For efficient adaptive immunity, the lymph nodes (LNs) are equipped with a strategically organized microarchitecture, which is largely supported by the reticular network (RN). The RN can be clearly visualized by fluorescence immunohistochemistry coupled with confocal imaging using a monoclonal antibody, ER-TR7, and can be subdivided into four structurally distinct regions, each of which correlates well with the location of distinct immune cell subsets. In addition, we noticed a characteristic reticular structure designated the 'cortical ridge' at the boundary of the T and B zone, in which dendritic cells are preferentially accumulated. In vitro adhesion assays of frozen sections demonstrated a preference of dendritic cells for the cortical ridge rather than the deeper cortex. Adoptive transfer experiments also demonstrated that antigen-bearing dendritic cells migrated to this region from peripheral tissues, especially in the vicinity of the high endothelial venules, and were anchored on the reticular fibers waiting to interact with the antigen-specific T cells. Taken together, the findings obtained in this study provide new insights into how the LN stromal reticulum works as a specialized 'immuno-platform' for tissue compartmentalization and the immune response.

Front–rear asymmetry in motile cells is crucial for efficient directional movement. The uropod in migrating lymphocytes is a posterior protrusion in which several proteins, including CD44 and ezrin/radixin/moesin (ERM), are concentrated. In EL4.G8 T-lymphoma cells, Thr567 phosphorylation in the COOH-terminal domain of ezrin regulates the selective localization of ezrin in the uropod. Overexpression of the phosphorylation-mimetic T567D ezrin enhances uropod size and cell migration. T567D ezrin also induces construction of the CD44-associated polar cap, which covers the posterior cytoplasm in staurosporine-treated, uropod-disrupted EL4.G8 cells or in naturally unpolarized X63.653 myeloma cells in an actin cytoskeleton–dependent manner. Rho-associated coiled coil–containing protein kinase (ROCK) inhibitor Y-27632 disrupts the uropod but not the polar cap, indicating that Rho–ROCK signaling is required for posterior protrusion but not for ERM phosphorylation. Phosphorylated ezrin associates with Dbl through its NH2-terminal domain and causes Rho activation. Moreover, constitutively active Q63L RhoA is selectively localized in the rear part of the cells. Thus, phosphorylated ERM has a potential function in establishing plasma membrane “posteriority” in the induction of the uropod in T lymphocytes.

We introduce an integration of dynamic light scattering (DLS) and optical coherence tomography (OCT) for high-resolution 3D imaging of heterogeneous diffusion and flow. DLS analyzes fluctuations in light scattered by particles to measure diffusion or flow of the particles, and OCT uses coherence gating to collect light only scattered from a small volume for high-resolution structural imaging. Therefore, the integration of DLS and OCT enables high-resolution 3D imaging of diffusion and flow. We derived a theory under the assumption that static and moving particles are mixed within the OCT resolution volume and the moving particles can exhibit either diffusive or translational motion. Based on this theory, we developed a fitting algorithm to estimate dynamic parameters including the axial and transverse velocities and the diffusion coefficient. We validated DLS-OCT measurements of diffusion and flow through numerical simulations and phantom experiments. As an example application, we performed DLS-OCT imaging of the living animal brain, resulting in 3D maps of the absolute and axial velocities, the diffusion coefficient, and the coefficient of determination.