Visualizing dendritic cell migration within the skin

Effect of Dry Eye Disease on the Kinetics of Lacrimal Gland Dendritic Cells as Visualized by Intravital Multi-Photon Microscopy

The lacrimal gland (LG) is the main source of the tear film aqueous layer and its dysfunction results in dry eye disease (DED), a chronic immune-mediated disorder of the ocular surface. The desiccating stress (DS) murine model that mimics human DED, results in LG dysfunction, immune cell infiltration, and consequently insufficient tear production. To date, the immune cell kinetics in DED are poorly understood. The purpose of this study was to develop a murine model of intravital multi-photon microscopy (IV-MPM) for the LG, and to investigate the migratory kinetics and 3D morphological properties of conventional dendritic cells (cDCs), the professional antigen presenting cells of the ocular surface, in DED. Mice were placed in a controlled environmental chamber with low humidity and increased airflow rate for 2 and 4 weeks to induce DED, while control naïve transgenic mice were housed under standard conditions. DED mice had significantly decreased tear secretion and increased fluorescein staining (p < 0.01) compared to naïve controls. Histological analysis of the LG exhibited infiltrating mononuclear and polymorphonuclear cells (p < 0.05), as well as increased LG swelling (p < 0.001) in DED mice compared to controls. Immunofluorescence staining revealed increased density of cDCs in DED mice (p < 0.001). IV-MPM of the LG demonstrated increased density of cDCs in the LGs of DED mice, compared with controls (p < 0.001). cDCs were more spherical in DED at both time points compared to controls (p < 0.001); however, differences in surface area were found at 2 weeks in DED compared with naïve controls (p < 0.001). Similarly, 3D cell volume was significantly lower at 2 weeks in DED vs. the naïve controls (p < 0.001). 3D instantaneous velocity and mean track speed were significantly higher in DED compared to naïve mice (p < 0.001). Finally, the meandering index, an index for directionality, was significant increased at 4 weeks after DED compared with controls and 2 weeks of DED (p < 0.001). Our IV-MPM study sheds light into the 3D morphological alterations and cDC kinetics in the LG during DED. While in naïve LGs, cDCs exhibit a more dendritic morphology and are less motile, they became more spherical with enhanced motility during DED. This study shows that IV-MPM represents a robust tool to study immune cell trafficking and kinetics in the LG, which might elucidate cellular alterations in immunological diseases, such as DED.

Spheroids of Endothelial Cells and Vascular Smooth Muscle Cells Promote Cell Migration in Hyaluronic Acid and Fibrinogen Composite Hydrogels

Cell migration plays a pivotal role in many pathological and physiological processes. So far, most of the studies have been focused on 2-dimensional cell adhesion and migration. Herein, the migration behaviors of cell spheroids in 3D hydrogels obtained by polymerization of methacrylated hyaluronic acid (HA-MA) and fibrinogen (Fg) with different ratios were studied. The Fg could be released to the medium gradually along with time prolongation, achieving the dynamic change of hydrogel structures and properties. Three types of cell spheroids, i.e., endothelial cell (EC), smooth muscle cell (SMC), and EC-SMC spheroids, were prepared with 10,000 cells in each, whose diameters were about 343, 108, and 224 μm, respectively. The composite hydrogels with an intermediate ratio of Fg allowed the fastest 3D migration of cell spheroids. The ECs-SMCs migrated longest up to 3200 μm at day 14, whereas the SMC spheroids migrated slowest with a distance of only ~400 μm at the same period of time. The addition of free RGD or anti-CD44 could significantly reduce the migration distance, revealing that the cell-substrate interactions take the major roles and the migration is mesenchymal dependent. Moreover, addition of anti-N-cadherin and MMP inhibitors also slowed down the migration rate, demonstrating that the degradation of hydrogels and cell-cell interactions are also largely involved in the cell migration. RT-PCR measurement showed that expression of genes related to cell adhesion and antiapoptosis, and angiogenesis was all upregulated in the EC-SMC spheroids than single EC or SMC spheroids, suggesting that the use of composite cell spheroids is more promising to promote cell-substrate interactions and maintenance of cell functions.

Lymphatic Migration of Immune Cells

Lymphatic vessels collect interstitial fluid that has extravasated from blood vessels and return it to the circulatory system. Another important function of the lymphatic network is to facilitate immune cell migration and antigen transport from the periphery to draining lymph nodes. This migration plays a crucial role in immune surveillance, initiation of immune responses and tolerance. Here we discuss the significance and mechanisms of lymphatic migration of innate and adaptive immune cells in homeostasis, inflammation and cancer.

