Intravital microscopy: a practical guide on imaging intracellular structures in live animals

Multi-scale in vivo imaging of tumour development using a germline conditional triple-reporter system

Imaging reporter genes are indispensable for visualising biological processes in living subjects, particularly in cancer research where they have been used to observe tumour development, cancer cell dissemination, and treatment response. Engineering reporter genes into the germline frequently involves single imaging modality reporters operating over limited spatial scales. To address these limitations, we developed an inducible triple-reporter mouse model (Rosa26LSL - NRL) that integrates reporters for complementary imaging modalities, flfluorescence, bioluminescence and positron emission tomography (PET), along with inducible Cre-lox functionality for precise spatiotemporal control of reporter expression. We demonstrated robust reporter inducibility across various tissues in the Rosa26LSL - NRL mouse, facilitating effective tracking and characterisation of tumours in liver and lung cancer mouse models. We precisely pinpointed tumour location using multimodal whole-body imaging which guided in situ lung microscopy to visualise cell-cell interactions within the tumour microenvironment. The triple-reporter system establishes a robust new platform technology for multi-scale investigation of biological processes within whole animals, enabling tissue-specific and sensitive cell tracking, spanning from the whole-body to cellular scales.

Real-Time Multiphoton Intravital Microscopy of Drug Extravasation in Tumours during Acoustic Cluster Therapy

Optimising drug delivery to tumours remains an obstacle to effective cancer treatment. A prerequisite for successful chemotherapy is that the drugs reach all tumour cells. The vascular network of tumours, extravasation across the capillary wall and penetration throughout the extracellular matrix limit the delivery of drugs. Ultrasound combined with microbubbles has been shown to improve the therapeutic response in preclinical and clinical studies. Most studies apply microbubbles designed as ultrasound contrast agents. Acoustic Cluster Therapy (ACT®) is a novel approach based on ultrasound-activated microbubbles, which have a diameter 5-10 times larger than regular contrast agent microbubbles. An advantage of using such large microbubbles is that they are in contact with a larger part of the capillary wall, and the oscillating microbubbles exert more effective biomechanical effects on the vessel wall. In accordance with this, ACT® has shown promising therapeutic results in combination with various drugs and drug-loaded nanoparticles. Knowledge of the mechanism and behaviour of drugs and microbubbles is needed to optimise ACT®. Real-time intravital microscopy (IVM) is a useful tool for such studies. This paper presents the experimental setup design for visualising ACT® microbubbles within the vasculature of tumours implanted in dorsal window (DW) chambers. It presents ultrasound setups, the integration and alignment of the ultrasound field with the optical system in live animal experiments, and the methodologies for visualisation and analysing the recordings. Dextran was used as a fluorescent marker to visualise the blood vessels and to trace drug extravasation and penetration into the extracellular matrix. The results reveal that the experimental setup successfully recorded the kinetics of extravasation and penetration distances into the extracellular matrix, offering a deeper understanding of ACT's mechanisms and potential in localised drug delivery.

Preclinical Models for Cryptococcosis of the CNS and Their Characterization Using In Vivo Imaging Techniques

Infections caused by Cryptococcus neoformans and Cryptococcus gattii remain a challenge to our healthcare systems as they are still difficult to treat. In order to improve treatment success, in particular for infections that have disseminated to the central nervous system, a better understanding of the disease is needed, addressing questions like how it evolves from a pulmonary to a brain disease and how novel treatment approaches can be developed and validated. This requires not only clinical research and research on the microorganisms in a laboratory environment but also preclinical models in order to study cryptococci in the host. We provide an overview of available preclinical models, with particular emphasis on models of cryptococcosis in rodents. In order to further improve the characterization of rodent models, in particular the dynamic aspects of disease manifestation, development, and ultimate treatment, preclinical in vivo imaging methods are increasingly used, mainly in research for oncological, neurological, and cardiac diseases. In vivo imaging applications for fungal infections are rather sparse. A second aspect of this review is how research on models of cryptococcosis can benefit from in vivo imaging methods that not only provide information on morphology and tissue structure but also on function, metabolism, and cellular properties in a non-invasive way.

K2P2.1 is a regulator of inflammatory cell responses in idiopathic inflammatory myopathies

K2P2.1 (TREK1), a two-pore domain potassium channel, has emerged as regulator of leukocyte transmigration into the central nervous system. In the context of skeletal muscle, immune cell infiltration constitutes the pathogenic hallmark of idiopathic inflammatory myopathies (IIMs). However, the underlying mechanisms remain to be elucidated. In this study, we investigated the role of K2P2.1 in the autoimmune response of IIMs. We detected K2P2.1 expression in primary skeletal muscle and endothelial cells of murine and human origin. We observed an increased pro-inflammatory cell response, adhesion and transmigration by pharmacological blockade or genetic deletion of K2P2.1 in vitro and in in vivo myositis mouse models. Of note, our findings were not restricted to endothelial cells as skeletal muscle cells with impaired K2P2.1 function also demonstrated a strong pro-inflammatory response. Conversely, these features were abrogated by activation of K2P2.1 and improved the disease course of a myositis mouse model. In humans, K2P2.1 expression was diminished in IIM patients compared to non-diseased controls arguing for the translatability of our findings. In summary, K2P2.1 may regulate the inflammatory response of skeletal muscle. Further research is required to understand whether K2P2.1 could serve as novel therapeutic target.

The immune response to systemically administered endotoxin in the murine intestinal microcirculation under pentobarbital versus isoflurane anesthesia

BACKGROUND

Pentobarbital and isoflurane are commonly used veterinary anesthetics. Due to the dangers of overdose by repeat-bolus regimen of pentobarbital, isoflurane has been recommended. However, literature suggests isoflurane-induced inhibition of cytokine and adhesion molecule release, impacting leukocyte adhesion.

OBJECTIVE

This study aims to characterize the impacts of pentobarbital versus isoflurane on leukocyte interactions within the intestinal microcirculation with and without endotoxin challenge.

METHODS

Female BALB/c mice were subjected to pentobarbital or isoflurane (N = 20) and challenged with endotoxin or saline by intraperitoneal injection. The mice were kept under anesthesia for 2 hours. Fluorochromes, rhodamine-6 G and fluorescein isothiocyanate, were injected intravenously. To visualize leukocyte adhesion within the intestinal microcirculation, laparotomy and intravital microscopy was performed. Leukocyte rolling and adhesion was quantified offline in a blinded fashion.

