Perinatal immunity to group B beta-hemolytic streptococcus type Ia

Area of Science:

• Immunology
• Microbiology
• Infectious Diseases

Background:

• Group B Streptococcus (GBS) is a leading cause of neonatal sepsis and meningitis.
• Effective vaccines and immunotherapies against GBS are lacking.
• Understanding protective immune responses is crucial for developing interventions.

Purpose of the Study:

• To investigate the protective and bactericidal activities of human sera against virulent group B Streptococcus serotype Ia.
• To characterize the immunoglobulin classes involved in protective immunity.
• To assess the correlation between in vivo protection and in vitro bactericidal activity.

Main Methods:

• Murine model of intraperitoneal challenge with GBS serotype Ia.
• In vitro bactericidal assays using human sera and polymorphonuclear leukocytes.
• Immunoglobulin class determination (IgG, IgM) of protective sera.
• Evaluation of heat-labile serum factors' role in opsonic activity.

Main Results:

• Sera from 14/56 adult women conferred protection against GBS challenge in mice.
• Sera from 7/25 nonparturient women demonstrated significant in vitro bactericidal activity (>99%).
• Protective activity was predominantly attributed to IgG antibodies, with one instance of IgM.
• Opsonic activity showed partial dependence on heat-labile serum factors.
• Maternal sera showed protective capacity, but cord sera did not always correlate.
• Pooled human gamma-globulin provided protection in vivo.

Conclusions:

• Human sera contain protective and bactericidal antibodies against GBS serotype Ia.
• IgG antibodies are key mediators of this protective immunity.
• In vivo protection strongly correlates with in vitro bactericidal assays.
• Human gamma-globulin demonstrates therapeutic potential against GBS infection.