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C N Metz

Publications and source records attributed to C N Metz.

At least 19 recordsLinked to original sources
PubMed2003

The p53-dependent effects of macrophage migration inhibitory factor revealed by gene targeting.

Macrophage migration inhibitory factor (MIF) is a mediator of host immunity and functions as a high, upstream activator of cells within the innate and the adaptive immunological systems. Recent studies have suggested a potentially broader role for MIF in growth regulation because of its ability to antagonize p53-mediated gene activation and apoptosis. To better understand MIF's activity in growth control, we generated and characterized a strain of MIF-knockout (MIF-KO) mice in the inbred, C57BL/6 background. Embryonic fibroblasts from MIF-KO mice exhibit p53-dependent growth alterations, increased p53 transcriptional activity, and resistance to ras-mediated transformation. Concurrent deletion of the p53 gene in vivo reversed the observed phenotype of cells deficient in MIF. In vivo studies showed that fibrosarcomas induced by the carcinogen benzo[alpha]pyrene are smaller in size and have a lower mitotic index in MIF-KO mice relative to their WT counterparts. The data provide direct genetic evidence for a functional link between MIF and the p53 tumor suppressor and indicate an important and previously unappreciated role for MIF in carcinogenesis.

Alleles↗
PubMed2003

Fibrocytes: a unique cell population implicated in wound healing.

Following tissue damage, host wound healing ensues. This process requires an elaborate interplay between numerous cell types which orchestrate a series of regulated and overlapping events. These events include the initiation of an antigen-specific host immune response, blood vessel formation, as well as the production of critical extracellular matrix molecules, cytokines and growth factors which mediate tissue repair and wound closure. Connective tissue fibroblasts are considered essential for successful wound healing; however, their origin remains a mystery. A unique cell population, known as fibrocytes, has been identified and characterized. One of the unique features of these blood-borne cells is their ability to home to sites of tissue damage. This article reviews the identification and characterization of fibrocytes, summarizes the potential role of fibrocytes in the numerous steps of the wound-healing process and highlights the potential role of fibrocytes in fibrotic disease pathogenesis.

Animals↗
PubMed2001

Urine macrophage migration inhibitory factor concentrations as a diagnostic tool in human renal allograft rejection.

BACKGROUND: Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine that is a potent activator of macrophages and T cells. Previous studies have shown that local MIF production is increased in acute renal allograft rejection, suggesting that it may play an important role in the rejection process. AIMS: To determine if urine and serum MIF concentrations: (1) are increased in acute rejection, and (2) can be used as noninvasive tools to discriminate between acute rejection (AR) and cyclosporine nephrotoxicity (CyA toxicity). METHODS: In a prospective study of nine renal allograft patients (five acute rejection and four stable), serial urine MIF concentrations were measured by ELISA in the first 14 days after transplantation. In a retrospective study, MIF concentrations in urine and serum were measured in 24 patients who were biopsied for acute renal transplant dysfunction (11 AR, 13 CyA toxicity). Urine and serum MIF were also measured in 23 stable renal transplant patients and 10 normals. RESULTS: MIF was readily detected in the urine of normal healthy controls (106+/-61 pg/micromol creatinine). In the prospective study, the urinary MIF concentration was increased substantially on day 1 posttransplantation and subsequently fell in parallel with the serum creatinine. However, urine MIF increased before episodes of biopsy proven acute rejection. The retrospective study showed that urine MIF concentrations in patients with AR were increased 5-fold compared to normal controls (439+/-313 pg/micromol Cr; P<0.01). In contrast, urine MIF concentrations in CyA toxicity were not significantly different to normal controls (145+/-119 pg/micromol Cr; P=NS). A marked increase in MIF immunostaining was seen in biopsies of AR, but not in CyA toxicity. No significant differences were evident in serum MIF levels between normals and any transplant patient group. CONCLUSIONS: These results suggest that measurement of urine MIF concentration may be useful in monitoring renal transplant patients for acute rejection and as a discriminator from cyclosporine nephrotoxicity.

Adult↗
PubMed2001

Peripheral blood fibrocytes: differentiation pathway and migration to wound sites.

