The effect of abatacept on T-cell activation is not long-lived in vivo

Abatacept, a co-stimulatory blocker comprising the extracellular portion of human CTLA-4 linked to the Fc region of IgG1, is approved for the treatment of rheumatoid arthritis. By impairing the interaction between CD28 on T cells and CD80/CD86 on APCs, its mechanisms of action include the suppression of follicular T helper cells (preventing the breach of self-tolerance in B cells), inhibition of cell cycle progression holding T cells in a state described as 'induced naïve' and reduction in DC conditioning. However, less is known about how long these inhibitory effects might last, which is a critical question for therapeutic use in patients. Herein, employing a murine model of OVA-induced DTH, we demonstrate that the effect of abatacept is short-lived in vivo and that the inhibitory effects diminish markedly when treatment is ceased.

Review: Unravelling the Role of DNA Sensing in Alum Adjuvant Activity

Public interest in vaccines is at an all-time high following the SARS-CoV-2 global pandemic. Currently, over 6 billion doses of various vaccines are administered globally each year. Most of these vaccines contain Aluminium-based adjuvants (alum), which have been known and used for almost 100 years to enhance vaccine immunogenicity. However, despite the historical use and importance of alum, we still do not have a complete understanding of how alum works to drive vaccine immunogenicity. In this article, we critically review studies investigating the mechanisms of action of alum adjuvants, highlighting some of the misconceptions and controversies within the area. Although we have emerged with a clearer understanding of how this ubiquitous adjuvant works, we have also highlighted some of the outstanding questions in the field. While these may seem mainly of academic interest, developing a more complete understanding of these mechanisms has the potential to rationally modify and improve the immune response generated by alum-adjuvanted vaccines.

Revealing stromal and lymphoid sources of Col3a1-expression during inflammation using a novel reporter mouse

One of the earliest signs of dysregulation of the homeostatic process of fibrosis, associated with pathology in chronic conditions such as rheumatoid arthritis, is the overexpression of collagen type III (COL-3). Critically, there is still relatively little known regarding the identity of the cell types expressing the gene encoding COL-3 (Col3a1). Identifying and characterizing Col3a1-expressing cells during the development of fibrosis could reveal new targets for the diagnosis and treatment of fibrosis-related pathologies. As such, a reporter mouse expressing concomitantly Col3a1 and mKate-2, a fluorescent protein, was generated. Using models of footpad inflammation, we demonstrated its effectiveness as a tool to measure the expression of COL-3 during the repair process and provided an initial characterization of some of the stromal and immune cells responsible for Col3a1 expression.

Orally administered antigen can reduce or exacerbate pathology in an animal model of inflammatory arthritis dependent upon the timing of administration

Currently, treatments for rheumatoid arthritis (RA) are focussed on management of disease symptoms rather than addressing the cause of disease, which could lead to remission and cure. Central to disease development is the induction of autoimmunity through a breach of self-tolerance. Developing approaches to re-establish antigen specific tolerance is therefore an important emerging area of RA research. A crucial step in this research is to employ appropriate animal models to test prospective antigen specific immunotherapies. In this short communication, we evaluate our previously developed model of antigen specific inflammatory arthritis in which ovalbumin-specific T cell receptor transgenic T cells drive breach of tolerance to endogenous antigens to determine the impact that the timing of therapy administration has upon disease progression. Using antigen feeding to induce tolerance we demonstrate that administration prior to articular challenge results in a reduced disease score as evidenced by pathology and serum antibody responses. By contrast, feeding antigen after initiation of disease had the opposite effect and resulted in the exacerbation of pathology. These preliminary data suggest that the timing of antigen administration may be key to the success of tolerogenic immunotherapies. This has important implications for the timing of potential tolerogenic therapies in patients.

Dissecting the molecular control of immune cell accumulation in the inflamed joint

Mechanisms governing entry and exit of immune cells into and out of inflamed joints remain poorly understood. We sought herein to identify the key molecular pathways regulating such migration. Using murine models of inflammation in conjunction with mice expressing a photoconvertible fluorescent protein, we characterized the migration of cells from joints to draining lymph nodes and performed RNA-Seq analysis on isolated cells, identifying genes associated with migration and retention. We further refined the gene list to those specific for joint inflammation. RNA-Seq data revealed pathways and genes previously highlighted as characteristic of rheumatoid arthritis in patient studies, validating the methodology. Focusing on pathways associated with cell migration, adhesion, and movement, we identified genes involved in the retention of immune cells in the inflamed joint, namely junctional adhesion molecule A (JAM-A), and identified a role for such molecules in T cell differentiation in vivo. Thus, using a combination of cell-tracking approaches and murine models of inflammatory arthritis, we identified genes, pathways, and anatomically specific tissue signatures regulating cell migration in a variety of inflamed sites. This skin- and joint-specific data set will be an invaluable resource for the identification of therapeutic targets for arthritis and other inflammatory disorders.

Preclinical models of arthritis for studying immunotherapy and immune tolerance

Increasingly earlier identification of individuals at high risk of rheumatoid arthritis (RA) (eg, with autoantibodies and mild symptoms) improves the feasibility of preventing or curing disease. The use of antigen-specific immunotherapies to reinstate immunological self-tolerance represent a highly attractive strategy due to their potential to induce disease resolution, in contrast to existing approaches that require long-term treatment of underlying symptoms.

Preclinical animal models have been used to understand disease mechanisms and to evaluate novel immunotherapeutic approaches. However, models are required to understand critical processes supporting disease development such as the breach of self-tolerance that triggers autoimmunity and the progression from asymptomatic autoimmunity to joint pain and bone loss. These models would also be useful in evaluating the response to treatment in the pre-RA period.

This review proposes that focusing on immune processes contributing to initial disease induction rather than end-stage pathological consequences is essential to allow development and evaluation of novel immunotherapies for early intervention. We will describe and critique existing models in arthritis and the broader field of autoimmunity that may fulfil these criteria. We will also identify key gaps in our ability to study these processes in animal models, to highlight where further research should be targeted.