RESULTS

Within collecting venules, leukocyte rolling and adhesion showed no significant differences between pentobarbital and isoflurane anesthesia under basal conditions. Endotoxin challenge caused a similar response in both anesthetic groups. Within postcapillary venules, no statistical differences between the two anesthetics were found for adhering leukocytes under basal conditions or following endotoxin challenge either. However, leukocyte rolling after LPS-challenge was significantly decreased in postcapillary venules during isoflurane anesthesia compared to pentobarbital anesthesia.

CONCLUSIONS

Isoflurane anesthesia showed only minor differences in the immune response to endotoxin within the intestinal microcirculation compared to pentobarbital anesthesia. Due to the superior safety profile of volatile anesthetics, immunological studies may choose isoflurane over pentobarbital as the veterinary anesthetic of choice.

Intravital Microscopy of Lipopolysaccharide-Induced Inflammatory Changes in Different Organ Systems-A Scoping Review

Intravital microscopy (IVM) is a powerful imaging tool that captures biological processes in real-time. IVM facilitates the observation of complex cellular interactions in vivo, where ex vivo and in vitro experiments lack the physiological environment. IVM has been used in a multitude of studies under healthy and pathological conditions in different organ systems. IVM has become essential in the characterization of the immune response through visualization of leukocyte-endothelial interactions and subsequent changes within the microcirculation. Lipopolysaccharide (LPS), a common inflammatory trigger, has been used to induce inflammatory changes in various studies utilizing IVM. In this review, we provide an overview of IVM imaging of LPS-induced inflammation in different models, such as the brain, intestines, bladder, and lungs.

Multiscale Label-Free Imaging of Fibrillar Collagen in the Tumor Microenvironment

With recent advances in cancer therapeutics, there is a great need for improved imaging methods for characterizing cancer onset and progression in a quantitative and actionable way. Collagen, the most abundant extracellular matrix protein in the tumor microenvironment (and the body in general), plays a multifaceted role, both hindering and promoting cancer invasion and progression. Collagen deposition can defend the tumor with immunosuppressive effects, while aligned collagen fiber structures can enable tumor cell migration, aiding invasion and metastasis. Given the complex role of collagen fiber organization and topology, imaging has been a tool of choice to characterize these changes on multiple spatial scales, from the organ and tumor scale to cellular and subcellular level. Macroscale density already aids in the detection and diagnosis of solid cancers, but progress is being made to integrate finer microscale features into the process. Here we review imaging modalities ranging from optical methods of second harmonic generation (SHG), polarized light microscopy (PLM), and optical coherence tomography (OCT) to the medical imaging approaches of ultrasound and magnetic resonance imaging (MRI). These methods have enabled scientists and clinicians to better understand the impact collagen structure has on the tumor environment, at both the bulk scale (density) and microscale (fibrillar structure) levels. We focus on imaging methods with the potential to both examine the collagen structure in as natural a state as possible and still be clinically amenable, with an emphasis on label-free strategies, exploiting intrinsic optical properties of collagen fibers.

In vivo fluorescence imaging: success in preclinical imaging paves the way for clinical applications

Advances in diagnostic imaging have provided unprecedented opportunities to detect diseases at early stages and with high reliability. Diagnostic imaging is also crucial to monitoring the progress or remission of disease and thus is often the central basis of therapeutic decision-making. Currently, several diagnostic imaging modalities (computed tomography, magnetic resonance imaging, and positron emission tomography, among others) are routinely used in clinics and present their own advantages and limitations. In vivo near-infrared (NIR) fluorescence imaging has recently emerged as an attractive imaging modality combining low cost, high sensitivity, and relative safety. As a preclinical tool, it can be used to investigate disease mechanisms and for testing novel diagnostics and therapeutics prior to their clinical use. However, the limited depth of tissue penetration is a major challenge to efficient clinical use. Therefore, the current clinical use of fluorescence imaging is limited to a few applications such as image-guided surgery on tumors and retinal angiography, using FDA-approved dyes. Progress in fluorophore development and NIR imaging technologies holds promise to extend their clinical application to oncology, cardiovascular diseases, plastic surgery, and brain imaging, among others. Nanotechnology is expected to revolutionize diagnostic in vivo fluorescence imaging through targeted delivery of NIR fluorescent probes using antibody conjugation. In this review, we discuss the latest advances in in vivo fluorescence imaging technologies, NIR fluorescent probes, and current and future clinical applications.

Mouse models and human islet transplantation sites for intravital imaging

Human islet transplantations into rodent models are an essential tool to aid in the development and testing of islet and cellular-based therapies for diabetes prevention and treatment. Through the ability to evaluate human islets in an in vivo setting, these studies allow for experimental approaches to answer questions surrounding normal and disease pathophysiology that cannot be answered using other in vitro and in vivo techniques alone. Intravital microscopy enables imaging of tissues in living organisms with dynamic temporal resolution and can be employed to measure biological processes in transplanted human islets revealing how experimental variables can influence engraftment, and transplant survival and function. A key consideration in experimental design for transplant imaging is the surgical placement site, which is guided by the presence of vasculature to aid in functional engraftment of the islets and promote their survival. Here, we review transplantation sites and mouse models used to study beta cell biology in vivo using intravital microscopy and we highlight fundamental observations made possible using this methodology.

Intravital microscopy for real-time monitoring of drug delivery and nanobiological processes

Intravital microscopy (IVM) expands our understanding of cellular and molecular processes, with applications ranging from fundamental biology to (patho)physiology and immunology, as well as from drug delivery to drug processing and drug efficacy testing. In this review, we highlight modalities, methods and model organisms that make up today's IVM landscape, and we present how IVM - via its high spatiotemporal resolution - enables analysis of metabolites, small molecules, nanoparticles, immune cells, and the (tumor) tissue microenvironment. We furthermore present examples of how IVM facilitates the elucidation of nanomedicine kinetics and targeting mechanisms, as well as of biological processes such as immune cell death, host-pathogen interactions, metabolic states, and disease progression. We conclude by discussing the prospects of IVM clinical translation and examining the integration of machine learning in future IVM practice.

