GPI-anchor deficiency in myeloid cells causes impaired FcγR effector functions

Abstract

Signaling by transmembrane immunoglobulin G (IgG)-Fc receptors (FcγRs) in response to ligand involves association with membrane microdomains that contain glycosyl phosphatidylinositol (GPI)-anchored proteins. Recent in vitro studies showed enhancement of fcγR signaling by forced monoclonal antibody-mediated cocrosslinking with various GPI-anchored proteins. Here, the possibility that GPI-anchored proteins are involved in normal physiologic FcγR effector functions in response to a model ligand was studied using myeloid-specific GPI-anchor-deficient mice, generated by CreloxP conditional targeting. GPI-anchor-deficient primary myeloid cells exhibited normal FcγR expression and binding or endocytosis of IgG-immune complexes (IgG-ICs). Strikingly, after stimulation with IgG-ICs, tumor necrosis factor-α release, dendritic cell maturation, and antigen presentation were strongly reduced by GPI-anchor deficiency. Tyrosine phosphorylation of the FcR α-chain in response to IgG-IC was impaired in GPI-anchor-deficient cells. Myeloid GPI-anchor deficiency resulted in attenuated in vivo inflammatory processes during IgG-IC-mediated alveolitis. This study provides the first genetic evidence for an essential role of GPI-anchored proteins in physiologic FcγR effector functions in vitro and in vivo. © 2004 by The American Society of Hematology.