Junctional adhesion molecule-A on dendritic cells regulates Th1 differentiation

The junctional adhesion molecule-A (JAM-A) is an adhesion molecule present in the surface of several cell types, such as endothelial cells and leukocytes as well as Dendritic Cells (DC). Given the potential relevance of JAM-A in diverse pathological conditions such as inflammatory diseases and cancer, we investigated the role of JAM-A in CD4+ T cell priming. We demonstrate that JAM-A is present in the immunological synapse formed between T cells and DC during priming. Furthermore, an antagonistic anti-JAM-A mAb could disrupt the interaction between CD4+ T cell and DC. Antagonism of JAM-A also attenuated T cell activation and proliferation with a decrease in T-bet expression and increased IL-6 and IL-17 secretion. These findings demonstrate a functional role for JAM-A in interactions between CD4+ T cells and DCs during T cell priming as a positive regulator of Th1 differentiation.

TCRβ Sequencing Reveals Spatial and Temporal Evolution of Clonal CD4 T Cell Responses in a Breach of Tolerance Model of Inflammatory Arthritis

Effective tolerogenic intervention in Rheumatoid Arthritis (RA) will rely upon understanding the evolution of articular antigen specific CD4 T cell responses. TCR clonality of endogenous CD4 T cell infiltrates in early inflammatory arthritis was assessed to monitor evolution of the TCR repertoire in the inflamed joint and associated lymph node (LN). Mouse models of antigen-induced breach of self-tolerance and chronic polyarthritis were used to recapitulate early and late phases of RA. The infiltrating endogenous, antigen experienced CD4 T cells in inflamed joints and LNs were analysed using flow cytometry and TCRβ sequencing. TCR repertoires from inflamed late phase LNs displayed increased clonality and diversity compared to early phase LNs, while inflamed joints remained similar with time. Repertoires from late phase LNs accumulated clones with a diverse range of TRBV genes, while inflamed joints at both phases contained clones expressing similar TRBV genes. Repertoires from LNs and joints at the late phase displayed reduced CDR3β sequence overlap compared to the early disease phase, however the most abundant clones in LNs accumulate in the joint at the later phase. The results indicate CD4 T cell repertoire clonality and diversity broadens with progression of inflammatory arthritis and is first reflected in LNs before mirroring in the joint. These observations imply that antigen specific tolerogenic therapies could be more effective if targeted at earlier phases of disease when CD4 T cell clonality is least diverse.

Targeting Opposing Immunological Roles of the Junctional Adhesion Molecule-A in Autoimmunity and Cancer

The junctional adhesion molecule-A (JAM-A) is a cell surface adhesion molecule expressed on platelets, epithelial cells, endothelial cells and leukocytes (e. g. monocytes and dendritic cells). JAM-A plays a relevant role in leukocyte trafficking and its therapeutic potential has been studied in several pathological conditions due to its capacity to induce leukocyte migration out of inflamed sites or infiltration into tumor sites. However, disruption of JAM-A pathways may worsen clinical pathology in some cases. As such, the effects of JAM-A manipulation on modulating immune responses in the context of different diseases must be better understood. In this mini-review, we discuss the potential of JAM-A as a therapeutic target, summarizing findings from studies manipulating JAM-A in the context of inflammatory diseases (e.g. autoimmune diseases) and cancer and highlighting described mechanisms.

The Impact of Malaria Parasites on Dendritic Cell-T Cell Interaction

Malaria is caused by apicomplexan parasites of the genus Plasmodium. While infection continues to pose a risk for the majority of the global population, the burden of disease mainly resides in Sub-Saharan Africa. Although immunity develops against disease, this requires years of persistent exposure and is not associated with protection against infection. Repeat infections occur due to the parasite's ability to disrupt or evade the host immune responses. However, despite many years of study, the mechanisms of this disruption remain unclear. Previous studies have demonstrated a parasite-induced failure in dendritic cell (DCs) function affecting the generation of helper T cell responses. These T cells fail to help B cell responses, reducing the production of antibodies that are necessary to control malaria infection. This review focuses on our current understanding of the effect of Plasmodium parasite on DC function, DC-T cell interaction, and T cell activation. A better understanding of how parasites disrupt DC-T cell interactions will lead to new targets and approaches to reinstate adaptive immune responses and enhance parasite immunity.

To the Skin and Beyond: The Immune Response to African Trypanosomes as They Enter and Exit the Vertebrate Host

African trypanosomes are single-celled extracellular protozoan parasites transmitted by tsetse fly vectors across sub-Saharan Africa, causing serious disease in both humans and animals. Mammalian infections begin when the tsetse fly penetrates the skin in order to take a blood meal, depositing trypanosomes into the dermal layer. Similarly, onward transmission occurs when differentiated and insect pre-adapted forms are ingested by the fly during a blood meal. Between these transmission steps, trypanosomes access the systemic circulation of the vertebrate host via the skin-draining lymph nodes, disseminating into multiple tissues and organs, and establishing chronic, and long-lasting infections. However, most studies of the immunobiology of African trypanosomes have been conducted under experimental conditions that bypass the skin as a route for systemic dissemination (typically via intraperitoneal or intravenous routes). Therefore, the importance of these initial interactions between trypanosomes and the skin at the site of initial infection, and the implications for these processes in infection establishment, have largely been overlooked. Recent studies have also demonstrated active and complex interactions between the mammalian host and trypanosomes in the skin during initial infection and revealed the skin as an overlooked anatomical reservoir for transmission. This highlights the importance of this organ when investigating the biology of trypanosome infections and the associated immune responses at the initial site of infection. Here, we review the mechanisms involved in establishing African trypanosome infections and potential of the skin as a reservoir, the role of innate immune cells in the skin during initial infection, and the subsequent immune interactions as the parasites migrate from the skin. We suggest that a thorough identification of the mechanisms involved in establishing African trypanosome infections in the skin and their progression through the host is essential for the development of novel approaches to interrupt disease transmission and control these important diseases.

Developing a xenograft model of human vasculature in the mouse ear pinna

Humanised xenograft models allow for the analysis of human tissue within a physiological environment in vivo. However, current models often rely on the angiogenesis and ingrowth of recipient vasculature to perfuse tissues, preventing analysis of biological processes and diseases involving human blood vessels. This limits the effectiveness of xenografts in replicating human physiology and may lead to issues with translating findings into human research. We have designed a xenograft model of human vasculature to address this issue. Human subcutaneous fat was cultured in vitro to promote blood vessel outgrowth prior to implantation into immunocompromised mice. We demonstrate that implants survived, retained human vasculature and anastomosed with the circulatory system of the recipient mouse. Significantly, by performing transplants into the ear pinna, this system enabled intravital observation of xenografts by multiphoton microscopy, allowing us to visualise the steps leading to vascular cytoadherence of erythrocytes infected with the human parasite Plasmodium falciparum. This model represents a useful tool for imaging the interactions that occur within human tissues in vivo and permits visualization of blood flow and cellular recruitment in a system which is amenable to intervention for various studies in basic biology together with drug evaluation and mechanism of action studies.

