Platelet-derived neutrophil adherence-inhibiting factor in humans

The effect of constituents of human platelets on leukocyte adherence was examined. Adherence-inhibiting factors (AIFs), which strongly inhibited neutrophil adherence to glass, were present in both cytosol and granule fractions of human platelets. On the Superose 6 gel chromatography (Pharmacia LKB Biotechnology, Uppsala, Sweden), the granular AIF was eluted as a single active peak (2,600 Kd), whereas cytosolic AIFs were eluted at two different positions (2,600 and 480 Kd). When platelets were stimulated by thrombin, granular AIF was released extracellularly without releasing a cytosolic marker. Using DE32 anion exchange chromatography and Superose 6 gel filtration, granular AIF was completely purified. Sodium dodecyl sulfate- polyacrylamide gel electrophoresis analysis suggests that granular AIF consists of two subunits with molecular masses of approximately 340 and 190 Kd. Purified granular AIF inhibited human neutrophil adherence to glass, plastic, and type IV collagen-coated plastic, whereas it did not affect monocyte adherence. These results suggest that granular AIF inhibits neutrophil adherence not only via nonspecific adsorption sites, but also via type IV collagen receptors.