The cervical lymph node preparation: a novel approach to study lymphocyte homing by intravital microscopy

Evaluation of a fluorescence endoscope in murine in-vivo auto-fluorescence glioma models

INTRODUCTION

The value of extended and radical resection of high grade gliomas remains controversial, but the neurosurgical procedure is still vital for effective cancer treatment. Fluorescence guided surgery provides aggressive resection within the tumor margins even on microscopic levels. Aim of this study was to evaluate if a new developed fluorescence endoscope can improve intraoperative vision and tumor delineation.

METHODS

An autofluoresence C6 glioma cell line was established via GFP-transfection. These GFP-C6 glioma cells were transplanted both in a dorsal skinfold chamber of the mouse and orthotopically in a cranial window chamber of the mouse. After five days, tumors were examinated by intravital fluorescence microscopy, a standard fluorescence operation microscope and a fluorescence endoscope. Images were compared in terms of visualization, magnification and delineation of tumor cells from host tissue.

RESULTS

The fluorescence endoscope showed improved image quality and higher magnifications compared to the operation microscope. Even smallest tumor extensions were visualized by the fluorescence endoscope nearly reaching the quality of an intravital fluorescence microscope.

CONCLUSIONS

In summary better visualization can improve the intraoperative decision making of the surgeons. So endoscopic assistance can be seen as a promising tool for the fluorescence guided resection of high grade gliomas in the next years.

CD112 Regulates Angiogenesis and T Cell Entry into the Spleen

Junctional adhesion proteins play important roles in controlling angiogenesis, vascular permeability and leukocyte trafficking. CD112 (nectin-2) belongs to the immunoglobulin superfamily and was shown to engage in homophilic and heterophilic interactions with a variety of binding partners expressed on endothelial cells and on leukocytes. Recent in vitro studies suggested that CD112 regulates human endothelial cell migration and proliferation as well as transendothelial migration of leukocytes. However, so far, the role of CD112 in endothelial cell biology and in leukocyte trafficking has not been elucidated in vivo. We found CD112 to be expressed by lymphatic and blood endothelial cells in different murine tissues. In CD112-deficient mice, the blood vessel coverage in the retina and spleen was significantly enhanced. In functional in vitro studies, a blockade of CD112 modulated endothelial cell migration and significantly enhanced endothelial tube formation. An antibody-based blockade of CD112 also significantly reduced T cell transmigration across endothelial monolayers in vitro. Moreover, T cell homing to the spleen was significantly reduced in CD112-deficient mice. Overall, our results identify CD112 as a regulator of angiogenic processes in vivo and demonstrate a novel role for CD112 in T cell entry into the spleen.

Murine chronic lymph node window for longitudinal intravital lymph node imaging

Chronic imaging windows in mice have been developed to allow intravital microscopy of many different organs and have proven to be of paramount importance in advancing our knowledge of normal and disease processes. A model system that allows long-term intravital imaging of lymph nodes would facilitate the study of cell behavior in lymph nodes during the generation of immune responses in a variety of disease settings and during the formation of metastatic lesions in cancer-bearing mice. We describe a chronic lymph node window (CLNW) surgical preparation that allows intravital imaging of the inguinal lymph node in mice. The CLNW is custom-made from titanium and incorporates a standard coverslip. It allows stable longitudinal imaging without the need for serial surgeries while preserving lymph node blood and lymph flow. We also describe how to build and use an imaging stage specifically designed for the CLNW to prevent (large) rotational changes as well as respiratory movement during imaging. The entire procedure takes approximately half an hour per mouse, and subsequently allows for longitudinal intravital imaging of the murine lymph node and surrounding structures for up to 14 d. Small-animal surgery experience is required to successfully carry out the protocol.

A Deeper Look into Type 1 Diabetes - Imaging Immune Responses during Onset of Disease

Cytotoxic T lymphocytes execute the killing of insulin-producing beta cells during onset of type 1 diabetes mellitus (T1D). The research community has come far in dissecting the major events in the development of this disease, but still the trigger and high-resolved information of the immunological events leading up to beta cell loss are missing. During the past decades, intravital imaging of immune responses has led to significant scientific breakthroughs in diverse models of disease, including T1D. Dynamic imaging of immune cells at the pancreatic islets during T1D onset has been made possible through the development of both advanced microscopes, and animal models that allow long-term immobilization of the pancreas. The use of these modalities has revealed a milling microenvironment at the pancreatic islets during disease onset with a plethora of active players. Clues to answering the remaining questions in this disease may lie in intravital imaging, including how key immune cells traffic to and from the pancreas, and how cells interact at this target tissue. This review highlights and discusses recent studies, models, and techniques focused to understand the immune responses during T1D onset through intravital imaging.

