Association between low concentrations of antibodies to protein alpha and Rib and invasive neonatal group B streptococcal infection.

Background: Infection with group B streptococci (GBS) is a serious neonatal disease. The GBS cell surface proteins alpha and Rib elicit protective immunity in animal models and have been suggested as potential antigens in a vaccine against human GBS disease.

Aims: To test the hypothesis that transplacentally transferred maternal antibodies to GBS proteins contribute to the protection of the neonate from GBS infection.

Methods: Thirty neonates with invasive infection were included in a case-control study. IgG antibody concentrations were measured in sera from these neonates, their mothers, and from 60 non-infected controls, neonates as well as mothers.

Results: A clear association was found between concentrations of antibody to proteins alpha and Rib in neonatal and maternal sera, indicating that transplacental transfer had occurred. Moreover, low concentrations of antibodies to alpha and Rib in neonatal sera were associated with invasive GBS infection caused by strains expressing the Rib protein. The odds ratio was 0.0007 (95% confidence interval 0.000 to 0.54) for antibodies to alpha and 0.002 (95% confidence interval 0.000 to 0.57) for antibodies to Rib.

Conclusion: These findings support the notion that antibodies to GBS surface proteins contribute to the protection against neonatal infection.