Most tissues are populated by tissue-resident memory T cells (TRM cells), which are adapted to their niche and appear to be indispensable for local protection against pathogens. Here we show that human white matter-derived brain CD8+ T cells can be subsetted into CD103−CD69+ and CD103+CD69+ T cells both with a phenotypic and transcription factor profile consistent with TRM cells. Specifically, CD103 expression in brain CD8+ T cells correlates with reduced expression of differentiation markers, increased expression of tissue-homing chemokine receptors, intermediate and low expression of the transcription factors T-bet and eomes, increased expression of PD-1 and CTLA-4, and low expression of cytolytic enzymes with preserved polyfunctionality upon activation. Brain CD4+ T cells also display TRM cell-associated markers but have low CD103 expression. We conclude that the human brain is surveilled by TRM cells, providing protection against neurotropic virus reactivation, whilst being under tight control of key immune checkpoint molecules.

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Mechanisms underlying the onset and perpetuation of chronic immune activation in individuals without overt infectious or autoimmune diseases are unclear. Cytomegalovirus (CMV) is a persistent virus that induces a permanent increase of highly differentiated, interferon-gamma-secreting effector T cells. We hypothesized that, because of this increase, CMV also induces a systemic inflammatory response. We measured acute phase proteins, cytokines, and chemokines in serum samples from renal transplant recipients who developed a primary CMV infection and healthy CMV serum-positive or -negative individuals. Primary CMV infection induced a clear proinflammatory response that was maintained during latency. This response was characterized by increased levels of acute phase proteins, such as serum amyloid-A and C-reactive protein, and type 1 cytokines, such as interleukin-18, interferon-inducible protein-10, and interferon-gamma. This continuous activation of the immune system may play a role in the pathogenesis of chronic allograft rejection and potentially contribute to the acceleration of chronic diseases.

Microglia are key players in the central nervous system in health and disease. Much pioneering research on microglia function has been carried out in vivo with the use of genetic animal models. However, to fully understand the role of microglia in neurological and psychiatric disorders, it is crucial to study primary human microglia from brain donors. We have developed a rapid procedure for the isolation of pure human microglia from autopsy tissue using density gradient centrifugation followed by CD11b-specific cell selection. The protocol can be completed in 4 h, with an average yield of 450,000 and 145,000 viable cells per gram of white and grey matter tissue respectively. This method allows for the immediate phenotyping of microglia in relation to brain donor clinical variables, and shows the microglia population to be distinguishable from autologous choroid plexus macrophages. This protocol has been applied to samples from over 100 brain donors from the Netherlands Brain Bank, providing a robust dataset to analyze the effects of age, post-mortem delay, brain acidity, and neurological diagnosis on microglia yield and phenotype. Our data show that cerebrospinal fluid pH is positively correlated to microglial cell yield, but donor age and post-mortem delay do not negatively affect viable microglia yield. Analysis of CD45 and CD11b expression showed that changes in microglia phenotype can be attributed to a neurological diagnosis, and are not influenced by variation in ante- and post-mortem parameters. Cryogenic storage of primary microglia was shown to be possible, albeit with variable levels of recovery and effects on phenotype and RNA quality. Microglial gene expression substantially changed due to culture, including the loss of the microglia-specific markers, showing the importance of immediate microglia phenotyping. We conclude that primary microglia can be isolated effectively and rapidly from human post-mortem brain tissue, allowing for the study of the microglial population in light of the neuropathological status of the donor.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-017-0418-8) contains supplementary material, which is available to authorized users.