Spatiotemporal Modeling of the Key Migratory Events During the Initiation of Adaptive Immunity

Initiation of adaptive immunity involves distinct migratory cell populations coming together in a highly dynamic and spatially organized process. However, we lack a detailed spatiotemporal map of these events due to our inability to track the fate of cells between anatomically distinct locations or functionally identify cell populations as migratory. We used photo-convertible transgenic mice (Kaede) to spatiotemporally track the fate and composition of the cell populations that leave the site of priming and enter the draining lymph node to initiate immunity. We show that following skin priming, the lymph node migratory population is principally composed of cells recruited to the site of priming, with a minor contribution from tissue resident cells. In combination with the YAe/Eα system, we also show that the majority of cells presenting antigen are CD103⁺CD11b⁺ dendritic cells that were recruited to the site of priming during the inflammatory response. This population has previously only been described in relation to mucosal tissues. Comprehensive phenotypic profiling of the cells migrating from the skin to the draining lymph node by mass cytometry revealed that in addition to dendritic cells, the migratory population also included CD4⁺ and CD8⁺ T cells, B cells, and neutrophils. Taking our complex spatiotemporal data set, we then generated a model of cell migration that quantifies and describes the dynamics of arrival, departure, and residence times of cells at the site of priming and in the draining lymph node throughout the time-course of the initiation of adaptive immunity. In addition, we have identified the mean migration time of migratory dendritic cells as they travel from the site of priming to the draining lymph node. These findings represent an unprecedented, detailed and quantitative map of cell dynamics and phenotypes during immunization, identifying where, when and which cells to target for immunomodulation in autoimmunity and vaccination strategies.

Effects of host-derived chemokines on the motility and viability of Trypanosoma brucei

African trypanosomes (Trypanosoma brucei spp.) are extracellular, hemoflagellate, protozoan parasites. Mammalian infection begins when the tsetse fly vector injects trypanosomes into the skin during blood feeding. The trypanosomes then reach the draining lymph nodes before disseminating systemically. Intravital imaging of the skin post-tsetse fly bite revealed that trypanosomes were observed both extravascularly and intravascularly in the lymphatic vessels. Whether host-derived cues play a role in the attraction of the trypanosomes towards the lymphatic vessels to aid their dissemination from the site of infection is not known. Since chemokines can mediate the attraction of leucocytes towards the lymphatics, in vitro chemotaxis assays were used to determine whether chemokines might also act as chemoattractants for trypanosomes. Although microarray data suggested that the chemokines CCL8, CCL19, CCL21, CCL27 and CXCL12 were highly expressed in mouse skin, they did not stimulate the chemotaxis of T brucei. Certain chemokines also possess potent antimicrobial properties. However, none of the chemokines tested exerted any parasiticidal effects on T brucei. Thus, our data suggest that host-derived chemokines do not act as chemoattractants for T brucei. Identification of the mechanisms used by trypanosomes to establish host infection will aid the development of novel approaches to block disease transmission.

In vivo multiplex molecular imaging of vascular inflammation using surface-enhanced Raman spectroscopy

Vascular immune-inflammatory responses play a crucial role in the progression and outcome of atherosclerosis. The ability to assess localized inflammation through detection of specific vascular inflammatory biomarkers would significantly improve cardiovascular risk assessment and management; however, no multi-parameter molecular imaging technologies have been established to date. Here, we report the targeted in vivo imaging of multiple vascular biomarkers using antibody-functionalized nanoparticles and surface-enhanced Raman scattering (SERS).

Methods: A series of antibody-functionalized gold nanoprobes (BFNP) were designed containing unique Raman signals in order to detect intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and P-selectin using SERS.

Results: SERS and BFNP were utilized to detect, discriminate and quantify ICAM-1, VCAM-1 and P-selectin in vitro on human endothelial cells and ex vivo in human coronary arteries. Ultimately, non-invasive multiplex imaging of adhesion molecules in a humanized mouse model was demonstrated in vivo following intravenous injection of the nanoprobes.

Conclusion: This study demonstrates that multiplexed SERS-based molecular imaging can indicate the status of vascular inflammation in vivo and gives promise for SERS as a clinical imaging technique for cardiovascular disease in the future.

A Novel Cellular Pathway of Antigen Presentation and CD4 T Cell Activation in vivo

Dendritic cell activation of CD4 T cells in the lymph node draining a site of infection or vaccination is widely considered the central event in initiating adaptive immunity. The accepted dogma is that this occurs by stimulating local activation and antigen acquisition by dendritic cells, with subsequent lymph node migration, however the generalizability of this mechanism is unclear. Here we show that in some circumstances antigen can bypass the injection site inflammatory response, draining freely and rapidly to the lymph nodes where it interacts with subcapsular sinus (SCS) macrophages resulting in their death. Debris from these dying SCS macrophages is internalized by monocytes recruited from the circulation. This coordinated response leads to antigen presentation by monocytes and interactions with naïve CD4 T cells that can drive the initiation of T cell and B cell responses. These studies demonstrate an entirely novel pathway leading to initiation of adaptive immune responses in vivo.

Non-Invasive Multiphoton Imaging of Islets Transplanted Into the Pinna of the NOD Mouse Ear Reveals the Immediate Effect of Anti-CD3 Treatment in Autoimmune Diabetes

We present a novel and readily accessible method facilitating cellular time-resolved imaging of transplanted pancreatic islets. Grafting of islets to the mouse ear pinna allows non-invasive, in vivo longitudinal imaging of events in the islets and enables improved acquisition of experimental data and use of fewer experimental animals than is possible using invasive techniques, as the same mouse can be assessed for the presence of islet infiltrating cells before and after immune intervention. We have applied this method to investigating therapeutic protection of beta cells through the well-established use of anti-CD3 injection, and have acquired unprecedented data on the nature and rapidity of the effect on the islet infiltrating T cells. We demonstrate that infusion of anti-CD3 antibody leads to immediate effects on islet infiltrating T cells in islet grafts in the pinna of the ear, and causes them to increase their speed and displacement within 20 min of infusion. This technique overcomes several technical challenges associated with intravital imaging of pancreatic immune responses and facilitates routine study of beta islet cell development, differentiation, and function in health and disease.

