Differential Effect of Cytokine Treatment on Fcα Receptor I- and Fcγ Receptor I-Mediated Tumor Cytotoxicity by Monocyte-Derived Macrophages

Abstract

Macrophages represent an important effector cell for Ab-mediated tumor therapy. Previous studies have documented that cytokines can influence Fc receptor (FcR) expression and function. In this study we examined the tumoricidal activities of the type I receptors for IgG (FcγRI) and the IgA FcR (FcαRI) on monocyte-derived macrophages (MDM) cultured in the presence of IFN-γ, M-CSF, or GM-CSF. Bispecific Abs were used to target a Her2/neu breast carcinoma cell line, SKBR-3, to FcαRI or FcγRI on MDM. Although FcαRI and FcγRI share a common signaling pathway contingent on association with the γ-chain (FcRγ subunit), a marked difference in their efficiency in mediating tumoricidal functions was seen in response to specific cytokines. M-CSF- and GM-CSF-treated MDM mediated efficient phagocytosis of SKBR-3 cells by FcαRI and FcγRI; however, IFN-γ-treated MDM phagocytosed tumor cells only with the FcγRI-directed bispecific Abs. Similarly, IFN-γ-cultured MDM lysed tumor cells more efficiently via FcγRI then by FcαRI as measured in Ab-dependent cellular cytotoxicity assays. Conversely, GM-CSF-treated MDM mediated more efficient lysis of tumor cells via FcαRI than FcγRI, while M-CSF-cultured MDM were relatively less efficient in mediating Ab-dependent cellular cytotoxicity through either receptor. With the exception of IFN-γ-mediated enhancement of FcγRI expression and FcγRI γ-chain complexes, the regulation of FcγRI- or FcαRI-mediated activity occurred without significant change in either receptor expression or total complexes with γ subunit. These data suggest that the efficiency of Ab-mediated tumor therapy, which depends on FcR effector cell functions, may be modified by the use of specific cytokines.