Macrophage inhibitory factor (MIF) is an inflammatory cytokine. MIF is released to the blood stream upon stimulation of white blood cells by bacterial antigens. MIF contains two different catalytic sites. A phenylpyruvate tautomerase site is located in the N terminal. A disulfide reductase site is located in the tetrapeptide Cys-Ala-Leu-Cys in position 57-60.