HUMAN IMMUNITY TO GROUP-B STREPTOCOCCI MEASURED BY INDIRECT IMMUNOFLUORESCENCE - CORRELATION WITH PROTECTION IN CHICK-EMBRYOS

An indirect immunofluorescence (IF) assay has been developed as a useful semiquanti-tative method for determination of type-specific IgG antibody in human sera to the five serotypes of group B Streptococcus. Antibody titers measured by IF correlated with passive protection in chick embryos, and antibody titers associated with chick embryo protection were delineated. Except for types la and Ic, IF antibody to each of the streptococcal types was completely absorbed by homologous strains, and antibody titers were unchanged by incubation with heterologous bacteria. For types la and Ic, IF antibody was absorbed by either the la or the Ic strain and by native la carbohydrate antigen. Antibody titers measured by IF and chick embryo protection against types la and Ic were similar, but were divergent for lb and Ic, a finding suggesting that antibody is predominantly directed to the major carbohydrate determinants. In addition, 29 of 31 sera that had been tested in chick embryos yielded comparable results in mice against challenge with type la group B Streptococcus, a finding further validating the chick embryo assay. Sera from all of 43 mothers of infants infected with group B streptococci had antibody titers by IF that were less than titers associated with protection in chick embryos. © 1979 by The University of Chicago.