Prolactin in autoimmune diseases

The immune system is still regarded by many as autonomous, and prolactin (Prl) has traditionally been considered as a lactogenic hormone. Over the last 10 years, the total number of publications considering Prl is decreasing, while the number of those investigating its role in immunity sustainly increased. In addition to the pituitary gland, Prl-like peptides can be produced by activated leukocytes and fibroblasts. Elevated serum levels of Prl in (rat) adjuvant arthritis, (murine) collagen type II-induced arthritis, (murine and human) systemic lupus erythematosus (SLE), and (murine and rat) autoimmune type I diabetes may influence the outcome of the disease. It is suggested that mild hyperprolactinemia is a risk factor for the development of autoimmunity. This can occur under certain circumstances, for example adrenocortical deficiency or postpartum. In human SLE, Prl appears to favor the production of anti-double stranded DNA. While glucocorticoids would damp the immune reactivity, Prl constitutes a stimulatory link between the neuroendocrine and immune systems. Future directions should include: 1) multicenter projects for evaluation of the therapy with Prl-inhibiting compounds in SLE, considering for example the HLA-DRB1 *0301 status; and 2) the regulation of extra-pituitary Prl-like cytokines ("proliferins") (e.g., in rheumatoid arthritis synovium) and their role in the production of catabolic enzymes.