The Role of Optical Imaging in Translational Nanomedicine

Nanomedicines have been a major research focus in the past two decades and are increasingly emerging in a broad range of clinical applications. However, a proper understanding of their biodistribution is required to further progress the field of nanomedicine. For this, imaging methods to monitor the delivery and therapeutic efficacy of nanoparticles are urgently needed. At present, optical imaging is the most common method used to study the biodistribution of nanomaterials, where the unique properties of nanomaterials and advances in optical imaging can jointly result in novel methods for optimal monitoring of nanomaterials in preclinical animal models. This review article aims to give an introduction to nanomedicines and their translational impact to highlight the potential of optical imaging to study the biodistribution of nanoparticles and to monitor the delivery and therapeutic efficacy at the preclinical level. After introducing both domains, the review focuses on different techniques that can be used to overcome some intrinsic limitations of optical imaging and how this can specifically benefit nanoparticle studies. Finally, we point out some important key features of nanoparticles that currently hinder their full potential in the clinic and how the advances in optical imaging can help to provide us with the information needed to further boost the clinical translation and expand the field of nanomedicines.

Extracellular vesicles through the blood-brain barrier: a review

Extracellular vesicles (EVs) are particles naturally released from cells that are delimited by a lipid bilayer and are unable to replicate. How the EVs cross the Blood–Brain barrier (BBB) in a bidirectional manner between the bloodstream and brain parenchyma remains poorly understood. Most in vitro models that have evaluated this event have relied on monolayer transwell or microfluidic organ-on-a-chip techniques that do not account for the combined effect of all cellular layers that constitute the BBB at different sites of the Central Nervous System. There has not been direct transcytosis visualization through the BBB in mammals in vivo, and evidence comes from in vivo experiments in zebrafish. Literature is scarce on this topic, and techniques describing the mechanisms of EVs motion through the BBB are inconsistent. This review will focus on in vitro and in vivo methodologies used to evaluate EVs transcytosis, how EVs overcome this fundamental structure, and discuss potential methodological approaches for future analyses to clarify these issues. Understanding how EVs cross the BBB will be essential for their future use as vehicles in pharmacology and therapeutics.

In vivo molecular and single cell imaging

Molecular imaging is used to improve the disease diagnosis, prognosis, monitoring of treatment in living subjects. Numerous molecular targets have been developed for various cellular and molecular processes in genetic, metabolic, proteomic, and cellular biologic level. Molecular imaging modalities such as Optical Imaging, Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and Computed Tomography (CT) can be used to visualize anatomic, genetic, biochemical, and physiologic changes in vivo. For in vivo cell imaging, certain cells such as cancer cells, immune cells, stem cells could be labeled by direct and indirect labeling methods to monitor cell migration, cell activity, and cell effects in cell-based therapy. In case of cancer, it could be used to investigate biological processes such as cancer metastasis and to analyze the drug treatment process. In addition, transplanted stem cells and immune cells in cell-based therapy could be visualized and tracked to confirm the fate, activity, and function of cells. In conventional molecular imaging, cells can be monitored in vivo in bulk non-invasively with optical imaging, MRI, PET, and SPECT imaging. However, single cell imaging in vivo has been a great challenge due to an extremely high sensitive detection of single cell. Recently, there has been great attention for in vivo single cell imaging due to the development of single cell study. In vivo single imaging could analyze the survival or death, movement direction, and characteristics of a single cell in live subjects. In this article, we reviewed basic principle of in vivo molecular imaging and introduced recent studies for in vivo single cell imaging based on the concept of in vivo molecular imaging.

Imaging Neutrophil Migration in the Mouse Skin to Investigate Subcellular Membrane Remodeling Under Physiological Conditions

The study of immune cell recruitment and function in tissues has been a very active field over the last two decades. Neutrophils are among the first immune cells to reach the site of inflammation and to participate in the innate immune response during infection or tissue damage. So far, neutrophil migration has been successfully visualized using various in vitro experimental systems based on uniform stimulation, or confined migration under agarose, or micro-fluidic channels. However, these models do not recapitulate the complex microenvironment that neutrophils encounter in vivo. The development of multiphoton microscopy (MPM)-based techniques, such as intravital subcellular microscopy (ISMic), offer a unique tool to visualize and investigate neutrophil dynamics at subcellular resolutions under physiological conditions. In particular, the ear of a live anesthetized mouse provides an experimental advantage to follow neutrophil interstitial migration in real-time due to its ease of accessibility and lack of surgical exposure. ISMic provides the optical resolution, speed, and depth of acquisition necessary to track both cellular and, more importantly, subcellular processes in 3D over time (4D). Moreover, multi-modal imaging of the interstitial microenvironment (i.e., blood vessels, resident cells, extracellular matrix) can be readily accomplished using a combination of transgenic mice expressing select fluorescent markers, exogenous labeling via fluorescent probes, tissue intrinsic fluorescence, and second/third harmonic generated signals. This protocol describes 1) the preparation of neutrophils for adoptive transfer into the mouse ear, 2) different settings for optimal sub-cellular imaging, 3) strategies to minimize motion artifacts while maintaining a physiological response, 4) examples of membrane remodeling observed in neutrophils using ISMic, and 5) a workflow for the quantitative analysis of membrane remodeling in migrating neutrophils in vivo.

The consequence of endothelial remodelling on the blood spinal cord barrier and nociception

Nociception is a fundamental acute protective mechanism that prevents harm to an organism. Understanding the integral processes that control nociceptive processing are fundamental to our appreciation of which cellular and molecular features underlie this process. There is an extensive understanding of how sensory neurons interpret differing sensory modalities and intensities. However, it is widely appreciated that the sensory neurons do not act alone. These work in harmony with inflammatory and vascular systems to modulate pain perception. The spinal cord has an extensive interaction with the capillary network in the form of a blood spinal cord barrier to ensure homeostatic control of the spinal cord neuron milieu. However, there is an extensive appreciation that disturbances in the blood spinal cord barrier contribute to the onset of chronic pain. Enhanced vascular permeability and impaired blood perfusion have both been highlighted as contributors to chronic pain manifestation. Here, we discuss the evidence that demonstrates alterations in the blood spinal cord barrier influences nociceptive processing and perception of pain.

