The immunomodulatory properties of adult skin-derived precursor Schwann cells: implications for peripheral nerve injury therapy Jo Anne Stratton, 1,2,3 Prajay T. Shah, 1,2,3 Ranjan Kumar, 1,2,3 Morgan G. Stykel, 2,3 Yuval Shapira, 1 Joey Grochmal, 1,3 Gui Fang Guo, 1,3 Jeff Biernaskie 2,3 and Rajiv Midha 1,3,4 1 Department of Clinical Neurosciences, University of Calgary, Calgary, AB, Canada 2 Comparative Biology and Experimental Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada 3 Hotchkiss Brain Institute, Calgary, AB, Canada 4 Cumming School of Medicine, University of Calgary, Calgary, AB, Canada Keywords: cytokines, interleukin-6, macrophages, neutralisation, rat Abstract Skin-derived precursor Schwann cell (SKPSC) therapy has been identified as a potentially beneficial treatment for peripheral nerve injuries. One hypothesised mechanism by which SKPSCs enhance recovery is via the modulation of macrophages. In the present study, we investigated the immunomodulatory properties of adult rat SKPSCs, and demonstrated that these cells expressed a bat- tery of cytokines, including interferon-c (IFN-c), interleukin (IL)-1b, and, most abundantly, IL-6. Whereas macrophages exposed to depleted or fibroblast-conditioned medium secreted minimal amounts of tumor necrosis factor-a (TNF-a), in the presence of SKPSC-conditioned medium, macrophages secreted > 500 pg/mL TNF-a. Following the transplantation of SKPSCs into injured rat sciatic nerves, we observed an SKPSC density-dependent increase in the number of macrophages (Pearson’s r = 0.66) and an SKPSC density-dependent decrease in myelin debris (Pearson’s r = –0.68). To determine the effect of IL-6 in a proinflammatory context, macrophage cultures were primed with either lipopolysaccharide (LPS)/IFN-c/IL-1b or LPS/IFN-c/IL-1b + IL-6, and this showed a 212% and 301% increase in the number of inducible nitric oxide synthase (iNOS)-positive proinflammatory macrophages respectively. In contrast to neurons exposed to conditioned medium from unprimed macrophages, neurons treated with conditioned medium from proinflammatory-primed macrophages showed a 13–26% reduction in neurite outgrowth. Anti-IL-6 antibody combined with SKPSC transplant therapy following nerve injury did not alter macrophage numbers or debris clearance, but instead reduced iNOS expression as compared with SKPSC + IgG-treated rats. SKPSC + anti-IL-6 treatment also resulted in a two-fold increase in gastrocnemius compound muscle action potential amplitudes as compared with SKPSC + IgG treatment. Understanding the mech- anisms underlying immunomodulatory aspects of SKPSC therapy and developing approaches to manipulate these responses are important for advancing Schwann cell-based therapies. Introduction Peripheral nerve injury (PNI) affects 2.8% of trauma patients (Noble et al., 1998), with severe PNI insults resulting in long-lived perma- nent disability (Siemionow & Brzezicki, 2009). Currently, the use of cell therapy for these patients is propitious, with trials using cell transplants in spinal cord injury already demonstrating its efficacy (Guest et al., 2013; Tabakow et al., 2014). Cell therapy with Schwann cells (SCs) derived from skin-derived SC precursors (SKPSCs) has great potential (Biernaskie et al., 2006, 2007; Biernaskie & Miller, 2010; Khuong et al., 2014). Two major arguments in favor of SKPSC therapy are as follows: (i) SKPSCs can be derived conveniently from adult skin, making harvesting a relatively non-invasive procedure, avoiding the need for anti-rejec- tion drugs; and (ii) SKPSCs are highly proliferative glial cells, and have already been shown to enhance functional recovery after rodent spinal cord injury and PNI (Biernaskie et al., 2007; Khuong et al., 2014). Although the mechanisms underlying the improved functional outcome following SKPSC transplantation are complex, Khuong et al. (2014) demonstrated a striking reduction in the amount of myelin debris in SKPSC-transplanted nerves, suggesting that one of the mechanisms by which SKPSCs enhance recovery might be modulation of the immune response. In particular, it was proposed that SKPSCs might enhance macrophage recruitment to injury sites, resulting in more efficient debris clearance (Martini et al., 2008). It is well known that the inflammatory response following injury, which is based on cytokine and chemokine signaling, is a Correspondence: Jeff Biernaskie, 2 Comparative Biology and Experimental Medicine, as above. E-mail: jabierna@ucalgary.ca J.A.S and P.T.S. contributed equally to this work. Received 19 March 2015, revised 11 June 2015, accepted 23 June 2015 © 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd European Journal of Neuroscience, Vol. 43, pp. 365–375, 2016 doi:10.1111/ejn.13006