The 70-90,000 molecular weight (MW) alpha (alpha) component of the human lymphotoxin (LT) system has been purified to electrophoretic homogeneity. The alpha LT containing supernatants were obtained from a phorbol myristate (PMA) stimulated cloned continuous human B lymphoblastoid cell line IR 3.4. Supernatants were subjected to a biochemical separation scheme that consisted of chromatography on control pore glass beads, DEAE ion-exchange chromatography, lentil-lectin affinity chromatography, and electrophoresis on 7% native preparative polyacrylamide gels. The specific activity of the alpha LT in the final fractions was from 10(7) to 5 X 10(7) units of LT activity/mg protein. Approximately 3 to 5% of the initial alpha LT was recovered in the final fractions and a purification factor of 25,000 to 30,000 fold was required to achieve homogeneity. The alpha LT preparation from preparative PAGE exhibited concident migration of bioactivity and radioactivity on 5 and 7% native PAGE tube gels. Only a single protein peak was observed when the radiolabeled alpha LT was subjected to a two-dimensional SDS-reducing slab gel.
