Variability of CD3 membrane expression and T cell activation capacity.

BACKGROUND: AlphabetaT cells have a wide distribution of CD3 membrane density. The aim of this article was to evaluate the significance of the CD3 differential expression on T cell subsets. Analysis was performed on healthy donors and renal transplant patients by flow cytometry. The results obtained are: (1) CD3 expression was widely distributed (CV = 38.3 +/- 3.1 to 43 +/- 2.3%). (2) The CD4, CD8, CD45 and forward scatter were similarly distributed. (3) The diversity of CD3 expression was directly related to the clonotypes: gamma9, non gamma9 from gammadeltaT cells and Vbeta clonotype from alphabetaT cells (e.g., Vbeta3FITC 7,980 +/- 1,628 Vbeta8PE: Vbeta20-FITC 11,768 +/- 1,510). (4) Using a computer simulation, we could confirm differential kinetics of T cell activation according to the initial parameters. Finally, in vitro activation was significantly higher on Vbeta8 and Vbeta9 (high CD3) compared with Vbeta2 and Vbeta3 (low CD3, P = 0.040-0.0003). In conclusion, T cells have highly heterogeneous CD3 expression, possibly predetermined and with clear functional significance.

Light extinction at agglomerates of spheres--a practical test on the submicroscale.

Today's theories applied to the inversion of measurement data from optical measurement devices are restricted to single spherical particles. However, particles formed in industrial processes such as precipitation and crystallization are often nonspherical or agglomerates. Theoretical approaches to describe the optical behavior of such particle systems have already been proposed. The verification of these theories has mostly been done using microwave scattering experiments with agglomerates in the millimeter range. This paper provides a first but surely not all-embracing practical test for a general extension of the Mie theory to agglomerates of submicroscale spheres. For the sake of simplicity and from practical viewpoints of online-sensor development only light extinction of an agglomerated suspension has been examined. The required rigid agglomerates have been produced using a spray-drying method that generates particles with a much higher mechanical stability than can be obtained by the usual procedures. Subsequent fractionation of the suspension delivers systems with only a limited number of agglomerate configurations. Extinction measurements at multiple wavelengths using dynamic extinction spectroscopy have been conducted to determine the extinction cross section of the agglomerated dispersions. These data are compared with computations of agglomerates scattering.

Influence of nonwetting on the aggregation dynamics of micronic solid particles in a turbulent medium.

The aim of this work was to determine and to interpret the influence of nonwetting on the aggregation dynamics of micronic solid particles in a turbulent medium. Two silica granular samples were studied: one was naturally hydrophilic; the other was made hydrophobic. Aggregation in an aqueous ethanol solution was followed by in situ turbidimetry. The influence of stirring rate and deaeration was determined. Aggregates of hydrophilic particles were small and fragile, whereas aggregates of hydrophobic particles were large and solid. Moreover, they differred greatly in optical properties. Within the proposed approach, different features of the aggregate morphology were identified: fractal dimension, maximum size, and gas content of the hydrophobic clusters. These elements are taken into account in the models of aggregation dynamics proposed here.

Formation of Small Silica Aggregates by Turbulent Aggregation.

Aggregation of silica powder in water has been experimentally studied by turbidimetry. Aggregation was carried out in a stirred tank under physicochemical conditions corresponding to attractive interparticle forces. The effects of different primary particle sizes and stirring rates on aggregation dynamics have been studied. The scattering cross sections of silica aggregates were calculated in the framework of the anomalous diffraction approximation of light scattering theory. Aggregation has been studied by using Kusters's and Brakalov's approaches. By comparison between experimental and theoretical turbidity changes with time it has been shown that aggregates are small and slightly porous. The aggregation process is characterized by a weak fractal dimension D(wf) and an aggregate limit size L.D(wf) is found in the range 2.4-2.5. D(wf) (respectively L) is a weakly increasing (respectively decreasing) function of the stirring rate or of the shear rate. Copyright 2001 Academic Press.