Immune modulation by the macrophage migration inhibitory factor (MIF) family: D-dopachrome tautomerase (DDT) is not (always) a backup system

•DDT and MIF have different roles in disease.•D-dopachrome tautomerase (DDT) is a more specific CD74 agonist than MIF.•Post-translational modifications greatly affect MIF activity.•The effect of inhibitors/antibodies on DDT and MIF depend on their specificity.•The activity of both DDT and MIF should be considered in clinical approaches.