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A monoclonal antibody identifies a protective C-protein alpha-antigen epitope in group B streptococci
L C Madoff1, J L Michel, D L Kasper
1Channing Laboratory, Brigham and Women's Hospital, Boston, Massachusetts.
Insights
Group B streptococci (GBS) cause severe neonatal infections. A new monoclonal antibody, 4G8, targets a protective C-protein alpha-antigen, offering potential for new GBS vaccines and therapies.
Area of Science:
- Microbiology
- Immunology
- Vaccine Development
Background:
- Group B streptococci (GBS) are a major cause of neonatal sepsis and meningitis.
- Current therapies have limitations, and GBS C-protein antigens are crucial for immunity but poorly understood.
- Existing GBS C-proteins lack complete characterization regarding structure and function.
Purpose of the Study:
- To develop a novel method for extracting GBS surface proteins.
- To characterize GBS C-protein antigens and identify protective epitopes.
- To generate and evaluate monoclonal antibodies against GBS C-proteins.
Main Methods:
- Utilized mutanolysin for novel extraction of surface proteins from GBS strain A909.
- Generated rabbit polyclonal and mouse monoclonal antibodies against extracted proteins.
- Characterized monoclonal antibody 4G8's reactivity and epitope on GBS C-protein alpha-antigen via SDS-PAGE and functional assays.
Main Results:
- Mutanolysin extraction yielded partially purified GBS surface proteins.
- Antibodies conferred passive protection against lethal GBS infection in mice.
- Monoclonal antibody 4G8 identified a specific epitope on the alpha-antigen, appearing as multiple bands on SDS-PAGE.
- 4G8 induced opsonic killing and protected mice from lethal GBS challenge.
Conclusions:
- The 4G8 monoclonal antibody recognizes a fully protective epitope on the GBS C-protein alpha-antigen.
- This finding advances understanding of GBS immunity and antigen structure.
- The 4G8 antibody represents a promising candidate for GBS vaccine development and therapeutic strategies.
Abstract:
Group B streptococci (GBS) are the leading causes of neonatal sepsis and meningitis in the United States, with a high rate of fatality and serious morbidity despite appropriate therapy. The C-protein antigens of GBS appear to be important in immunity to experimental infection, yet these antigens remain incompletely characterized with respect to their number, structure, and function. None of these proteins has yet been purified to homogeneity. We have developed a novel method for extraction of surface proteins from the A909 (Ia/c) strain of GBS by using mutanolysin. Antibodies raised in rabbits against these partially purified proteins conferred passive protection to lethal GBS infection in mice challenged with a GBS strain expressing C proteins with a heterologous capsule type. In addition, mouse monoclonal antibodies were produced and identified by reactivity with the mutanolysin-extracted proteins. One of these monoclonal antibodies (4G8) identifies an epitope on the alpha-antigen of the GBS C proteins (identified by protease susceptibility and mouse protection). On sodium dodecyl sulfate-polyacrylamide gels, this epitope appears as a series of regularly spaced bands ranging in apparent molecular mass from 160,000 to 30,000 Da. The monoclonal antibody 4G8 induces opsonic killing of GBS and protects mice from lethal challenge with GBS. Thus, the 4G8 monoclonal antibody identifies a fully protective epitope on the C-protein alpha-antigen of GBS.