A cryptic cycle in haematopoietic niches promotes initiation of malaria transmission and evasion of chemotherapy

Blood stage human malaria parasites may exploit erythropoietic tissue niches and colonise erythroid progenitors; however, the precise influence of the erythropoietic environment on fundamental parasite biology remains unknown. Here we use quantitative approaches to enumerate Plasmodium infected erythropoietic precursor cells using an in vivo rodent model of Plasmodium berghei. We show that parasitised early reticulocytes (ER) in the major sites of haematopoiesis establish a cryptic asexual cycle. Moreover, this cycle is characterised by early preferential commitment to gametocytogenesis, which occurs in sufficient numbers to generate almost all of the initial population of circulating, mature gametocytes. In addition, we show that P. berghei is less sensitive to artemisinin in splenic ER than in blood, which suggests that haematopoietic tissues may enable origins of recrudescent infection and emerging resistance to antimalarials. Continuous propagation in these sites may also provide a mechanism for continuous transmission and infection in malaria endemic regions.

Visualising the interaction of CD4 T cells and DCs in the evolution of inflammatory arthritis

OBJECTIVES

Successful early intervention in rheumatoid arthritis (RA) with the aim of resetting immunological tolerance requires a clearer understanding of how specificity, cellular kinetics and spatial behaviour shape the evolution of articular T cell responses. We aimed to define initial seeding of articular CD4⁺ T cell responses in early experimental arthritis, evaluating their dynamic behaviour and interactions with dendritic cells (DCs) in the inflamed articular environment.

METHODS

Antigen-induced arthritis was used to model articular inflammation. Flow cytometry and PCR of T cell receptor (TCR) diversity genes allowed phenotypic analysis of infiltrating T cells. The dynamic interactions of T cells with joint residing DCs were visualised using intravital multiphoton microscopy.

RESULTS

Initial recruitment of antigen-specific T cells into the joint was paralleled by accumulation of CD4⁺ T cells with diverse antigen-receptor expression and ability to produce tumour necrosis factor alpha (TNFα) and interferon gamma (IFNγ) on mitogenic restimulation. A proportion of this infiltrate demonstrated slower motility speeds and engaged for longer periods with articular DCs in vivo. Abatacept treatment did not disrupt these interactions but did reduce T cell expression of inducible costimulatory (ICOS) molecule. We also demonstrated that non-specific CD4⁺ T cells could be recruited during these early articular events.

CONCLUSIONS

We demonstrate that CD4⁺ T cells engage with articular DCs supporting antigen specific T cell reactivation. This cellular dialogue can be targeted therapeutically to reduce local T cell activation.

Model answers: Rational application of murine models in arthritis research

Advances in targeted immune therapeutics have profoundly improved clinical outcomes for patients with inflammatory arthropathies particularly rheumatoid arthritis. The landscape of disease that is observed and the treatment outcomes desired for the future have also progressed. As such there is an increasing move away from traditional models of end‐stage, chronic disease with recognition of the need to consider the earliest phases of pathogenesis as a target for treatment leading to resolution and/or cure. In order to continue the discovery process and enhance our understanding of disease and treatment, we therefore need to continuously revisit the animal models we employ and assess their relevance and utility in the light of contemporary therapeutic goals. In this review, we highlight the areas where we consider new developments in animal models and their application are most required. Thus, we have contextualised the relevant mouse models and their use within the current concepts of human inflammatory arthritis pathogenesis and highlight areas of need.

MicroRNA-34a dependent regulation of AXL controls the activation of dendritic cells in inflammatory arthritis

Current treatments for rheumatoid arthritis (RA) do not reverse underlying aberrant immune function. A genetic predisposition to RA, such as HLA-DR4 positivity, indicates that dendritic cells (DC) are of crucial importance to pathogenesis by activating auto-reactive lymphocytes. Here we show that microRNA-34a provides homoeostatic control of CD1c⁺ DC activation via regulation of tyrosine kinase receptor AXL, an important inhibitory DC auto-regulator. This pathway is aberrant in CD1c⁺ DCs from patients with RA, with upregulation of miR-34a and lower levels of AXL compared to DC from healthy donors. Production of pro-inflammatory cytokines is reduced by ex vivo gene-silencing of miR-34a. miR-34a-deficient mice are resistant to collagen-induced arthritis and interaction of DCs and T cells from these mice are reduced and do not support the development of Th17 cells in vivo. Our findings therefore show that miR-34a is an epigenetic regulator of DC function that may contribute to RA.

Multispectral oximetry of murine tendon microvasculature with inflammation

We report a novel multispectral imaging technique for localised measurement of vascular oxygen saturation (SO₂) in vivo. Annular back-illumination is generated using a Schwarzchild-design reflective objective. Analysis of multispectral data is performed using a calibration-free oximetry algorithm. This technique is applied to oximetry in mice to measure SO₂ in microvasculature supplying inflamed tendon tissue in the hind leg. Average SO₂ for controls was 94.8 ± 7.0 % (N = 6), and 84.0 ± 13.5 % for mice with inflamed tendon tissue (N = 6). We believe this to be the first localised measurement of hypoxia in tendon microvasculature due to inflammation. Quantification of localised SO₂ is important for the study of inflammatory diseases such as rheumatoid arthritis, where hypoxia is thought to play a role in pathogenesis.

Where are we? The anatomy of the murine cortical meninges revisited for intravital imaging, immunology, and clearance of waste from the brain

Rapid progress is being made in understanding the roles of the cerebral meninges in the maintenance of normal brain function, in immune surveillance, and as a site of disease. Most basic research on the meninges and the neural brain is now done on mice, major attractions being the availability of reporter mice with fluorescent cells, and of a huge range of antibodies useful for immunocytochemistry and the characterization of isolated cells. In addition, two-photon microscopy through the unperforated calvaria allows intravital imaging of the undisturbed meninges with sub-micron resolution. The anatomy of the dorsal meninges of the mouse (and, indeed, of all mammals) differs considerably from that shown in many published diagrams: over cortical convexities, the outer layer, the dura, is usually thicker than the inner layer, the leptomeninx, and both layers are richly vascularized and innervated, and communicate with the lymphatic system. A membrane barrier separates them and, in disease, inflammation can be localized to one layer or the other, so experimentalists must be able to identify the compartment they are studying. Here, we present current knowledge of the functional anatomy of the meninges, particularly as it appears in intravital imaging, and review their role as a gateway between the brain, blood, and lymphatics, drawing on information that is scattered among works on different pathologies.

