A Novel Role for Pro-Coagulant Microvesicles in the Early Host Defense against Streptococcus pyogenes

Abstract

Previous studies have shown that stimulation of whole blood or peripheral blood mononuclear cells with bacterial virulence factors results in the sequestration of pro-coagulant microvesicles (MVs). These particles explore their clotting activity via the extrinsic and intrinsic pathway of coagulation; however, their pathophysiological role in infectious diseases remains enigmatic. Here we describe that the interaction of pro-coagulant MVs with bacteria of the species Streptococcus pyogenes is part of the early immune response to the invading pathogen. As shown by negative staining electron microscopy and clotting assays, pro-coagulant MVs bind in the presence of plasma to the bacterial surface. Fibrinogen was identified as a linker that, through binding to the M1 protein of S. pyogenes, allows the opsonization of the bacteria by MVs. Surface plasmon resonance analysis revealed a strong interaction between pro-coagulant MVs and fibrinogen with a KD value in the nanomolar range. When performing a mass-spectrometry-based strategy to determine the protein quantity, a significant up-regulation of the fibrinogen-binding integrins CD18 and CD11b on pro-coagulant MVs was recorded. Finally we show that plasma clots induced by pro-coagulant MVs are able to prevent bacterial dissemination and possess antimicrobial activity. These findings were confirmed by in vivo experiments, as local treatment with pro-coagulant MVs dampens bacterial spreading to other organs and improved survival in an invasive streptococcal mouse model of infection. Taken together, our data implicate that pro-coagulant MVs play an important role in the early response of the innate immune system in infectious diseases.

Comparative Genomics of Streptococcus pyogenes M1 isolates differing in virulence and propensity to cause systemic infection in mice

“…Although S. pyogenes is a human-specific pathogen, part of its infection pathogenesis and host interactions can be studied in murine models. These models use some of the few strains that are pathogenic in mice, such as the M1 strains 5448 or its progeny 5448AP (Buchanan et al, 2006;Cole et al, 2006;Zinkernagel et al, 2012Zinkernagel et al, , 2008Walker et al, 2007) or AP1 (Oehmcke et al, 2009;Oehmcke et al, 2013;Shannon et al, 2010). However, little is known about the streptococcal factors that govern the infection pathogenesis in mice.…”

“…Furthermore, the virulence factor SIC (Streptococcal Inhibitor of Complement) was first discovered in AP1 (Åkesson et al, 1996). The M1 protein of this strain induces vascular leakage in the lungs after intravenous injection into mice (Herwald et al, 2004) and subcutaneous inoculation of AP1 evokes a systemic infection in Balb/c (Oehmcke et al, 2009;Oehmcke et al, 2013) as well as in C57BL/6 (Shannon et al, 2010) mice. Strain 5448, a MGAS5005-like isolate (Maamary et al, 2012), also derives from a clinical isolate and was employed in a murine model of necrotizing fasciitis (Buchanan et al, 2006) and in other mouse models of skin and tissue infections in several studies (Cole et al, 2006;Zinkernagel et al, 2012Zinkernagel et al, , 2008.…”

Disease Manifestations and Pathogenic Mechanisms of Group A Streptococcus

“…The level of procoagulant microvesicles increases significantly in a mouse model of invasive streptococcal infection, and these microvesicles appear to bind to the streptococcal surface, leading to the entrapment of the bacteria within a dense fibrin network (386). Thus, the coagulation system and the early immune response to GAS infection are tightly linked, and dysregulation of this system by GAS appears to contribute significantly to invasive pathogenesis.…”

The role of coagulation/fibrinolysis during Streptococcus pyogenes infection

“…This interaction leads to an alteration of the bacterial surface into a pro-coagulative state and immobilization of S. pyogenes within a clot (Oehmcke et al, 2013). The clots generated in the presence of pro-coagulant microvesicles have antimicrobial activity against S. pyogenes , which could be mediated by the antimicrobial peptides and other immune response proteins present in the microvesicles (Oehmcke et al, 2013).…”