Cerebral beta-amyloidosis, one of the pathological hallmarks of Alzheimer's disease (AD), elicits a well-characterised, microglia-mediated local innate immune response. In contrast, it is not clear whether cells of the adaptive immune system, in particular T-cells, react to cerebral amyloidosis in AD. Even though parenchymal T-cells have been described in post-mortem brains of AD patients, it is not known whether infiltrating T-cells are specifically recruited to the extracellular deposits of beta-amyloid, and whether they are locally activated into proliferating, effector cells upon interaction with antigen-presenting cells (APCs). To address these issues we have analysed by confocal microscopy and flow-cytometry the localisation and activation status of both T-cells and APCs in transgenic (tg) mice models of AD-like cerebral amyloidosis. Increased numbers of infiltrating T-cells were found in amyloid-burdened brain regions of tg mice, with concomitant up-regulation of endothelial adhesion molecules ICAM-1 and VCAM-1, compared to non-tg littermates. The infiltrating T-cells in tg brains did not co-localise with amyloid plaques, produced less interferon-gamma than those in controls and did not proliferate locally. Bona-fide dendritic cells were virtually absent from the brain parenchyma of both non-tg and tg mice, and APCs from tg brains showed an immature phenotype, with accumulation of MHC-II in intracellular compartments. These results indicate that cerebral amyloidosis promotes T-cell infiltration but interferes with local antigen presentation and T-cell activation. The inability of the brain immune surveillance to orchestrate a protective immune response to amyloid-beta peptide might contribute to the accumulation of amyloid in the progression of the disease.

IntroductionIn Alzheimer’s disease, accumulation and pathological aggregation of amyloid β-peptide is accompanied by the induction of complex immune responses, which have been attributed both beneficial and detrimental properties. Such responses implicate various cell types of the innate and adaptive arm of the immunesystem, both inside the central nervous system, and in the periphery. To investigate the role of the adaptive immune system in brain β-amyloidosis, PSAPP transgenic mice, an established mouse model of Alzheimer’s disease, were crossbred with the recombination activating gene-2 knockout (Rag2 ko) mice lacking functional B and T cells. In a second experimental paradigm, aged PSAPP mice were reconstituted with bone marrow cells from either Rag2 ko or wildtype control mice.ResultsAnalyses from both experimental approaches revealed reduced β-amyloid pathology and decreased brain amyloid β-peptide levels in PSAPP mice lacking functional adaptive immune cells. The decrease in brain β-amyloid pathology was associated with enhanced microgliosis and increased phagocytosis of amyloid β-peptide aggregates.ConclusionThe results of this study demonstrate an impact of the adaptive immunity on cerebral β-amyloid pathology in vivo and suggest an influence on microglia-mediated amyloid β-peptide clearance as a possible underlying mechanism.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-015-0251-x) contains supplementary material, which is available to authorized users.

The field of neuroimmunology endorses the involvement of the adaptive immune system in central nervous system (CNS) health, disease, and aging. While immune cell trafficking into the CNS is highly regulated, small numbers of antigen-experienced lymphocytes can still enter the cerebrospinal fluid (CSF)-filled compartments for regular immune surveillance under homeostatic conditions. Meningeal lymphatics facilitate drainage of brain-derived antigens from the CSF to deep cervical lymph nodes to prime potential adaptive immune responses. During aging and CNS disorders, brain barriers and meningeal lymphatic functions are impaired, and immune cell trafficking and antigen efflux are altered. In this context, alterations in the immune cell repertoire of blood and CSF and T and B cells primed against CNS-derived autoantigens have been observed in various CNS disorders. However, for many diseases, a causal relationship between observed immune responses and neuropathological findings is lacking. Here, we review recent discoveries about the association between the adaptive immune system and CNS disorders such as autoimmune neuroinflammatory and neurodegenerative diseases. We focus on the current challenges in identifying specific T cell epitopes in CNS diseases and discuss the potential implications for future diagnostic and treatment options.

INTRODUCTIONFast and minimally invasive approaches for early diagnosis of Alzheimer's disease (AD) are highly anticipated. Evidence of adaptive immune cells responding to cerebral β‐amyloidosis has raised the question of whether immune markers could be used as proxies for β‐amyloid accumulation in the brain.METHODSHere, we apply multidimensional mass‐cytometry combined with unbiased machine‐learning techniques to immunophenotype peripheral blood mononuclear cells from a total of 251 participants in cross‐sectional and longitudinal studies.RESULTSWe show that increases in antigen‐experienced adaptive immune cells in the blood, particularly CD45RA‐reactivated T effector memory (TEMRA) cells, are associated with early accumulation of brain β‐amyloid and with changes in plasma AD biomarkers in still cognitively healthy subjects.DISCUSSIONOur results suggest that preclinical AD pathology is linked to systemic alterations of the adaptive immune system. These immunophenotype changes may help identify and develop novel diagnostic tools for early AD assessment and better understand clinical outcomes.

