Suspensions of prolate spheroids in Stokes flow. Part 2. Statistically homogeneous dispersions

The simulation method for prolate spheroids in Stokes flow introduced in a companion paper (Claeys & Brady 1993a) is extended to handle statistically homogeneous unbounded dispersions. The convergence difficulties associated with the slow decay of velocity disturbances at zero Reynolds number are overcome by applying O';Brien's renormalization procedure. The Ewald summation technique is employed to accelerate the evaluation of all mobility interactions. As a first application of this new method, the hydrodynamic transport properties of equilibrium hard-ellipsoid structures are calculated for aspect ratios ranging from 3 to 50. Calculated viscosities in the isotropic phase agree reasonably well with published experimental measurements

Suspensions of prolate spheroids in Stokes flow. Part 3. Hydrodynamic transport properties of crystalline dispersions

The short-time limit of the hydrodynamic transport properties is calculated for crystalline dispersions of parallel prolate spheroids using a moment expansion technique similar in concept to the simulation method known as Stokesian dynamics. The concentration dependence of the sedimentation rate, the hindered diffusivity and the Theological behaviour of face-centred lattices are examined for concentrations up to regular close packing (74% by volume). The influence of the detailed microstructure of the dispersion is also investigated by considering different arrangements of parallel ellipsoids. Useful reference configurations are proposed as standard geometries for regular arrays of prolate spheroids

Suspensions of prolate spheroids in Stokes flow. Part 1. Dynamics of a finite number of particles in an unbounded fluid

A new simulation method is presented for low-Reynolds-number flow problems involving elongated particles in an unbounded fluid. The technique extends the principles of Stokesian dynamics, a multipole moment expansion method, to ellipsoidal particle shapes. The methodology is applied to prolate spheroids in particular, and shown to be efficient and accurate by comparison with other numerical methods for Stokes flow. The importance of hydrodynamic interactions is illustrated by examples on sedimenting spheroids and particles in a simple shear flow

Contrasting Roles for TLR Ligands in HIV-1 Pathogenesis

The first line of a host's response to various pathogens is triggered by their engagement of cellular pattern recognition receptors (PRRs). Binding of microbial ligands to these receptors leads to the induction of a variety of cellular factors that alter intracellular and extracellular environment and interfere directly or indirectly with the life cycle of the triggering pathogen. Such changes may also affect any coinfecting microbe. Using ligands to Toll-like receptors (TLRs) 5 and 9, we examined their effect on human immunodeficiency virus (HIV)-1 replication in lymphoid tissue ex vivo. We found marked differences in the outcomes of such treatment. While flagellin (TLR5 agonist) treatment enhanced replication of CC chemokine receptor 5 (CCR 5)-tropic and CXC chemokine receptor 4 (CXCR4)-tropic HIV-1, treatment with oligodeoxynucleotide (ODN) M362 (TLR9 agonist) suppressed both viral variants. The differential effects of these TLR ligands on HIV-1 replication correlated with changes in production of CC chemokines CCL3, CCL4, CCL5, and of CXC chemokines CXCL10, and CXCL12 in the ligand-treated HIV-1-infected tissues. The nature and/or magnitude of these changes were dependent on the ligand as well as on the HIV-1 viral strain. Moreover, the tested ligands differed in their ability to induce cellular activation as evaluated by the expression of the cluster of differentiation markers (CD) 25, CD38, CD39, CD69, CD154, and human leukocyte antigen D related (HLA)-DR as well as of a cell proliferation marker, Ki67, and of CCR5. No significant effect of the ligand treatment was observed on apoptosis and cell death/loss in the treated lymphoid tissue ex vivo. Our results suggest that binding of microbial ligands to TLRs is one of the mechanisms that mediate interactions between coinfected microbes and HIV-1 in human tissues. Thus, the engagement of appropriate TLRs by microbial molecules or their mimetic might become a new strategy for HIV therapy or prevention

Nuclear magnetic relaxation study of hindered rotational diffusion in gels

Polymeric gels are widely used in biotechnology, primarily for purification purposes in separation processes, but also as matrices for the physical entrapment of cells and macromolecules, or for the covalent attachment of enzymes and ligands (Mosbach. 1976). The restricted diffusion of molecules through these gels is an important concern in the design and operation of chromatographic separations, bioreactors, electrophoretic media, etc. Yet the fundamental aspects of the interactions between the gel fibers and the diffusing substances are still poorly understood. In this research note, nuclear magnetic relaxation is shown to be a useful probe pf the tumbling motion of molecules embedded in a gel. The technique is applied to study the rotational diffusion of cyclic guanosine monophosphate (cGMP) in polyacrylamide and agarose matrices