Cryptococcus neoformans ex vivo capsule size is associated with intracranial pressure and host immune response in HIV-associated cryptococcal meningitis.

BACKGROUND: The Cryptococcus neoformans polysaccharide capsule is a well-characterized virulence factor with immunomodulatory properties. The organism and/or shed capsule is postulated to raise intracranial pressure (ICP) in cryptococcal meningitis (CM) by mechanical obstruction of cerebrospinal fluid (CSF) outflow. Little is known regarding capsule phenotype in human cryptococcosis. We investigated the relationship of ex vivo CSF capsular phenotype with ICP and CSF immune response, as well as in vitro phenotype. METHODS: In total, 134 human immunodeficiency virus (HIV)-infected Ugandan adults with CM had serial lumbar punctures with measurement of CSF opening pressures, quantitative cultures, ex vivo capsule size and shedding, viscosity, and CSF cytokines; 108 had complete data. Induced capsular size and shedding were measured in vitro for 48 C. neoformans isolates. RESULTS: Cryptococcal strains producing larger ex vivo capsules in the baseline (pretreatment) CSF correlated with higher ICP (P = .02), slower rate of fungal clearance (P = .02), and paucity of CSF inflammation, including decreased CSF white blood cell (WBC) count (P < .001), interleukin (IL)-4 (P = .02), IL-6 (P = .01), IL-7 (P = .04), IL-8 (P = .03), and interferon γ (P = .03). CSF capsule shedding did not correlate with ICP. On multivariable analysis, capsule size remained independently associated with ICP. Ex vivo capsular size and shedding did not correlate with that of the same isolates grown in vitro. CONCLUSIONS: Cryptococcal capsule size ex vivo is an important contributor to virulence in human cryptococcal meningitis.

Counterflow dielectrophoresis for trypanosome enrichment and detection in blood.

Human African trypanosomiasis or sleeping sickness is a deadly disease endemic in sub-Saharan Africa, caused by single-celled protozoan parasites. Although it has been targeted for elimination by 2020, this will only be realized if diagnosis can be improved to enable identification and treatment of afflicted patients. Existing techniques of detection are restricted by their limited field-applicability, sensitivity and capacity for automation. Microfluidic-based technologies offer the potential for highly sensitive automated devices that could achieve detection at the lowest levels of parasitemia and consequently help in the elimination programme. In this work we implement an electrokinetic technique for the separation of trypanosomes from both mouse and human blood. This technique utilises differences in polarisability between the blood cells and trypanosomes to achieve separation through opposed bi-directional movement (cell counterflow). We combine this enrichment technique with an automated image analysis detection algorithm, negating the need for a human operator.

Heavy ellipsoids in creeping shear flow: transitions of the particle rotation rate and orbit shape.

The motion of an inertial ellipsoid in a creeping linear shear flow of a Newtonian fluid is studied numerically. This constitutes a fundamental system that is used as a basis for simulations and analysis of flows with heavy nonspherical particles. The torque on the ellipsoid is given analytically by Jeffery [Proc. R. Soc. London, Ser. A 102, 161 (1922)]. This torque is coupled with the angular-momentum equation for the particle. The motion is then governed by the Stokes number St=rho(e)gammal(2)/mu, where rho(e) is the density of the ellipsoid, gamma is the rate of shear, l is the length of the major axis of the ellipsoid, and mu is the dynamic viscosity of the fluid. For low St (the numerical value depends on the aspect ratio of the particle), the particle motion is similar to the Jeffery orbits obtained for inertia-free particles with the addition of an orbit drift so that the particle eventually lies in the flow-gradient plane. At higher St, more drastic effects are seen. For particles oriented in the flow-gradient plane, the rotation rate increases rather abruptly to half the shear rate in a narrow range of St. For particles with other orientations, the motion goes from a kayaking motion to rotation around an oblique axis. It is suggested that, depending on aspect and density ratios, particle inertia might be sufficient to explain and model orbit drift observed previously at low Reynolds numbers. It is discussed how and when the assumption of negligible fluid inertia and strong particle inertia can be justified from a fundamental perspective for particles of different aspect ratios.