Increased membrane heterogeneity in stimulated human granulocytes

AbstractTMA-DPH fluorescence decay in human PMN before and after stimulation with FMLP was studied using frequency domain fluorometry. Membrane heterogeneity was assessed by the width of the continuous distributions of lifetime values of Lorentzian shape used to describe the fluorescence decay. In non-stimulated granulocytes TMA-DPH fluorescence decay is characterized by two distributions of lifetime values centered at 6.5 and 1.0 ns and full width at half maximum of 0.3 and 1.2 ns, respectively. Within 15 min after stimulation, the center values of the two distribution components were 5.1 and 0.8 ns and the distribution width was 0.8 and 0.6 ns, respectively. These results indicate changes of membrane domain organization which can be ascribed to compositional changes redistribution of membrane components

Biological effects of contaminated silicon carbide particles from a workstation in a plant producing abrasives.

A sample of silicon carbide dust taken in the field from a plant producing abrasives was studied in vitro. The SiC particles (part unmilled and part milled) were able to disturb the structure of erythrocyte membranes and to lead to blood red-cell lysis; they also either interfered with complement and activated the alternate pathway, or interacted with biological media and polymorphonuclear leucocyte membranes, thus eliciting reactive oxygen species production. These in vitro properties were detected both in original large particles and unmilled particles, over 40% of which were of respirable size. The ability of these SiC particles to produce complement activation in vitro lends support to the previous hypothesis, that the radiographic opacities found in two workers employed in the same area of the plant from which the dust tested was taken are due to a reaction by pulmonary interstitial structures to SiC particle inhalation. It is speculated that SiC particles could act like asbestos, the ability of which to activate complement through the alternate pathway is considered to be one of the mechanisms by which the initial asbestotic lesions and subsequent fibrotic inflammatory infiltrates are generated in the lung

Cleavage of the fifth component of human complement and release of a split product with C5a-like activity by crystalline silica through free radical generation and kallikrein activation

The effects of the same form of crystalline silica variously modified were compared to investigate the mechanisms by which silica activates C5 molecules. After incubation in human plasma, silica generated C5a-type fragments that stimulated polymorphonuclear leukocyte chemotaxis. This activity was totally abolished when plasma, adsorbed with antiserum against C5a or thermally inactivated, was used. Pretreatment of plasma with deferoxamine, 1,3 dimethyl-2-thiourea, or aprotinin markedly inhibited or totally abolished C5 activation. Finally, a significant increase in kallikrein activity was detected after incubation of silica particles in plasma. The results seem to indicate that the activation of C5 by crystalline silica occurs through a complex mechanism: the redox-active iron possibly present at the silica surface catalyzes, via Haber-Weiss cycles, the production of hydroxyl radicals, which in turn convert native C5 to an oxidized C5-like form. This product is then cleaved by kallikrein, activated by the same silica particles, yielding oxidized C5a with the same functional properties as C5a. The different types of the same form of silica exhibited different reactivity. Two separate properties of the dusts seem to contribute to C5 activation: the potential to release hydroxyl radicals and the extent of C5 adsorption at the surface. The degree of surface hydrophobicity/hydrophilicity appeared sufficient to explain the different responses