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A4742 - Mesenchymal Stromal Cells Enhance IgG-Mediated Phagocytosis and Modulate Fcγ Receptor Expression and Binding Activity in Human Macrophages Partly Through Lipoxin A4/IL-10 Pathway
Author Block: R. Rabani1, A. Volchuk1, M. Gupta1, C. H. Masterson1, M. Jerkic1, J. Laffey1, S. Grinstein2, K. Szaszi1, G. F. Curley1; 1St. Michael's Hospital, Toronto, ON, Canada, 2The Hospital for Sick Children, Toronto, ON, Canada.
Introduction: Human Mesenchymal Stem/Stromal Cells (hMSCs) have potential as cell- based therapies for a number of inflammatory conditions including sepsis. MSCs have been reported to attenuate lung injury in mice, partly through production of soluble factors including interleukin 10 (IL-10) and the pro-resolving lipid mediator lipoxin A4 (LXA4). Although some studies have shown that MSCs enhance phagocytosis by macrophages, the molecular events behind this effect is unclear. Thus, this study explored the mechanisms underlying phagocytic response of human macrophages to MSC exposure.
Methods: Human monocyte-derived macrophages or THP-1 macrophages were co-cultured with MSCs in a transwell system for 48h. To assess phagocytosis, macrophages were incubated with serum opsonized zymosan (SOZ) or IgG-opsonized with sheep red blood cells (IgG-SRBCs), and internalization of SOZ and IgG-SRBCs were assessed by fluorescent confocal microscopy. Changes in transcript levels of Fcγ receptors were analyzed by quantitative PCR and protein levels were assessed doing immunofluorescence staining and flow cytometry. To investigate the role of LXA4 in MSCs-induced enhancement of phagocytosis, we used the 15-lypoxygenase inhibitor (PD146176). The importance of production of IL-10 was interrogated by exposure of macrophages to MSCs in the presence of IL-10 neutralizing antibody. Furthermore, frozen lung tissue from a mouse model of lung bacterial sepsis were sectioned and immunoassayed to detect F4/80, a mouse macrophage marker or Fcγ receptor specific antibodies.
Results: MSCs significantly enhanced macrophage phagocytosis of serum-opsonized zymosan and IgG-opsonized sheep red blood cells in vitro. MSC exposure enhanced transcript level and cell surface expression of the activating phagocytic Fcγ receptor FcγRIIa and increased the number of FcγRIII positive macrophages. In contrast, MSC exposure had no effect on the levels of FcγRI, although it significantly enhanced macrophage binding of monomeric human IgG. Enhanced IgG-binding was dependent on MSC production of lipoxin A4 and required IL-10. Importantly, an increase in Fcγ receptor positive cells was also observed in lung tissue from a mouse model of bacterial sepsis treated with MSCs.
Conclusion: Our results demonstrate that MSCs enhance macrophage phagocytosis of IgG-opsonized targets in part by enhancing Fcγ receptor expression or ligand binding efficiency through a LXA4/IL-10 process.
This abstract is funded by St. Michael’s Foundation Translational Innovation Fund and by Government of Ontario, Ministry of Research, Innovation and Science, Early Researcher Award