Further Studies on Migration Inhibitory Factor (MIF): Evidence for its Glycoprotein Nature

Abstract

Migration inhibitory factor (MIF) obtained from sensitized guinea pig lymph node lymphocytes that had been stimulated by specific antigen (o-chlorobenzoyl-bovine γ globulin) was characterized by enzymatic treatment and isopycnic centrifugation in a CsCl density gradient. MIF incubated with water-insoluble chymotrypsin lost its biologic activity. Further, neuraminidase, which hydrolyzes terminal sialic acid, abolished MIF activity. When MIF was centrifuged in CsCl density gradients, it had a buoyant density (ρ25 = 1.430) slightly greater than that of the protein reference substance (ρ25 = 1.352), which is consistent with its being a glycoprotein. The results indicated that MIF is a glycoprotein and that sialic acid is necessary for its biologic activity.