Kinetics of corneal leukocytes by intravital multiphoton microscopy

Corneal immune privilege is integral in maintaining the clear avascular window to the foreign world. The presence of distinct populations of corneal leukocytes (CLs) in the normal cornea has been firmly established. However, their precise function and kinetics remain, as of yet, unclear. Through intravital multiphoton microscopy (IV-MPM), allowing the means to accumulate critical spatial and temporal cellular information, we provide details for long-term investigation of CL morphology and kinetics under steady state and following inflammation. Significant alterations in size and morphology of corneal CD11c+ dendritic cells (DCs) were noted following acute sterile inflammation, including cell volume (4364.4 ± 489.6 vs. 1787.6 ± 111.0 μm3, P < 0.001) and sphericity (0.82 ± 0.01 vs. 0.42 ± 0.02, P < 0.001) compared with steady state. Furthermore, IV-MPM analyses revealed alterations in both the CD11c+ DC and major histocompatibility complex class II (MHC)-II+ mature antigen-presenting cell population kinetics during inflammation, including track displacement length (CD11c: 16.57 ± 1.41 vs. 4.64 ± 0.56 μm, P < 0.001; MHC-II: 9.03 ± 0.37 vs. 4.09 ± 0.39, P < 0.001) and velocity (CD11c: 1.91 ± 0.07 μm/min vs. 1.73 ± 0.1302 μm/min; MHC-II: 2.97 ± 0.07 vs. 1.62 ± 0.08, P < 0.001) compared with steady state. Our results reveal in vivo evidence of sessile CL populations exhibiting dendritic morphology under steady state and increased velocity of spherical leukocytes following inflammation. IV-MPM represents a powerful tool to study leukocytes in corneal diseases in context.-Seyed-Razavi, Y., Lopez, M. J., Mantopoulos, D., Zheng, L., Massberg, S., Sendra, V. G., Harris, D. L., Hamrah, P. Kinetics of corneal leukocytes by intravital multiphoton microscopy.

Unraveling the Mechanobiology of the Immune System

Cells respond and actively adapt to environmental cues in the form of mechanical stimuli. This extends to immune cells and their critical role in the maintenance of tissue homeostasis. Multiple recent studies have begun illuminating underlying mechanisms of mechanosensation in modulating immune cell phenotypes. Since the extracellular microenvironment is critical to modify cellular physiology that ultimately determines the functionality of the cell, understanding the interactions between immune cells and their microenvironment is necessary. This review focuses on mechanoregulation of immune responses mediated by macrophages, dendritic cells, and T cells, in the context of modern mechanobiology.

Dendritic Cell Migration to Skin-Draining Lymph Nodes Is Controlled by Dermatan Sulfate and Determines Adaptive Immunity Magnitude

For full activation of naïve adaptive lymphocytes in skin-draining lymph nodes (LNs), presentation of peptide:MHC complexes by LN-resident and skin-derived dendritic cells (DCs) that encountered antigens (Ags) is an absolute prerequisite. To get to the nearest draining LN upon intradermal immunization, DCs need to migrate from the infection site to the afferent lymphatics, which can only be reached by traversing a collagen-dense network located in the dermis of the skin through the activity of proteolytic enzymes. Here, we show that mice with altered collagen fibrillogenesis resulting in thicker collagen fibers in the skin display a reduced DC migration to the draining LN upon immune challenge. Consequently, the initiation of the cellular and humoral immune response was diminished. Ag-specific CD8+ and CD4+ T cells as well as Ag-specific germinal center B cells and serum immunoglobulin levels were significantly decreased. Hence, we postulate that alterations to the production of extracellular matrix, as seen in various connective tissue disorders, may in the end affect the qualitative outcome of adaptive immunity.

Inducing Ischemia-reperfusion Injury in the Mouse Ear Skin for Intravital Multiphoton Imaging of Immune Responses

Ischemia-reperfusion injury (IRI) occurs when there is transient hypoxia due to the obstruction of blood flow (ischemia) followed by a subsequent re-oxygenation of the tissues (reperfusion). In the skin, ischemia-reperfusion (IR) is the main contributing factor to the pathophysiology of pressure ulcers. While the cascade of events leading up to the inflammatory response has been well studied, the spatial and temporal responses of the different subsets of immune cells to an IR injury are not well understood. Existing models of IR using the clamping technique on the skin flank are highly invasive and unsuitable for studying immune responses to injury, while similar non-invasive magnet clamping studies in the skin flank are less-than-ideal for intravital imaging studies. In this protocol, we describe a robust model of non-invasive IR developed on mouse ear skin, where we aim to visualize in real-time the cellular response of immune cells after reperfusion via multiphoton intravital imaging (MP-IVM).

