Macrophage migration inhibitory factor (MIF): a key player in protozoan infections

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine produced by the pituitary gland and multiple cell types, including macrophages (Mø), dendritic cells (DC) and T-cells. Upon releases MIF modulates the expression of several inflammatory molecules, such as TNF-α, nitric oxide and cyclooxygenase 2 (COX-2). These important MIF characteristics have prompted investigators to study its role in parasite infections. Several reports have demonstrated that MIF plays either a protective or deleterious role in the immune response to different pathogens. Here, we review the role of MIF in the host defense response to some important protozoan infections.     

Macrophage migration inhibitory factor (MIF) promotes fibroblast migration in scratch-wounded monolayers in vitro

MIF was recently redefined as an inflammatory cytokine, which functions as a critical mediator of diseases such as septic shock, rheumatoid arthritis, atherosclerosis, and cancer. MIF also regulates wound healing processes. Given that fibroblast migration is a central event in wound healing and that MIF was recently demonstrated to promote leukocyte migration through an interaction with G-protein-coupled receptors, we investigated the effect of MIF on fibroblast migration in wounded monolayers in vitro. Transient but not permanent exposure of primary mouse or human fibroblasts with MIF significantly promoted wound closure, a response that encompassed both a proliferative and a pro-migratory component. Importantly, MIF-induced fibroblast activation was accompanied by an induction of calcium signalling, whereas chronic exposure with MIF down-regulated the calcium transient, suggesting receptor desensitization as the underlying mechanism.     

Macrophage migration inhibitory factor (MIF): mechanisms of action and role in disease

Macrophage migration inhibitory factor (MIF) is a unique cytokine and critical mediator of host defenses with a role in septic shock and chronic inflammatory and autoimmune diseases. Its mechanism of action is incompletely understood. Here, we attempt to correlate current knowledge on the molecular pathways of MIF activity with its functions in immunity and disease.     

Macrophage migration inhibitory factor (MIF)--its role in catecholamine metabolism.

Macrophage migration inhibitory factor (MIF) was originally identified several decades ago as a lymphokine-derived protein that inhibited monocyte migration. Recently, it has been reported that MIF has D-dopachrome tautomerase, phenylpyruvate tautomerase and thiol protein oxidoreductase activities, although the physiological significance of those activities is not yet clear. Here we show that MIF is able to catalyze the conversion of dopaminechrome and norepinephrinechrome, toxic quinone products of the neurotransmitters dopamine and norepinephrine, respectively, to indole derivatives that may serve as precursors to neuromelanin. Since MIF is highly expressed in human brain, these observations raise the possibility that MIF participates in a detoxification pathway for catecholamine products and could therefore have an important role for neural tissues. The potential role of MIF in the formation of neuromelanin from catecholamines is also an extremely interesting possibility.     

Macrophage migration inhibitory factor (MIF) acetylation protects neurons from ischemic injury

Ischemia-induced neuronal death leads to serious lifelong neurological deficits in ischemic stroke patients. Histone deacetylase 6 (HDAC6) is a promising target for neuroprotection in many neurological disorders, including ischemic stroke. However, the mechanism by which HDAC6 inhibition protects neurons after ischemic stroke remains unclear. Here, we discovered that genetic ablation or pharmacological inhibition of HDAC6 reduced brain injury after ischemic stroke by increasing macrophage migration inhibitory factor (MIF) acetylation. Mass spectrum analysis and biochemical results revealed that HDAC6 inhibitor or aspirin treatment promoted MIF acetylation on the K78 residue. MIF K78 acetylation suppressed the interaction between MIF and AIF, which impaired MIF translocation to the nucleus in ischemic cortical neurons. Moreover, neuronal DNA fragmentation and neuronal death were impaired in the cortex after ischemia in MIF K78Q mutant mice. Our results indicate that the neuroprotective effect of HDAC6 inhibition and aspirin treatment results from MIF K78 acetylation; thus, MIF K78 acetylation may be a therapeutic target for ischemic stroke and other neurological diseases.Subject terms: Cell death in the nervous system, Stroke     

Macrophage migration inhibitory factor (MIF) interacts with Bim and inhibits Bim-mediated apoptosis

