Streptococcal pyrogenic exotoxin B (SpeB) boosts the contact system via binding of alpha-1 antitrypsin
Résumé
The Streptococcus pyogenes cysteine protease, SpeB, is important for the invasive potential of the bacteria, but its production is down-regulated following systemic infection. This prompted us to investigate if SpeB potentiated the host immune response after systemic spreading. Addition of SpeB to human plasma increased plasma-mediated bacterial killing and prolonged coagulation time through the intrinsic pathway of coagulation. This effect was independent of the enzymatic activity of SpeB and was mediated by a non-covalent medium-affinity binding and modification of the serpin alpha-1 antitrypsin. Consequently, supplement of alpha-1 antitrypsin to plasma increased bacterial survival. Sequestration of alpha-1 antitrypsin by SpeB led to enhanced contact system activation, supported by increased bacterial growth in prekallikrein deficient plasma. In a mouse model of systemic infection administration of SpeB significantly reduced bacterial dissemination. The findings reveal an additional layer of complexity to host-microbe interactions which may be of benefit in treatment of severe bacterial infections.
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