Partial Purification of Human Lymphocyte Activating Factor

Abstract

Lymphocyte Activating Factor (LAF) is a T lymphocyte stimulant released by human monocytes cultured for 18–24 hours in tissue culture medium containing 5% human serum and the non-specific immunostimulant lipopoly-saccharide. The purification of LAF is essentially the separation of low MW LAF (∼13.000) from the human serum proteins required for production of the activity. Hollow fiber ultrafiltration has been found to effect a rapid separation of low MW LAF from serum proteins, but with a yield of only 20% of the original activity. Isoelectric focusing (IEF) efficiently separates LAF from all traces of human serum, resulting in a purified sample containing no measurable protein and revealing no bands on polyacrylamide gels. The IEF purified material is about 2% of the low MW activity present in the unfractionated culture medium and is highly active in the biological assay system.