Current Evidence for a Role of the Kynurenine Pathway of Tryptophan Metabolism in Multiple Sclerosis

The kynurenine pathway (KP) is the major metabolic pathway of the essential amino acid tryptophan (TRP). Stimulation by inflammatory molecules, such as interferon-γ (IFN-γ), is the trigger for induction of the KP, driving a complex cascade of production of both neuroprotective and neurotoxic metabolites, and in turn, regulation of the immune response and responses of brain cells to the KP metabolites. Consequently, substantial evidence has accumulated over the past couple of decades that dysregulation of the KP and the production of neurotoxic metabolites are associated with many neuroinflammatory and neurodegenerative diseases, including Parkinson’s disease, AIDS-related dementia, motor neurone disease, schizophrenia, Huntington’s disease, and brain cancers. In the past decade, evidence of the link between the KP and multiple sclerosis (MS) has rapidly grown and has implicated the KP in MS pathogenesis. KP enzymes, indoleamine 2,3-dioxygenase (IDO-1) and tryptophan dioxygenase (highest expression in hepatic cells), are the principal enzymes triggering activation of the KP to produce kynurenine from TRP. This is in preference to other routes such as serotonin and melatonin production. In neurological disease, degradation of the blood–brain barrier, even if transient, allows the entry of blood monocytes into the brain parenchyma. Similar to microglia and macrophages, these cells are highly responsive to IFN-γ, which upregulates the expression of enzymes, including IDO-1, producing neurotoxic KP metabolites such as quinolinic acid. These metabolites circulate systemically or are released locally in the brain and can contribute to the excitotoxic death of oligodendrocytes and neurons in neurological disease principally by virtue of their agonist activity at N-methyl-d-aspartic acid receptors. The latest evidence is presented and discussed. The enzymes that control the checkpoints in the KP represent an attractive therapeutic target, and consequently several KP inhibitors are currently in clinical trials for other neurological diseases, and hence may make suitable candidates for MS patients. Underpinning these drug discovery endeavors, in recent years, several advances have been made in how KP metabolites are assayed in various biological fluids, and tremendous advancements have been made in how specimens are imaged to determine disease progression and involvement of various cell types and molecules in MS.

Binding of WIP to actin is essential for T cell actin cytoskeleton integrity and tissue homing

The Wiskott-Aldrich syndrome protein (WASp) is important for actin polymerization in T cells and for their migration. WASp-interacting protein (WIP) binds to and stabilizes WASp and also interacts with actin. Cytoskeletal and functional defects are more severe in WIP(-/-) T cells, which lack WASp, than in WASp(-/-) T cells, suggesting that WIP interaction with actin may be important for T cell cytoskeletal integrity and function. We constructed mice that lack the actin-binding domain of WIP (WIPΔABD mice). WIPΔABD associated normally with WASp but not F-actin. T cells from WIPΔABD mice had normal WASp levels but decreased cellular F-actin content, a disorganized actin cytoskeleton, impaired chemotaxis, and defective homing to lymph nodes. WIPΔABD mice exhibited a T cell intrinsic defect in contact hypersensitivity and impaired responses to cutaneous challenge with protein antigen. Adoptively transferred antigen-specific CD4(+) T cells from WIPΔABD mice had decreased homing to antigen-challenged skin of wild-type recipients. These findings show that WIP binding to actin, independently of its binding to WASp, is critical for the integrity of the actin cytoskeleton in T cells and for their migration into tissues. Disruption of WIP binding to actin could be of therapeutic value in T cell-driven inflammatory diseases.

A quantitative approach to histopathological dissection of elastin-related disorders using multiphoton microscopy

BACKGROUND

Multiphoton microscopy (MPM) is a novel imaging technology that has recently become applicable for diagnostic purposes. The use of (near) infrared light in MPM allows for deep tissue imaging. In addition, this modality exploits the autofluorescent nature of extracellular matrix fibres within the skin.

OBJECTIVES

To quantitate the structure and abundance of elastic fibres in human dermis in three dimensions utilizing autofluorescent signals generated by MPM for the objective examination of elastin-related skin disorders.

METHODS

Cross-sections of skin samples from elastin-related disorders were analysed by MPM and correlated to histopathology. In situ visualization of elastic fibres by MPM was conducted by en face imaging of ex vivo skin samples through the intact epidermis. Image analysis software was used to quantify elastic fibres in three dimensions.

