Purification and partial characterization of platelet-derived adherence-inhibiting factor in guinea pig

Purification and partial characterization of adherence-inhibiting factor (AIF) of platelet-granule fraction in guinea pig were studied. When freshly prepared platelet-granule fraction was subjected to a gel filtration, two neutrophil adherence-inhibiting peaks, designated AIF-I (2,800 kDa) and AIF-II (12 kDa), appeared. AIF-I was sensitive to diisopropylfluorophosphate (DFP) and originated from lysosomes, whereas AIF-II was insensitive to DEP and localized in alpha-granules. Both AIFs were released from platelets by a thrombin stimulation. As the total activity of AIF-I was about 5-fold higher than that of AIF-II, AIF-I was purified and characterized. When purified AIF-I was analyzed on SDS-polyacrylamide gel electrophoresis, the 340 kDa protein band and the other large protein band were observed. Under reducing condition, AIF-I was separated into three components (340, 190 and 165 kDa). AIF-I significantly inhibited neutrophil adherence to artificial substrata and to type IV collagen-coated plastic surface, but not to fibronectin- or plasma-coated plastic surfaces, suggesting that AIF-I inhibits neutrophil adherence not only via nonspecific adsorption sites but also via type IV collagen receptors.