Two Migration Inhibitory Factors with Different Chromatographic Behavior and Isoelectric Points

Migration inhibitory factor (MIF), produced by stimulation of guinea pig lymph node cells with concanavalin A, was fractionated by Sephadex G-100 gel filtration, sucrose density gradient electrophoresis, and isoelectrofocussing. Two distinct species were identified and separated. One, pH 3-MIF, has an isoelectric point of 3.0 to 4.5 and elutes from Sephadex G-75 columns with molecules having an apparent m.w. of 65,000 (Kd of 0.05 to 0.12). The other, pH 5-MIF, has an isoelectric point of 5.0 to 5.5 and elutes with molecules having an apparent m.w. between 25,000 and 43,000 (Kd of 0.15 to 0.23).