

Prolactin (PRL) is a versatile hormone that is produced by the anterior pituitary gland and various extrapituitary sites including immune cells. Furthermore, PRL has widespread influences on proliferation and differentiation of a variety of cells in the immune system and is, in effect, a cytokine. PRL-receptors (PRL-R) are distributed throughout the immune system and are included as members of the cytokine receptor superfamily. PRL-R signal transduction is mediated by a complex array of signaling molecules of which JAK2, Stat1 and Stat5 pathway have been well studied. In PRL-stimulated T cells, the transcription factor gene, interferon regulatory factor-1 provides a mechanism whereby PRL can regulate the immune response. The human PRL gene is situated on the short arm of chromosome 6 close to the major histocompatibility complex. Polymorphisms of the human PRL gene have implications for production of lymphocyte PRL in SLE. Mild and moderate hyperprolactinemia (HPRL) has been demonstrated in 20-30% of SLE patients and is associated with active disease. HPRL may have a role in lupus nephritis and central nervous system involvement of SLE patients. HPRL stimulated the production of autoantibodies. These evidences support the important role of PRL in autoimmunity and autoimmune diseases, mainly SLE.