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Distinct profiles of immunoglobulin G-binding-protein expression by invasive serotype M1 isolates of Streptococcus
Abstract:
Analysis of immunoglobulin G (IgG)-binding-protein expression by invasive group A streptococcal isolates of the M1 serotype collected as part of a Centers for Disease Control and Prevention surveillance study revealed two distinct phenotypes. One group of type M1 isolates expressed a surface protein reactive with all four human IgG subclasses (type IIo), while a second group expressed a surface protein demonstrating significant reactivity only with human IgG3 (type IIb). The functional forms of IgG-binding protein were antigenically related, and both were recognized by a rabbit polyclonal antiserum to serotype M1 but not by normal rabbit serum. While the quantities of antigenic M1 protein present in the extracts of representative isolates displaying each phenotype differed, the functional differences were found to be qualitative and not solely quantitative. The IgG-binding properties of these antigenically related M1 proteins could be readily distinguished from those of another IgG-binding protein, protein H. Type M1 isolates of the IIb phenotype differed from those of the IIo phenotype by secreting larger amounts of a casein-hydrolyzing protease into culture supernatants.
Insights
Two types of M1 group A Streptococcus express different immunoglobulin G (IgG)-binding proteins. These distinct proteins influence bacterial interactions and protease secretion, impacting disease.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Invasive group A Streptococcus (iGAS) M1 serotype is a significant human pathogen.
- Understanding pathogen-host interactions is crucial for developing effective treatments.
- Immunoglobulin G (IgG) binding proteins on bacterial surfaces can modulate the host immune response.
Purpose of the Study:
- To characterize the immunoglobulin G (IgG)-binding proteins expressed by invasive M1 group A Streptococcus isolates.
- To investigate the functional differences between distinct IgG-binding protein phenotypes.
- To explore the relationship between IgG-binding phenotypes and protease secretion.
Main Methods:
- Analysis of IgG-binding protein expression in M1 iGAS isolates using Centers for Disease Control and Prevention surveillance data.
- Phenotypic characterization of IgG subclass reactivity (all four vs. IgG3 only).
- Antigenic relatedness assessment using rabbit polyclonal antiserum and comparison with Protein H.
Main Results:
- Two distinct IgG-binding protein phenotypes (type IIo and type IIb) were identified in M1 iGAS isolates.
- Type IIo isolates expressed proteins reactive with all IgG subclasses, while type IIb isolates showed reactivity primarily with IgG3.
- Type IIb isolates secreted significantly higher amounts of casein-hydrolyzing protease compared to type IIo isolates.
Conclusions:
- M1 group A Streptococcus exhibits distinct IgG-binding protein phenotypes with differential functional properties.
- These phenotypic variations are qualitative, not solely quantitative, and impact protease secretion.
- The identified differences in IgG-binding proteins and protease activity may play a role in the pathogenesis of M1 iGAS infections.