In vitro propagation and homing of liver-derived dendritic cell progenitors to lymphoid tissues of allogeneic recipients: Implications for the establishment and maintenance of donor cell chimerism following liver transplantation

Dendritic cell (DC) progenitors were propagated in liquid culture from nonparenchymal cells resident in normal mouse (B10.BR; H-2k, I-E+) liver in response to granulocyte-macrophage colony stimulating factor (GM-CSF). The liver-derived DC progenitors were MHC class II-/dim and did not express counter receptors for CTLA-4, a structural homologue of the Т cell activation molecule CD28. Following subcutaneous or intravenous injection, these liver-derived cells migrated to Т cell-dependent areas of lymph nodes and spleen of unmodified, allogeneic (BIO; H-2b; I-E_) recipients, where they were identified 1-5 days, and 1 and 2 months after injection by their strong surface expression of donor MHC class II (I-Ek) and their dendritic morphology. Maximal numbers of liver-derived DC in the spleen were recorded 5 days after injection. Both clusters of strongly donor MHC class II+ cells— and (more rarely) dividing cells—could also be identified, suggesting cell replication in situ. Using the same techniques employed to generate DC progenitors from normal liver, GM-CSF-stimulated cells were propagated for 10 days from the bone marrow and spleen of nonimmunosuppressed mice sacrificed 14 days after orthotopic liver transplantation (B10;H-2b → C3H;H-2k). Immunocytochemical staining for recipient and donor MHC class II phenotype revealed the growth both of host cells with DC characteristics, and of cells expressing donor alloantigens (I-Ab). These results are consistent with the growth, in response to GM-CSF, of donor-derived DC from progenitors seeded from the liver allograft to recipient lymphoid tissue. The functional activity of the progenitors of chimeric DC and the possible role of these cells in the establishment and maintenance of donor-specific tolerance following liver transplantation remain to be determined. © 1995 by Williams and Wilkins

Dynamic Modes of Microcapsules in Steady Shear Flow: Effects of Bending and Shear Elasticities

The dynamics of microcapsules in steady shear flow was studied using a theoretical approach based on three variables: The Taylor deformation parameter $\alpha_{\rm D}$, the inclination angle $\theta$, and the phase angle $\phi$ of the membrane rotation. It is found that the dynamic phase diagram shows a remarkable change with an increase in the ratio of the membrane shear and bending elasticities. A fluid vesicle (no shear elasticity) exhibits three dynamic modes: (i) Tank-treading (TT) at low viscosity $\eta_{\rm {in}}$ of internal fluid ($\alpha_{\rm D}$ and $\theta$ relaxes to constant values), (ii) Tumbling (TB) at high $\eta_{\rm {in}}$ ($\theta$ rotates), and (iii) Swinging (SW) at middle $\eta_{\rm {in}}$ and high shear rate $\dot\gamma$ ($\theta$ oscillates). All of three modes are accompanied by a membrane ($\phi$) rotation. For microcapsules with low shear elasticity, the TB phase with no $\phi$ rotation and the coexistence phase of SW and TB motions are induced by the energy barrier of $\phi$ rotation. Synchronization of $\phi$ rotation with TB rotation or SW oscillation occurs with integer ratios of rotational frequencies. At high shear elasticity, where a saddle point in the energy potential disappears, intermediate phases vanish, and either $\phi$ or $\theta$ rotation occurs. This phase behavior agrees with recent simulation results of microcapsules with low bending elasticity.Comment: 11 pages, 14 figure

