Distinct immunoregulatory properties of macrophage migration inhibitory factors encoded by Eimeria parasites and their chicken host

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that plays an important role in host defense against a variety of microorganisms including protozoan parasites. Interestingly, some microbial pathogens also express a MIF-like protein, although its role in disease pathogenesis is not well understood. The aim of this study was to compare an Eimeria-encoded MIF (E.MIF) protein with chicken MIF (C.MIF) on the basis of their structural, immunological, and biological properties. E.MIF and C.MIF proteins, each with a glutathione S-transferase epitope tag, were expressed in Escherichia coli or COS-7 cells and purified by glutathione affinity chromatography. Rabbit antisera against the purified proteins demonstrated their mutual immunological cross-reactivity on Western blots, and immunolocalized intracellular native E.MIF to the Eimeria schizont, merozoite, and oocyst life cycle stages. HD11 chicken macrophages treated in vitro with C.MIF recombinant protein expressed increased levels of transcripts encoding interleukin-6 (IL-6), IL-17, and tumor necrosis factor superfamily member 15 (TNFSF15), but decreased levels of IL-8 transcripts, compared with cells treated with the PBS control; similar treatment with E.MIF only down-regulated IL-8 transcripts. Unlike recombinant E.MIF, C.MIF exhibited in vitro chemotactic activity for HD11 cells. Conversely, E.MIF, but not C.MIF, enhanced protection against experimental Eimeria infection, compared with the PBS control. These studies provide evidence for overlapping structural and antigenic properties, but distinct immunoregulatory roles, of E.MIF and C.MIF.