Imaging Endocytosis Dynamics in Health and Disease

Endocytosis is a critical process for cell growth and viability. It mediates nutrient uptake, guarantees plasma membrane homeostasis, and generates intracellular signaling cascades. Moreover, it plays an important role in dead cell clearance and defense against external microbes. Finally, endocytosis is an important cellular route for the delivery of nanomedicines for therapeutic treatments. Thus, it is not surprising that both environmental and genetic perturbation of endocytosis have been associated with several human conditions such as cancer, neurological disorders, and virus infections, among others. Over the last decades, a lot of research has been focused on developing advanced imaging methods to monitor endocytosis events with high resolution in living cells and tissues. These include fluorescence imaging, electron microscopy, and correlative and super-resolution microscopy. In this review, we outline the major endocytic pathways and briefly discuss how defects in the molecular machinery of these pathways lead to disease. We then discuss the current imaging methodologies used to study endocytosis in different contexts, highlighting strengths and weaknesses.

Methods to Evaluate Bacterial Motility and Its Role in Bacterial–Host Interactions

Bacterial motility is a widespread characteristic that can provide several advantages for the cell, allowing it to move towards more favorable conditions and enabling host-associated processes such as colonization. There are different bacterial motility types, and their expression is highly regulated by the environmental conditions. Because of this, methods for studying motility under realistic experimental conditions are required. A wide variety of approaches have been developed to study bacterial motility. Here, we present the most common techniques and recent advances and discuss their strengths as well as their limitations. We classify them as macroscopic or microscopic and highlight the advantages of three-dimensional imaging in microscopic approaches. Lastly, we discuss methods suited for studying motility in bacterial–host interactions, including the use of the zebrafish model.

Multidimensional Fluorescence Imaging of Embryonic and Postnatal Mammary Gland Development

Multidimensional fluorescence imaging represents a powerful approach for studying the dynamic cellular processes underpinning the development, function, and maintenance of the mammary gland. Here, we describe key multidimensional imaging strategies that enable visualization of mammary branching morphogenesis and epithelial cell fate dynamics during postnatal and embryonic mammary gland development. These include 4-dimensional intravital microscopy and ex vivo imaging of embryonic mammary cultures, in addition to methods that facilitate 3-dimensional imaging of the ductal epithelium at single-cell resolution within its native stroma. Collectively, these approaches provide a window into mammary developmental dynamics, and the perturbations underlying tissue dysfunction and disease.

Real-Time Imaging of Immune Modulation by Cannabinoids Using Intravital Fluorescence Microscopy

Introduction: The endocannabinoid system (ECS) is an endogenous regulatory system involved in a wide range of physiologic and disease processes. Study of ECS regulation provides novel drug targets for disease treatment. Intravital microscopy (IVM), a microscopy-based imaging method that allows the observation of cells and cell-cell interactions within various tissues and organs in vivo, has been utilized to study tissues and cells in their physiologic microenvironment. This article reviews the current state of the IVM techniques used in ECS-related inflammation research. Methodological Aspects of IVM: IVM with focus on conventional fluorescent microscope has been introduced in investigation of microcirculatory function and the behavior of individual circulating cells in an in vivo environment. Experimental setting, tissue protection under physiologic condition, and microscopical observation are described. Application of IVM in Experimental Inflammatory Disorders: Using IVM to investigate the effects of immune modulation by cannabinoids is extensively reviewed. The inflammatory disorders include sepsis, arthritis, diabetes, interstitial cystitis, and inflammatory conditions in the central nervous system and eyes. Conclusion: IVM is a critical tool in cannabinoid and immunology research. It has been applied to investigate the role of the ECS in physiologic and disease processes. This review demonstrates that the IVM technique provides a unique means in understanding ECS regulation on immune responses in diseases under their physical conditions, which could not be achieved by other methods.

Intravital microscopy imaging of kidney injury and regeneration

Acute kidney injury (AKI) is a common clinical symptom, which is mainly manifested by elevated serum creatinine and blood urea nitrogen levels. When AKI is not repaired in time, the patient is prone to develop chronic kidney disease (CKD). The kidney is composed of more than 30 different cells, and its structure is complex. It is extremely challenging to understand the lineage relationships and cell fate of these cells in the process of kidney injury and regeneration. Since the 20th century, lineage tracing technology has provided an important mean for studying organ development, tissue damage repair, and the differentiation and fate of single cells. However, traditional lineage tracing methods rely on sacrificing animals to make tissue slices and then take snapshots with conventional imaging tools to obtain interesting information. This method cannot achieve dynamic and continuous monitoring of cell actions on living animals. As a kind of intravital microscopy (IVM), two-photon microscopy (TPM) has successfully solved the above problems. Because TPM has the ability to penetrate deep tissues and can achieve imaging at the single cell level, lineage tracing technology with TPM is gradually becoming popular. In this review, we provided the key technical elements of lineage tracing, and how to use intravital imaging technology to visualize and quantify the fate of renal cells.

Actually Seeing What Is Going on - Intravital Microscopy in Tissue Engineering

Intravital microscopy (IVM) study approach offers several advantages over in vitro, ex vivo, and 3D models. IVM provides real-time imaging of cellular events, which provides us a comprehensive picture of dynamic processes. Rapid improvement in microscopy techniques has permitted deep tissue imaging at a higher resolution. Advances in fluorescence tagging methods enable tracking of specific cell types. Moreover, IVM can serve as an important tool to study different stages of tissue regeneration processes. Furthermore, the compatibility of different tissue engineered constructs can be analyzed. IVM is also a promising approach to investigate host reactions on implanted biomaterials. IVM can provide instant feedback for improvising tissue engineering strategies. In this review, we aim to provide an overview of the requirements and applications of different IVM approaches. First, we will discuss the history of IVM development, and then we will provide an overview of available optical modalities including the pros and cons. Later, we will summarize different fluorescence labeling methods. In the final section, we will discuss well-established chronic and acute IVM models for different organs.

Intravital Imaging of Pulmonary Immune Response in Inflammation and Infection

Intravital microscopy (IVM) is a unique imaging method providing insights in cellular functions and interactions in real-time, without the need for tissue extraction from the body. IVM of the lungs has specific challenges such as restricted organ accessibility, respiratory movements, and limited penetration depth. Various surgical approaches and microscopic setups have been adapted in order to overcome these challenges. Among others, these include the development of suction stabilized lung windows and the use of more advanced optical techniques. Consequently, lung IVM has uncovered mechanisms of leukocyte recruitment and function in several models of pulmonary inflammation and infection. This review focuses on bacterial pneumonia, aspiration pneumonia, sepsis-induced acute lung Injury, and cystic fibrosis, as examples of lung inflammation and infection. In addition, critical details of intravital imaging techniques of the lungs are discussed.

