Human Macrophage Migration Inhibitory Factor

Abstract

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory mediator with the ability to induce various immunomodulatory responses and override glucocorticoid-driven immunosuppression. Some of these functions have been linked to the unusual enzymatic properties of the protein, namely tautomerase and oxidoreductase activities. However, there are conflicting reports regarding the functional role of these enzymatic properties in normal physiological homeostasis and disease progression. Therefore, we have produced a highly pure, virtually endotoxin-free recombinant MIF preparation and fully characterized this using a variety of biochemical and biophysical approaches. The recombinant protein, with demonstrable enzymatic activity, was then used to systematically examine the biological activity of MIF. Surprisingly, treatment with MIF alone failed to induce cytokine expression, with the exception of IL-8. However, co-treatment of lipopolysaccharide (LPS) in conjunction with MIF produced synergistic secretion of tumor necrosis factor-␣, interleukin (IL)-1, and IL-8 compared with LPS alone. The potentiating effect of MIF was seen at physiologically relevant concentrations. These data suggest that MIF has no conventional cytokine activity but, rather, acts to modulate and amplify the response to LPS. MIF2 is a highly evolutionarily conserved 12.5-kDa protein that was assigned a unique combination of hormone-like, cytokine, and thioredoxin-like properties (1). Significant interest in MIF as a pro-inflammatory mediator involved in human disease was based on the following important findings: (i) raised MIF concentrations in peripheral blood and specific tissue specimens in a broad range of diseases, including inflammatory conditions, various tumors, and metabolic disorders such as atherosclerosis, diabetes, and obesity (2-7); (ii) genetic evidence of linkage with juvenile idiopathic arthritis (8), rheumatoid arthritis (9); (iii) neutralization of MIF by anti-MIF antibodies, shown to be therapeutically beneficial in a variety of animal models of inflammatory diseases, including sepsis, rheumatoid arthritis, pulmonary infections, and atherosclerosis (4, 7, 9, 10).MIF has no homology with any other pro-inflammatory cytokines, and the mechanism(s) by which MIF exerts its biological effects remain unclear. Attempts to identify a cell surface MIF transmembrane receptor, which would explain some of the reported MIF regulatory effects in relation to extracellular signal-regulated protein kinase-1/2 (11), synovial cell p38 kinase (12), and p53 (13, 14), have been unsuccessful. CD74 (invariant polypeptide of MHC type II) was found to be a putative MIF receptor (15), although there is no compelling evidence of any potential link between this antigen-processing molecule and intracellular signaling pathways. The absence of a validated signal transduction mechanism via a transmembrane receptor suggests that MIF may mediate its effects mainly by non-receptor mediated endocytosis (16).In contrast to all other known cytokines, MIF has...

The Macrophage Migration Inhibitory Factor Homolog of Entamoeba histolytica Binds to and Immunomodulates Host Macrophages

“…Macrophages incubated with endotoxin-free EhMIF only did not show any significant increase in TNF-␣ secretion (Fig. 3C), in agreement with a previous study done with mammalian MIF (10).…”

“…Proinflammatory functions include the following: (i) MIF induces the secretion of inflammatory mediators, such as interleukin-6 (IL-6); (ii) MIF enhances TNF-␣ production by lipopolysaccharide (LPS)-stimulated immune cells; and (iii) MIF can counterregulate the anti-inflammatory activities of glucocorticoids (9)(10)(11)(12)(13)(14)(15)(16)(17). Many of the inflammatory effects of MIF are initiated via direct binding to its cell surface receptor, CD74 (18).…”

Identification of Iguratimod as an Inhibitor of Macrophage Migration Inhibitory Factor (MIF) with Steroid-sparing Potential

“…Although the production of cytokines in response to MIF stimulation alone is controversial, the production of IL-8 by MIF stimulation of peripheral blood monocytes has been confirmed in multiple contexts (46,69). Human peripheral blood monocytes purified by adherence were plated at a density of ϳ2 ϫ 10 5 cells/ well in a 96-well plate.…”

“…Although these compounds hold great potential for clinical application, preclinical studies of MIF inhibitors have proven problematic, in large part due to a lack of a unified approach to developing bioassays for MIF activity. Although many candidate assays are employed, including cytokine production (46), signal transduction through the ERK pathway (6), proliferation and apoptosis studies (5,47), and chemotaxis experiments (4), these assays do not always produce robust results and are easily confounded by factors such as contaminating endotoxin in recombinant protein preparations.…”

Hypoxia and glucocorticoid signaling converge to regulate macrophage migration inhibitory factor gene expression

“…Currently, the exact role of MIF in the regulation of the immune response is a subject of controversy. Numerous studies have shown that MIF activates or promotes the expression of tumor necrosis factor ␣ (TNF␣), interleukin-1 (IL-1), IL-2, IL-6, IL-8, and IL-12 from a variety of cell types, including macrophages and T cells (1)(2)(3)(4)(5)(6); other studies have failed to establish a cytokine or cytokine-inducing role of MIF (7)(8)(9)(10). However, MIF is capable of overriding the antiinflammatory actions of glucocorticoids, thus impairing glucocorticoid action (1,2,11).…”