RESULTS

Based on the MPM-detected elastin-specific autofluorescence, we developed the Dermal Elastin Morphology Index (DEMI), calculated as the ratio of elastic fibre surface area and volume. This enabled objective three-dimensional quantification of elastic fibres. Quantitative scoring of sun-damaged skin using DEMI correlated with qualitative histopathological grading of the severity of solar elastosis. Furthermore, this approach was applied to changes in elastic fibre architecture in other disorders, such as pseudoxanthoma elasticum (PXE), PXE-like syndrome, elastofibroma, focal dermal elastosis, anetoderma, mid-dermal elastolysis and striae distensae. We imaged elastic fibres in intact ex vivo skin imaged en face through the epidermis, indicating that this approach could be used in vivo.

CONCLUSIONS

MPM has the potential for noninvasive in vivo visualization of elastic fibres in the dermis with near histological resolution. DEMI allows objective assessment of elastic fibres to support diagnosis and monitoring of disease progress or therapy of elastin-related skin disorders.

Application of Confocal Laser Scanning Microscopy in Biology and Medicine

Fluorescence confocal laser scanning microscopy and reflectance confocal laser scanning microscopy are up-to-date highend study methods. Confocal microscopy is used in cell biology and medicine. By using confocal microscopy, it is possible to study bioplasts and localization of protein molecules and other compounds relative to cell or tissue structures, and to monitor dynamic cell processes. Confocal microscopes enable layer-by-layer scanning of test items to create demonstrable 3D models. As compared to usual fluorescent microscopes, confocal microscopes are characterized by a higher contrast ratio and image definition.

Langerhans cell maturation is accompanied by induction of N-cadherin and the transcriptional regulators of epithelial-mesenchymal transition ZEB1/2

Langerhans cells (LCs) are a unique subset of dendritic cells (DCs) that express epithelial adhesion molecules, allowing them to form contacts with epithelial cells and reside in epidermal/epithelial tissues. The dynamic regulation of epithelial adhesion plays a decisive role in the life cycle of LCs. It controls whether LCs remain immature and sessile within the epidermis or mature and egress to initiate immune responses. So far, the molecular machinery regulating epithelial adhesion molecules during LC maturation remains elusive. Here, we generated pure populations of immature human LCs in vitro to systematically probe for gene-expression changes during LC maturation. LCs down-regulate a set of epithelial genes including E-cadherin, while they upregulate the mesenchymal marker N-cadherin known to facilitate cell migration. In addition, N-cadherin is constitutively expressed by monocyte-derived DCs known to exhibit characteristics of both inflammatory-type and interstitial/dermal DCs. Moreover, the transcription factors ZEB1 and ZEB2 (ZEB is zinc-finger E-box-binding homeobox) are upregulated in migratory LCs. ZEB1 and ZEB2 have been shown to induce epithelial-to-mesenchymal transition (EMT) and invasive behavior in cancer cells undergoing metastasis. Our results provide the first hint that the molecular EMT machinery might facilitate LC mobilization. Moreover, our study suggests that N-cadherin plays a role during DC migration.

Detection and Discrimination of Non-Melanoma Skin Cancer by Multimodal Imaging

Non-melanoma skin cancer (NMSC) belongs to the most frequent human neoplasms. Its exposed location facilitates a fast ambulant treatment. However, in the clinical practice far more lesions are removed than necessary, due to the lack of an efficient pre-operational examination procedure: Standard imaging methods often do not provide a sufficient spatial resolution. The demand for an efficient in vivo imaging technique might be met in the near future by non-linear microscopy. As a first step towards this goal, the appearance of NMSC in various microspectroscopic modalities has to be defined and approaches have to be derived to distinguish healthy skin from NMSC using non-linear optical microscopy. Therefore, in this contribution the appearance of ex vivo NMSC in a combination of coherent anti-Stokes Raman scattering (CARS), second harmonic generation (SHG) and two photon excited fluorescence (TPEF) imaging—referred as multimodal imaging—is described. Analogous to H&E staining, an overview of the distinct appearances and features of basal cell and squamous cell carcinoma in the complementary modalities is derived, and is expected to boost in vivo studies of this promising technological approach.

Cutaneous immunosurveillance and regulation of inflammation by group 2 innate lymphoid cells

Type 2 immunity is critical for defense against cutaneous infections but also underlies the development of allergic skin diseases. We report the identification in normal mouse dermis of an abundant, phenotypically unique group 2 innate lymphoid cell (ILC2) subset that depended on interleukin 7 (IL-7) and constitutively produced IL-13. Intravital multiphoton microscopy showed that dermal ILC2 cells specifically interacted with mast cells, whose function was suppressed by IL-13. Treatment of mice deficient in recombination-activating gene 1 (Rag1(-/-)) with IL-2 resulted in the population expansion of activated, IL-5-producing dermal ILC2 cells, which led to spontaneous dermatitis characterized by eosinophil infiltrates and activated mast cells. Our data show that ILC2 cells have both pro- and anti-inflammatory properties and identify a previously unknown interactive pathway between two innate populations of cells of the immune system linked to type 2 immunity and allergic diseases.

