Human antibody to the group-specific polysaccharide of group B Streptococcus.

IgG antibody to purified group polysaccharide of group B Streptococcus was detected with a specific, reproducible enzyme-linked immunosorbent assay in sera of 178 human subjects: 106 parturient patients, 67 of their healthy infants, and 5 adults with invasive infection. Antibody concentrations in 44 parturient carriers of group B streptococci were significantly greater than in 44 noncarriers (geometric mean level, 3.5 and 1.2 micrograms/ml, respectively). Cord serum levels agreed closely with maternal serum levels. The sera of 18 mothers of infants with early-onset streptococcal infection contained levels (geometric mean level, 5.5 micrograms/ml) similar to those of carriers and significantly higher than noncarriers. Of five adults with invasive group B streptococcal infection, three demonstrated significant increases in antibody titer in consecutive sera, and four had antibody concentrations greater than most (93%) noncarriers. These findings suggest that group B polysaccharide is immunogenic in humans and that levels of specific IgG antibody increase with colonization or infection of adults with group B streptococci.