Abstract
Guinea-pig platelets contain adherence-inhibiting factor (AIF) in the granule and cytosol fractions. In this study, subgranular localization and properties of granular AIF were examined.
Two AIF molecules, designated AIF-I (about void volume of the column) and AIF-II (about 12 kDa), were eluted, when platelet-granule fraction was subjected to a superose 12 gel chromatography. The neutrophil adherence-inhibiting activity of AIF-I was about fivefold higher than that of AIF-II . AIF-I was sensitive to diisopropylfluoro-phosphate (DFP) and localized in lysosomes, whereas AIF-II was insensitive to DFP and localized in α-granules. Both AIF-I and AIF-II inhibited neutrophil adherence to glass and polystyrene surfaces, but did not inhibit neutrophil adherence to fibronectin-coated polystyrene surface. AIF-II hardly affected neutrophil adherence to type IV collagen-coated polystyrene surface. In contrast, AIF-I significantly inhibited type IV collagen mediated neutrophil adherence.
These results suggest that AIF-II only inhibits neutrophil adherence via nonspecific adsorption sites, whereas AIF-I inhibits neutrophil adherence both via nonspecific adsorption sites and type IV collagen receptors.
