Quantitative determination in human sera of vaccine-induced antibody to type-specific polysaccharides of group B streptococci using an enzyme-linked immunosorbent assay.

The humoral immune response of human volunteers vaccinated with highly purified type II-or type III-specific polysaccharide of group B streptococci was evaluated using an enzyme-linked immunosorbent assay standardized with quantitative precipitin analysis, a method which permits calculation of the micrograms of specific antibody protein per milliliter of serum, rather than expression of the data as titers. By inhibition studies, the assays were shown to be specific for antibody to the undegraded type II or III polysaccharide antigen. Purity of the antigens and the specificity of the immune response to them were evidenced by an increase in level of antibody only to the type-specific antigen used for immunization. The isotype of the antibody raised in the sera of immunized volunteers was primarily IgG, thus confirming the potential utility of vaccination against group B streptococci using polysaccharide vaccines to induce antibodies which will cross the human placenta.