RT Journal Article SR Electronic(1) A1 Åkesson, Per A1 Herwald, Heiko A1 Rasmussen, Magnus A1 HÅkansson, Katarina A1 Abrahamson, Magnus A1 Hasan, Ahmed A. K. A1 Schmaier, Alvin H. A1 Müller-Esterl, Werner A1 Björck, LarsYR 2010 T1 Streptococcal inhibitor of complement-mediated lysis (SIC): an anti-inflammatory virulence determinant JF Microbiology, VO 156 IS 12 SP 3660 OP 3668 DO https://doi.org/10.1099/mic.0.039578-0 PB Microbiology Society, SN 1465-2080, AB Since the late 1980s, a worldwide increase of severe Streptococcus pyogenes infections has been associated with strains of the M1 serotype, strains which all secrete the streptococcal inhibitor of complement-mediated lysis (SIC). Previous work has shown that SIC blocks complement-mediated haemolysis, inhibits the activity of antibacterial peptides and has affinity for the human plasma proteins clusterin and histidine-rich glycoprotein; the latter is a member of the cystatin protein family. The present work demonstrates that SIC binds to cystatin C, high-molecular-mass kininogen (HK) and low-molecular-mass kininogen, which are additional members of this protein family. The binding sites in HK are located in the cystatin-like domain D3 and the endothelial cell-binding domain D5. Immobilization of HK to cellular structures plays a central role in activation of the human contact system. SIC was found to inhibit the binding of HK to endothelial cells, and to reduce contact activation as measured by prolonged blood clotting time and impaired release of bradykinin. These results suggest that SIC modifies host defence systems, which may contribute to the virulence of S. pyogenes strains of the M1 serotype., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.039578-0