The anti-FcγRIII MAb 3G8 induces neutrophil activation via a cooperative action of FcγRIIIb and FcγRIIa

Abstract

Human neutrophils express two types of Fcγ receptors, the transmembrane FcγRIIa and the glycan-phosphatidylinositol-anchored FcγRIIIb, that show synergism in provoking a cellular response. To analyse further the requirements for this synergism to occur we used the monoclonal antibody 3G8, directed against FcγRIII This antibody is able to induce neutrophil activation, as measured by an increase in the intracellular free Ca 2+ concentration and homotypic neutrophil aggregation, but only when the Fe part of the antibody is able to interact with FcγRIIa. We observed that binding of the Fab parts of 3G8 mAb to two FcγRIIIb molecules and binding of the Fc part to one FcγRIIa molecule is required, because a bispecific antibody, 2B1, in which only one 3G8 Fab is present, did not induce neutrophil activation. Moreover, engagement of one FcγRIIa molecule and two FcγRIIIb molecules on the same cell is instrumental to achieve activation of the mAb 3G8. The activation of neutrophils by the 3G8 antibody represents a further example of synergistic activation of neutrophils via Fcγ receptors.