Two-photon microscopy analysis of leukocyte trafficking and motility

Experimental pathology by intravital microscopy and genetically encoded fluorescent biosensors

The invention of two‐photon excitation microscopes widens the potential application of intravital microscopy (IVM) to the broad field of experimental pathology. Moreover, the recent development of fluorescent protein‐based, genetically encoded biosensors provides an ideal tool to visualize the cell function in live animals. We start from a brief review of IVM with two‐photon excitation microscopes and genetically encoded biosensors based on the principle of Förster resonance energy transfer (FRET). Then, we describe how IVM using biosensors has revealed the pathogenesis of several disease models.

Live Imaging of Interstitial T Cell Migration Using Lymph Node Slices

Live imaging using various microscopic technologies is an indispensable tool for investigating the dynamic nature of immune cells. One of the most powerful techniques is the two-photon laser-scanning microscopy (TP-LSM), which has various advantages in observing deep tissues in vivo. Interstitial T cell migration in the lymph node (LN) is a phenomenon intensively examined using TP-LSM in the field of immunology. Intravital and explant methods have been standards for imaging T cell behaviors in the LN, though there are several limitations. Live imaging of LN slices, an LN explant sliced by a vibratome to expose tissue parenchyma, could provide an alternative approach with technical advantages for an in-depth analysis of interstitial T cell migration in vivo.

Inflammation-induced interstitial migration of effector CD4⁺ T cells is dependent on integrin αV

Leukocytes must traverse inflamed tissues to effectively control local infection. Although motility in dense tissues appears to be integrin-independent actin-myosin based, during inflammation changes to the extracellular matrix (ECM) may necessitate distinct motility requirements. Indeed, we found that T cell interstitial motility was critically dependent on RGD-binding integrins in the inflamed dermis. Inflammation-induced deposition of fibronectin was functionally linked to increased α_v integrin expression on effector CD4⁺ T cells. Using intravital multi-photon imaging, we found that CD4⁺ T cell motility was dependent on α_v expression. Selective α_v blockade or knockdown arrested T_H1 motility in the inflamed tissue and attenuated local effector function. These data show a context-dependent specificity of lymphocyte movement in inflamed tissues that is essential for protective immunity.

Lymphocytes and the adventitial immune response in atherosclerosis

Although much of the research on atherosclerosis has focused on the intimal accumulation of lipids and inflammatory cells, there is an increasing amount of interest in the role of the adventitia in coordinating the immune response in atherosclerosis. In this review of the contributions of the adventitia and adventitial lymphocytes to the development of atherosclerosis, we discuss recent research on the formation and structural nature of adventitial immune aggregates, potential mechanisms of crosstalk between the intima, media, and adventitia, specific contributions of B lymphocytes and T lymphocytes, and the role of the vasa vasorum and surrounding perivascular adipose tissue. Furthermore, we highlight techniques for the imaging of lymphocytes in the vasculature.

Multiphoton intravital microscopy of the transplanted mouse kidney

Graft outcomes after kidney transplantation continue to be adversely affected by ischemia-reperfusion injury and rejection. High-resolution, real-time imaging of the transplanted kidney could shed valuable insights into these dynamic processes, but such methodology has not been established. Here we describe a technique for intravital imaging of the transplanted mouse kidney using multiphoton fluorescence microscopy. The technique enabled real-time, high-resolution imaging and quantitation of renal filtration, cell death, leukocyte adhesion and capillary blood flow after transplantation. Using this technique, we found that brief graft ischemia associated with the transplantation procedure led to a rapid decline in renal filtration accompanied by a significant increase in microvascular leakage and renal tubular epithelial cell death within the first 3 h after transplantation. No significant changes in leukocyte adhesion or capillary blood flow were observed during the same time period. This report establishes multiphoton fluorescence microscopy as a sensitive tool for simultaneously studying functional and structural perturbations that occur in the mouse kidney after transplantation and for investigating the migration of leukocytes to the graft.

Intravital imaging of phagocyte recruitment

Extravasation of neutrophils and monocytes is a hallmark event in acute and chronic inflammation. Owing to recent improvements in optical imaging techniques, the classical leukocyte extravasation cascade has been refined with intermediate steps being added. Further studies have shown tissue specific leukocyte recruitment patterns, thus allowing for more selective targeting. Here we focus on recent advances in intravital imaging of leukocyte recruitment by means of optical imaging techniques and emphasise the translation thereof into tissue-specific recruitment to the lungs, the liver and large arteries.