Nel, Jan GertDurandt, ChrisnaMitchell, Timothy J.Feldman, CharlesAnderson, RonaldTintinger, Gregory Ronald2016-06-232016-08Nel, JG, Durandt, C, Mitchell, TJ, Feldman, C, Anderson, R & Tintinger, GR 2016, 'Pneumolysin mediates platelet activation in vitro', Lung, vol. 194, no. 4, pp. 589-593.0341-2040 (print)1432-1750 (online)10.1007/s00408-016-9900-5http://hdl.handle.net/2263/53368This study has explored the role of the pneumococcal toxin, pneumolysin (Ply), in activating human platelets. Following exposure to Ply [10–80 nanograms (ng)/ml], platelet activation and cytosolic Ca2+ concentrations were measured flow cytometrically according to the level of expression of CD62P (P-selectin) and spectrofluorimetrically respectively. Exposure to Ply resulted in marked upregulation of expression of platelet CD62P, achieving statistical significance at concentrations of 40 ng/ml and higher (p<0.05), in the setting of increased influx of Ca2+. These potentially pro-thrombotic actions of Ply were attenuated by depletion of Ca2+ from the extracellular medium, or by exposure of the cells to a pneumolysoid devoid of pore-forming activity. These findings are consistent with a mechanism of Plymediated platelet activation involving sub-lytic pore formation, Ca2+ influx, and mobilization of CD62P-expressing α-granules, which, if operative in vivo, may contribute to the pathogenesis of associated acute lung and myocardial injury during invasive pneumococcal disease.en© Springer Science+Business Media New York 2016. The original publication is available at http://link.springer.com/journal/408.CalciumCD62PCommunity-acquired pneumoniaPneumococcusP-selectinStreptococcus pneumoniaePostprint Article