Partial purification of human lymphocyte-activating factor (LAF) by ultrafiltration and electrophoretic techniques

Lymphocyte-activating factor (LAF) has been produced by culturing human peripheral blood leukocytes in the presence of lipopolysaccharide and autologous human serum. The major LAF activity, identifiable by Sephadex chromatography (m.w. 13,000) was separated from most serum proteins in the culture medium by ultrafiltration with a hollow fiber device. Sucrose gradient isoelectric focusing of the concentrated ultrafiltrate yielded a single peak of LAF activity with an average isoelectric point of pH 6.8. Semi-preparative polyacrylamide gel electrophoresis of the isoelectric focusing sample resulted in separation of the LAF activity from detectable amounts of serum proteins. The recovered LAF activity was estimated to be purified more than 16,000-fold and is judged to be active in submicrogram amounts.