Fast and minimally invasive approaches for early, preclinical diagnosis of neurodegenerative Alzheimer's disease (AD) are highly anticipated. Evidence of adaptive immune cells responding to cerebral beta-amyloidosis, one of the pathological hallmarks of AD, has raised the question of whether immune markers could be used as proxies for beta-amyloid accumulation in the brain. Here, we deploy multidimensional mass cytometry combined with unbiased machine learning techniques to immunophenotype peripheral blood mononuclear cells from study participants in cross-sectional and longitudinal cohorts. We show that increases in antigen-experienced adaptive immune cells in the blood, particularly CD45RA-reactivated T effector memory (TEMRA) cells, are associated with early accumulation of brain beta-amyloid and with changes in plasma AD biomarkers in still cognitively healthy subjects. Our results suggest that preclinical AD pathology is linked to systemic alterations of the adaptive immune system. These immunophenotype changes may help in the future to identify and develop novel diagnostic tools for early AD assessment and to better understand clinical outcomes.

Recently, we have reported that, in addition to macrophages, also neutrophil granulocytes can phagocytose apoptotic neutrophils. Based on this finding, we hypothesized that “cannibalistic” neutrophils at sites of acute infection/inflammation play a major role in the clearance of apoptotic neutrophils. Since at sites of infection/inflammation neutrophils are exposed to microbial constituents and proinflammatory cytokines, in the present study we analyzed the effect of TLR-ligands and cytokines on the ability of neutrophils to phagocytose apoptotic cells in vitro. We observed that exposure to ligands of TLR2 (Malp2, Pam3CSK4), TLR4 (LPS), TLR7/TLR8 (R848), and TLR9 (ODN 2006) led to increased phagocytosis of apoptotic cells by neutrophils. In addition, proinflammatory cytokines such as TNF and GM-CSF strongly enhanced the uptake of apoptotic cells by neutrophils. These results support the hypothesis that neutrophils acquire the ability to phagocytose apoptotic cells at sites of acute infection/inflammation and thereby can contribute to the resolution of inflammation.

Genetic, clinical, biochemical and histochemical data indicate a crucial involvement of inflammation in Alzheimer's disease (AD), but harnessing the immune system to cure or prevent AD has so far proven difficult. Clarifying the cellular heterogeneity and signaling pathways associated with the presence of the AD hallmarks beta-amyloid and tau in the brain, would help to identify potential targets for therapy. While much attention has been so far devoted to microglia and their homeostatic phagocytic activity, additional cell types and immune functions might be affected in AD. Beyond microglia localized in the brain parenchyma, additional antigen-presenting cell (APC) types might be affected by beta-amyloid toxicity. Here, we investigated potential immunomodulatory properties of oligomeric species of beta-amyloid-peptide (Aβ) on microglia and putative APCs. We performed a comprehensive characterization of time-and pathology-dependent APC and T-cell alterations in a model of AD-like brain beta-amyloidosis, the APP-PS1-dE9 mouse model. We show that the deposition of first beta-amyloid plaques is accompanied by a significant reduction in MHC class II surface levels on brain APCs. Furthermore, taking advantage of customized in vitro systems and RNAseq, we demonstrate that a preparation containing various forms of oligomeric Aβ1-42 inhibits antigen presentation by altering the transcription of key immune mediators in dendritic cells. These results suggest that, beyond their neurotoxic effects, certain oligomeric Aβ forms can act as immunomodulatory agents on cerebral APCs and interfere with brain antigen presentation. Impaired brain immune surveillance might be one of the factors that facilitate Aβ and tau spreading in AD.

Atherosclerosis is a disease of the cardiovascular system characterized by local chronic inflammation. The disease’s hallmarks are vessel stenosis, stiffening, and hyperplasia, which are the most prominent underlying causes of cardiovascular complications. Cells from the innate immune response have a central role in disease development as they orchestrate inflammatory events leading to the deposition of fatty streaks in the sub-endothelium. The negative remodeling of atherosclerotic vessels is exacerbated by local variations of intraluminal hemodynamic load, where disturbed blood flow aggravates plaque deposition. Despite pioneering efforts to explore the relationship between inflammation and hemodynamics in the disease framework, interactions between these two elements have never been investigated in vitro before due to the lack of modeling systems with an adequate degree of complexity. Here, we employed a multifaced approach combining computational fluid dynamics (CFD) and tissue-engineering to achieve, for the first time in vitro, the full development of human atherosclerotic plaques within a one-month timeframe. We established the atherosclerosis-on-a-chip model using human induced pluripotent stem cells-derived populations assembled into tissue-engineered arterial vessels and cultured in atheroprone conditions. We reliably predicted regions of plaque deposition within the vessels via tailored CFD modeling. Using machine-learning-aided immunophenotyping and molecular analyses, we found that immune cell populations and extracellular matrix (ECM) components from modeled plaques were comparable to those in human carotid lesions. Furthermore, we discovered similarities between the ECM tensional state of tissue-engineered and native plaques by performing nanoprobe-based tensile analyses. Our results provide the in vitro proof of the link between hemodynamics and inflammation in atherosclerosis and present a personalized, up-scalable tool to study human arterial atherosclerosis onset and progression. We anticipate our work to represent a milestone in the atherosclerosis modeling and precision medicine arena and to serve as a starting point for in-depth analyses targeted at more specific disease progression stages.