Fibrocytes are a distinct population of blood-borne cells that display a unique cell surface phenotype (collagen I+/CD11b+/CD13+/CD34+/CD45RO+/MHC class II+/CD86+) and exhibit potent immunostimulatory activities. Circulating fibrocytes rapidly enter sites of tissue injury, suggesting an important role for these cells in wound repair. However, the regulatory processes that govern the differentiation of blood-borne fibrocytes and the mechanisms that underlie the migration of these cells to wound sites are currently not known. We report herein that ex vivo cultured fibrocytes can differentiate from a CD14+-enriched mononuclear cell population and that this process requires contact with T cells. Furthermore, we demonstrate that TGF-beta1 (1-10 ng/ml), an important fibrogenic and growth-regulating cytokine involved in wound healing, increases the differentiation and functional activity of cultured fibrocytes. Because fibrocytes home to sites of tissue injury, we examined the role of chemokine/chemokine receptor interactions in fibrocyte trafficking. We show that secondary lymphoid chemokine, a ligand of the CCR7 chemokine receptor, acts as a potent stimulus for fibrocyte chemotaxis in vitro and for the homing of injected fibrocytes to sites of cutaneous tissue injury in vivo. Finally, we demonstrate that differentiated, cultured fibrocytes express alpha smooth muscle actin and contract collagen gels in vitro, two characteristic features of wound-healing myofibroblasts. These data provide important insight into the control of fibrocyte differentiation and trafficking during tissue repair and significantly expand their potential role during wound healing.

Animals↗
PubMed2001

Regulation of the CTL response by macrophage migration inhibitory factor.

Macrophage migration inhibitory factor (MIF) has been shown to be a pivotal cytokine that mediates host inflammatory and immune responses. Recently, immunoneutralization of MIF has been found to inhibit tumor growth in mice; however, the contributing mechanisms underlying this effect have not been well defined. We investigated whether MIF plays a regulatory role in the expression of CTL activity. In a mouse model of the CTL response using the OVA-transfected tumor cell line EL4 (EG.7), we found that cultures of splenocytes obtained from EG.7-primed mice secrete high levels of MIF following Ag stimulation in vitro. Notably, parallel splenocyte cultures treated with neutralizing anti-MIF mAb showed a significant increase in the CTL response directed against EG.7 cells compared with control mAb-treated cultures. This effect was accompanied by elevated expression of IFN-gamma. Histological examination of the EG. 7 tumors from anti-MIF-treated animals showed a prominent increase in both CD4(+) and CD8(+) T cells as well as apoptotic tumor cells, consistent with the observed augmentation of CTL activity in vivo by anti-MIF. This increased CTL activity was associated with enhanced expression of the common gamma(c)-chain of the IL-2R that mediates CD8(+) T cell survival. Finally, CD8(+) T lymphocytes obtained from the spleens of anti-MIF-treated EG.7 tumor-bearing mice, when transferred into recipient tumor-bearing mice, showed increased accumulation in the tumor tissue. These data provide the first evidence of an important role for MIF in the regulation and trafficking of anti-tumor T lymphocytes in vivo.

Adjuvants, Immunologic↗
PubMed2001

Regulation of synoviocyte phospholipase A2 and cyclooxygenase 2 by macrophage migration inhibitory factor.

OBJECTIVE: Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine with known actions in macrophage and T cell activation. MIF also has the unique capacity to reverse the inhibitory effects of glucocorticoids on these cells. We have recently demonstrated MIF expression in human rheumatoid arthritis (RA) synovium and cultured fibroblast-like synoviocytes (FLS), as well as the ability of FLS-derived MIF to induce monocyte release of tumor necrosis factor alpha. We investigated the effects of MIF on aspects of RA FLS activation, including the induction of phospholipase A2 (PLA2) and cyclooxygenase (COX). METHODS: PLA2 activity was measured by 3H-arachidonic acid released from treated FLS supernatants. COX activity was measured by prostaglandin E2 enzyme-linked immunosorbent assay. Cytosolic PLA2 (cPLA2) and COX-2 messenger RNA (mRNA) were determined using semiquantitative reverse transcriptase-polymerase chain reaction. RESULTS: Constitutive PLA2 activity was detected in RA FLS. Recombinant human MIF up-regulated PLA2 activity (P < 0.01) and cPLA2 mRNA expression, but had no effect on secretory PLA2. Recombinant human MIF up-regulated COX activity (P < 0.05) and COX-2 mRNA, but had no observable effect on COX-1. Interleukin-1beta (IL-1beta) significantly up-regulated PLA2 activity (P < 0.005) and cPLA2 mRNA expression while anti-MIF monoclonal antibody (mAb) significantly inhibited this IL-1beta-induced PLA2 activity (P < 0.02). Anti-MIF mAb significantly reduced IL-1beta-induced COX activity (P < 0.05) and COX-2 mRNA expression. CONCLUSION: MIF exerts a proinflammatory effect on key aspects of RA FLS activation. That anti-MIF mAb inhibited IL-1beta up-regulation of FLS indicates an additional cofactor role for MIF in IL-1beta-induced FLS activation. These data suggest that MIF antagonism has important therapeutic potential in RA.