Method for Acute Intravital Imaging of the Large Intestine in Live Mice

Intravital microscopy is an imaging technique aimed at the visualization of the dynamics of biological processes in live animals. In the last decade, the development of nonlinear optical microscopy has enormously increased the use of this technique, thus addressing key biological questions in different fields such as immunology, neurobiology and tumor biology. In addition, new upcoming strategies to minimize motion artifacts due to animal respiration and heartbeat have enabled the visualization in real time of biological processes at cellular and subcellular resolution. Recently, intravital microscopy has been applied to analyze different aspect of mucosal immunity in the gut. However, the majority of these studies have been performed on the small intestine. Although crucial aspects of the biology of this organ have been unveiled, the majority of intestinal pathologies in humans occur in the large intestine.Here, we describe a method to surgically expose and stabilize the large intestine in live mice and to perform short-term (up to 2 h) intravital microscopy.

Live Imaging

Being able to vizualize a pathogen at a site of interaction with a host is an aesthetically appealing idea and the resulting images can be both informative as well as enjoyable to view. Moreover, the approaches used to derive these images can be powerful in terms of offering data unobtainable by other methods. In this article, we review three primary modalities for live imaging Borrelia spirochetes: whole animal imaging, intravital microscopy and live cell imaging. Each method has strengths and weaknesses, which we review, as well as specific purposes for which they are optimally utilized. Live imaging borriliae is a relatively recent development and there was a need of a review to cover the area. Here, in addition to the methods themselves, we also review areas of spirochete biology that have been significantly impacted by live imaging and present a collection of images associated with the forward motion in the field driven by imaging studies.

Platelet Imaging

The knowledge gained through imaging platelets has formed the backbone of our understanding of their biology in health and disease. Early investigators relied on conventional light microscopy with limited resolution and were primarily able to identify the presence and basic morphology of platelets. The advent of high resolution technologies, in particular, electron microscopy, accelerated our understanding of the dynamics of platelet ultrastructure dramatically. Further refinements and improvements in our ability to localize and reliably identify platelet structures have included the use of immune-labeling techniques, correlative-fluorescence light and electron microscopy, and super-resolution microscopies. More recently, the expanded development and application of intravital microscopy in animal models has enhanced our knowledge of platelet functions and thrombus formation in vivo, as these experimental systems most closely replicate native biological environments. Emerging improvements in our ability to characterize platelets at the ultrastructural and organelle levels include the use of platelet cryogenic electron tomography with quantitative, unbiased imaging analysis, and the ability to genetically label platelet features with electron dense markers for analysis by electron microscopy.

The Secretive Life of Neutrophils Revealed by Intravital Microscopy

Neutrophils are the most abundant circulating leukocyte within the blood stream and for many years the dogma has been that these cells migrate rapidly into tissues in response to injury or infection, forming the first line of host defense. While it has previously been documented that neutrophils marginate within the vascular beds of the lung and liver and are present in large numbers within the parenchyma of tissues, such as spleen, lymph nodes, and bone marrow (BM), the function of these tissue resident neutrophils under homeostasis, in response to pathogen invasion or injury has only recently been explored, revealing the unexpected role of these cells as immunoregulators or immune helpers and also unraveling their heterogeneity and plasticity. Neutrophils are highly motile cells and the use of intravital microscopy (IVM) to image cells within their environment with little manipulation has dramatically increased our understanding of the function, migratory behavior, and interaction of these short-lived cells with other innate and adaptive immune cells. Contrary to previous dogma, these studies have shown that marginated and tissue resident neutrophils are the first responders to pathogens and injury, critical in limiting the spread of infection and contributing to the orchestration of the subsequent immune response. The interplay of neutrophils, with other neutrophils, leukocytes, and stroma cells can also modulate and tune their early and late response in order to eradicate pathogens, minimize tissue damage, and, in certain circumstances, contribute to tissue repair. In this review, we will follow the extraordinary journey of neutrophils from their origin in the BM to their death, exploring their role as tissue resident cells in the lung, spleen, lymph nodes, and skin and outlining the importance of neutrophil subsets, their functions under homeostasis, and in response to infection. Finally, we will comment on how understanding these processes in greater detail at a molecular level can lead to development of new therapeutics.

Cellular plasticity: A mechanism for homeostasis in the kidney

Cellular plasticity is a topical subject with interest spanning a wide range of fields from developmental biology to regenerative medicine. Even the nomenclature is a subject of debate, and the underlying mechanisms are still under investigation. On top of injury repair, cell plasticity is a constant physiological process in adult organisms and tissues, in response to homeostatic challenges. In this review we discuss two examples of plasticity for the maintenance of homeostasis in the renal system-namely the renin-producing juxtaglomerular cells (JG cells) and cortical collecting duct (CCD) cells. JG cells show plasticity through recruitment mechanisms, answering the demand for an increase in renin production. In the CCD, cells appear to have the ability to transdifferentiate between principal and intercalated cells to help maintain the highly regulated solute transport levels of that segment. These two cases highlight the complexity of plasticity processes and the role they can play in the kidney.

Beyond the Green Fluorescent Protein: Biomolecular Reporters for Anaerobic and Deep-Tissue Imaging

Fluorescence imaging represents cornerstone technology for studying biological function at the cellular and molecular levels. The technology's centerpiece is a prolific collection of genetic reporters based on the green fluorescent protein (GFP) and related analogs. More than two decades of protein engineering have endowed the GFP repertoire with an incredible assortment of fluorescent proteins, allowing scientists immense latitude in choosing reporters tailored to various cellular and environmental contexts. Nevertheless, GFP and derivative reporters have specific limitations that hinder their unrestricted use for molecular imaging. These challenges have inspired the development of new reporter proteins and imaging mechanisms. Here, we review how these developments are expanding the frontiers of reporter gene techniques to enable nondestructive studies of cell function in anaerobic environments and deep inside intact animals-two important biological contexts that are fundamentally incompatible with the use of GFP-based reporters.

Smart diagnostic nano-agents for cerebral ischemia

A summary of the latest developments on imaging techniques and smart nano-diagnostics used for ischemic stroke.

Recent advances in tissue imaging for cancer research

Image analysis in clinical research has evolved at fast pace in the last decade. This review discusses basic concepts ranging from immunohistochemistry to advanced techniques such as multiplex imaging, digital pathology, flow cytometry and intravital microscopy. Tissue imaging ex vivo is still one of the gold-standards in the field due to feasibility. We describe here different protocols and applications of digital analysis providing basic and clinical researchers with an overview on how to analyse tissue images. In vivo imaging is not easily accessible to researchers; however, it provides invaluable dynamic information. Overall, we discuss a plethora of techniques that - when combined - constitute a powerful platform for basic and translational cancer research.

