Eva Mattsson

Staphylococcus aureus induces release of bradykinin in human plasma.

ABSTRACT Staphylococcus aureus is a prominent human pathogen. Here we report that intact S. aureus bacteria activate the contact system in human plasma in vitro, resulting in a massive release of the potent proinflammatory and vasoactive peptide bradykinin. In contrast, no such effect was recorded withStreptococcus pneumoniae. In the activation of the contact system, blood coagulation factor XII and plasma kallikrein play central roles, and a specific inhibitor of these serine proteinases inhibited the release of bradykinin by S. aureus in human plasma. Furthermore, fragments of the cofactor H-kininogen of the contact system efficiently blocked bradykinin release. The results suggest that activation of the contact system at the surface ofS. aureus and the subsequent release of bradykinin could contribute to the hypovolemic hypotension seen in patients with severeS. aureus sepsis. The data also suggest that the contact system could be used as a target in the treatment of S. aureus infections.

Low Antibody Levels against Cell Wall-Attached Proteins of Streptococcus pyogenes Predispose for Severe Invasive Disease

Acute-phase serum samples from 70 patients with group A streptococcal (GAS) invasive disease were analyzed for IgG antibodies against 6 recently characterized GAS virulence factors (SclA, SclB, GRAB, MtsA, EndoS, and IdeS) and SpeB. Antibody levels against the cell wall-attached GAS antigens SclA, SclB, and GRAB were significantly lower in patients with severe invasive disease (streptococcal toxic shock syndrome [STSS] and/or necrotizing fasciitis [NF]; n=35), compared with levels in patients with nonsevere GAS bacteremia (n=35). Among patients with severe invasive disease, significantly lower antibody levels against GRAB were found in patients with STSS (n=10) than in patients with NF (n=17). Antibody levels against SpeB in patients with severe bacteremia were similar to those in patients with nonsevere bacteremia, and levels in patients with STSS were similar to those in patients with NF. The data indicate that immunity to cell wall-attached proteins may play a role in the protection against severe invasive disease and that antibodies against GRAB may be of importance in the pathogenesis of STSS.

Peptidoglycan from Staphylococcus aureus induces tissue factor expression and procoagulant activity in human monocytes

ABSTRACT Staphylococcus aureus is one of the most significant pathogens in human sepsis and endocarditis. S. aureus can initiate blood coagulation, leading to the formation of microthrombi and multiorgan dysfunction in sepsis, whereas in endocarditis the bacterium induces fibrin clots on the inner surface of the heart, so-called endocardial vegetations. In the present study, we show that live and heat-killed S. aureus bacteria are potent inducers of procoagulant activity in human peripheral blood mononuclear cells. Furthermore, purified peptidoglycan, the main cell wall component of S. aureus, induced procoagulant activity in mononuclear cells in a concentration-dependent fashion. The procoagulant activity in these cells was dependent on expression of tissue factor, since antibodies to tissue factor inhibited the effect of peptidoglycan. In mononuclear cells stimulated with peptidoglycan, reverse transcription-PCR showed tissue factor gene expression, and the gene product was detected by enzyme-linked immunosorbent assay. Finally, flow cytometry identified tissue factor at the surface of CD14-positive monocytes. Peptidoglycan is known to induce proinflammatory cytokine production in monocytes. The present investigation shows that peptidoglycan also activates the extrinsic pathway of coagulation by inducing the expression of tissue factor in these cells. This mechanism helps to explain the procoagulant activity, which plays such an important role in the pathogenicity of severe S. aureus infections.

Highly Purified Lipoteichoic Acid from Staphylococcus aureus Induces Procoagulant Activity and Tissue Factor Expression in Human Monocytes but Is a Weak Inducer in Whole Blood: Comparison with Peptidoglycan

ABSTRACT Lipoteichoic acid from Staphylococcus aureus was a potent inducer of procoagulant activity in isolated mononuclear cells but not in whole blood. In contrast, staphylococcal peptidoglycan showed equal levels of potency in isolated mononuclear cells and whole blood, suggesting that peptidoglycan is an important inducer of procoagulant activity in severe sepsis involving gram-positive bacteria.

Superantigens from Staphylococcus aureus induce procoagulant activity and monocyte tissue factor expression in whole blood and mononuclear cells via IL-1beta.

Summary.  Background: Staphylococcus aureus is one of the most common bacteria in human sepsis, a condition in which the activation of blood coagulation plays a critical pathophysiological role. During severe sepsis and septic shock microthrombi and multiorgan dysfunction are observed as a result of bacterial interference with the host defense and coagulation systems. Objectives: In the present study, staphylococcal superantigens were tested for their ability to induce procoagulant activity and tissue factor (TF) expression in human whole blood and in peripheral blood mononuclear cells. Methods and results: Determination of clotting time showed that enterotoxin A, B and toxic shock syndrome toxin 1 from S. aureus induce procoagulant activity in whole blood and in mononuclear cells. The procoagulant activity was dependent on the expression of TF in monocytes since antibodies to TF inhibited the effect of the toxins and TF was detected on the surface of monocytes by flow cytometry. In the supernatants from staphylococcal toxin‐stimulated mononuclear cells, interleukin (IL)‐1β was detected by ELISA. Furthermore, the increased procoagulant activity and TF expression in monocytes induced by the staphylococcal toxins were inhibited in the presence of IL‐1 receptor antagonist, a natural inhibitor of IL‐1β. Conclusions: The present study shows that superantigens from S. aureus activate the extrinsic coagulation pathway by inducing expression of TF in monocytes, and that the expression is mainly triggered by superantigen‐induced IL‐1β release.

Peptidoglycan Induces Mobilization of the Surface Marker for Activation Marker CD66b in Human Neutrophils but Not in Eosinophils.

ABSTRACT Peptidoglycan from Staphylococcus aureus mobilized CD66b in human neutrophils but did not upregulate surface activation markers in eosinophils. In addition, Toll-like receptor 2, implicated in the recognition of peptidoglycan, was detected on the surface of resting neutrophils but not on eosinophils. These findings suggest roles for neutrophils but not eosinophils in innate recognition of peptidoglycan.