Shedding light on cutaneous innate immune responses: the intravital microscopy approach

The skin is under constant assault by environmental factors and microbes. Innate immune cells in epidermis and dermis regulate immune responses against pathogens while maintaining tolerance against commensal bacteria and autoantigens. The introduction of intravital imaging approaches, in particular multiphoton microscopy, has enabled studying the cellular and molecular regulation of cutaneous immunity in real time within intact skin. Here, we discuss recent advances in our understanding of innate immune cell behaviour in the skin, as unravelled by intravital microscopy, with emphasis on the function of myeloid cells, including dendritic cells, neutrophils and monocytes.

Effect of the poly(ethylene glycol) (PEG) density on the access and uptake of particles by antigen-presenting cells (APCs) after subcutaneous administration

Lymphatic trafficking of particles to the secondary lymphoid organs, such as lymph nodes, and the cell types that particles access are critical factors that control the quality and quantity of immune responses. In this study, we evaluated the effect of PEGylation on the lymphatic trafficking and accumulation of particles in draining lymph nodes (dLNs) as well as the cell types that internalized particles. As a model system, 200 nm polystyrene (PS) particles were modified with different densities of poly(ethylene glycol) (PEG) and administered subcutaneously to mice. PEGylation enhanced the efficiency of particle drainage away from the injection site as well as the access of particles to dendritic cells (DCs). The accumulation of particles in dLNs was dependent on the PEG density. PEGylation also enhanced uptake by DCs while reducing internalization by B cells at the single cell level. Our results indicate that PEGylation facilitated the trafficking of particles to dLNs either through enhanced trafficking in lymphatic vessels or by enhanced internalization by migratory DCs. This study provides insight into utilizing PEGylated particles for the development of synthetic vaccines.

Mouse models for Chikungunya virus: deciphering immune mechanisms responsible for disease and pathology

Chikungunya virus (CHIKV), an alphavirus, has been responsible for large epidemic outbreaks with serious economic and social impact during the last 6 years. Transmitted by Aedes mosquitoes, it causes Chikungunya fever, an acute illness in patients with a stooped posture often associated with chronic and incapacitating arthralgia. The unprecedented re-emergence has stimulated renewed interest in CHIKV. This review discusses the advantages and disadvantages of different animal models for CHIKV infections and their importance to study the role of the immune system in different pathologies caused by CHIKV. We also reveal how such studies still present a difficult challenge, but are indispensible for mechanistic studies to further understand the pathophysiology of CHIKV infections.

Lymph node homing of T cells and dendritic cells via afferent lymphatics

The continuous migration of immune cells is of utmost importance for the induction of both protective immunity as well as immunological tolerance. However, relatively little is known about the molecular cues that regulate the entry of immune cells from peripheral, nonlymphoid tissues into afferent lymph vessels and, in particular, their subsequent transmigration from afferent lymphatics into the parenchyma of draining lymph nodes (LNs). Here, we review the requirements for T cells and dendritic cells (DCs) to enter initial afferent lymph vessels of the skin. We discuss how these cells subsequently gain access to the paracortex of draining lymph nodes; a location that allows for efficient interaction between both cell populations, providing the right environment for the induction of immunity as well as tolerance.

Intravital multiphoton imaging of immune responses in the mouse ear skin

Multiphoton (MP) microscopy enables the direct in vivo visualization, with high spatial and temporal resolution, of fluorescently tagged immune cells, extracellular matrix and vasculature in tissues. This approach, therefore, represents a powerful alternative to traditional methods of assessing immune cell function in the skin, which are mainly based on flow cytometry and histology. Here we provide a step-by-step protocol describing experimental procedures for intravital MP imaging of the mouse ear skin, which can be easily adapted to address many specific skin-related biological questions. We demonstrate the use of this procedure by characterizing the response of neutrophils during cutaneous inflammation, which can be used to perform in-depth analysis of neutrophil behavior in the context of the skin microanatomy, including the epidermis, dermis and blood vessels. Such experiments are typically completed within 1 d, but as the procedures are minimally invasive, it is possible to perform longitudinal studies through repeated imaging.

Acute and chronic rejection in upper extremity transplantation: what have we learned?

