Macrophage migration inhibitory factor: an emerging therapeutic target in rheumatoid arthritis

An update on the cytokine network in rheumatoid arthritis

PURPOSE OF REVIEW

To update the knowledge accumulated on the contribution of cytokines to rheumatoid arthritis and related animal models. Publications from the end of 2002 and 2003 period were analyzed for a selection.

RECENT FINDINGS

A better understanding of the clinical results with tumor necrosis factor-alpha inhibitors has come from studies in treated patients. The expected effect of infliximab on the apoptosis of cells expressing tumor necrosis factor-alpha was not observed in synovium biopsy specimens. The mode of action of tumor necrosis factor-alpha on bone destruction has been clarified in gene-defective mice. Tumor necrosis factor-alpha acts through osteoclasts--an effect that is inhibited with osteoprotegerin. New interleukin-1 inhibitors with a potential for increased efficacy, such as interleukin-1trap, have been manufactured and are now being tested in rheumatoid arthritis. The list of cytokines of interest for therapeutic intervention has been growing rapidly. The results with animal models have provided clues to control arthritis with natural interleukin-18 inhibitors, such as interleukin-18 BP. Additional results have been accumulated that indicate the contribution of T cell subsets in inflammation and destruction through the production of interleukin-17. Synergistic interactions with other cytokines are critical in the interleukin-17 tuning effects. Macrophage inhibitory factor was described many years ago. Its comeback is based on properties of synoviocyte activation and proliferation.

SUMMARY

Such findings are critical for a better understanding of response heterogeneity in patients treated with the cytokine inhibitors now on the market. New therapeutic approaches are been planned from these results.

A functional promoter haplotype of macrophage migration inhibitory factor is linked and associated with juvenile idiopathic arthritis

OBJECTIVE

To establish linkage and replicate the association of macrophage migration inhibitory factor (MIF) with juvenile idiopathic arthritis (JIA).

METHODS

Three hundred twenty-one Caucasian simplex families from the UK were genotyped for polymorphisms of MIF using SNaPshot ddNTP primer extension, or by a fluorescently labeled primer method, and capillary gel electrophoresis. The functional significance of the promoter polymorphisms was studied using luciferase-based reporter gene assays in human T lymphoblast and epithelial cell lines.

RESULTS

MIF was linked and associated with JIA (P = 0.0016). Specifically, a 2-point promoter haplotype, CATT(7)-MIF-173*C, was found to be transmitted in excess (38 transmitted: 21 not transmitted) in the JIA patients. Conditional extended transmission disequilibrium test and pairwise extended transmission disequilibrium test predicted functional interaction between the 2 polymorphic positions. The interaction of the CATT repeat with MIF-173*G/C was found to be specific to the cell type.

CONCLUSION

Replication of an association and linkage of MIF with JIA has been established. Functional interaction between the polymorphic positions on the linked haplotype has also been shown. The molecular mechanism of this interaction is currently being investigated.

Xenopus laevis Macrophage Migration Inhibitory Factor Is Essential for Axis Formation and Neural Development

Macrophage migration inhibitory factor (MIF) is an immunoregulatory cytokine involved in both acquired and innate immunity. MIF also has many functions outside the immune system, such as isomerase and oxidoreductase activities and control of cell proliferation. Considering the involvement of MIF in various intra- and extracellular events, we expected that MIF might also be important in vertebrate development. To elucidate the possible role of MIF in developmental processes, we knocked down MIF in embryos of the African clawed frog Xenopus laevis, using MIF-specific morpholino oligomers (MOs). For the synthesis of the MOs, we cloned a cDNA for a Xenopus homolog of MIF. Sequence analysis, determination of the isomerase activity, and x-ray crystallographic analysis revealed that the protein encoded by the cDNA was the ortholog of mammalian MIF. We carried out whole mount in situ hybridization of MIF mRNA and found that MIF was expressed at high levels in the neural tissues of normal embryos. Although early embryogenesis of MO-injected embryos proceeded normally until the gastrula stage, their neurulation was completely inhibited. At the tailbud stage, the MO-injected embryos lacked neural and mesodermal tissues, and also showed severe defects in their head and tail structures. Thus, MIF was found to be essential for axis formation and neural development of Xenopus embryos.

Cytokines in the rheumatic diseases

Extensive data has accumulated over the last 10 to 15 years to implicate various cytokines in pathways of pathophysiology in rheumatic diseases. Abnormalities in cytokine production are not the cause of these diseases, but reflect continual production by immune and inflammatory cells. Cytokines are heterogeneous and function in an overlapping and redundant network. An important principle to emerge is that the net biologic response in a diseased organ or tissue reflects a balance between the local levels of proinflammatory and anti-inflammatory cytokines and factors. Thus, a chronic disease may result from the excess production of proinflammatory cytokines or the inadequate production of anti-inflammatory cytokines. This article summarizes the role of cytokines in rheumatic diseases by focusing on each disease and the involved pathways of pathophysiology.

Regulated secretion of macrophage migration inhibitory factor is mediated by a non-classical pathway involving an ABC transporter

The cytokine macrophage migration inhibitory factor (MIF) is inducibly secreted by immune cells and certain other cell types to critically participate in the regulation of the host immune response. However, MIF does not contain a N-terminal signal sequence and the mechanism of MIF secretion is unknown. Here we show in a model of endotoxin-stimulated THP-1 monocytes that MIF does not enter the endoplasmatic reticulum and that MIF secretion is not inhibited by monensin or brefeldin A, demonstrating that MIF secretion occurs via a non-classical export route. Glyburide and probenicide but not other typical inhibitors of non-classical protein export strongly block MIF secretion, indicating that the export pathway of MIF involves an ABCA1 transporter.