RESEARCH ARTICLE CD11c-Positive Cells from Brain, Spleen, Lung, and Liver Exhibit Site-Specific Immune Phenotypes and Plastically Adapt to New Environments Kerstin Immig, 1 Martin Gericke, 1 Franziska Menzel, 1 Felicitas Merz, 1 Martin Krueger, 1 Fridtjof Schiefenh€ ovel, 1 Andreas L € osche, 2 Kathrin J€ ager, 2 Uwe-Karsten Hanisch, 3 Knut Biber, 4 and Ingo Bechmann 1 The brain’s immune privilege has been also attributed to the lack of dendritic cells (DC) within its parenchyma and the adja- cent meninges, an assumption, which implies maintenance of antigens rather than their presentation in lymphoid organs. Using mice transcribing the green fluorescent protein under the promoter of the DC marker CD11c (itgax), we identified a juxtavascular population of cells expressing this DC marker and demonstrated their origin from bone marrow and local micro- glia. We now phenotypically compared this population with CD11c/CD45 double-positive cells from lung, liver, and spleen in healthy mice using seven-color flow cytometry. We identified unique, site-specific expression patterns of F4/80, CD80, CD86, CX3CR1, CCR2, FLT3, CD103, and MHC-II. Furthermore, we observed the two known CD45-positive populations (CD45 high and CD45 int ) in the brain, whereas liver, lung, and spleen exhibited a homogeneous CD45 high population. CD11c-positive microglia lacked MHC-II expression and CD45 high /CD11c-positive cells from the brain have a lower percentage of MHC-II- positive cells. To test whether phenotypical differences are fixed by origin or specifically develop due to environmental fac- tors, we transplanted brain and spleen mononuclear cells on organotypic slice cultures from brain (OHSC) and spleen (OSSC). We demonstrate that adaption and ramification of MHC-II-positive splenocytes is paralleled by down-regulation of MHC-II, whereas brain-derived mononuclear cells neither ramified nor up-regulated MHC-II in OSSCs. Thus, brain-derived mononu- clear cells maintain their MHC-II-negative phenotype within the environment of an immune organ. Intraparenchymal CD11c- positive cells share immunophenotypical characteristics of DCs from other organs but remain unique for their low MHC-II expression. GLIA 2014;00:000–000 Key words: Key words CD11c-positive cells, immune privilege, microglia Introduction D endritic cells (DC) were first described in 1973 (Stein- man and Cohn, 2007) and represent key players in the initiation of the innate and adaptive immune responses. They are specialized antigen-processing and antigen-presenting cells (APCs), which are capable of migration to T-cell zones where they present antigens and activate na € ıve T-cells during infec- tion (Steinman et al., 2003b). Under steady state conditions, immature DCs are important for peripheral tolerance, dele- tion of T-cells (Mohammad et al., 2012; Steinman et al., 2003a) or expansion of regulatory T-cells (Proietto et al., 2008). Different subsets of DCs were described in lymphoid tissues (lymph nodes and spleen) and nonlymphoid organs, such as liver and lung (Mesnil et al., 2012; Nakamoto et al., 2012; van Rijt, 2005). However, besides their function, murine DCs are mainly distinguished by their expression of View this article online at wileyonlinelibrary.com. DOI: 10.1002/glia.22771 Published online Month 00, 2014 in Wiley Online Library (wileyonlinelibrary.com). Received Sep 3, 2014, Accepted for publication Nov 6, 2014. Address correspondence to Ingo Bechmann, Institute of Anatomy, Medical Faculty, Leipzig University, Liebigstraße 13, 04103, Leipzig, Germany. E-mail: Ingo.Bech- mann@medizin.uni-leipzig.de From the 1 Institute of Anatomy, Leipzig University, Leipzig, Germany; 2 IZKF-FACS-Core Unit, Leipzig University, Leipzig, Germany; 3 Institute of Neuropathology, University of G€ ottingen, G€ ottingen, Germany; 4 Department of Psychiatry and Psychotherapy, Section of Molecular Psychiatry, University of Freiburg, Freiburg, Germany Additional Supporting Information may be found in the online version of this article. V C 2014 Wiley Periodicals, Inc. 1