To date, 78 upper extremity transplants have been performed in 55 recipients around the world. The purpose of this article is to provide an overview of acute and chronic rejection (CR) and to summarize collective insights in upper extremity transplantation. To date, almost all patients experienced AR that is pathophysiologically similar to that in solid organs. The spectre of chronic rejection is just emerging. Upper extremity transplantation has significant potential as a reconstructive option only if efforts are invested in strategies to reduce risks of prolonged immunosuppression and in approaches to better diagnose, monitor and treat AR and CR.

Visualizing the neutrophil response to sterile tissue injury in mouse dermis reveals a three-phase cascade of events

Neutrophil granulocytes traffic into sites of organ injury in which they may not only participate in tissue repair and pathogen clearance but may also contribute to collateral cell damage through the release of noxious mediators. The dynamics and mechanisms of neutrophil migration in the extravascular space toward loci of tissue damage are not well understood. Here, we have used intravital multi-photon microscopy to dissect the behavior of neutrophils in response to tissue injury in the dermis of mice. We found that, following confined physical injury, initially rare scouting neutrophils migrated in a directional manner toward the damage focus. This was followed by the attraction of waves of additional neutrophils, and finally stabilization of the neutrophil cluster around the injury. Although neutrophil migration in the steady state and during the scouting phase depended on pertussis toxin-sensitive signals, the amplification phase was sensitive to interference with the cyclic adenosine diphosphate ribose pathway. We finally demonstrated that neutrophil scouts also transit through the non-inflamed dermis, suggesting immunosurveillance function by these cells. Together, our data unravel a three-step cascade of events that mediates the specific accumulation of neutrophils at sites of sterile tissue injury in the interstitial space.

Cutaneous immunosurveillance by self-renewing dermal gammadelta T cells

The dermis contains a novel population of γδT cells that are distinct from epidermal γδT cells and produce IL-17 in response to mycobacterial infection.

The presence of γδ T cell receptor (TCR)–expressing cells in the epidermis of mice, termed dendritic epidermal T cells (DETCs), is well established. Because of their strict epidermal localization, it is likely that DETCs primarily respond to epithelial stress, such as infections or the presence of transformed cells, whereas they may not participate directly in dermal immune responses. In this study, we describe a prominent population of resident dermal γδ T cells, which differ from DETCs in TCR usage, phenotype, and migratory behavior. Dermal γδ T cells are radioresistant, cycle in situ, and are partially depend on interleukin (IL)-7, but not IL-15, for their development and survival. During mycobacterial infection, dermal γδ T cells are the predominant dermal cells that produce IL-17. Absence of dermal γδ T cells is associated with decreased expansion in skin draining lymph nodes of CD4⁺ T cells specific for an immunodominant Mycobacterium tuberculosis epitope. Decreased CD4⁺ T cell expansion is related to a reduction in neutrophil recruitment to the skin and decreased BCG shuttling to draining lymph nodes. Thus, dermal γδ T cells are an important part of the resident cutaneous immunosurveillance program. Our data demonstrate functional specialization of T cells in distinct microcompartments of the skin.

Intravital microscopy as a tool to study drug delivery in preclinical studies

The technical developments in the field of non-linear microscopy have made intravital microscopy one of the most successful techniques for studying physiological and pathological processes in live animals. Intravital microscopy has been utilized to address many biological questions in basic research and is now a fundamental tool for preclinical studies, with an enormous potential for clinical applications. The ability to dynamically image cellular and subcellular structures combined with the possibility to perform longitudinal studies have empowered investigators to use this discipline to study the mechanisms of action of therapeutic agents and assess the efficacy on their targets in vivo. The goal of this review is to provide a general overview of the recent advances in intravital microscopy and to discuss some of its applications in preclinical studies.

TGF-beta is required to maintain the pool of immature Langerhans cells in the epidermis

The pivotal role of TGF-beta in Langerhans cell (LC) development has been previously established in TGF-beta-deficient mice, which lack epidermal LCs. As to whether TGF-beta also governs LC homeostasis and function remains elusive. To assess the role of TGF-beta-mediated control of cutaneous dendritic cells (DCs) in vivo, we generated mice with a conditional knockout of the TGF-beta receptor 1 (TbetaR1) under a DC-specific promoter (DC-TbetaR1(del) mice). While initial LC seeding occurred in DC-TbetaR1(del) mice, the cells disappeared from the epidermis during the first week of life. TbetaR1-deficient LCs demonstrated spontaneous maturation and gained migratory potential based on increased surface expression of MHC class II, costimulatory molecules, and CCR7 and downregulation of E-cadherin. In parallel to their early loss from the epidermis, migrating LCs were reduced in the dermis and skin-draining lymph nodes of adult DC-TbetaR1(del) mice, whereas the number of Langerin(+) dermal DCs was similar to wild-type. In the absence of LCs, low-dose contact hypersensitivity in DC-TbetaR1(del) mice was significantly diminished. In contrast, ear swelling was restored to wild-type levels when a higher hapten dose was applied to efficiently target TbetaR1-deficient dermal DCs. In conclusion, TGF-beta inhibits in vivo LC maturation and migratory phenotype, identifying TGF-beta as a critical factor controlling LC homeostasis in the steady state.

