Human Leukocyte Migration Inhibitory Factor (LIF)

Abstract

The activity of LIF obtained from Sephadex-G-100-chromatographed supernatants of concanavalin-A-stimulated human lymphocytes was suppressed by 2 synthetic serine esterase and serine protease inhibitors [di-isopropylfluorophosphate (DFP) and phenylmethylsulfonyl fluoride (PMSF)]. LIF activity was also reduced by the naturally occurring protease inhibitors soybean trypsin inhibitor and aprotinin. The observed effect of DFP and PMSF was irreversible, since elimination of the inhibitors by dialysis did not restore LIF activity. The effect of PMSF was dose-, time- and temperature-dependent, and hydrolytic products of PMSF as well as NaF were inactive in blocking LIF. LIF may act as a serine esterase or a serine protease, or both of these; this putative enzyme is probably present in an activated form in supernatants from mitogen-stimulated mononuclear cells.