The mouse cortical meninges are the site of immune responses to many different pathogens, and are accessible to intravital imaging

A wide range of viral and microbial infections are known to cause meningitis, and there is evidence that the meninges are the gateway to pathogenic invasion of the brain parenchyma. Hence observation of these regions has wide application to understanding host-pathogen interactions. Interactions between pathogens and cells of the immune response can be modified by changes in their environment, such as suppression of the flow of blood and lymph, and, particularly in the case of the meninges, with their unsupported membranes, invasive dissection can alter the tissue architecture. For these reasons, intravital imaging through the unperforated skull is the method of choice. We give a protocol for a simple method of two-photon microscopy through the thinned cortical skull of the anesthetized mouse to enable real-time imaging with sub-micron resolution through the meninges and into the superficial brain parenchyma. In reporter mice in which selected cell types express fluorescent proteins, imaging after infection with fluorescent pathogens (lymphocytic choriomeningitis virus, Trypanosoma brucei or Plasmodium berghei) has shown strong recruitment to the cortical meninges of immune cells, including neutrophils, T cells, and putative dendritic cells and macrophages. Without special labeling, the boundaries between the dura mater, the leptomeninx, and the parenchyma are not directly visualized in intravital two-photon microscopy, but other landmarks and characteristics, which we illustrate, allow the researcher to identify the compartment being imaged. While most infectious meningitides are localized mainly in the dura mater, others involve recruitment of immune cells to the leptomeninx.

Neutrophil swarming and extracellular trap formation play a significant role in Alum adjuvant activity

There are over 6 billion vaccine doses administered each year, most containing aluminium-based adjuvants, yet we still do not have a complete understanding of their mechanisms of action. Recent evidence has identified host DNA and downstream sensing as playing a significant role in aluminium adjuvant (aluminium hydroxide) activity. However, the cellular source of this DNA, how it is sensed by the immune system and the consequences of this for vaccination remains unclear. Here we show that the very early injection site reaction is characterised by inflammatory chemokine production and neutrophil recruitment. Intravital imaging demonstrates that the Alum injection site is a focus of neutrophil swarms and extracellular DNA strands. These strands were confirmed as neutrophil extracellular traps due to their sensitivity to DNAse and absence in mice deficient in peptidylarginine deiminase 4. Further studies in PAD4−/− mice confirmed a significant role for neutrophil extracellular trap formation in the adjuvant activity of Alum. By revealing neutrophils recruited to the site of Alum injection as a source of the DNA that is detected by the immune system this study provides the missing link between Alum injection and the activation of DNA sensors that enhance adjuvant activity, elucidating a key mechanism of action for this important vaccine component.

Researchers have identified the mechanism of action in which aluminium hydroxide (alum) boosts the efficacy of co-administered vaccines. In this study, James Brewer and colleagues from the University of Glasgow, UK, studied the effects of alum co-administration in a mouse model, finding that the compound induces immune cells, called neutrophils, to swarm around the site of immunization and produce neutrophil extracellular traps (NETs). NETs, webs of DNA and cell contents formed under certain conditions of neutrophil cell death, immobilize pathogens and promote their elimination. This study builds on previous research and demonstrates that alum artificially stimulates this pathway to boost the adaptive immune response to vaccine antigens, increasing their immunogenicity. The authors also suggest further study into neutrophil components as potential therapeutic agents.

Visualizing and Tracking T Cell Motility In Vivo

Advanced cellular tracking and imaging techniques allow the dynamic nature of immune responses to be studied in detail and in a physiological context. Here we describe two methods applying multiphoton laser scanning microscopy to the visualization and tracking of fluorescently labeled CD4⁺ T cells and dendritic cells (DCs) within the complex lymph node (LN) environment. Ex vivo imaging of LNs allows the study of cell populations without the need for skilled surgical techniques while providing comparable data. While more technically demanding, intravital imaging of the popliteal LN allows aspects of T cell/DC responses to be studied in the context of an intact lymph and blood supply. We also describe methods to aid the acquisition of time series data suitable for cellular tracking, providing a quantitative approach to real-time analysis of DC and T cell LN responses.

Assessment of murine collagen-induced arthritis by longitudinal non-invasive duplexed molecular optical imaging

OBJECTIVE

In the present study we evaluated the use of four commercially available fluorescent probes to monitor disease activity in murine CIA and its suppression during glucocorticoid therapy.

METHODS

Arthritis was induced in male DBA/1 mice by immunization with type II collagen in Complete Freund's Adjuvant, followed by a boost of collagen in PBS. Four fluorescent probes from PerkinElmer in combination [ProSense 750 fluorescent activatable sensor technology (FAST) with Neutrophil Elastase 680 FAST and MMPSense 750 FAST with CatK 680 FAST] were used to monitor disease development from day 5 through to day 40 post-immunization. Fluorescence generated in vivo by the probes was correlated with clinical and histological score and paw measurements.

RESULTS

The fluorescence intensity emitted by each probe was shown to correlate with the conventional measurements of disease. The highest degree of correlation was observed with ProSense 750 FAST in combination with Neutrophil Elastase 680 FAST; these probes were then used to successfully assess CIA suppression during dexamethasone treatment.

CONCLUSION

We have demonstrated that longitudinal non-invasive duplexed optical fluorescence imaging provides a simple assessment of arthritic disease activity within the joints of mice following the induction of CIA and may represent a powerful tool to monitor the efficacy of drug treatments in preclinical studies.

Artery Tertiary Lymphoid Organs Control Aorta Immunity and Protect against Atherosclerosis via Vascular Smooth Muscle Cell Lymphotoxin β Receptors

Tertiary lymphoid organs (TLOs) emerge during nonresolving peripheral inflammation, but their impact on disease progression remains unknown. We have found in aged Apoe^−/− mice that artery TLOs (ATLOs) controlled highly territorialized aorta T cell responses. ATLOs promoted T cell recruitment, primed CD4⁺ T cells, generated CD4⁺, CD8⁺, T regulatory (Treg) effector and central memory cells, converted naive CD4⁺ T cells into induced Treg cells, and presented antigen by an unusual set of dendritic cells and B cells. Meanwhile, vascular smooth muscle cell lymphotoxin β receptors (VSMC-LTβRs) protected against atherosclerosis by maintaining structure, cellularity, and size of ATLOs though VSMC-LTβRs did not affect secondary lymphoid organs: Atherosclerosis was markedly exacerbated in Apoe^−/−Ltbr^−/− and to a similar extent in aged Apoe^−/−Ltbr^fl/flTagln-cre mice. These data support the conclusion that the immune system employs ATLOs to organize aorta T cell homeostasis during aging and that VSMC-LTβRs participate in atherosclerosis protection via ATLOs.

