INTRACELLULAR EXPRESSION OF FC-GAMMA-RIII (CD16) AND ITS MOBILIZATIONBY CHEMOATTRACTANTS IN HUMAN EOSINOPHILS

We characterized the existence, translocation, and reabsorption during cellular activation of a constitutively expressed intracellular CD16 in the human eosinophil, By two-color flow cytometry, we showed that 6 .5 +/- 0.3% of nonpurified eosinophils expressed surface CD16, After d igestion with phosphotidylinositol-specific phospholipase C, surface C D16 on both neutrophils and eosinophils decreased substantially, sugge sting that eosinophil CD16 is a glycosyl-phosphatidylinositol-linked i soform. However, CD16 was substantially expressed intracellularly in h uman eosinophils, Epitope-specific binding to CLB-gran11 mAb from non- NA2/NA2 donors demonstrated that intracellular eosinophil CD16 also di ffered from the transmembrane isoform of CD16 expressed on NK cells or macrophages, Western blot analysis performed with 3G8 or DJ130c mAb s howed a broad band at similar to 65 to 80 kDa, which was the same as n eutrophil CD16 from the same NA2/NA2 donors. Upon stimulation by chcmo attractants C5a, FMLP, or platelet-activating-factor, eosinophilic int racellular CD16 was rapidly translocated to the eosinophil surface, ex pressed maximally at 30 s, and then gradually disappeared from the cel l surface during the next 10 min. Intracellular flow cytometry of stim ulated eosinophils and sandwich ELISA of stimulated eosinophil superna tants demonstrated that the disappearance was due to its rapid release into medium and reabsorption by the cells. Our data identify a CD16B that is consistently expressed intracellularly but only rarely on the surface of nonactivated human eosinophils, This CD16 is transiently ex pressed during stimulation by chemoattractants.