DEVELOPMENT OF IGM ANTIBODY TO GROUP-B STREPTOCOCCUS TYPE-III IN HUMAN INFANTS

An ELISA was developed to measure IgM antibody to albumin-coupled native capsular polysaccharide of type III group B streptococcus (GBS). The assay was standardized by two double-label label methods that agreed within 33%. In quantitative assays, the range of IgM antibody to type III GBS in the sera of 94 adult pregnant women was 1.2-50.6-mu-g/ml (median, 5.4), while each of 38 cord serum samples contained <0.03-mu-g/ml IgM antibody. Neonatal rats were passively immunized with a serially diluted human serum containing 15-mu-g/ml IgM and undetectable IgG antibody to type III GBS. The rats were protected against lethal infection with an IgM antibody concentration of 0.5-mu-g/ml. In single serum samples from 31 healthy infants < 2 years old and serial specimens from 5 infants with type III GBS infections, specific IgM antibody was detectable by 3 months of age. Levels greater-than-or-equal-to 0.5-mu-g/ml were present in all samples from infants > 7 months of age. The acquisition of specific IgM antibody is inversely correlated with the age-limited incidence of type III GBS infections in young children.