Antibodies, Blocking↗
PubMed2001

Development of chronic colitis is dependent on the cytokine MIF.

The cytokine macrophage-migration inhibitory factor (MIF) is secreted by a number of cell types upon induction by lipopolysaccharide (LPS). Because colitis is dependent on interplay between the mucosal immune system and intestinal bacteria, we investigated the role of MIF in experimental colitis. MIF-deficient mice failed to develop disease, but reconstitution of MIF-deficient mice with wild-type innate immune cells restored colitis. In addition, established colitis could be treated with anti-MIF immunoglobulins. Thus, murine colitis is dependent on continuous MIF production by the innate immune system. Because we found increased plasma MIF concentrations in patients with Crohn's disease, these data suggested that MIF is a new target for intervention in Crohn's disease.

Adoptive Transfer↗
PubMed2001

Identification and characterization of a homologue of the pro-inflammatory cytokine Macrophage Migration Inhibitory Factor in the tick, Amblyomma americanum.

Studying tick feeding and digestion, we discovered in a cDNA library from partially fed Amblyomma americanum ticks the first known arthropod homologue of a human cytokine, the pro-inflammatory Macrophage Migration Inhibitory Factor (MIF). The tick origin of the MIF cDNA clone was confirmed by sequencing a genomic fragment that contained the full-length tick MIF gene with two introns. Antiserum to a tick MIF-specific peptide as well as antiserum to complete tick MIF revealed the expression of tick MIF in the salivary gland and midgut tissues of A. americanum ticks. In an in vitro functional assay, recombinant tick MIF inhibited the migration of human macrophages to the same extent that recombinant human MIF did.

Amino Acid Sequence↗
PubMed2001

Fibrocytes induce an angiogenic phenotype in cultured endothelial cells and promote angiogenesis in vivo.

Angiogenesis is an ordered process requiring the inter-play of numerous cellular and humoral factors. Studies over the past 20 years have identified several growth factors, cytokines, and enzymes that promote blood vessel formation. Most have revealed how individual factors promote an angiogenic phenotype in endothelial cells in vitro or contribute to blood vessel formation in vivo. However, the fundamental question that remains unanswered is how the cellular microenvironment contributes to angiogenesis. Fibrocytes are a recently characterized mesenchymal cell type isolated from peripheral blood that rapidly enter subcutaneously implanted wound chambers and sites of tissue injury. Here we describe the induction of an angiogenic phenotype in microvascular endothelial cells in vitro and promotion of angiogenesis in vivo by cultured fibrocytes. Fibrocytes constitutively secrete extracellular matrix-degrading enzymes, primarily matrix metalloproteinase 9, which promotes endothelial cell invasion. In addition, fibrocytes secrete several proangiogenic factors including VEGF, bFGF, IL-8, PDGF, and hematopoietic growth factors that promote endothelial cell migration, proliferation, and/or tube formation. By contrast, they do not produce representative antiangiogenic factors. Finally, both autologous fibrocytes and fibrocyte-conditioned media were found to induce blood vessel formation in vivo using the Matrigel angiogenesis model.

3T3 Cells↗
PubMed2000

Protection from septic shock by neutralization of macrophage migration inhibitory factor.

Identification of new therapeutic targets for the management of septic shock remains imperative as all investigational therapies, including anti-tumor necrosis factor (TNF) and anti-interleukin (IL)-1 agents, have uniformly failed to lower the mortality of critically ill patients with severe sepsis. We report here that macrophage migration inhibitory factor (MIF) is a critical mediator of septic shock. High concentrations of MIF were detected in the peritoneal exudate fluid and in the systemic circulation of mice with bacterial peritonitis. Experiments performed in TNFalpha knockout mice allowed a direct evaluation of the part played by MIF in sepsis in the absence of this pivotal cytokine of inflammation. Anti-MIF antibody protected TNFalpha knockout from lethal peritonitis induced by cecal ligation and puncture (CLP), providing evidence of an intrinsic contribution of MIF to the pathogenesis of sepsis. Anti-MIF antibody also protected normal mice from lethal peritonitis induced by both CLP and Escherichia coli, even when treatment was started up to 8 hours after CLP. Conversely, co-injection of recombinant MIF and E. coli markedly increased the lethality of peritonitis. Finally, high concentrations of MIF were detected in the plasma of patients with severe sepsis or septic shock. These studies define a critical part for MIF in the pathogenesis of septic shock and identify a new target for therapeutic intervention.

