Studies on human migration inhibitory factor: characterization of three molecular species

Human migration inhibitory factor (MIF), obtained from supernatants of peripheral blood mononuclear cells stimulated with concanavalin A, was analyzed by gel filtration, isoelectrofocusing, and CsCl density gradient centrifugation. A distinct pattern of heterogeneity was determined on the basis of its harvesting time and biochemical criteria. Supernatants from cells cultured for 1 day contained a single peak of MIF activity with an isoelectric point of 4.3 to 5.2, an apparent m.w. of 23,000, and a density of 1.314 g/ml, the same as the density of the marker protein, 125I-HSA (1st day pH 5-MIF). Furthermore, this species of human MIF was sensitive to treatment with trypsin, strongly suggesting its being a protein, but not to treatment with neuraminidase and corresponds therefore to guinea pig pH 5-MIF. However, when 2nd day supernatants were analyzed under the same conditions, 2 MIF species were found. One species with an isoelectric point of 2.4 to 3.3 had an apparent m.w. of 65,000 (2nd day 3-MIF). The other species with an isoelectric point of 4.3 to 5.6 had an apparent m.w. of 23-43,000 (2nd day pH 5-MIF). Upon centrifugation in CsCl density gradients, the density (rho 25 of 1.314 to 1.414 g/ml) of both species was found to be greater than that of the pure protein, 125I-HSA. In addition, both species were chymotrypsin and neuraminidase sensitive but not trypsin sensitive, further suggesting their glycoprotein nature.