1 3 Acta Neuropathol (2013) 126:525–535 DOI 10.1007/s00401-013-1155-0 ORIGINAL PAPER Characteristics of differentiated CD8 + and CD4 + T cells present in the human brain Joost Smolders · Ester B. M. Remmerswaal · Karianne G. Schuurman · Jeroen Melief · Corbert G. van Eden · René A. W. van Lier · Inge Huitinga · Jörg Hamann Received: 15 May 2013 / Revised: 23 June 2013 / Accepted: 9 July 2013 / Published online: 24 July 2013 © Springer-Verlag Berlin Heidelberg 2013 cells expressing the lymph node-homing receptor CCR7. Despite the late-differentiated phenotype, CC T cells had high expression of the IL-7 receptor α-chain CD127 and did not contain the neurotoxic cytolytic enzymes perforin, granzyme A, and granzyme B. We postulate that CNS T cells make up a population of tissue-adapted differenti- ated cells, which use CX3CR1 and CXCR3 to home into the perivascular space, use IL-7 for maintenance, and lack immediate cytolytic activity, thereby preventing immuno- pathology in response to low or non-specific stimuli. The presence of these cells in this tightly regulated environment likely enables a fast response to local threats. Our results will enable future detailed exploration of T-cell subsets in the brain involved in neurological diseases. Keywords Human brain · Immune surveillance · T cells · Flow cytometry Introduction The central nervous system (CNS) has long been regarded as an immune-privileged site. This idea was grounded on the observation that the brain does not reject foreign tissue grafts [29]. However, with time, this view has been modi- fied, and the CNS is currently regarded more an immune- specialized organ, which is under surveillance of peripheral leukocytes that are tightly regulated [34, 36]. Most knowledge on the characteristics and dynamics of leukocytes trafficking into the CNS has been retrieved from studies in virus infection and experimental autoim- mune encephalomyelitis (EAE) models in mice [17, 31, 37, 49]. However, the translation of these findings to healthy individuals without a marked local inflammatory response in the CNS is uncertain and has triggered studies aiming Abstract Immune surveillance of the central nervous system (CNS) by T cells is important to keep CNS-trophic viruses in a latent state, yet our knowledge of the char- acteristics of CNS-populating T cells is incomplete. We performed a comprehensive, multi-color flow-cytomet- ric analysis of isolated T cells from paired corpus callo- sum (CC) and peripheral blood (PB) samples of 20 brain donors. Compared to PB, CC T cells, which were mostly located in the perivascular space and sporadically in the parenchyma, were enriched for cells expressing CD8. Both CD4 + and CD8 + T cells in the CC had a late-differentiated phenotype, as indicated by lack of expression of CD27 and CD28. The CC contained high numbers of T cells express- ing chemokine receptor CX3CR1 and CXCR3 that allow for homing to inflamed endothelium and tissue, but hardly I. Huitinga and J. Hamann equally contributed to this study. Electronic supplementary material The online version of this article (doi:10.1007/s00401-013-1155-0) contains supplementary material, which is available to authorized users. J. Smolders · K. G. Schuurman · J. Melief · C. G. van Eden · I. Huitinga (*) Neuroimmunology Research Group, Netherlands Institute for Neuroscience, Meibergdreef 47, 1105 BA Amsterdam, The Netherlands e-mail: i.huitinga@nin.knaw.nl E. B. M. Remmerswaal · J. Hamann (*) Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands e-mail: j.hamann@amc.uva.nl R. A. W. van Lier Division of Research, Sanquin Research and Landsteiner Laboratory, Amsterdam, The Netherlands