Adolescent↗
PubMed2000

Expression of macrophage migration inhibitory factor in human glomerulonephritis.

BACKGROUND: We have recently demonstrated that macrophage migration inhibitory factor (MIF) plays a pathogenic role in experimental glomerulonephritis (GN). The aim of the current study was to investigate MIF expression in human GN. METHODS: MIF expression was examined by in situ hybridization and immunohistochemistry staining in 65 biopsies from a variety of glomerulonephridities. RESULTS: There is constitutive expression of MIF mRNA and protein in normal human kidney that is largely restricted to tubular epithelial cells and to some glomerular epithelial cells. There was little change in the pattern of MIF expression in nonproliferative forms of GN such as minimal change disease and membranous GN. However, there was a marked increase in both glomerular and tubular MIF expression in proliferative forms of GN, including focal segmental glomerulosclerosis (FGS), lupus nephritis, crescentic GN, and mesangiocapillary proliferative GN. The prominent macrophage and T-cell infiltrate in these diseases were largely restricted to areas with marked up-regulation of MIF expression, contributing to glomerular hypercellularity, glomerular focal segmental lesions, crescent formation, tubulitis, and granulomatous lesions. De novo MIF expression was evident in glomerular endothelial cells and mesangial cells in proliferative forms of GN. In addition, many infiltrating macrophages and T cells showed MIF mRNA and protein expression. Quantitative analysis found that increased glomerular and tubular MIF expression gave a highly significant correlation with macrophage and T-cell accumulation, the severity of histologic lesions, and the loss of creatinine clearance. CONCLUSIONS: Renal MIF expression is markedly up-regulated in proliferative forms of human GN, and this correlates with leukocyte infiltration, histologic damage, and renal function impairment. These results suggest that MIF may be an important mediator of renal injury in progressive forms of human GN. Based on these findings, together with the known pathogenic role of MIF in experimental GN, we propose that MIF is an attractive therapeutic target in the treatment of progressive forms of GN.

Adolescent↗
PubMed2000

Macrophage migration inhibitory factor release by macrophages after ingestion of Plasmodium chabaudi-infected erythrocytes: possible role in the pathogenesis of malarial anemia.

Human falciparum malaria, caused by Plasmodium falciparum infection, results in 1 to 2 million deaths per year, mostly children under the age of 5 years. The two main causes of death are severe anemia and cerebral malaria. Malarial anemia is characterized by parasite red blood cell (RBC) destruction and suppression of erythropoiesis (the mechanism of which is unknown) in the presence of a robust host erythropoietin response. The production of a host-derived erythropoiesis inhibitor in response to parasite products has been implicated in the pathogenesis of malarial anemia. The identity of this putative host factor is unknown, but antibody neutralization studies have ruled out interleukin-1beta, tumor necrosis factor alpha, and gamma interferon while injection of interleukin-12 protects susceptible mice against lethal P. chabaudi infection. In this study, we report that ingestion of P. chabaudi-infected erythrocytes or malarial pigment (hemozoin) induces the release of macrophage migration inhibitory factor (MIF) from macrophages. MIF, a proinflammatory mediator and counter-regulator of glucocorticoid action, inhibits erythroid (BFU-E), multipotential (CFU-GEMM), and granulocyte-macrophage (CFU-GM) progenitor-derived colony formation. MIF was detected in the sera of P. chabaudi-infected BALB/c mice, and circulating levels correlated with disease severity. Liver MIF immunoreactivity increased concomitant with extensive pigment and parasitized RBC deposition. Finally, MIF was elevated three- to fourfold in the spleen and bone marrow of P. chabaudi-infected mice with active disease, as compared to early disease, or of uninfected controls. In summary, the present results suggest that MIF may be a host-derived factor involved in the pathophysiology of malaria anemia.

Anemia↗
PubMed1999

Sustained mitogen-activated protein kinase (MAPK) and cytoplasmic phospholipase A2 activation by macrophage migration inhibitory factor (MIF). Regulatory role in cell proliferation and glucocorticoid action.

