interleukin-8 and Soft-Tissue-Infections

Streptococcus dysgalactiae subsp. equisimilis (SDSE) has emerged as an important cause of severe skin and soft tissue infections, but little is known of the pathogenic mechanisms underlying tissue pathology. Patient samples and a collection of invasive and non-invasive group G SDSE strains (n = 69) were analyzed with respect to virulence factor expression and cytotoxic or inflammatory effects on human cells and 3D skin tissue models. SDSE strains efficiently infected the 3D-skin model and severe tissue pathology, inflammatory responses and altered production of host structural framework proteins associated with epithelial barrier integrity were evident already at 8 hours post-infection. Invasive strains were significantly more cytotoxic towards keratinocytes and expressed higher Streptokinase and Streptolysin O (SLO) activities, as compared to non-invasive strains. The opposite was true for Streptolysin S (SLS). Fractionation and proteomic analysis of the cytotoxic fractions implicated SLO as a factor likely contributing to the keratinocyte cytotoxicity and tissue pathology. Analyses of patient tissue biopsies revealed massive bacterial load, high expression of slo, as well as immune cell infiltration and pro-inflammatory markers. Our findings suggest the contribution of SLO to epithelial cytotoxicity and tissue pathology in SDSE tissue infections.

Topics: Bacterial Proteins; Cell Culture Techniques; Cell Proliferation; Cell Survival; Cells, Cultured; Cytokines; Enzyme-Linked Immunosorbent Assay; HMGB1 Protein; Humans; Interleukin-8; Keratinocytes; Leukocytes, Mononuclear; Proteome; Skin; Soft Tissue Infections; Streptococcal Infections; Streptococcus; Streptolysins; Tandem Mass Spectrometry; Virulence Factors

The ScpC protease of Streptococcus pyogenes degrades interleukin-8 (IL-8), a chemokine that mediates neutrophil transmigration and activation. The ability to degrade IL-8 differs dramatically among clinical isolates of S. pyogenes. Bacteria expressing ScpC overcome immune clearance by preventing the recruitment of neutrophils in soft tissue infection of mice. To study the role of ScpC in streptococcal sepsis, we generated an ScpC mutant that did not degrade IL-8 and thus failed to prevent the recruitment of immune cells as well as to cause disease after soft tissue infection. In a murine model of sepsis, challenge with the ScpC mutant resulted in more severe systemic disease with higher bacteremia levels and mortality than did challenge with the wild-type strain. As expected, the blood level of KC, the murine IL-8 homologue, increased in mice infected with the ScpC mutant. However, the elevated KC levels did not influence neutrophil numbers in blood, as it did in soft tissue, indicating that additional factors contributed to neutrophil transmigration in blood. In addition, the absence of ScpC increased tumor necrosis factor, IL-6, and C5a levels in blood, which contributed to disease severity. Thus, the ScpC mutant triggers high neutrophil infiltration but not lethal outcome after soft tissue infection, whereas intravenous infection leads to highly aggressive systemic disease.

Topics: Animals; Bacterial Proteins; Blood; Cell Line; Complement C5a; Humans; Interleukin-6; Interleukin-8; Mice; Mutation, Missense; Peptide Hydrolases; Sepsis; Skin; Soft Tissue Infections; Streptococcal Infections; Streptococcus pyogenes; Survival Analysis; Tumor Necrosis Factor-alpha; Virulence Factors