Active and passive re-expression of Fc gamma receptors on human lymphocytes.

Modulation of receptors for IgG (Fc gamma R) on human lymphocytes was induced by the interaction with erythrocyte-IgG antibody (EAG) complexes followed by incubation at 37 degrees C. The re-expression of Fc gamma R could be achieved by two independent processes. (a) Active synthesis, susceptible to inhibition by puromycin or cycloheximide was shown to peak 4 to 6 h after removal of EAG complexes; it required addition of at least 2% fetal calf serum. (b) Insertion of soluble Fc gamma R into the membrane of modulated lymphocytes was shown to occur within 20 min of contact between cells and Fc gamma R-containing supernatants; it was not altered by protein synthesis inhibitors. Fc gamma R-like material, spontaneously released by unstimulated peripheral blood lymphocytes or by polymorphonuclear cells, was taken up by modulated lymphocytes. This soluble material was fully absorbed on polymerized human IgG; it was non-dialyzable, thermolabile (56 degrees C, 30 min) and partially destroyed by freezing and thawing; it was recovered as two broad peaks from chromatography on polyacrylamide gel; it was shown to bind to both T and non-T Fc gamma R-bearing lymphocytes capable of forming EAG rosettes before modulation; and it could be inserted into allogeneic lymphocytes. These results remonstrate that the Fc gamma R structure bears two active sites, one binding to the Fc gamma and the other to the surface of EAG rosette-forming cells. Rapid release of soluble Fc gamma R from the cells and their possible insertion into the membrane may have important implications with respect to the biological functions associated with these receptors.