Macrophage migration inhibitory factor (MIF) is an important pro-inflammatory mediator with the unique ability to counter-regulate the inhibitory effects of glucocorticoids on immune cell activation. MIF is released from cells in response to glucocorticoids, certain pro-inflammatory stimuli, and mitogens and acts to regulate glucocorticoid action on the ensuing inflammatory response. To gain insight into the molecular mechanism of MIF action, we have examined the role of MIF in the proliferation and intracellular signaling events of the well characterized, NIH/3T3 fibroblast cell line. Both endogenously secreted and exogenously added MIFs stimulate the proliferation of NIH/3T3 cells, and this response is associated with the activation of the p44/p42 extracellular signal-regulated (ERK) mitogen-activated protein kinases (MAP). The MIF-induced activation of these kinases was sustained for a period of at least 24 h and was dependent upon protein kinase A activity. We further show that MIF regulates cytosolic phospholipase A2 activity via a protein kinase A and ERK dependent pathway and that the glucocorticoid suppression of cytokine-induced cytoplasmic phospholipase A2 activity and arachidonic acid release can be reversed by the addition of recombinant MIF. These studies indicate that the sustained activation of p44/p42 MAP kinase and subsequent arachidonate release by cytoplasmic phospholipase A2 are important features of the immunoregulatory and intracellular signaling events initiated by MIF and provide the first insight into the mechanisms that underlie the pro-proliferative and inflammatory properties of this mediator.

3T3 Cells↗
PubMed1999

A switch in the cellular localization of macrophage migration inhibitory factor in the rat testis after ethane dimethane sulfonate treatment.

Macrophage migration inhibitory factor (MIF), one of the first cytokines to be discovered, has recently been localized to the Leydig cells in adult rat testes. In the following study, the response of MIF to Leydig cell ablation by the Leydig cell-specific toxin ethane dimethane sulfonate (EDS) was examined in adult male rats. Testicular MIF mRNA and protein in testicular interstitial fluid measured by ELISA and western blot were only marginally reduced by EDS treatment, in spite of the fact that the Leydig cells were completely destroyed within 7 days. Immunohistochemistry using an affinity-purified anti-mouse MIF antibody localized MIF exclusively to the Leydig cells in control testes. At 7 days post-EDS treatment, there were no MIF immunopositive Leydig cells in the interstitium, although distinct MIF immunostaining was observed in the seminiferous tubules, principally in Sertoli cells and residual cytoplasm, and some spermatogonia. A few peritubular and perivascular cells were also labelled at this time, which possibly represented mesenchymal Leydig cell precursors. At 14 and 21 days, Sertoli cell MIF immunoreactivity was observed in only a few tubule cross-sections, while some peritubular and perivascular mesenchymal cells and the re-populating immature Leydig cells were intensely labeled. At 28 days after EDS-treatment, the MIF immunostaining pattern was identical to that of untreated and control testes. The switch in the compartmentalization of MIF protein at 7 days after EDS-treatment was confirmed by western blot analysis of interstitial tissue and seminiferous tubules separated by mechanical dissection. These data establish that Leydig cell-depleted testes continue to produce MIF, and suggest the existence of a mechanism of compensatory cytokine production involving the Sertoli cells. This represents the first demonstration of a hitherto unsuspected pattern of cellular interaction between the Leydig cells and the seminiferous tubules which is consistent with an essential role for MIF in male testicular function.

Animals↗
PubMed1998

Macrophage migration inhibitory factor expression in human renal allograft rejection.

BACKGROUND: Macrophage migration inhibitory factor (MIF) plays a pivotal role in immune-mediated diseases. Despite the long-standing association of MIF with the delayed-type hypersensitivity response, the potential role of MIF in allograft rejection is unknown. METHODS: MIF expression was assessed by in situ hybridization and immunohistochemistry staining in 62 biopsies of human renal allograft rejection and in normal human kidney. RESULTS: MIF mRNA and protein is constitutively expressed in normal kidney, being largely restricted to tubular epithelial cells, some glomerular epithelial cells, and vascular smooth muscle cells. In both acute and chronic renal allograft rejection, there was marked up-regulation of MIF mRNA and protein expression by intrinsic kidney cells such as tubular epithelial cells and vascular endothelial and smooth muscle cells. There was also MIF expression by infiltrating macrophages and T cells. Of note, macrophage and T cell infiltrates were largely restricted to areas with marked up-regulation of MIF expression, potentially contributing to the development of severe tubulitis and intimal or transmural arteritis. Quantitative analysis found that increased MIF expression in allograft rejection gave a highly significant correlation with macrophage and T cell accumulation in both the glomerulus and interstitium (P<0.001). In addition, the number of MIF+ tubules and interstitial MIF+ cells correlated significantly with the severity of allograft rejection (P<0.01), and the loss of renal function (P<0.01). In contrast, no up-regulation of renal MIF expression and no leukocyte accumulation was seen in allograft biopsies without evidence of rejection. CONCLUSIONS: This is the first study to demonstrate that local MIF expression is up-regulated during allograft rejection. The association between up-regulation of MIF expression, macrophage and T cell infiltration and the severity of renal allograft rejection suggests that MIF may be an important mediator in the process of allograft rejection.

