Antibodies protect platelet damage by pneumolysin

Objective Community-acquired pneumonia is one of the most common acute infections and a leading cause of morbidity and mortality and mostly caused by Streptococcus pneumoniae. The pore-forming pneumococcal toxin pneumolysin renders platelets non-functional and prevents them from covering endothelial cell lesions. This leads to extravasation of fluid and respiratory impairment. We aim to investigate whether antibodies protect platelets from damage by pneumolysin.

Material and Methods Platelets were isolated from healthy donors (n≥3) and incubated with 300 ng/mL pneumolysin in the absence or presence of a polyclonal rabbit-anti-pneumolysin-antibody, a monoclonal mouse-anti-pneumolysin-antibody (abcam) and human derived pharmaceutical i. v.IgG. We assessed the impact of neutralized pneumolysin on platelet viability using RealTime-Glo cell viability kit and on platelet activation by measuring cytosolic Ca2+ and CD62P expression. Subsequent TRAP-6-stimulation (20µM final) was performed to assess remaining platelet functionality. Adhesion and pore-sealing capacity was tested in a Boyden-chamber-assay and thrombus formation on collagen-surfaces was measured in a flow chamber.

Results Both, specific antibodies as well as i. v.IgG, protect platelets from pneumolysin-induced cell death (Fig. 1A). The antibodies also prevent increase of free cytosolic Ca2+ and CD62P-expression induced otherwise by pneumolysin (Fig. 1B). In the presence of pneumolysin and antibodies, platelets remained sensitive to subsequent TRAP-6 stimulation (Fig. 1B). Platelets are able to adhere to Boyden-chamber membranes and seal pores in the presence of antibodies, which is otherwise severely affected by pneumolysin (Fig. 2A). Addition of i. v.IgG also preserved thrombus formation in whole blood (Fig. 2B).

Conclusion Specific antibodies as well as i. v.IgG can protect platelets against pneumolysin-induced perforation and preserve platelet functionality. This indicates that antibody treatment might be able to prevent acute respiratory distress syndrome in pneumococcal infections by preserving platelet function and prevention of capillary leakage.

This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number 374031971 – TRR 240.

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Publication History

Article published online:
18 June 2021