Generation and characterization of a plasminogen-binding group A streptococcal M-protein/streptokinase-sensitive mouse line

Background: Streptococcus pyogenes (GAS) is a human bacterial pathogen that generates various mild to severe diseases. Worldwide, there are approximately 700 million cases of GAS infections per year. In some strains of GAS, the surface-resident M-protein, plasminogen-binding group A streptococcal M-protein (PAM), binds directly to human host plasminogen (hPg), where it is activated to plasmin through a mechanism involving a Pg/bacterial streptokinase (SK) complex as well as endogenous activators. Binding to Pg and its activation are dictated by selected sequences within the human host Pg protein, making it difficult to generate animal models to study this pathogen.Objectives: To develop a murine model for studying GAS infection by minimally modifying mouse Pg to enhance the affinity to bacterial PAM and sensitivity to GAS-derived SK.Methods: We used a targeting vector that contained a mouse albumin-promoter and mouse/human hybrid plasminogen cDNA targeted to the Rosa26 locus. Characteriza-tion of the mouse strain consisted of both gross and histological techniques and determination of the effects of the modified Pg protein through surface plasmon resonance measurements, Pg activation analyses, and mouse survival post-GAS infection.Results: We generated a mouse line expressing a chimeric Pg protein consisting of 2 amino acid substitutions in the heavy chain of Pg and a complete replacement of the mouse Pg light chain with the human Pg light chain.Conclusion: This protein demonstrated an enhanced affinity for bacterial PAM and sensitivity to activation by the Pg-SK complex, making the murine host susceptible to the pathogenic effects of GAS.