Human leukocyte inhibitory factor (LIF): a lymphocyte mediator with esteratic properties.

Sensitized human or guinea pig lymphocytes stimulated by specific antigen or nonspecifically by mitogens elaborate a soluble leukocyte inhibitory factor (LIF) that selectively inhibits the random migration of polymorphonuclear (PMN) leukocytes. LIF has the properties of a protein and is unique among lymphocyte mediators because of its esterase nature. While its natural substrate on PMN leukocytes is unknown, a synthetic amino acid derivative ([3H]benzoyl arginine ethyl ester) has been shown to be capable of serving as an artificial substrate. Through the use of selective esterase inhibitors it may eventually be possible to develop a biochemical assay for its detection in lieu of the biologic assay. LIF-containing supernatants have been shown to enhance a number of PMN leukocyte functions, including adherence, phagocytosis, metabolism, and electrophoretic mobility. In a chemotactic assay, LIF was found to induce the release of a low molecular weight peptide (neutrophil immobilization factor) from PMN leukocytes which decreased their spontaneous random movement and directed movement in the presence of a chemoattractant. This latter pathway may provide an amplification of LIF activity on the migration of PMN leukocytes.