Abstract
Macrophage migration inhibitory factor (MIF) from the guinea pig was recently shown to reside in two discrete and separable proteins referred to as pH 3 MIF and pH 5 MIF. One subfraction of pH 3 MIF has now been purified to apparent homogeneity from supernatants of stimulated lymph node cells. To monitor purification, biosynthetically radiolabeled MIF was prepared. Sensitized lymphocytes were stimulated in the presence of [3H]leucine by concanavalin A to produce radiolabeled mediators. MIF was purified approximately 30,000-fold from the culture fluid by using gel filtration, sucrose density gradient electrophoresis, isoelectric focusing, and hydrophobic affinity chromatography. This procedure yielded a single 3H-labeled polypeptide with an apparent Mr of 35,000 that coincides with MIF activity.