A common epitope is recognized by monoclonal antibodies prepared against purified human neutrophil Fc gamma RIII (CD16)

Abstract

Fc gamma RIII is one of two Fc gamma R constitutively expressed by human neutrophils. We have prepared a panel of anti-Fc gamma RIII mAb following immunization of mice with Fc gamma RIII purified from human neutrophils. Ten mAb which reacted with neutrophils, NK cells, and monocyte-derived macrophages were produced. Immunohistochemical staining demonstrated that these mAb also identified macrophages in the red pulp of spleen. Competitive cross-inhibition binding assays demonstrated that nine of the ten mAb reacted with a common epitope that is spatially associated with the ligand binding site. These nine mAb blocked the binding of immune complexes to neutrophils by 65 to 90%. In addition, two other anti-CD16 mAb, which also blocked immune complex binding to neutrophils, inhibited the binding of each of these nine mAb to neutrophils. One of the mAb produced here, 214.1, failed to block immune complex binding. In addition to immunoprecipitating the native Fc gamma RIII glycoprotein, mAb 214.1 was capable of immunoprecipitating a 28-kDa polypeptide following deglycosylation of Fc gamma RIII isolated from neutrophils. The results of cross-competition experiments suggest that mAb 214.1 may recognize the epitope identified by mAb BW209/2. Thus mAb 214.1 identifies a polypeptide epitope distinct from the ligand binding site of Fc gamma RIII on neutrophils.