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C5a peptidase alters clearance and trafficking of group A streptococci by infected mice
Y Ji1, L McLandsborough, A Kondagunta
1Department of Microbiology, University of Minnesota School of Medicine, Minneapolis 55455, USA.
Abstract:
Group A streptococcal C5a peptidase (SCPA) specifically cleaves the human serum chemotaxin C5a at the polymorphonuclear leukocyte (PMNL) binding site. This study tested the proposal that SCPA contributes to virulence by retarding the influx of inflammatory cells and clearance of streptococci during the first few hours after infection. To investigate the specific contribution of SCPA to the virulence of group A streptococci, scpA insertion and deletion mutants were created by directed plasmid insertion into scpA and gene replacement. The precise locations of insertion and deletion mutations were confirmed by PCR and DNA sequence analysis. The impact of mutation on virulence was investigated with a mouse air sac model of inflammation. Experiments evaluated clearance of streptococci from the air sac within 4 h after infection. SCPA- streptococci were cleared more efficiently than wild-type bacteria. Localization of streptococci in lymph nodes and spleens of infected mice revealed a significant difference between mutant and wild-type streptococci. PMNLs and other granulocytes that infiltrated the air sac were quantitated by single-color flow cytometry. The total cellular infiltrate was greater and PMNLs dominated the granulocytic infiltrates of air sacs inoculated with SCPA- mutant bacteria. The data obtained are consistent with the possibility that SCPA- streptococci are initially cleared from the site of infection primarily by PMNLs. Moreover, mutant and wild-type streptococci followed different paths of dissemination. SCPA- bacteria were transported to lymph nodes, whereas wild-type streptococci avoided transport to the lymph nodes and rapidly spread to the spleen.
Insights
Group A streptococcal C5a peptidase (SCPA) hinders immune cell response. Removing SCPA enhances bacterial clearance and alters streptococcal dissemination, suggesting SCPA aids virulence.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Group A Streptococcus (GAS) is a significant human pathogen.
- GAS virulence is multifactorial, involving secreted and cell-surface proteins.
- Group A streptococcal C5a peptidase (SCPA) cleaves the human complement component C5a, a key chemoattractant for neutrophils.
Purpose of the Study:
- To investigate the role of SCPA in GAS virulence.
- To determine if SCPA impairs the early host inflammatory response and bacterial clearance.
- To elucidate the impact of SCPA on bacterial dissemination.
Main Methods:
- Generation of scpA insertion and deletion mutants in GAS using directed plasmid insertion and gene replacement.
- Confirmation of mutation sites via PCR and DNA sequencing.
- Assessment of bacterial clearance and host inflammatory response in a mouse air sac model.
- Quantification of immune cell infiltration using flow cytometry.
- Analysis of bacterial dissemination to lymph nodes and spleen.
Main Results:
- Mice infected with SCPA-deficient GAS showed enhanced clearance of bacteria within 4 hours compared to wild-type.
- SCPA-deficient GAS induced a greater inflammatory infiltrate, dominated by neutrophils, in the air sac.
- Wild-type GAS rapidly disseminated to the spleen, while SCPA-deficient GAS were primarily found in lymph nodes.
Conclusions:
- SCPA contributes to GAS virulence by inhibiting early neutrophil influx and bacterial clearance.
- The absence of SCPA leads to increased neutrophil recruitment and more efficient bacterial elimination at the infection site.
- SCPA influences bacterial dissemination pathways, with SCPA-deficient strains showing altered migration patterns.