Three-dimensional intravital imaging in bone research

Intravital imaging has emerged as a novel and efficient tool for visualization of in situ dynamics of cellular behaviors and cell-microenvironment interactions in live animals, based on desirable microscopy techniques featuring high resolutions, deep imaging and low phototoxicity. Intravital imaging, especially based on multi-photon microscopy, has been used in bone research for dynamics visualization of a variety of physiological and pathological events at the cellular level, such as bone remodeling, hematopoiesis, immune responses and cancer development, thus, providing guidance for elucidating novel cellular mechanisms in bone biology as well as guidance for new therapies. This review is aimed at interpreting development and advantages of intravital imaging in bone research, and related representative discoveries concerning bone matrices, vessels, and various cells types involved in bone physiologies and pathologies. Finally, current limitations, further refinement, and extended application of intravital imaging in bone research are concluded.

Intravital microscopy in mammalian multicellular organisms

Imaging subcellular processes in live animals is no longer a dream. The development of Intravital Subcellular Microscopy (ISMic) combined with the astounding repertoire of available mouse models makes it possible to investigate processes such as membrane trafficking in mammalian living tissues under native conditions. This has provided the unique opportunity to answer questions that cannot be otherwise addressed in reductionist model systems and to link cell biology to tissue pathophysiology.

State of the Art of Natural Killer Cell Imaging: A Systematic Review

Natural killer (NK) cell therapy is a promising alternative to conventional T cell-based treatments, although there is a lack of diagnostic tools to predict and evaluate therapeutic outcomes. Molecular imaging can offer several approaches to non-invasively address this issue. In this study, we systematically reviewed the literature to evaluate the state of the art of NK cell imaging and its translational potential. PubMed and Scopus databases were searched for published articles on the imaging of NK cells in humans and preclinical models. Study quality was evaluated following Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) criteria. We pooled studies as follows: Optical, magnetic resonance imaging (MRI) and nuclear medicine imaging with a total of 21 studies (n = 5, n = 8 and n = 8, respectively). Considering the limitation of comparing different imaging modalities, it appears that optical imaging (OI) of NK cells is very useful in a preclinical setting, but has the least translational potential. MRI provides high quality images without ionizing radiations with lower sensitivity. Nuclear medicine is the only imaging technique that has been applied in humans (four papers), but results were not outstanding due to a limited number of enrolled patients. At present, no technique emerged as superior over the others and more standardization is required in conducting human and animal studies.

In vivo imaging of type 1 diabetes immunopathology using eye-transplanted islets in NOD mice

AIMS/HYPOTHESIS

Autoimmune attack against the insulin-producing beta cells in the pancreatic islets results in type 1 diabetes. However, despite considerable research, details of the type 1 diabetes immunopathology in situ are not fully understood mainly because of difficult access to the pancreatic islets in vivo.

METHODS

Here, we used direct non-invasive confocal imaging of islets transplanted in the anterior chamber of the eye (ACE) to investigate the anti-islet autoimmunity in NOD mice before, during and after diabetes onset. ACE-transplanted islets allowed longitudinal studies of the autoimmune attack against islets and revealed the infiltration kinetics and in situ motility dynamics of fluorescence-labelled autoreactive T cells during diabetes development. Ex vivo immunostaining was also used to compare immune cell infiltrations into islet grafts in the eye and kidney as well as in pancreatic islets of the same diabetic NOD mice.

RESULTS

We found similar immune infiltration in native pancreatic and ACE-transplanted islets, which established the ACE-transplanted islets as reliable reporters of the autoimmune response. Longitudinal studies in ACE-transplanted islets identified in vivo hallmarks of islet inflammation that concurred with early immune infiltration of the islets and preceded their collapse and hyperglycaemia onset. A model incorporating data on ACE-transplanted islet degranulation and swelling allowed early prediction of the autoimmune attack in the pancreas and prompted treatments to intercept type 1 diabetes.

CONCLUSIONS/INTERPRETATION

The current findings highlight the value of ACE-transplanted islets in studying early type 1 diabetes pathogenesis in vivo and underscore the need for timely intervention to halt disease progression.

Megakaryocyte volume modulates bone marrow niche properties and cell migration dynamics

All hematopoietic cells that develop in the bone marrow must cross the endothelial barrier to enter the blood circulation. Blood platelets, however, are released by bigger protrusions of huge progenitor cells, named megakaryocytes, and enter the blood stream as so-called proplatelets before fragmenting into mature platelets. Recently, a second function of megakaryocytes has been identified, as they modulate the quiescence of hematopoietic stem cells, mostly via different soluble factors. We know from light sheet fluorescence microscopy images that megakaryocytes are distributed throughout the bone marrow facing a dense vascular network. Here, we used such three-dimensional images to provide a realistic simulation template reflecting the in vivo cell-vessel distributions resulting in reliable whole-bone analysis in silico Combining this approach with an automated image analysis pipeline, we found that megakaryocytes influence migration of neutrophils and hematopoietic stem cells, and thus act as biomechanical restrainers modulating cell mobility and extravasation. Indeed, as a consequence of increased megakaryocyte volumes in platelet-depleted mice neutrophil mobility was reduced in these animals.

Quantifying in situ adaptive immune cell cognate interactions in humans

Two-photon excitation microscopy (TPEM) has revolutionized the understanding of adaptive immunity. However, TPEM usually requires animal models and is not amenable to the study of human disease. The recognition of antigen by T cells requires cell contact and is associated with changes in T cell shape. We postulated that by capturing these features in fixed tissue samples, we could quantify in situ adaptive immunity. Therefore, we used a deep convolutional neural network to identify fundamental distance and cell-shape features associated with cognate help (cell-distance mapping (CDM)). In mice, CDM was comparable to TPEM in discriminating cognate T cell-dendritic cell (DC) interactions from non-cognate T cell-DC interactions. In human lupus nephritis, CDM confirmed that myeloid DCs present antigen to CD4+ T cells and identified plasmacytoid DCs as an important antigen-presenting cell. These data reveal a new approach with which to study human in situ adaptive immunity broadly applicable to autoimmunity, infection, and cancer.

