Cross-linking of human FcγRIIIb induces the production of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor by polymorphonuclear neutrophils

We have reported that human autoantibodies reacting with the polymorphonuclear neutrophil (PMN)-anchored Fc gamma RIIIb (CD16) protect these cells from spontaneous apoptosis. In this study, we used anti-CD16 F(ab')(2) to delineate the mechanism(s) whereby the PMN life span is extended. As documented using four methods, CD16 cross-linking impeded spontaneous apoptosis, whereas anti-CD18 F(ab')(2) exerted no effect. Incubation of PMNs with anti-CD16 prevented the up-regulation of beta (2) integrins, particularly CD11b, which is the a-chain of complement receptor type 3, but also CD18, which is its beta -chain, as well as CD11a and CD11c. Anti-CD16-conditioned supernatant of PMNs diminished the percentage of annexin V-binding fresh PMNs after another 18 h in culture, whereas the negative control anti-CD18 had no effect. The expression of mRNA for G-CSF and GM-CSF was induced by anti-CD16, followed by the release of G-CSF and GM-CSF in a dose-dependent manner. Anti-G-CSF and anti-GM-CSF mAbs abrogated the antiapoptotic effect of the related growth factors. The delay in apoptosis was accompanied by a down-regulated expression of Bax, and a partial reduction of caspase-3 activity. These data suggest an autocrine involvement of anti-CD16-induced survival factors in the rescue of PMNs from spontaneous apoptosis. Thus, apoptosis of aged PMNs can be modulated by signaling through Fc gamma RIIIb, which may occur in patients with PMN-binding anti-Fc gamma RIIIb autoantibodies.