Amplification of the activity of human leukocyte inhibitory factor (LIF) by the generation of a low molecular weight inhibitor of PMN leukocyte chemotaxis.

Leukocyte inhibitory factor (LIF), which was derived from human peripheral blood lymphocytes by stimulation with concanavalin A ad partially purified by Sephadex G-100 gel filtration, inhibited the in vitro spontaneous migration and chemotaxis of human PMN leukocytes as assessed in a Boyden chamber micropore filter assay. The inhibitory activity was attributed to LIF, a principle defined in terms of its inhibition of PMN leukocyte migration from glass capillary tubes since it was preferentially directed to PMN leukocytes as compared to mononuclear leukocytes, exhibited a size comparable to LIF by gel filtration, and was inactivated by diisopropyl fluorophosphate in parallel with LIF. Incubation of PMN leukocytes with LIF released additional inhibitory activity, distinct from LIF, which resembled the neutrophil-immobilizing factor (NIF) by virtue of its approximate m.w. of 4000 by filtration on Sephadex G-25, inactivation by trypsin digestion, and preferential noncytotoxic inhibition of spontaneous migration and chemotaxis of PMN leukocytes as compared to mononuclear leukocytes. Thus LIF inhibits PMN leukocyte migration both by a direct action on the cells and by an amplification pathway that is mediated by low m.w. chemotactic inhibitors similar to NIF.