Cell Migration in Microfluidic Devices: Invadosomes Formation in Confined Environments

The last 20 years have seen the blooming of microfluidics technologies applied to biological sciences. Microfluidics provides effective tools for biological analysis, allowing the experimentalists to extend their playground to single cells and single molecules, with high throughput and resolution which were inconceivable few decades ago. In particular, microfluidic devices are profoundly changing the conventional way of studying the cell motility and cell migratory dynamics. In this chapter we will furnish a comprehensive view of the advancements made in the research domain of confinement-induced cell migration, thanks to the use of microfluidic devices. The chapter is subdivided in three parts. Each section will be addressing one of the fundamental questions that the microfluidic technology is contributing to unravel: (i) where cell migration takes place, (ii) why cells migrate and, (iii) how the cells migrate. The first introductory part is devoted to a thumbnail, and partially historical, description of microfluidics and its impact in biological sciences. Stress will be put on two aspects of the devices fabrication process, which are crucial for biological applications: materials used and coating methods. The second paragraph concerns the cell migration induced by environmental cues: chemical, leading to chemotaxis, mechanical, at the basis of mechanotaxis, and electrical, which induces electrotaxis. Each of them will be addressed separately, highlighting the fundamental role of microfluidics in providing the well-controlled experimental conditions where cell migration can be induced, investigated and ultimately understood. The third part of the chapter is entirely dedicated to how the cells move in confined environments. Invadosomes (the joint name for podosomes and invadopodia) are cell protrusion that contribute actively to cell migration or invasion. The formation of invadosomes under confinement is a research topic that only recently has caught the attention of the scientific community: microfluidic design is helping shaping the future direction of this emerging field of research.

Morphology-Based Distinction Between Healthy and Pathological Cells Utilizing Fourier Transforms and Self-Organizing Maps

The appearance and the movements of immune cells are driven by their environment. As a reaction to a pathogen invasion, the immune cells are recruited to the site of inflammation and are activated to prevent a further spreading of the invasion. This is also reflected by changes in the behavior and the morphological appearance of the immune cells. In cancerous tissue, similar morphokinetic changes have been observed in the behavior of microglial cells: intra-tumoral microglia have less complex 3-dimensional shapes, having less-branched cellular processes, and move more rapidly than those in healthy tissue. The examination of such morphokinetic properties requires complex 3D microscopy techniques, which can be extremely challenging when executed longitudinally. Therefore, the recording of a static 3D shape of a cell is much simpler, because this does not require intravital measurements and can be performed on excised tissue as well. However, it is essential to possess analysis tools that allow the fast and precise description of the 3D shapes and allows the diagnostic classification of healthy and pathogenic tissue samples based solely on static, shape-related information. Here, we present a toolkit that analyzes the discrete Fourier components of the outline of a set of 2D projections of the 3D cell surfaces via Self-Organizing Maps. The application of artificial intelligence methods allows our framework to learn about various cell shapes as it is applied to more and more tissue samples, whilst the workflow remains simple.

Preparation of Murine Submandibular Salivary Gland for Upright Intravital Microscopy

The submandibular salivary gland (SMG) is one of the three major salivary glands, and is of interest for many different fields of biological research, including cell biology, oncology, dentistry, and immunology. The SMG is an exocrine gland comprised of secretory epithelial cells, myofibroblasts, endothelial cells, nerves, and extracellular matrix. Dynamic cellular processes in the rat and mouse SMG have previously been imaged, mostly using inverted multi-photon microscope systems. Here, we describe a straightforward protocol for the surgical preparation and stabilization of the murine SMG in anesthetized mice for in vivo imaging with upright multi-photon microscope systems. We present representative intravital image sets of endogenous and adoptively transferred fluorescent cells, including the labeling of blood vessels or salivary ducts and second harmonic generation to visualize fibrillar collagen. In sum, our protocol allows for surgical preparation of mouse salivary glands in upright microscopy systems, which are commonly used for intravital imaging in the field of immunology.

Making Thymus Visible: Understanding T-Cell Development from a New Perspective

T-cell development is coupled with a highly ordered migratory pattern. Lymphoid progenitors must follow a precise journey; starting from the hematopoietic tissue, they move toward the thymus and then migrate into and out of distinct thymic microenvironments, where they receive signals and cues required for their differentiation into naïve T-cells. Knowing where, when, and how these cells make directional “decisions” is key to understanding T-cell development. Such insights can be gained by directly observing developing T-cells within their environment under various conditions and following specific experimental manipulations. In the last decade, several model systems have been developed to address temporal and spatial aspects of T-cell development using imaging approaches. In this perspective article, we discuss the advantages and limitations of these systems and highlight a particularly powerful in vivo model that has been recently established. This model system enables the migratory behavior of all thymocytes to be studied simultaneously in a noninvasive and quantitative manner, making it possible to perform systems-level studies that reveal fundamental principles governing T-cell dynamics during development and in disease.

Pseudomonas aeruginosa Takes a Multi-Target Approach to Achieve Junction Breach

Pseudomonas aeruginosa is an opportunistic pathogen which uses a number of strategies to cross epithelial and endothelial barriers at cell–cell junctions. In this review, we describe how the coordinated actions of P. aeruginosa's virulence factors trigger various molecular mechanisms to disarm the junctional gate responsible for tissue integrity.

Visualizing Leukocyte Rolling and Adhesion in Angiotensin II-Infused Mice: Techniques and Pitfalls

Epifluorescence intravital video microscopy (IVM) of blood vessels is an established method to evaluate the activation of immune cells and their ability to role and adhere to the endothelial layer. Visualization of circulating cells by injection of fluorescent dyes or fluorophore-coupled antibodies is commonly used. Alternatively, fluorescent reporter mice can be used. Interactions of leukocytes, in particular lysozyme M⁺ (LysM⁺) monocytes, with the vessel wall play pivotal roles in promoting vascular dysfunction and arterial hypertension. We here present the technique to visualize and quantify leukocyte rolling and adhesion in carotid arteries in angiotensin II (AngII)-induced hypertension in mice by IVM.

