The staphylococcal toxin Panton-Valentine Leukocidin induces neutrophil extracellular trap (NET) formation that leads to platelet activation.

M. F. Brodde1, A. Bertling1, S. Niemann1, A. C. Fender2, H. Van de Vyver1, B. Schlott3, C. Heilmann1, G. Peters1, B. Löffler3, B. E. Kehrel1 (1Muenster, Germany, 2Duesseldorf, Germany, 3Jena, Germany)

Pediatric and Women Issues
Date: 17.02.2017,
Time: 11:00 - 12:00

Objective: Expression of the toxin Panton-Valentine Leukocidin (PVL) by Staphylococcus aureus has been linked to thrombosis in association with osteomyelitis especially in young immunocompetent patients. We therefore tested the effect of PVL on human platelets and neutrophils.

Methods: Human neutrophils were gently isolated from whole blood. The effect of recombinant PVL on platelet activation in the presence or absence of autologous neutrophils was measured by flow cytometry. PVL induced lysis of neutrophils was assessed by propidium iodide. Release of neutrophil myeloperoxidase and defensins was detected by ELISA. NET formation was analyzed by a fluorogenic assay using Syto13 binding to nucleic acids, a sandwich ELISA against histone-DNA complexes and by microscopy. The influence of known inhibitors of alpha defensin and of FDP-lysine carrying proteins induced platelet activation was studied.

Results: The toxin PVL strongly induced platelet activation, but only in the presence of human neutrophils. Labelled PVL subunit S (LukS) bound to the neutrophil surface, but not to platelets. Complete PVL induced neutrophil lysis and NET formation as well as the release of alpha defensins and myeloperoxidase. Neutrophil NETs were decorated with alpha defensin 1-3, and stained for FDP-lysine, a marker for acrolein adduct formation that induces platelet activation. PVL-induced platelet activation in the presence of neutrophils was inhibited by known defensin inhibitors as well as by resveratrol and glutathione (GSH). PVL actions were blocked by anti-PVL-antibodies in the plasma of several adult blood donors. GSH also inhibited PVL-induced lysis of human neutrophils and the release of defensins and myeloperoxidase.

Conclusion: Our data provide one possible explanation how thrombosis and osteomyelitis are connected in PVL-S. aureus infections and why especially young osteomyelitis patients with a presumably low antibody titer against PVL suffer more from this complication than adults. As the mechanism described might be a more general one, other bacterial toxins are under further investigation.