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Artery tertiary lymphoid organs control atherosclerosis T cell immunity

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Artery tertiary lymphoid organs generate effector memory T cells

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Artery tertiary lymphoid organs convert naive CD4⁺ T cells into induced Treg cells

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Artery tertiary lymphoid organs protect from atherosclerosis

Antigen presentation kinetics control T cell/dendritic cell interactions and follicular helper T cell generation in vivo

The production of high affinity, class switched antibodies produced by B cells hinges on the effective differentiation of T follicular helper (Tfh) cells. Here we define conditions specifically enhancing Tfh differentiation and providing protection in a model of influenza infection. Tfh responses were associated with prolonged antigen presentation by dendritic cells (DCs), which maintained T cell/DC interactions into stage 3 (>72 hr) of activation. Blocking stage 3 interactions ablated Tfh generation, demonstrating a causal link between T cell-DC behaviour and functional outcomes. The current data therefore explain how duration of antigen presentation affects the dynamics of T cell-DC interactions and consequently determine Tfh cell differentiation in the developing immune response.

DOI:http://dx.doi.org/10.7554/eLife.06994.001

The immune system protects the body from infections, cancer and other diseases. Invading microbes and cancerous cells exhibit proteins that are not normally found in the healthy cells of the body. Fragments of these molecules—known as antigens—may be detected by the immune system, which can then respond by producing antibodies and other responses that try to destroy the threat.

Antibodies are produced by one type of immune cell (known as B cells) with the help of other cells called follicular helper T (Tfh) cells. During an immune response, Tfh cells form from ‘naïve’ T cells that have not encountered an antigen before. This process has several stages and is activated when the naïve T cells interact with antigens that are displayed on the surface of dendritic cells and other immune cells. However, it is not clear exactly how this process works.

Here, Benson et al. studied the formation of Tfh cells in mice in response to antigens of different sizes. The experiments show that the dendritic cells displayed larger antigens for longer periods of time than they displayed the smaller antigens. Both the small and large antigens allowed dendritic cells to interact with T cells. However, only the dendritic cells that displayed the larger antigens maintained the interaction with T cells for longer periods of time (into the last stage of Tfh cell formation). This enhanced the production of Tfh cells, which boosted the production of antibodies against the antigens to generate immunity to infection.

Further experiments found that blocking the interaction between dendritic cells and T cells during the final stage of Tfh cell formation reduced the production of Tfh cells. Benson et al.'s findings show that the length of time that dendritic cells present antigens on their surface affects the production of Tfh cells and subsequent immune responses. Since Tfh cells are critical to the formation of long-lasting immunity against a virus, these findings could aid efforts to develop more effective vaccines against influenza and other diseases.

DOI:http://dx.doi.org/10.7554/eLife.06994.002

Intravital imaging of a massive lymphocyte response in the cortical dura of mice after peripheral infection by trypanosomes

Peripheral infection by Trypanosoma brucei, the protozoan responsible for sleeping sickness, activates lymphocytes, and, at later stages, causes meningoencephalitis. We have videoed the cortical meninges and superficial parenchyma of C56BL/6 reporter mice infected with T.b.brucei. By use of a two-photon microscope to image through the thinned skull, the integrity of the tissues was maintained. We observed a 47-fold increase in CD2+ T cells in the meninges by 12 days post infection (dpi). CD11c+ dendritic cells also increased, and extravascular trypanosomes, made visible either by expression of a fluorescent protein, or by intravenous injection of furamidine, appeared. The likelihood that invasion will spread from the meninges to the parenchyma will depend strongly on whether the trypanosomes are below the arachnoid membrane, or above it, in the dura. Making use of optical signals from the skull bone, blood vessels and dural cells, we conclude that up to 40 dpi, the extravascular trypanosomes were essentially confined to the dura, as were the great majority of the T cells. Inhibition of T cell activation by intraperitoneal injection of abatacept reduced the numbers of meningeal T cells at 12 dpi and their mean speed fell from 11.64 ± 0.34 μm/min (mean ± SEM) to 5.2 ± 1.2 μm/min (p = 0.007). The T cells occasionally made contact lasting tens of minutes with dendritic cells, indicative of antigen presentation. The population and motility of the trypanosomes tended to decline after about 30 dpi. We suggest that the lymphocyte infiltration of the meninges may later contribute to encephalitis, but have no evidence that the dural trypanosomes invade the parenchyma.

African trypanosomes are motile parasites that cause sleeping sickness. They multiply first in the blood then cause death mainly by effects on the brain: immune system cells, including T cells and dendritic cells, play major roles in this. Thinking we might see the attack on the brain, we infected mice with trypanosomes and used a two-photon microscope, which allowed us to image the superficial brain and the delicate tissue between the skull and the brain called the meninges without making a hole in the skull. The mice (which were anesthetized) had been genetically modified so that T cells and dendritic cells were fluorescent, as were the trypanosomes. We did not notice much happening in the brain itself, but in the meninges, in a compartment called the dura, huge numbers of T cells and dendritic cells appeared. Trypanosomes also moved from the blood into this compartment. Since T cells, dendritic cells and trypanosomes had not been videoed in the meninges before, we began by observing them carefully: their numbers, their movements and their interactions. The accumulation of lymphocytes is a sign of meningitis, a feature of infection by a wide range of pathogens and our results suggest interesting future work.

MHCII-mediated dialog between group 2 innate lymphoid cells and CD4(+) T cells potentiates type 2 immunity and promotes parasitic helminth expulsion

Group 2 innate lymphoid cells (ILC2s) release interleukin-13 (IL-13) during protective immunity to helminth infection and detrimentally during allergy and asthma. Using two mouse models to deplete ILC2s in vivo, we demonstrate that T helper 2 (Th2) cell responses are impaired in the absence of ILC2s. We show that MHCII-expressing ILC2s interact with antigen-specific T cells to instigate a dialog in which IL-2 production from T cells promotes ILC2 proliferation and IL-13 production. Deletion of MHCII renders IL-13-expressing ILC2s incapable of efficiently inducing Nippostrongylus brasiliensis expulsion. Thus, during transition to adaptive T cell-mediated immunity, the ILC2 and T cell crosstalk contributes to their mutual maintenance, expansion and cytokine production. This interaction appears to augment dendritic-cell-induced T cell activation and identifies a previously unappreciated pathway in the regulation of type-2 immunity.