Visualizing T Cell Migration in situ

Mounting a protective immune response is critically dependent on the orchestrated movement of cells within lymphoid tissues. The structure of secondary lymphoid organs regulates immune responses by promoting optimal cell-cell and cell-extracellular matrix interactions. Naïve T cells are initially activated by antigen presenting cells in secondary lymphoid organs. Following priming, effector T cells migrate to the site of infection to exert their functions. Majority of the effector cells die while a small population of antigen-specific T cells persists as memory cells in distinct anatomical locations. The persistence and location of memory cells in lymphoid and non-lymphoid tissues is critical to protect the host from re-infection. The localization of memory T cells is carefully regulated by several factors including the highly organized secondary lymphoid structure, the cellular expression of chemokine receptors and compartmentalized secretion of their cognate ligands. This balance between the anatomy and the ordered expression of cell surface and soluble proteins regulates the subtle choreography of T cell migration. In recent years, our understanding of cellular dynamics of T cells has been advanced by the development of new imaging techniques allowing in situ visualization of T cell responses. Here, we review the past and more recent studies that have utilized sophisticated imaging technologies to investigate the migration dynamics of naïve, effector, and memory T cells.

Non-invasive optical imaging of the lymphatic vasculature of a mouse

The lymphatic vascular system is an important component of the circulatory system that maintains fluid homeostasis, provides immune surveillance, and mediates fat absorption in the gut. Yet despite its critical function, there is comparatively little understanding of how the lymphatic system adapts to serve these functions in health and disease. Recently, we have demonstrated the ability to dynamically image lymphatic architecture and lymph "pumping" action in normal human subjects as well as in persons suffering lymphatic dysfunction using trace administration of a near-infrared fluorescent (NIRF) dye and a custom, Gen III-intensified imaging system. NIRF imaging showed dramatic changes in lymphatic architecture and function with human disease. It remains unclear how these changes occur and new animal models are being developed to elucidate their genetic and molecular basis. In this protocol, we present NIRF lymphatic, small animal imaging using indocyanine green (ICG), a dye that has been used for 50 years in humans, and a NIRF dye-labeled cyclic albumin binding domain (cABD-IRDye800) peptide that preferentially binds mouse and human albumin. Approximately 5.5 times brighter than ICG, cABD-IRDye800 has a similar lymphatic clearance profile and can be injected in smaller doses than ICG to achieve sufficient NIRF signals for imaging. Because both cABD-IRDye800 and ICG bind to albumin in the interstitial space, they both may depict active protein transport into and within the lymphatics. Intradermal (ID) injections (5-50 μl) of ICG (645 μM) or cABD-IRDye800 (200 μM) in saline are administered to the dorsal aspect of each hind paw and/or the left and right side of the base of the tail of an isoflurane-anesthetized mouse. The resulting dye concentration in the animal is 83-1,250 μg/kg for ICG or 113-1,700 μg/kg for cABD-IRDye800. Immediately following injections, functional lymphatic imaging is conducted for up to 1 hr using a customized, small animal NIRF imaging system. Whole animal spatial resolution can depict fluorescent lymphatic vessels of 100 microns or less, and images of structures up to 3 cm in depth can be acquired. Images are acquired using V++ software and analyzed using ImageJ or MATLAB software. During analysis, consecutive regions of interest (ROIs) encompassing the entire vessel diameter are drawn along a given lymph vessel. The dimensions for each ROI are kept constant for a given vessel and NIRF intensity is measured for each ROI to quantitatively assess "packets" of lymph moving through vessels.

L-selectin-mediated lymphocyte-cancer cell interactions under low fluid shear conditions

Cell migration in blood flow is mediated by engagement of specialized adhesion molecules that function under hemodynamic shear conditions, and many of the effectors of these adhesive interactions, such as the selectins and their ligands, are well defined. However, in contrast, our knowledge of the adhesion molecules operant under lymphatic flow conditions is incomplete. Among human malignancies, head and neck squamous cell cancer displays a marked predilection for locoregional lymph node metastasis. Based on this distinct tropism, we hypothesized that these cells express adhesion molecules that promote their binding to lymphoid tissue under lymphatic fluid shear stress. Accordingly, we investigated adhesive interactions between these and other cancer cells and the principal resident cells of lymphoid organs, lymphocytes. Parallel plate flow chamber studies under defined shear conditions, together with biochemical analyses, showed that human head and neck squamous cell cancer cells express heretofore unrecognized L-selectin ligand(s) that mediate binding to lymphocyte L-selectin at conspicuously low shear stress levels of 0.07-0.08 dynes/cm(2), consistent with lymphatic flow. The binding of head and neck squamous cancer cells to L-selectin displays canonical biochemical features, such as requirements for sialylation, sulfation, and N-glycosylation, but displays a novel operational shear threshold differing from all other L-selectin ligands, including those expressed on colon cancer and leukemic cells (e.g. HCELL). These data define a novel class of L-selectin ligands and expand the scope of function for L-selectin within circulatory systems to now include a novel activity within shear stresses characteristic of lymphatic flow.