A Modified ELISA for Measurement of High-Avidity IgG Antibodies to Meningococcal Serogroup C Polysaccharide that Correlate with Bactericidal Titers.

This chapter describes a modified enzyme-linked immunosorbent assay (ELISA) employing assay conditions that ensure specificity of antibody binding and favor detection primarily of high-avidity serum IgG antibodies to meningococcal serogroup C polysaccharide (1). Antibody-binding assays such as the ELISA offer a convenient and reproducible method for quantifying anticapsular antibody responses to vaccination or disease. However, the results do not always correlate well with assays of antibody functional activity, such as bactericidal activity. For example, a standardized ELISA for measurement of antibody responses to meningococcal C polysaccharide has been described (2). When used to assay relatively homogenous populations of serum antibodies, for example in sera from immunized adults (3), or from younger individuals given a single vaccine (4), the results of the standard ELISA correlated well with serum bactericidal titers. In contrast, much lower correlations were observed when assaying heterologous populations of serum antibodies from vaccinated infants or toddlers (5,6), particularly from clinical studies comparing antibody responses of different age groups (6), or studies comparing responses to a polysaccharide and conjugate vaccines (7,8).