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Genetic ablation of ILC2s impairs type-2 immunity

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MHCII-expressing ILC2s potentiate Th2 responses

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IL-2 from T cells promotes ILC2 proliferation and expression of type-2 cytokines

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MHCII and IL-13 expression by ILC2s is important for N. brasiliensis expulsion

In vivo imaging of trypanosome-brain interactions and development of a rapid screening test for drugs against CNS stage trypanosomiasis

HUMAN AFRICAN TRYPANOSOMIASIS (HAT) MANIFESTS IN TWO STAGES OF DISEASE: firstly, haemolymphatic, and secondly, an encephalitic phase involving the central nervous system (CNS). New drugs to treat the second-stage disease are urgently needed, yet testing of novel drug candidates is a slow process because the established animal model relies on detecting parasitemia in the blood as late as 180 days after treatment. To expedite compound screening, we have modified the GVR35 strain of Trypanosoma brucei brucei to express luciferase, and have monitored parasite distribution in infected mice following treatment with trypanocidal compounds using serial, non-invasive, bioluminescence imaging. Parasites were detected in the brains of infected mice following treatment with diminazene, a drug which cures stage 1 but not stage 2 disease. Intravital multi-photon microscopy revealed that trypanosomes enter the brain meninges as early as day 5 post-infection but can be killed by diminazene, whereas those that cross the blood-brain barrier and enter the parenchyma by day 21 survived treatment and later caused bloodstream recrudescence. In contrast, all bioluminescent parasites were permanently eliminated by treatment with melarsoprol and DB829, compounds known to cure stage 2 disease. We show that this use of imaging reduces by two thirds the time taken to assess drug efficacy and provides a dual-modal imaging platform for monitoring trypanosome infection in different areas of the brain.

Using lymph node transplantation as an approach to image cellular interactions between the skin and draining lymph nodes during parasitic infections

The growing use of protozoan parasites expressing fluorescent reporter genes, together with advances in microscopy, is enabling visualisation of their behaviour and functions within the host from the very earliest stages of infection with previously unparalleled spatiotemporal resolution. These developments have begun to provide novel insights, which are informing our understanding of where host immune responses may be initiated, which cells are involved and the types of response that are elicited. Here we will review some of these recent observations that highlight the importance of cellular communication between the site of infection and the draining lymph node (dLN) in establishing infection and immunity. We also highlight a number of remaining challenges and unknowns that arise through our inability to follow and fate map the journey of a single cell between spatially separated tissue sites. In response to these challenges, we review a recently described experimental strategy that extends the spatial and temporal limits of previous imaging approaches, most significantly allowing longitudinal analysis of cellular migration between the skin and draining lymph nodes in vivo, without the requirement for invasive surgery.

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Role of skin and LN communication in establishing infection and immunity

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A technique to extend the spatial and temporal limits of tissue imaging

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This approach does not require invasive surgery for imaging.

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We can follow the journey of a single cell between spatially separated tissue sites.

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We outline future applications for this approach.

Th17 effector cells support B cell responses outside of germinal centres

Th17 cells are pro-inflammatory CD4⁺T cells, which are important in immune responses against fungal pathogens and extracellular bacteria and have also been implicated in various autoimmune syndromes. However, their role in supporting B cell responses in these scenarios remains unclear, representing a significant lapse in our understanding of the role Th17 play in vaccine responses and the regulation of autoimmunity. We employed T cell and B cell receptor transgenic mice specific for model antigens, and adoptive transfer approaches that allowed the tracking of cognate B and T cells in situ and ex vivo using immunological methods. We have found that T cells activated under Th17 polarising conditions have a greater capacity to provide cognate B cell help compared with Th1 polarised populations, supporting higher expansion of antigen specific B cells and enhanced antibody titres. This advantage is associated with the increased persistence of Th17 polarised cells in areas of the lymph nodes where they can provide help (i.e. the B cell follicles). Also the Th17 cells are characterised by their higher expression of ICOS, a costimulatory molecule important for B cell help. Surprisingly, contrary to published reports, Th17 cells were not detected inside germinal centres, although they were found in close proximity to cognate B cells in the follicle early in the genesis of the humoral immune response. These data indicate that, Th17 cells have a more significant role earlier in the initiation/development of the germinal centre response and/or germinal centre-independent events, consistent with their early effector status.

Plasmacytoid dendritic cells: biomarkers or potential therapeutic targets in atherosclerosis?

Plasmacytoid dendritic cells (pDCs) represent a unique subset of dendritic cells that play distinct and critical roles in the immune response. Importantly, pDCs play a pivotal role in several chronic autoimmune diseases strongly characterized by an increased risk of vascular pathology. Clinical studies have shown that pDCs are detectable in atherosclerotic plaques and others have suggested an association between reduced numbers of circulating pDCs and cardiovascular events. Although the causal relationship between pDCs and atherosclerosis is still uncertain, recent results from mouse models are starting to define the specific role(s) of pDCs in the disease process. In this review, we will discuss the role of pDCs in innate and adaptive immunity, the emerging evidence demonstrating the contribution of pDCs to vascular pathology and we will consider the possible impact of pDCs on the acceleration of atherosclerosis in chronic inflammatory autoimmune diseases. Finally, we will discuss how pDCs could be targeted for therapeutic utility.

PP137. Posterior reversible encephalopathy syndrome (PRES) is a constant component of eclampsia

INTRODUCTION

Posterior reversible encephalopathy syndrome (PRES) has been reported to occur in patients with eclampsia. In both conditions there is evidence to suggest disordered cerebral autoregulation.

OBJECTIVES

We sought to investigate the concurrence of PRES with eclampsia and to describe the associated obstetric, radiologic and critical care correlates.

METHODS

Single center 2001-2010 retrospective cohort study of all patients with eclampsia who underwent neuroimaging via magnetic resonance imaging (MRI) or computerized tomography (CT) with or without contrast. The medical records of all patients with eclampsia during the study interval were identified, evaluated and extracted for pertinent data; a diagnosis of PRES was made by radiologists using standard criteria.

