Macrophage migration inhibitory factor of the parasitic nematode Trichinella spiralis

cDNAs were obtained for macrophage migration-inhibitory factor (MIF)/L-dopa chrome methyl ester tautomerase homologues from the parasitic nematodes Tri chinella spiralis (TsMIF) and Trichuris trichiura (TtMIF). The translated s equences, which were partly confirmed by sequencing of proteolytic fragment s, show 42 and 44%,, identity respectively with human or mouse MIF, and are shorter by one C-terminal residue. Unlike vertebrate MIF and MIF homologue s of filarial nematodes, neither TsMIF nor TtMIF contain cysteine residues. Soluble recombinant TsMIF, expressed in Escherichia coli showed secondary structure (by CD spectroscopy) and quaternary structure (by fight-scatterin g and gel filtration) similar to that of the trimeric mammalian MIFs and D- dopachrome tautomerase. The catalytic specificity of recombinant TsMIF in t he ketonization of phenylpyruvate (1.4 x 10(6) M-1 . s(-1)) was comparable with that of human MIF, while that of p-hydroxyphenylpyruvate (9.1 x 10(4) M-1. s(-1)) was 71-fold lower. TsMIF showed high specificity in tautomeriza tion of the methyl ester Of L-dopachrome compared with non-esterified L-dop achrome (> 87000-fold) and a high k(cat). (approximate to4 x 10(4) s(-1)) T he crystal structure, determined to 1.65 Angstrom (1 Angstrom = 0.1 nm), wa s generally similar to that of human MIF, but differed in the boundaries of the putative active-site pocket, which can explain the low activity toward s p-hydroxyphenylpyruvate. The central pore was blocked, but was continuous , with the three putative tautomerase sites. Recombinant TsMIF (5 ng/ml-5 p g/ml) inhibited migration of human peripheral-blood mononuclear cells in a man-ner similar to that shown by human MIF, but had no effect from 5 to 500 ng/ml on anti-CD3-stimulated murine T-cell proliferation. TsMIF was detect ed in supernatants of T. spiralis larvae cultured in vitro at 6 ng/ml (55 n g/mg total secreted protein). In conclusion TsMIF has structural, catalytic and cell-migration-inhibitory properties which indicate that it is partial ly orthologous to mammalian MIF.