Streptococcus pyogenes Activates Human Platelets via Streptolysin S-Mediated Calcium Ion Influx

Abstract

Introduction: Streptococcus pyogenes (group A streptococcus, GAS) is an exclusively human pathogen. It causes a wide spectrum of diseases, ranging from mild infections such as pharyngitis to severe life-threatening conditions such as streptococcal toxic shock syndrome (STSS). Thrombocytopenia is a common feature of STSS and is associated with severe outcome. GAS produce a plethora of virulence factors, including streptolysin S (SLS), which has lytic as well as immunomodulatory properties. However, its role in platelet activation remains unclear.

Methods: Washed human platelets were infected with GAS wild-type and SLS-deficient mutant (ΔsagA) strains. Platelet activation was assessed by measuring degranulation (CD62P expression). The role of calcium influx and the involvement of purinergic type 2 receptors (P2R) in platelet activation by GAS were assessed using chemical antagonists and calcium chelators.

Results: GAS activate human platelets via SLS-mediated calcium influx, marked by increased surface expression of CD62P. IVIG treatment improved platelet viability in wild-type infections but failed to prevent SLS-mediated activation. Blocking of P2 receptors via suramin or NF449 as well as the use of calcium chelators reduced SLS-mediated platelet activation.

Conclusion: This study identified SLS as an M-protein and consequently a serotype-independent activator of human platelets. While IVIG partially improved platelet viability in GAS infections, its inability to prevent excessive platelet activation underscores the need for additional treatment options in severe GAS infections.

Introduction: Streptococcus pyogenes (group A streptococcus, GAS) is an exclusively human pathogen. It causes a wide spectrum of diseases, ranging from mild infections such as pharyngitis to severe life-threatening conditions such as streptococcal toxic shock syndrome (STSS). Thrombocytopenia is a common feature of STSS and is associated with severe outcome. GAS produce a plethora of virulence factors, including streptolysin S (SLS), which has lytic as well as immunomodulatory properties. However, its role in platelet activation remains unclear.

Methods: Washed human platelets were infected with GAS wild-type and SLS-deficient mutant (ΔsagA) strains. Platelet activation was assessed by measuring degranulation (CD62P expression). The role of calcium influx and the involvement of purinergic type 2 receptors (P2R) in platelet activation by GAS were assessed using chemical antagonists and calcium chelators.

Results: GAS activate human platelets via SLS-mediated calcium influx, marked by increased surface expression of CD62P. IVIG treatment improved platelet viability in wild-type infections but failed to prevent SLS-mediated activation. Blocking of P2 receptors via suramin or NF449 as well as the use of calcium chelators reduced SLS-mediated platelet activation.

Conclusion: This study identified SLS as an M-protein and consequently a serotype-independent activator of human platelets. While IVIG partially improved platelet viability in GAS infections, its inability to prevent excessive platelet activation underscores the need for additional treatment options in severe GAS infections.

Keywords: Calcium; Platelets; Streptococcus pyogenes; Streptolysin S.