Human MEMs are a distinct high IL-6 producing macrophage subset with anti-inflammatory and radioprotective properties in vivo

Abstract

Abstract Macrophages (MØs) can polarize into subsets of “pro-inflammatory” (M1) MØs or “anti-inflammatory” (M2) MØs. Previously we described a unique population of MØs, termed human mesenchymal stem cell (MSC)-educated MØs (MEMs). In this study, we hypothesize that MEMs have potential to attenuate inflammation and promote tissue repair in vivo based on their immunophenotype and secretome. MEMs were generated by isolating monocytes from human peripheral blood and culturing them into MØs, followed by a co-culture with bone marrow-derived MSCs. RNA-Seq analysis showed genes associated with epithelial-mesenchymal transition, collagen formation, tissue development, and cell-cell adhesion were positively correlated with MEMs, while genes associated with oxidative phosphorylation were negatively correlated as compared to M1 MØs. We found increased expression of 8 genes implicated in wound healing, as well as genes representing remodeling enzymes, growth factors and the cytoskeleton. RT-PCR verified MEMs have increased CD206 (p<0.0001), IL-1β (p<0.001), TGFβ (p<0.001) and arginase-1 (p< 0.05), as well as increased IL-6 (p<0.0001) and CD73 (p<0.001) expression. MEMs produced over 4x greater amounts of IL-6 as compared to M2 MØs by ELISA (p<0.001), which could be enhanced with LPS stimulation (p<0.0001) or attenuated by inhibition of COX-2 (p<0.05), arginase-1 (p<0.01) or JAK1/JAK2 (p<0.05). In vivo, MEMs improved survival against lethal GVHD (p<0.01), in part by reducing T cell proliferation (p<0.001). MEMs also enhanced survival of mice from lethal radiation injury (p<0.01), in part by inducing host fibroblast proliferation (p<0.01). MEMs are a unique MØ subset with therapeutic potential for inflammatory disorders.