Intravital imaging of DSS-induced cecal mucosal damage in GFP-transgenic mice using two-photon microscopy

BACKGROUND

Two-photon laser-scanning microscopy (TPLSM) is a powerful diagnostic tool for real-time, high-resolution structural imaging. However, obtaining high-quality in vivo TPLSM images of intra-abdominal organs remains technically challenging.

MATERIALS AND METHODS

An organ-stabilizing system was applied to high-quality TPLSM imaging. Real-time imaging of visceral organs, such as the liver, spleen, kidney and intestine, of transgenic green fluorescent protein (GFP) mice was performed in vivo using TPLSM. The bacterial translocation model using dextran sodium sulfate (DSS)-induced colitis was also investigated in prepared GFP mice following simple surgery. This allowed the capture of morphological real images using in vivo TPLSM. Immunohistochemical analysis of ZO-1 was performed to support the morphological findings of TPLSM.

RESULTS AND CONCLUSIONS

We established an organ-stabilizing system to evaluate the real-time imaging of visceral organs in actin-GFP transgenic mice using in vivo TPLSM. DSS-induced colitis showed irregularity of crypt architecture, disappearance of crypts, inflammatory cell infiltration and increased rolling of white blood cells along the vasculature. In addition, the intercellular distance of mucosal cells in the crypt and vascular endothelial cells in the intestinal wall was increased in the intestinal mucosa during DSS colitis. In DSS colitis, there was remarkable loss of mucosal and vascular endothelial ZO-1 expression, as could be seen by a decrease in ZO-1 staining. In conclusion, our observations suggested the possibility that our TPLSM imaging system can be used to clarify the pathophysiological changes in various diseases using longitudinal studies of microscopic changes in the same animal over long periods of time.

Selective and site-specific mobilization of dermal dendritic cells and Langerhans cells by Th1- and Th2-polarizing adjuvants

Dendritic cells (DCs) initiate and polarize adaptive immune responses toward varying functional outcomes. By means of intravital two-photon microscopy, we report that dermal dendritic cells (DDCs) and Langerhans cells (LCs) are differentially mobilized during contact sensitization and by adjuvants such as unmethylated CpG oligonucleotide (CpG) and LPS that induce T helper type 1 (Th1) responses, or papain that induces T helper type 2 (Th2) responses. In ear pinna, contact sensitization, CpG, LPS, and papain all mobilized DDCs in three distinct phases: increased motility and dendritic probing, directed migration, and entry into lymphatic vessels. During the same treatments, the adjacent LCs in ear pinna remained immotile over a 48-hr period of observation. In contrast, footpads lacked DDCs and Th1-polarizing adjuvants selectively induced a delayed mobilization of LCs after 48 hr. Th1 polarization of CD4(+) T cells was independent of the immunization site, whereas ear immunization favored Th2 polarization, correlating with site-specific DC distribution and dynamics. Our results provide an initial description of peripheral DC dynamics in response to adjuvants and imply that LC mobilization enhances a Th1 response and is not sufficient to trigger a Th2 response, whereas mobilization of DDCs alone is sufficient to trigger T-cell proliferation and to polarize initial T-cell activation toward a Th2 response.

Intravital microscopy: a novel tool to study cell biology in living animals

Intravital microscopy encompasses various optical microscopy techniques aimed at visualizing biological processes in live animals. In the last decade, the development of non-linear optical microscopy resulted in an enormous increase of in vivo studies, which have addressed key biological questions in fields such as neurobiology, immunology and tumor biology. Recently, few studies have shown that subcellular processes can be imaged dynamically in the live animal at a resolution comparable to that achieved in cell cultures, providing new opportunities to study cell biology under physiological conditions. The overall aim of this review is to give the reader a general idea of the potential applications of intravital microscopy with a particular emphasis on subcellular imaging. An overview of some of the most exciting studies in this field will be presented using resolution as a main organizing criterion. Indeed, first we will focus on those studies in which organs were imaged at the tissue level, then on those focusing on single cells imaging, and finally on those imaging subcellular organelles and structures.

