Partial characterization of an immunoenhancing factor from allogeneic human lymphocyte cell lines.

The mixing of two histoincompatible human lymphocyte cell lines generated the release of a soluble factor which was capable on non-specifically enhancing the in vitro immune response of normal mouse spleen cells against sheep erythrocytes. The mediator was secreted into the supernatant of the allogeneic cell cultures within 24 h of cultuvation. The human enhancing factor (HEF) must be added to assay cultures on day 2, of a 5-day culture period, for its activity to be manifest. HEF was resistant to DNase, RNase and heating at 56 degrees for 30 min, but was inactivated by exposure to protease or elevated temperature (80 degrees for 30 min). The molecular weight of HEF, purified by ammonium sulphate fractionation, followed by Sephadex gel filtration, DEAE-cellulose chromatography and SDS-polyacrylamide gel electrophoresis, was approximately 38,000 Daltons.