The pro-apoptotic Bcl-2 family member Bim acts as a sensor for apoptotic stimuli and initiates apoptosis through the mitochondrial pathway. To identify novel regulators of Bim, we employed the yeast two-hybrid system and isolated the human gene encoding macrophage migration inhibitory factor (MIF), a ubiquitously expressed proinflammatory mediator that has also been implicated in cell proliferation, the cell cycle and carcinogenesis. The interaction between MIF and Bim was confirmed by both in vitro and in vivo protein interaction assays. Intriguingly, protein complexes between MIF and the three major Bim isoforms (BimEL/BimL/BimS) could be detected in HEK293 and K562 cells, especially in cells undergoing apoptosis. Moreover, exogenous expression of MIF partially inhibited Bim-induced apoptosis in HEK293 cells. SiRNA-mediated knockdown of MIF increased apoptosis in K562 cells exposed to the chemical oxidant diamide. Endogenous MIF may regulate the pro-apoptotic activity of Bim and inhibit the release of cytochrome c from mitochondria.     

Macrophage migration inhibitory factor (MIF) is necessary for progression of autoimmune diabetes mellitus

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine of the innate immune system that plays a major role in the induction of immunoinflammatory responses. To examine the role of endogenous MIF in the pathogenesis of type 1 diabetes (TID) we evaluated the effects of administration of neutralizing anti-MIF antibodies to NOD mice with accelerated forms of diabetes induced by injection of cyclophosphamide or by transfer of diabetogenic spleen cells. Both accelerated forms of diabetes were markedly reduced by anti-MIF antibody. Furthermore, MIF-deficient (MIF(-/-)) mice were less susceptible to the induction of immunoinflammatory diabetes, insulitis and apoptosis within the endocrine pancreas by multiple low doses of streptozotocin (MLD-STZ) than genetically matched wild type (WT) mice. MIF deficiency resulted in lower proliferation and lymphocyte adhesion, as well as reduced production from the spleens and peritoneal cells of a variety of inflammatory mediators typically associated with development of the disease including IL-12, IL-23, TNF-alpha, and IL-1beta. Furthermore, MIF deletion affected the production of IL-18, TNF-alpha, IL-1beta, and iNOS in the islets of Langerhans. These data, along with the higher expression of IL-4 and TGF-beta observed in the periphery and in the pancreas of MLD-STZ-challenged MIF(-/-) mice as compared to WT controls suggest that MIF deficiency has induced an immune deviation towards protective type 2/3 response. These results suggest that MIF participates in T1D by controlling the functional activity of monocytes/macrophages and T cells and modulating their secretory capacity of pro- and anti-inflammatory molecules.     

Macrophage migration inhibitory factor (MIF) contributes to the development of allergic rhinitis

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine whose expression has been found to be critical to the generation of antigen-specific immune responses. Recent studies suggested that MIF played a role in the initiation and maintenance of allergic diseases. To elucidate MIF's role in the pathogenesis of allergic rhinitis (AR), we sensitized MIF-deficient gene knockout (KO) mice and wild-type (WT) mice intraperitoneally with ovalbumin (OVA) and compared their clinical symptoms and allergic responses after intranasal challenge. Antigen-induced nasal symptoms were significantly reduced in MIF KO mice compared to WT mice. Histological examination of nasal mucosa showed that the number of infiltrating eosinophils in MIF KO mice was significantly lower than that in WT mice (P < 0.05). The concentration of TNF-alpha in nasal mucosa was also significantly lower in MIF KO mice than in WT mice (P < 0.05). We have demonstrated that the absence of MIF affects several aspects of experimental AR. One mechanism by which these effects might be mediated is by down regulating TNF-alpha. The block of allergic inflammation in MIF KO mice suggests that MIF may play a role in the allergic response.     

Macrophage migration inhibitory factor: a mediator of matrix metalloproteinase-2 production in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by destruction of bone and cartilage, which is mediated, in part, by synovial fibroblasts. Matrix metalloproteinases (MMPs) are a large family of proteolytic enzymes responsible for matrix degradation. Macrophage migration inhibitory factor (MIF) is a cytokine that induces the production of a large number of proinflammatory molecules and has an important role in the pathogenesis of RA by promoting inflammation and angiogenesis.     