Acute Disease↗
PubMed1998

Macrophage migration inhibitory factor is a critical mediator of the activation of immune cells by exotoxins of Gram-positive bacteria.

Discovered in the early 1960s as a T cell cytokine, the protein mediator known as macrophage migration inhibitory factor (MIF) has been found recently to be a pituitary peptide released during the physiological stress response, a proinflammatory macrophage cytokine secreted after LPS stimulation, and a T cell product expressed as part of the antigen-dependent activation response. We report herein that MIF also plays a critical role in the innate host response to staphylococcal and streptococcal exotoxins. In RAW 264.7 or elicited mouse peritoneal macrophages, peak MIF secretion was induced by concentrations of the staphylococcal toxic shock syndrome (TSS) toxin 1 (TSST-1) and the streptococcal pyrogenic exotoxin A as low as 10 pg/ml. Moreover, dose-response studies of splenocyte cytokine production showed that lower concentrations of TSST-1 (10 pg/ml) were needed to release MIF than to induce interleukin 2 or interferon-gamma secretion (1 ng/ml). We also studied the effect of neutralizing anti-MIF antibodies on TSST-1-induced lymphocyte proliferation and lethal toxic shock. Pretreatment of C57BL/6 mice with anti-MIF antibody 2 hr before TSST-1 injection prevented spleen enlargement and reduced by 50% the proliferation of splenocytes measured ex vivo. In a lethal mouse model of TSST-1-induced shock, anti-MIF antibody increased survival from 8% to 54% (P < 0.0001). These studies indicate that Gram-positive exotoxins are extremely potent inducers of MIF secretion and establish a critical role for MIF and the macrophage in the pathogenesis of the TSSs and in the innate immune response.

Animals↗
PubMed1998

Migration inhibitory factor induces killing of Leishmania major by macrophages: dependence on reactive nitrogen intermediates and endogenous TNF-alpha.

Macrophage migration inhibitory factor (MIF) is a product of activated T cells, anterior pituitary cells, and macrophages. MIF plays an important role in LPS-induced shock and delayed-type hypersensitivity. Furthermore, MIF exhibits a proinflammatory spectrum of action, promoting TNF-alpha production by macrophages, and counter-regulates glucocorticoid suppression of cytokine production. Here, we report that purified recombinant MIF activates murine macrophages to kill Leishmania major, with maximal effects at concentrations above 1 microg/ml. This MIF-mediated activation is specific, since it can be blocked completely by anti-MIF mAb. The MIF-mediated activation is dependent on TNF-alpha produced endogenously by macrophages, because the administration of anti-TNF-alpha antiserum markedly reduced the MIF effect. No MIF-mediated activation was observed in macrophages derived from TNF receptor p55 knockout mice, thus demonstrating the requirement of the smaller TNF receptor molecule for autocrine TNF-alpha signaling. A highly specific inhibitor of the inducible nitric oxide synthase (iNOS), L-N6-(1-iminoethyl)lysine, dihydrochloride, also inhibited the action of MIF, suggesting an important role for iNOS in the antiparasitic properties of MIF. In line with this, no MIF-mediated activation was detected analyzing macrophages derived from iNOS-deficient mice. The effect of MIF was blocked completely by the macrophage-deactivating cytokines IL-10, IL-13, and TGF-beta. Finally, the expression of MIF mRNA and protein was up-regulated in lymph nodes of mice during the first week after infection with L. major. MIF therefore represents a cytokine involved not only in the recruitment of proinflammatory cells during infection but also in the complex regulation of the antimicrobial activity of these cells.

Animals↗