Prolactin and autoimmunity: The hormone as an inflammatory cytokine

Nowadays, more than 80 autoimmune disorders are recognized, in which an aberrant immune response against different organs and tissues plays a crucial role. Hormonal homeostasis has great influence in achieving competent and healthy immune system function. Prolactin has a bioactive function acting as a hormone and a cytokine. It influences the immune system modulation, mainly inhibiting the negative selection of autoreactive B lymphocytes. Hyperprolactinemia has been detected in many patients with different autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome, multiple sclerosis, autoimmune thyroid disease, systemic sclerosis, among others, and its believed to play a crucial role in disease pathogenesis. A direct correlation between prolactin levels and disease activity was not clear. Genetic factors may have a role in humans as in animal models. Dopamine agonists have proven to offer clinical benefits among autoimmune patients and represent a promising therapy to be explored. In this review, the authors attempt to provide a critical overview on the role of prolactin in the immune system, exploring its contribution to the development of autoimmune diseases.

Prolactin and autoimmunity

Sex hormones, especially estrogen and prolactin (PRL), have an important role in modulating the immune response. PRL is secreted from the pituitary gland as well as other organs and cells particularly lymphocytes. PRL has an immune stimulatory effect and promotes autoimmunity. PRL interferes specifically with B cell tolerance induction, enhances proliferative response to antigens and mitogens and increases the production of immune globulins, cytokines and autoantibodies. Hyperprolactinemia (HPRL) in women present with clinical manifestations of galactorrhea, primary or secondary amenorrhea, delayed menarche or a change in the menses either in the amount or in the regularity. Furthermore in the last 2 decades multi-organ and organ specific autoimmune diseases like systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Sjogren's syndrome (SS), Hashimoto's thyroiditis (HT), multiple sclerosis (MS), psoriasis, hepatitis C patients, Behçet's disease, peripartum cardiomyopathy (PPCM) and active celiac disease were discussed to be associated with HPRL. There is data showing correlation between PRL level and diseases activity in few diseases. Genetic factors may have a role in humans as in animal models. The PRL isoforms based on the differences in the amino acid sequence and size of the cytoplasmic domain have an important effect on the bioactivity on prolactin receptors (PRL-Rs).