Dynamical regimes and hydrodynamic lift of viscous vesicles under shear

The dynamics of two-dimensional viscous vesicles in shear flow, with different fluid viscosities $\eta_{\rm in}$ and $\eta_{\rm out}$ inside and outside, respectively, is studied using mesoscale simulation techniques. Besides the well-known tank-treading and tumbling motions, an oscillatory swinging motion is observed in the simulations for large shear rate. The existence of this swinging motion requires the excitation of higher-order undulation modes (beyond elliptical deformations) in two dimensions. Keller-Skalak theory is extended to deformable two-dimensional vesicles, such that a dynamical phase diagram can be predicted for the reduced shear rate and the viscosity contrast $\eta_{\rm in}/\eta_{\rm out}$. The simulation results are found to be in good agreement with the theoretical predictions, when thermal fluctuations are incorporated in the theory. Moreover, the hydrodynamic lift force, acting on vesicles under shear close to a wall, is determined from simulations for various viscosity contrasts. For comparison, the lift force is calculated numerically in the absence of thermal fluctuations using the boundary-integral method for equal inside and outside viscosities. Both methods show that the dependence of the lift force on the distance $y_{\rm {cm}}$ of the vesicle center of mass from the wall is well described by an effective power law $y_{\rm {cm}}^{-2}$ for intermediate distances $0.8 R_{\rm p} \lesssim y_{\rm {cm}} \lesssim 3 R_{\rm p}$ with vesicle radius $R_{\rm p}$. The boundary-integral calculation indicates that the lift force decays asymptotically as $1/[y_{\rm {cm}}\ln(y_{\rm {cm}})]$ far from the wall.Comment: 13 pages, 13 figure

Linear instability of tilted parallel shear flow in a strongly stratified and viscous medium

A linear stability analysis is performed on a tilted parallel wake in a strongly stratified fluid at low Reynolds numbers. A particular emphasis of the present study is given to the understanding of the low-Froude-number mode observed by the recent experiment (Meunier in J Fluid Mech 699:174–197, 2012). In the limit of low Froude number, the linearised equations of motion can be reduced to the Orr–Sommerfeld equation on the horizontal plane, except the viscous term that contains vertical dissipation. Based on this equation, it is proposed that the low-Froude-number mode would be a horizontal inflectional instability and should remain two-dimensional at small tilting angles as long as the Reynolds number is sufficiently low. To support this claim, the asymptotic regime where this analysis is strictly valid is subsequently discussed in relation to previous work on the proper vertical length scale. The absolute and convective instability analysis of parallel wake is further performed, showing qualitatively good agreement with the experimental result. The low-Froude-number mode is found to be stabilised on increasing Froude number, as in the experiment. It is shown that the emergence of small vertical velocity at finite Froude number, the size of which is proportional to the square of Froude number, plays the key role in the stabilisation by modifying the inflectional instability and paradoxically creating stabilising buoyancy effect with the increase of Froude number

Charging mechanism in a SiO 2 matrix embedded with Si nanocrystals

One of the applications of a Si nanocrystals (nc-Si) embedded in a Si O2 matrix is in the area of nonvolatile memory devices based on the charge storage in the material system. However, whether the charge trapping mainly occurs at the nc-SiSi O2 interface or in the nc-Si is still unclear. In this work, by x-ray photoemission spectroscopy analysis of the Si 2p peaks, the concentrations of both the nc-Si and the Si suboxides that exist at the nc-SiSi O2 interface are determined as a function of thermal annealing, and the charging effect is also measured by monitoring the shift of the surface C 1s peak. It is observed that the annealing-caused reduction of the total concentration of the interfacial suboxides is much faster than that of both the C 1s shift and the nc-Si concentration. In addition, the trend of the C 1s shift coincides with that of the nc-Si concentration. The results suggest that the Si nanocrystal, rather than the nc-SiSi O2 interface, plays the dominant role in the charging effect. © 2006 American Institute of Physics.published_or_final_versio

Capacitance switching in SiO 2 thin film embedded with Ge nanocrystals caused by ultraviolet illumination

A structure of indium tin oxide/ SiO 2 embedded with Ge nanocrystal (nc-Ge) /p-Si substrate was fabricated. The capacitance of the structure can be switched to a high-capacitance or low-capacitance state by an ultraviolet (UV) illumination. The increase (or decrease) in the capacitance is accompanied with the decrease (or increase) in the oxide resistance. The capacitance switching is explained in terms of the UV illumination-induced charging and discharging in the nc-Ge. © 2009 American Institute of Physics.published_or_final_versio