HUMAN NEUTROPHILS LOSE THEIR SURFACE FC-GAMMA-RIII AND ACQUIRE ANNEXIN-V BINDING-SITES DURING APOPTOSIS IN-VITRO

We have previously reported that neutrophilic granulocytes rapidly rel ease part of their Fc gamma RIII from the plasma membrane upon in vitr o activation, probably by proteolytic cleavage. In plasma and other bo dy fluids, released or soluble Fc gamma RIII has been found in conside rable amounts. In the present study, neutrophils were kept in maintena nce culture for 18 to 24 hours. Forty percent of the neutrophils compl etely lost Fc gamma RIII, and the remainder of the cells showed a 60% decrease in Fc gamma RIII expression on their surface. Released Fc gam ma RIII was detected in the culture supernatant. Nevertheless, more th an 90% of the cells was viable as judged by hydrolysis of fluorescein diacetate. The presence of interferon gamma, granulocyte colony-stimul ating factor, or granulocyte-macrophage colony-stimulating factor, but not interleukin-3 (IL-3), IL-6, or IL-8, in the culture medium increa sed the number of cells that still expressed Fc gamma RIII. We found t hat this loss of Fc gamma RIII was not the result of cell activation b ut correlated strongly with apoptosis. The Fc gamma RIII-negative subp opulation exhibited typical morphologic changes, such as nuclear conde nsation and DNA fragmentation. Furthermore, this subpopulation appeare d to have acquired the property of binding Annexin V, a calcium-depend ent, phospholipid-binding protein with high affinity for phosphatidyls erine. The external exposure of this phospholipid by cells has been re ported to occur during apoptosis. The property of Annexin V binding wa s not shared by the nonapoptotic, Fc gamma RIII-positive subpopulation . In this respect, we identified binding of Annexin V as an convenient marker for apoptotic cells. Our results indicate that soluble Fc gamm a RIII in body fluids might be derived for a large part from neutrophi ls undergoing apoptosis in the tissues. (C) 1995 by The American Socie ty of Hematology.