Macrophage migration inhibitory factor (MIF) produced by a human T cell hybridoma clone

A human T cell hybridoma clone, F5, producing high levels of macrophage migration inhibitory factor (MIF) was established by the emetine-actinomycin D selection method. This clone produced two species of MIF which were separated on a Phenyl Sepharose column. We purified MIF-2 (the more hydrophobic species of the two) to homogeneity from the conditioned medium of stimulated F5 cells by a series of steps that included hydrophobic chromatography, ion-exchange chromatography. Ricinus communis lectin affinity chromatography, and high-performance liquid chromatography on anion exchange and reverse-phase columns. Purified MIF was digested with endoproteinase Lys-C and Asp-N. The amino acid sequences of the generated peptides were determined. No sequence similarity with any other protein was found. The molecular weight of MIF-2 was estimated to be 45 kDa from sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immunoprecipitates with anti-peptide antibodies. These results show that F5MIF-2 is a novel cytokine.     

Neuroendocrine properties of macrophage migration inhibitory factor (MIF)

The cytokine macrophage migration inhibitory factor (MIF) is produced by neuroendocrine and immune tissues and possesses several features that allow it to be characterized as a neuroendocrine mediator. Its pro-inflammatory action and its pathogenic role in inflammatory diseases, such as septic shock, arthritis and other diseases, have clearly been demonstrated and may be based in part on neuroendocrine mechanisms. Macrophage migration inhibitory factor possesses glucocorticoid-antagonist properties within the immune system and participates in the regulation of several endocrine circuits. This review summarizes the current state of MIF research and focuses on MIF expression and function in nervous and endocrine tissues.     

Macrophage migration inhibitory factor (MIF) is rendered enzymatically inactive by myeloperoxidase-derived oxidants but retains its immunomodulatory function

Macrophage migration inhibitory factor (MIF) is an important player in the regulation of the inflammatory response. Elevated plasma MIF is found in sepsis, arthritis, cystic fibrosis and atherosclerosis. Immunomodulatory activities of MIF include the ability to promote survival and recruitment of inflammatory cells and to amplify pro-inflammatory cytokine production. MIF has an unusual nucleophilic N-terminal proline with catalytic tautomerase activity. It remains unclear whether tautomerase activity is required for MIF function, but small molecules that inhibit tautomerase activity also inhibit the pro-inflammatory activities of MIF. A prominent feature of the acute inflammatory response is neutrophil activation and production of reactive oxygen species, including myeloperoxidase (MPO)-derived hypochlorous acid and hypothiocyanous acid. We hypothesized that MPO-derived oxidants would oxidize the N-terminal proline of MIF and alter its biological activity. MIF was exposed to hypochlorous acid and hypothiocyanous acid and the oxidative modifications on MIF were examined by LC-MS/MS. Imine formation and carbamylation was observed on the N-terminal proline in response to MPO-dependent generation of hypochlorous and hypothiocyanous acid, respectively. These modifications led to a complete loss of tautomerase activity. However, modified MIF still increased CXCL-8/IL-8 production by peripheral blood mononuclear cells (PBMCs) and blocked neutrophil apoptosis, indicating that tautomerase activity is not essential for these biological functions. Pre-treatment of MIF with hypochlorous acid protected the protein from covalent modification by the MIF inhibitor 4-iodo-6-phenylpyrimidine (4-IPP). Therefore, oxidant generation at inflammatory sites may protect MIF from inactivation by more disruptive electrophiles, including drugs designed to target the tautomerase activity of MIF.     

Tumor-derived macrophage migration inhibitory factor (MIF) inhibits T lymphocyte activation

Macrophage migration inhibitory factor (MIF) is a multi-functional cytokine that is considered a pro-inflammatory cytokine. However, our studies show that MIF, when produced in super-physiological levels by a murine neuroblastoma cell line (Neuro-2a) exceeding those normally seen during an immune response, inhibits cytokine-, CD3-, and allo-induced T-cell activation. MIF is also able to inhibit T cells that have already received an activation signal. The T-cell inhibitory effects of culture supernatants from neuroblastoma cells were reversed when the cells were transfected with dicer-generated si-RNA to MIF. When T cells were activated in vitro by co-culture with interleukin (IL)-2 and IL-15 and analyzed for cytokine production in the presence or absence of MIF-containing culture supernatant, inhibition of T-cell proliferation and induced cell death were observed even as the treated T cells produced high levels of interferon-gamma (IFN-gamma). The inhibitory effects of MIF were partially reversed when lymphocytes from IFN-gamma knockout mice were tested. We propose that the high levels of MIF produced by neuroblastoma cause activation induced T-cell death through an IFN-gamma pathway and may eliminate activated T cells from the tumor microenvironment and thus contribute to escape from immune surveillance.