Analysis of the effects of Macrophage Migration Inhibitory Factor (MIF) on the activation of Toll-like receptor 4 (TLR4)

Macrophage Migration Inhibitory Factor (MIF) was one of the first cytokines to be discovered over 50 years ago and has been characterised in a wide range of mammalian and parasite species. This unique protein possesses the characteristics of a cytokine, chemokine and hormone along with two distinct enzymatic activities. MIF has been shown to be involved in innate and adaptive immunity by modulating Toll-like receptor 4 (TLR4) intermediates such as MAPK and downstream pathways in inflammation and in cell growth and differentiation, thus playing a key role in chronic inflammation and tumorigenesis. In this study, the role of parasitic and mammalian MIF in TLR4 signalling was investigated. Mus musculus MIF1 (MmMIF1) cDNA was isolated by gene cloning and recombinant fusion MmMIF1 was purified alongside Trichinella spiralis MIF1 (TsMIF1) by affinity and ion exchange chromatography. The effects of MIF on TLR4 signalling were examined by analysing the downstream activation of NFκB and AP-1 via a transcriptional reporter using HEK-Blue™-hTLR4 cells as a model. It was found that upon co-administration of TsMIF1 with LPS, NFκB activation was significantly reduced when compared to LPS treatment alone while MmMIF1 caused no significant changes in the activation levels of TLR4. Since no changes were observed in the NFκB and AP-1 activation levels upon co-administration of MIF in the Tumour necrosis factor receptor 1 (TNFR1) pathway, this downstream effect of TsMIF1 can be said to occur within the TLR4 cascade upstream of Transforming growth factor beta-activated kinase 1 (TAK1).