RESULTS

Forty-six of forty-seven (97.9%) patients with eclampsia revealed PRES on neuroimaging using one or more modalities: MRI without contrast=41 (87.2%), MRI with contrast=27 (57.4%), CT without contrast=16 (34%), CT with contrast=7 (14.8%) and/or MRA/MRV=2 (4.3%). PRES was identified within the parietal (36, 78.3%), occipital (35, 76.1%), frontal (29, 63%), temporal (13, 28.3%) and basal ganglia/ brainstem/cerebellum (12, 26.1%). Eclampsia occurred antepartum in 23 patients, postpartum in 24 patients with 22 vaginal/25 cesarean deliveries at a mean maternal age of 21.8 years (range 15-39) and a mean gestational age of 33.9 weeks (range 22.4-41.7 weeks). Ethnicity was African-American in 38 patients. Headache was the most common presenting symptom (87.2%) followed by altered mental status (51.1%), visual disturbances (34%) and nausea/vomiting (19.1%). Severe systolic hypertension was present in 22 (47%) of patients.Use of antihypertensives (87%), magnesium sulfate (100%), diuretics (66%) and corticosteroids (50%) facilitated maternal recovery in all cases with usually a brief hospitalization (mean 3.9 days, range 1-20 days).

CONCLUSION

The common finding of PRES in patients with eclampsia suggests that PRES may be part of the pathogenesis of eclampsia. We speculate that therapy targeted at prevention or reversal of PRES pathogenesis will prevent or facilitate recovery from eclampsia.

Acute inflammatory response to cobalt chromium orthopaedic wear debris in a rodent air-pouch model

This study used a rodent air-pouch model to assess the acute inflammatory response to cobalt-chromium (CoCr) alloy wear debris from a metal-on-metal hip resurfacing implant that may contribute to joint failure. Air-pouches were injected with either sterile phosphate-buffered saline, 1 μg lipopolysaccharide (LPS) or 2.5 mg CoCr wear debris. The in situ inflammatory response was monitored 4, 24, 48 and 72 h and 7 days later. A flow cytometric analysis of the inflammatory exudates showed that CoCr wear debris induced a different inflammatory pattern compared with LPS. LPS induced a strong early (4 h) neutrophil influx, with monocyte/macrophage influx peaking at 24 h, whereas CoCr wear debris initiated almost equal numbers of early monocyte/macrophage and neutrophil recruitment. Histological analyses also showed CoCr debris accumulated in the pouch wall and this was accompanied by vast cellular infiltration and fibrosis around the debris throughout the duration of the experiment. Assessment of inflammatory gene transcripts from air-pouch tissue showed that CoCr wear debris increased the expression of cytokines involved in promoting inflammation and fibrosis (IL-1β, TGF-β) and chemokines that promote the recruitment of neutrophils and monocytes/macrophages (CXCL2 and CCL2). The data suggest that inflammatory responses to CoCr debris induce a specific acute process in which the recruitment of monocytes/macrophages is key.

A novel method to allow noninvasive, longitudinal imaging of the murine immune system in vivo

In vivo imaging has revolutionized understanding of the spatiotemporal complexity that subserves the generation of successful effector and regulatory immune responses. Until now, invasive surgery has been required for microscopic access to lymph nodes (LNs), making repeated imaging of the same animal impractical and potentially affecting lymphocyte behavior. To allow longitudinal in vivo imaging, we conceived the novel approach of transplanting LNs into the mouse ear pinna. Transplanted LNs maintain the structural and cellular organization of conventional secondary lymphoid organs. They participate in lymphocyte recirculation and exhibit the capacity to receive and respond to local antigenic challenge. The same LN could be repeatedly imaged through time without the requirement for surgical exposure, and the dynamic behavior of the cells within the transplanted LN could be characterized. Crucially, the use of blood vessels as fiducial markers also allowed precise re-registration of the same regions for longitudinal imaging. Thus, we provide the first demonstration of a method for repeated, noninvasive, in vivo imaging of lymphocyte behavior.

Antigen depot is not required for alum adjuvanticity

Alum adjuvants have been in continuous clinical use for more than 80 yr. While the prevailing theory has been that depot formation and the associated slow release of antigen and/or inflammation are responsible for alum enhancement of antigen presentation and subsequent T- and B-cell responses, this has never been formally proven. To examine antigen persistence, we used the chimeric fluorescent protein EαGFP, which allows assessment of antigen presentation in situ, using the Y-Ae antibody. We demonstrate that alum and/or CpG adjuvants induced similar uptake of antigen, and in all cases, GFP signal did not persist beyond 24 h in draining lymph node antigen-presenting cells. Antigen presentation was first detectable on B cells within 6–12 h of antigen administration, followed by conventional dendritic cells (DCs) at 12–24 h, then finally plasmacytoid DCs at 48 h or later. Again, alum and/or CpG adjuvants did not have an effect on the magnitude or sequence of this response; furthermore, they induced similar antigen-specific T-cell activation in vivo. Notably, removal of the injection site and associated alum depot, as early as 2 h after administration, had no appreciable effect on antigen-specific T- and B-cell responses. This study clearly rules out a role for depot formation in alum adjuvant activity.—Hutchison, S., Benson, R. A., Gibson, V. B., Pollock, A. H., Garside, P., Brewer, J. M. Antigen depot is not required for alum adjuvanticity.

In vivo real-time multiphoton imaging of T lymphocytes in the mouse brain after experimental stroke

BACKGROUND AND PURPOSE

To gain a better understanding of T cell behavior after stroke, we have developed real-time in vivo brain imaging of T cells by multiphoton microscopy after middle cerebral artery occlusion.

METHODS

Adult male hCD2-GFP transgenic mice that exhibit green fluorescent protein-labeled T cells underwent permanent left distal middle cerebral artery occlusion by electrocoagulation (n=6) or sham surgery (n=6) and then multiphoton laser imaging 72 hours later.

RESULTS

Extravasated T cell number significantly increased after middle cerebral artery occlusion versus sham. Two T cell populations existed after middle cerebral artery occlusion, possibly driven by 2 T cell subpopulations; 1 had significantly lower and the other significantly higher track velocity and displacement rate than sham.

CONCLUSIONS

The different motilities and behaviors of T cells observed using our imaging approach after stroke could reveal important mechanisms of immune surveillance for future therapeutic exploitations.