The Opsonic Antibody Response of Female Rats to Type III Group B Streptococcal Immunization: a Model for Maternal Immunity

Group B streptococcus (GBS) remains a major cause of neonatal infection. Maternal immunization-induced GBS antibody may protect neonates from GBS disease. Since the opsonophagocytosis assay correlates well with survival in GBS infected suckling rats, we sought to determine an immunization schedule which would induce type III GBS opsonic antibody in rat dams above a predetermined level of 10 dilution −1 (dil −1). This schedule could then be used for future studies of maternal-fetal immunity. Wistar rat dams ( n=12) were given killed GBS type III using three immunization schedules (primary injection, initial booster at 7, 14 or 22 days and then weekly boosters). Opsonic GBS type III antibody and total immunoglobulin (IgG) were measured. Only the schedule with a 7-day initial booster resulted in GBS type-specific opsonic antibody consistently above 10 dil −1. The IgG (467±83 mg/100 ml) remained constant while the opsonic antibody increased significantly to 50 and 63 dil −1 ( P