Naturally occurring antibodies for the group B streptococcal surface immunogenic protein (Sip) in pregnant women and newborn babies

Sip is a surface-exposed protein of GBS, which causes severe neonatal disease. Because Sip elicits a protective immune response in mice, we assessed whether pregnant women and newborns have Sip antibodies. Sera were collected from 644 pregnant women and 176 of their healthy newborns, and 10 newborns with GBS disease and their mothers. Using ELISA, most (99%) women and newborns (97%) had serum Sip antibodies, as did most newborns followed through 6 months. This suggests that naturally occurring Sip antibodies cross the placenta and persist into infancy, which underscores the need to study Sip further as a potential vaccine candidate.