Localization of neutrophil adherence-inhibiting factor in guinea pig platelets

The effect of constituents of guinea pig platelets on neutrophil adherence was examined. The platelet sonicate supernatant contained adherence-inhibiting activity which strongly inhibited neutrophil adherence to glass. When the platelet sonicate supernatant was treated with neuraminidase or trypsin, the adherence-inhibiting activity was significantly inhibited, suggesting that the adherence-inhibiting factor (AIF) is a glycoprotein. The subcellular fractionation experiments indicated that the AIF activity was present at about 40% in both the cytosol and granule fractions. From the Sephadex G-200 gel filtration analysis, AIF of cytosol fraction and granule fraction proved to be different molecules, with molecular masses of about 230 and 12 kDa, respectively. When platelets were stimulated with thrombin, about 20% of total AIF was released extracellularly without the release of the cytoplasmic enzyme lactate dehydrogenase. These results suggest the possibility that a biologically active substance, AIF, is released from platelets in response to stimuli and regulates neutrophil functions through interference with neutrophil adherence.