Jürgen Bernhagen

For over 25 years, the cytokine known as macrophage migration inhibitory factor (MIF) has been considered to be a product of activated T lymphocytes. We recently identified the murine homolog of human MIF as a protein secreted by the pituitary in response to endotoxin administration. In the course of these studies, we also detected MIF in acute sera obtained from endotoxin-treated, T cell-deficient (nude), and hypophysectomized mice, suggesting that still more cell types produce MIF. Here, we report that cells of the monocyte/macrophage lineage are an important source of MIF in vitro and in vivo. We observed high levels of both preformed MIF protein and MIF mRNA in resting, nonstimulated cells. In the murine macrophage cell line RAW 264.7, MIF secretion was induced by as little as 10 pg/ml of lipopolysaccharide (LPS), peaked at 1 ng/ml, and was undetectable at LPS concentrations > 1 microgram/ml. A similar stimulation profile was observed in LPS-treated peritoneal macrophages; however, higher LPS concentrations were necessary to induce peak MIF production unless cells had been preincubated with interferon gamma (IFN-gamma). In RAW 264.7 macrophages, MIF secretion also was induced by tumor necrosis factor alpha (TNF-alpha) and IFN-gamma, but not by interleukins 1 beta or 6. Of note, MIF-stimulated macrophages were observed to secrete bioactive TNF-alpha. Although previously overlooked, the macrophage is both an important source and an important target of MIF in vivo. The activation of both central (pituitary) and peripheral (macrophage) sources of MIF production by inflammatory stimuli provides further evidence for the critical role of this cytokine in the systemic response to tissue invasion.

Sepsis and septic shock are among the leading causes of death in intensive care units worldwide. Numerous studies on their pathophysiology have revealed an imbalance in the inflammatory network leading to tissue damage, organ failure, and ultimately, death. Cytokines are important pleiotropic regulators of the immune response, which have a crucial role in the complex pathophysiology underlying sepsis. They have both pro- and anti-inflammatory functions and are capable of coordinating effective defense mechanisms against invading pathogens. On the other hand, cytokines may dysregulate the immune response and promote tissue-damaging inflammation. In this review, we address the current knowledge of the actions of pro- and anti-inflammatory cytokines in sepsis pathophysiology as well as how these cytokines and other important immunomodulating agents may be therapeutically targeted to improve the clinical outcome of sepsis.