Critical Role of Macrophage FcγR Signaling and Reactive Oxygen Species in Alloantibody-Mediated Hepatocyte Rejection

Abstract

Humoral alloimmunity negatively impacts both short- and long-term cell and solid organ transplant survival. We previously reported that alloantibody-mediated rejection (AMR) of transplanted hepatocytes is critically dependent on host macrophages. However, the effector mechanism(s) of macrophage-mediated injury to allogeneic liver parenchymal cells is not known. We hypothesized that macrophage-mediated destruction of allogeneic hepatocytes occurs by cell-cell interactions requiring Fcγ receptors (FcγRs). To examine this, alloantibody-dependent hepatocyte rejection in CD8-depleted wild-type and Fcγ chain KO (lacking all functional Fcγ receptors) transplant recipients was evaluated. Alloantibody-mediated hepatocellular allograft rejection was abrogated in recipients lacking FcγR compared to wild-type recipients. We also investigated anti-FcγRI mAb, anti-FcγRIII mAb, and inhibitors of intracellular signaling [to block phagocytosis, cytokines, and reactive oxygen species (ROS)] in an in vitro alloantibody-dependent, macrophage-mediated hepatocytoxicity assay. Results showed that in vitro alloantibody-dependent, macrophage-mediated hepatocytotoxicity was critically dependent on FcγRs and ROS. The adoptive transfer of wild-type macrophages into CD8-depleted FcγR-deficient recipients was sufficient to induce AMR, while adoptive transfer of macrophages from Fcγ chain KO mice or ROS-deficient (p47 KO) macrophages was not. These results provide first evidence that alloantibody-dependent hepatocellular allograft rejection is mediated by host macrophages through FcγR signaling and ROS cytotoxic effector mechanisms. These results support the investigation of novel immunotherapeutic strategies targeting macrophages, FcγRs and/or downstream molecules, including ROS, to inhibit humoral immune damage of transplanted hepatocytes and perhaps other cell and solid organ transplants.

Distinct hepatic immunological patterns are associated with the progression or inhibition of hepatocellular carcinoma

“…In fact, IL-17-producing Th17 cells are reported to exacerbate tumorigenesis and liver damage (Chang, 2019), while IL-22-producing Th17 cells could facilitate recovery of the liver from injury (Arshad et al, 2020). In regard to macrophages, M1 macrophages, while displaying anti-tumor function, could also cause liver damage (Zimmerer et al, 2018). Very recent analysis revealed that M1 macrophages with an M1 > M2 pattern were associated with aggressive cancer biology without any survival benefit (Oshi et al, 2020).…”

Microvascular Inflammation of the Renal Allograft: A Reappraisal of the Underlying Mechanisms

“…These are phagocytosis, antigen presentation, cytokine production and killing of infected host cells via ADCC. In transplantation, in vitro and in vivo experiments have shown that alloantibody-dependent allograft rejection is mediated by host macrophages through FcγRs and reactive oxygen species (ROS)-related cytotoxic effector mechanisms ( 165 ). In biopsies of kidney allografts, CD68 and CD163 are two main markers used to follow the presence of tissue-resident macrophages and monocyte-derived macrophages ( 151 , 152 , 166 ).…”

Reactive Oxygen Species in Autoimmune Cells: Function, Differentiation, and Metabolism

“…Further, ROS is an important contributor to marked up-regulation of the inhibitory costimulatory molecule, PD-L1, leading to immune escape ( 25 ); interestingly, the antioxidants, N-acetyl cysteine (NAC) and apigenin, can offset this change ( 26 ). In addition, alloantibody-FcγR I/FcγR III-dependent ROS production in macrophages is an important mediator of humoral immune damage during liver graft rejection ( 27 ). Opsonization of IgG on IFN-γ-activated macrophages led to diminished phagosomal processing of proteins in a PKC/Syk- NOX2-dependent manner, which occurs at the level of the individual phagosome ( 28 ).…”