Quantitative determination of immunoglobulin G specific for group B streptococcal β C protein in human maternal serum

The β C protein of group B streptococci (GBS) elicits antibody that is protective against GBS challenge in animals and is considered to be a potential component of a GBS conjugate vaccine. We developed a quantitative enzyme-linked immunosorbent assay to measure β-specific serum immunoglobulin G (IgG) levels and used it to compare β-specific IgG in a group of mothers of neonates with invasive type Ib/β GBS disease and a group of mothers colonized with Ib/β strains whose neonates remained well. β-Specific IgG concentrations from these 2 groups were similar. To investigate differences in β-specific antibody in animals and humans, protein fragments were generated that corresponded to major regions within the β C protein. A single major region was predominantly recognized in human and rabbit serum samples. Thus, in contrast to immunized animals, no relationship was seen between levels of naturally acquired human β-specific IgG and protection from neonatal disease. This difference was not explained by a major difference in epitope specificity.