MIF re-discovered: pituitary hormone and glucocorticoid-induced regulator of cytokine production.

The protein mediator known as macrophage migration inhibitory factor (MIF) was one of the first cytokine activities to be discovered and was described 30 years ago to be a T cell-derived factor that inhibited the random migration of macrophages. Despite the long-standing association of MIF with activated lymphocytes, the precise role of MIF in host responses remained undefined. Recent studies however, have led to the description of a pituitary mediator that appears to act as the natural, counter-regulatory hormone for glucocorticoid action within the immune system. Isolated as a product of an anterior pituitary cell line, this protein was sequenced and found to have the same structure as MIF. The major role of MIF appears to be to act at an inflammatory site or lymph node to counter-balance the inhibitory effects of steroids on the primary immune response, which must necessarily be mounted to eliminate the source of infection or tissue invasion.