Staphylococcus aureus alpha-toxin attack on human platelets promotes assembly of the prothrombinase complex

Area of Science:

• Hematology
• Microbiology
• Toxicology

Background:

• Staphylococcus aureus alpha-toxin is a major cytolysin.
• This toxin is known to promote blood coagulation through interaction with human platelets.

Purpose of the Study:

• To investigate the mechanisms by which alpha-toxin induces prothrombinase complex assembly on human platelets.
• To quantify the rate of thrombin generation induced by alpha-toxin.
• To determine if alpha-toxin-induced procoagulant activity is due to platelet lysis.

Main Methods:

• Treatment of gel-filtered human platelets with Staphylococcus aureus alpha-toxin.
• Measurement of prothrombinase complex assembly and thrombin generation.
• Assay for lactate dehydrogenase release to assess platelet lysis.
• Investigation of calcium dependence for factor V secretion and factor V(a) binding.

Main Results:

• Alpha-toxin treatment increased prothrombinase complex assembly up to 10-fold compared to controls.
• 0.1 microgram/ml alpha-toxin generated 1.4 units of thrombin/10(8) platelets.
• Platelet lysis was minimal (<1% lactate dehydrogenase release) at the effective alpha-toxin concentration.
• Two distinct mechanisms were identified: calcium-dependent exocytotic release of factor V and enhanced binding of external factor V(a).

Conclusions:

• Staphylococcus aureus alpha-toxin promotes blood coagulation by enhancing prothrombinase assembly on platelets.
• This effect is mediated by both the release of factor V and increased factor V(a) binding.
• The procoagulant action of alpha-toxin is independent of significant platelet lysis.