Human multipotent mesenchymal stromal cells (MSCs) are clinically applied to treat autoimmune diseases and graft-versus-host disease due to their immunomodulatory properties. Several molecules have been identified to mediate these effects, including constitutively expressed galectin-1. However, there are indications in the literature that MSCs exert enhanced immunosuppressive functions after interaction with an inflammatory environment. Therefore, we analyzed how inflammatory stimuli influence the expression of the galectin network in MSCs and functionally tested the relevance for the immunomodulatory effects of MSCs. We found that galectin-9 was strongly induced in MSCs upon interaction with activated PBMCs. Proinflammatory cytokines, such as interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α), and also ligands of the Toll-like receptors (TLRs) TLR2, TLR3, and TLR4 elicited similar induction of galectin-9 in activated PBMCs. Galectin-9 was not only upregulated intracellularly, but also released by MSCs in significant amounts into the supernatant after exposure to proinflammatory stimuli. In proliferation assays, MSCs with a galectin-9 knockdown lost a significant portion of their antiproliferative effects on T cells. In conclusion, we found that unlike constitutively expressed galectin-1, galectin-9 is induced by several proinflammatory stimuli and released by MSCs. Thus, galectin-9 contributes to the inducible immunomodulatory functions of MSCs.Keywords: Galectin-9 r Immunosuppressive effects r Mesenchymal stromal cells r Proinflammatory stimuli r T-cell proliferation
IntroductionHuman multipotent mesenchymal stromal cells (MSCs) possess immunomodulatory properties. In addition, MSCs migrate to sites Correspondence: Dr. Friederike Gieseke e-mail: gieseke@kinderkrebs-forschung.de of tissue injury or inflammation, where they participate in wound healing [1]. Initially, MSCs were thought to mediate tissue repair because of their differentiation potential. However, it has become more evident that the production of soluble factors is the critical step for tissue repair [2]. In addition, BM-derived MSCs, which are immunosuppressive in vitro and in vivo [3], use soluble factors to mediate these effects at least in vitro [4] Eur. J. Immunol. 2013. 43: 2741-2749 interest for treatment of immune-mediated diseases. In particular, promising results of i.v. infusion of MSCs for treatment of steroid refractory graft-versus-host disease (GvHD) have been observed [5][6][7]. Several soluble molecules are involved in immune suppression mediated by human MSCs, such as prostaglandin E2 (PGE2) [8], indoleamine-2,3-dioxygenase (IDO) [9], heme oxygenase-1 [10], human leukocyte antigen G (HLA-G5) [11], and galectin-1 [12], among others. Furthermore, it was shown that interactions between inflammatory cells and MSCs induce or activate the immunosuppressive properties of MSCs; in this process, interferon-gamma (IFN-γ) appeared to be the most important cytokine [9,13,14].In the present study, we focused on the role of gale...