Understanding the murine cutaneous dendritic cell network to improve intradermal vaccination strategies

Dendritic cells (DCs) form a heterogeneous group of antigen presenting cells that play different roles in tissue immunity. Recent studies have revealed the presence of distinct DC populations in murine skin, highlighting the complexity of the cutaneous DC network. In this review, we will define the major DC subsets that populate the different layers of the skin, focusing on their origin and the mechanisms controlling their homeostasis. We will also review recent evidence underlining the functional specialization of dermal DC subsets and its relevance in the design of novel vaccine approaches.

Extending the knowledge in histochemistry and cell biology

Central to modern Histochemistry and Cell Biology stands the need for visualization of cellular and molecular processes. In the past several years, a variety of techniques has been achieved bridging traditional light microscopy, fluorescence microscopy and electron microscopy with powerful software-based post-processing and computer modeling. Researchers now have various tools available to investigate problems of interest from bird's- up to worm's-eye of view, focusing on tissues, cells, proteins or finally single molecules. Applications of new approaches in combination with well-established traditional techniques of mRNA, DNA or protein analysis have led to enlightening and prudent studies which have paved the way toward a better understanding of not only physiological but also pathological processes in the field of cell biology. This review is intended to summarize articles standing for the progress made in "histo-biochemical" techniques and their manifold applications.

Molecular mechanisms of leukocyte trafficking in T-cell-mediated skin inflammation: insights from intravital imaging

Infiltration of T cells is a key step in the pathogenesis of the inflammatory skin diseases atopic dermatitis, allergic contact dermatitis and psoriasis. Understanding the mechanisms of T cell recruitment to the skin is therefore of fundamental importance for the discovery and application of novel therapies for these conditions. Studies of both clinical samples and experimental models of skin inflammation have implicated specific adhesion molecules and chemokines in lymphocyte recruitment. In particular, recent studies using advanced in vivo imaging techniques have greatly increased our understanding of the kinetics and molecular basis of this process. In this review, we summarise the current understanding of the cellular immunology of antigen-driven dermal inflammation and the roles of adhesion molecules and chemokines. We focus on results obtained using intravital microscopy to examine the dermal microvasculature and interstitium to determine the mechanisms of T cell recruitment and migration in experimental models of T-cell-mediated skin inflammation.

Dynamic Imaging of CD8(+) T cells and dendritic cells during infection with Toxoplasma gondii

To better understand the initiation of CD8⁺ T cell responses during infection, the primary response to the intracellular parasite Toxoplasma gondii was characterized using 2-photon microscopy combined with an experimental system that allowed visualization of dendritic cells (DCs) and parasite specific CD8⁺ T cells. Infection with T. gondii induced localization of both these populations to the sub-capsular/interfollicular region of the draining lymph node and DCs were required for the expansion of the T cells. Consistent with current models, in the presence of cognate antigen, the average velocity of CD8⁺ T cells decreased. Unexpectedly, infection also resulted in modulation of the behavior of non-parasite specific T cells. This TCR-independent process correlated with the re-modeling of the lymph node micro-architecture and changes in expression of CCL21 and CCL3. Infection also resulted in sustained interactions between the DCs and CD8⁺ T cells that were visualized only in the presence of cognate antigen and were limited to an early phase in the response. Infected DCs were rare within the lymph node during this time frame; however, DCs presenting the cognate antigen were detected. Together, these data provide novel insights into the earliest interaction between DCs and CD8⁺ T cells and suggest that cross presentation by bystander DCs rather than infected DCs is an important route of antigen presentation during toxoplasmosis.

Toxoplasma gondii is a protozoan parasite that can infect a wide range of hosts, including humans. Infection with T. gondii is potentially life threatening in immuno-compromised individuals and it can be detrimental during pregnancy, often leading to abortion of the fetus. Dendritic cells are thought to play a vital role in the development of protective immunity to Toxoplasma gondii through their ability to produce immunological signals such as cytokines and also process and present parasite derived peptides to T cells. However, little is known about the actual interactions between these cell types in an intact organ, such as the lymph node, during infection. Using the technology of live imaging by 2-photon microscopy we have identified a very early window of time during infection when dendritic cells and T cells make sustained contacts with one another, which appears crucial for the generation of protective responses. We also show that substantial changes are induced in the lymph node micro-architecture as a result of infection, which in turn could have effects on immune responses to secondary pathogens. Understanding the interaction between these immune cells in vivo that leads to resistance to active infection would help in the design of better strategies to develop protective immune responses against this pathogen in immuno-compromised individuals.