RESEARCH ARTICLE Astrocyte-targeted IL-10 production decreases proliferation and induces a downregulation of activated microglia/macrophages after PPT Mireia Recasens | Kalpana Shrivastava | Beatriz Almolda | Berta González | Bernardo Castellano Department of Cell Biology, Physiology and Immunology, Institute of Neuroscience, Universitat Autònoma de Barcelona, Barcelona, Spain Correspondence Beatriz Almolda, Unitat d'Histologia, Torre M5, Facultat de Medicina Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain. Email: beatriz.almolda@uab.cat Funding information Ministerio de Ciencia e Innovación, Grant/ Award Number: BFU2014-55459BFU2017-87843-R; Spanish Ministry of Science and Innovation, Grant/ Award Numbers: BFU2017-87843-R, BFU2014-55459 Abstract When central nervous system (CNS) homeostasis is altered, microglial cells become rapidly activated, proliferate and release a broad range of molecules. Among the plethora of mole- cules involved in the regulation of microglial activation, cytokines are considered crucial. Although production of interleukin-10 (IL-10) has been demonstrated after different types of CNS injuries and associated with protective functions, the specific role played by IL-10 modu- lating microglial cells remains unclear. Hence, the objective of this study was to evaluate the effects of transgenic astrocyte IL-10 production on microglial activation associated with axo- nal anterograde degeneration. To address it, the hippocampal area subjected to perforant pathway transection (PPT) was analyzed by immunohistochemistry (IHC), flow cytometry and protein microarray in transgenic (GFAP-IL10Tg) mice and their corresponding wild types (WT) littermates. Our results demonstrated increased microglial/macrophages density in non- lesioned and PPT-lesioned GFAP-IL10Tg animals when compared with nonlesioned and lesioned WT, respectively. This increase was not due to proliferation, as GFAP-IL10Tg mice showed a reduced proliferation of microglial cells, but was related to an increased population of CD11b+/CD45 high monocyte/macrophages. Despite this higher number, the microglia/ macrophage population in transgenic animals displayed a downregulated phenotype charac- terized by lower MHCII, ICOSL, and CD11c. Moreover, a sustained T-cell infiltration was found in transgenic animals. We strongly suggest these modifications must be associated with indirect effects derived from the influence of IL-10 on astrocytes and/or neurons, which express IL-10R. We finally suggested that TGF-β produced by astrocytes, along with IL-2 and CXCL10 might be crucial molecules mediating the effects of transgenic IL-10. KEYWORDS cytokines, flow cytometry, IL-10R, macrophage infiltration, T-cell 1 | INTRODUCTION Interleukin 10 (IL-10) is one of the most important immunoregulatory cytokines implicated in the immunological responses (Cooper et al., 2008; Moore, de Waal Malefyt, Coffman, & O'Garra, 2001). In the cen- tral nervous system (CNS), IL-10 is upregulated after a wide range of injuries including acute lesions, such as traumatic brain injury (TBI) (Kamm, Vanderkolk, Lawrence, Jonker, & Davis, 2006), as well as chronic neurodegenerative diseases like Alzheimer's disease (Apelt & Schliebs, 2001) and multiple sclerosis (Ledeboer et al., 2003). Both microglial cells and astrocytes (Hulshof, Montagne, De Groot, & Van Der Valk, 2002; Ledeboer et al., 2002) have been described as one of the principal sources of IL-10 in basal conditions as well as after CNS injury. This cytokine is able to exert its action through the IL-10 receptor (IL-10R), which, depending on the circumstance, could be expressed on microglia (Mizuno, Sawada, Marunouchi, & Suzumura, Received: 7 February 2018 Revised: 6 November 2018 Accepted: 12 November 2018 DOI: 10.1002/glia.23573 Glia. 2018;1–18. wileyonlinelibrary.com/journal/glia © 2018 Wiley Periodicals, Inc. 1