The implantation of a catheter damages the vascular wall and leads to altered blood cell responses. We compared different injection techniques and administration routes to visualize leukocytes in a LysMCre⁺IRG⁺ mouse with widespread expression of red fluorescent protein and conditional expression of green fluorescent protein in LysM⁺ cells. To study LysM⁺ cell activation, we used AngII infused mice in which rolling and adhesion of leukocytes to the endothelium is increased. We either injected acridine orange using a jugular catheter or directly though the tail vein and compared the amount of rolling and adhering cells. We found that jugular catheter implantation per se increased the number of rolling and adhering LysM⁺ cells in sham-infused LysMCre⁺IRG⁺ mice compared to controls. This activation was augmented in AngII-infused mice. Interestingly, injecting acridine orange directly through the tail vein did not increase LysM⁺ cell adhesion or rolling in sham-infused mice. We thereby demonstrated the importance of transgenic reporter mice expressing fluorescent proteins to not interfere with in vivo processes during experimentation. Furthermore, tail vein injection of fluorescent tracers might be a possible alternative to jugular catheter injections.

Two Photon Intravital Microscopy of Lyme Borrelia in Mice

Two-photon intravital microscopy is a powerful tool that allows visualization of cells in intact tissues in a live animal in real time. In recent years, this advanced technology has been applied to understand pathogen-host interactions using fluorescently labeled bacteria. In particular, infectious fluorescent transformants of the Lyme disease spirochete Borrelia burgdorferi, an Ixodes tick-transmitted pathogen, have been imaged by two-photon intravital microscopy to study bacterial motility and interactions of the pathogen with feeding ticks and host tissues. Here, we describe the techniques and equipment used to image mammalian-adapted spirochetes in the skin of living mice in vivo and in joints ex vivo using two-photon intravital microscopy.

Neutrophil extracellular traps and the dysfunctional innate immune response of cystic fibrosis lung disease: a review

BACKGROUND

Cystic Fibrosis (CF) is a devastating genetic disease characterised primarily by unrelenting lung inflammation and infection resulting in premature death and significant morbidity. Neutrophil Extracellular Traps (NETs) are possibly key to inflammation in the disease. This review aims to draw together existing research investigating NETs in the context of a dysfunctional innate immune system in CF.

MAIN BODY

NETs have a limited anti-microbial role in CF and studies have shown they are present in higher numbers in CF airways and their protein constituents correlate with lung function decline. Innate immune system cells express CFTR and myeloid-specific CFTR KO mice have greater neutrophil recruitment and higher pro-inflammatory cytokine production to both sterile and bacterial inflammatory challenges. CFTR KO neutrophils have impaired anti-microbial capacity and intrinsic abnormalities in the pH of their cytoplasm, abnormal protein trafficking, increased neutrophil elastase and myeloperoxidase function, and decreased hypochlorite concentrations in their phagolysosomes. Furthermore, neutrophils from CF patients have less intrinsic apoptosis and may be therefore more likely to make NETs. CFTR KO macrophages have high intraphagolysosomal pH and increased toll-like receptor 4 on their cell surface membranes, which inhibit their anti-microbial capacity and render them hyper-responsive to inflammatory stimuli, respectively. Pharmacological treatments for CF target these intrinsic abnormalities of immune dysfunction. Emerging evidence suggests that the absence of CFTR from neutrophils affects NETosis and the interaction of NETs with macrophages.

CONCLUSION

Current evidence suggests that NETs contribute to inflammation and lung destruction rather than working effectively in their anti-microbial capacity. Further studies focussing on the pro-inflammatory nature of NET constituents are required to identify the exact mechanistic role of NETs in CF and potential therapeutic interventions.

Fluorescence Lifetime Imaging of a Caspase-3 Apoptosis Reporter

Caspase-3 is a proteolytic enzyme that functions as a key effector in apoptotic cell death. Determining activity of caspase-3 provides critical information about cancer cell viability and response to treatment. To measure apoptosis in intact cells and living mice, a fluorescence imaging reporter that detects caspase-3 activity by Förster resonance energy transfer (FRET) was used. Changes in FRET by fluorescence lifetime imaging microscopy (FLIM) were measured. Unlike FRET measurements based on fluorescence intensity, lifetime measurements are independent of reporter concentration and scattering of light in tissue, making FLIM a robust method for imaging in 3D environments. Apoptosis of breast cancer cells in 2D culture, spheroids, and in vivo murine breast tumor xenografts in response to a variety of genetic and pharmacologic methods implicated in apoptosis of cancer cells was studied. This approach for quantifying apoptosis of cancer cells is based on caspase-3 activity at single-cell resolution using FLIM. © 2017 by John Wiley & Sons, Inc.

Surgical preparation of rats and mice for intravital microscopic imaging of abdominal organs

Intravital microscopy is a powerful research tool that can provide insight into cellular and subcellular events that take place in organs in the body. However, meaningful results can only be obtained from animals whose physiology is preserved during the process of microscopy. Here I discuss the importance of preserving the overall state of health of the animal, methods of anesthesia, surgical techniques for intravital microscopy of various abdominal organs, methods to maintain and monitor the physiology of the animal during microscopy and associated peri- and post-operative recovery considerations.

Intravital microscopy in historic and contemporary immunology

In this review, we discuss intravital microscopy of immune cells, starting from its historic origins to current applications in diverse organs. It is clear from a quantitative review of the literature that intravital microscopy is a key tool in both historic and contemporary immunological research, providing unique advances in our understanding of immune responses. We have chosen to focus this review on how intravital microscopy methodologies are used to image specific organs or systems and we present recent descriptions of fundamental immunological processes that could not have been achieved by other methods. The following target organs/systems are discussed in more detail: cremaster muscle, skin (ear and dorsal skin fold chamber), lymph node, liver, lung, mesenteric vessels, carotid artery, bone marrow, brain, spleen, foetus and lastly vessels of the knee joint.

Context-dependent intravital imaging of therapeutic response using intramolecular FRET biosensors

Intravital microscopy represents a more physiologically relevant method for assessing therapeutic response. However, the movement into an in vivo setting brings with it several additional considerations, the primary being the context in which drug activity is assessed. Microenvironmental factors, such as hypoxia, pH, fibrosis, immune infiltration and stromal interactions have all been shown to have pronounced effects on drug activity in a more complex setting, which is often lost in simpler two- or three-dimensional assays. Here we present a practical guide for the application of intravital microscopy, looking at the available fluorescent reporters and their respective expression systems and analysis considerations. Moving in vivo, we also discuss the microscopy set up and methods available for overlaying microenvironmental context to the experimental readouts. This enables a smooth transition into applying higher fidelity intravital imaging to improve the drug discovery process.