Pro-inflammatory cytokine involved in the innate immune response to bacterial pathogens (PubMed:15908412, PubMed:17443469, PubMed:23776208). The expression of MIF at sites of inflammation suggests a role as mediator in regulating the function of macrophages in host defense (PubMed:15908412, PubMed:17443469, PubMed:23776208). Counteracts the anti-inflammatory activity of glucocorticoids (PubMed:15908412, PubMed:17443469, PubMed:23776208). Has phenylpyruvate tautomerase and dopachrome tautomerase activity (in vitro), but the physiological substrate is not known (PubMed:11439086, PubMed:17526494). It is not clear whether the tautomerase activity has any physiological relevance, and whether it is important for cytokine activity (PubMed:11439086, PubMed:17526494). {ECO:0000269|PubMed:11439086, ECO:0000269|PubMed:15908412, ECO:0000269|PubMed:17443469, ECO:0000269|PubMed:17526494, ECO:0000269|PubMed:23776208}. This is the function of MIF (macrophage migration inhibitory factor, Ensembl gene identifier ENSG00000240972).