Isolation of two polypeptides comprising the neutrophil-immobilizing factor of human leucocytes

Human leucocyte lysosomal polypeptides of mol. wt 4000-5000, which constitute the neutrophil-immobolizing factor (NIF), were isolated from the 22,000 g supernate of sonicates of human neutrophils by filtration on Sephadex G-75. The larger (NIF-1) and smaller (NIF-2) of the polypeptides were resolved by filtration on Bio-Gel P6 and purified to homogeneity by sequential reverse-phase high performance liquid chromatography and paper electrophoresis. The results of analyses of amino acid composition indicated that NIF-1 and NIF-2 are distinct polypeptides composed of an apparent total of 41 and 38 amino acids, respectively. Both NIF polypeptides contain one cysteine and one methionine, lack isoleucine, tyrosine and phenylalanine, and are rich in histidine and proline. The sequence of 20 of the amino-terminal amino acids of both NIF polypeptides is identical, but NIF-2 possesses an additional alanine at the amino-terminus. Highly purified NIF-1 and NIF-2 inhibited human neutrophil random migration and chemotaxis to diverse stimuli in a concentration-dependent manner, with 50% inhibition of chemotaxis by 0.31-1 x 10(-8) M NIF-1 and 1-3 x 10(-7) M NIF-2. Neither NIF polypeptide was cytotoxic for neutrophils, altered neutrophil phagocytosis or release of lysosomal enzymes, or inhibited mononuclear leucocyte chemotaxis. The leucocyte and functional specificity of the NIF polypeptides and the quantitites released upon stimulation of the human leucocytes suggest that the transition to a mononuclear leucocyte population in chronic inflammation may be attributable in part to the NIF derived from the leucocyte infiltrates of acute responses.