and Increased Plasma Membrane Expression of the Glycoprotein

Mol , a glycoprotein heterodimer (gp 1 55,95) that functions as an adhesion promoting molecule and as the C3bi receptor of human myeloid cells, is expressed in increased amounts in the plasma membrane after exposure of polymorphonuclear leukocytes (PMNs) to various stimuli. Previous studies have suggested that secondary granules represent an intracellular pool of Mol that, upon degranulation, fuse with the plasma membrane resulting in a tenfold increase in surface expression of Mel . To determine the intracellular location of Mel , we monitored Mel expression by immunofluorescence and compared it to the release of myeloperoxidase (MPO. a marker for the primary granules), vitamin B12 binding protein (B12BP, secondary granules), and gelatinase (gelatinase-containing organelles) following exposure to various stimuli. Human neutrophils stimulated with 20 mmol/L fluoride for 16