Assessment of Functional Antibody Responses

For more than a century, humoral immunity has been recognized as the principal mechanism of defense against most bacterial infections. To evaluate the immunogenicity of vaccines, a variety of assays may be employed, although it is essential that the assay of choice should be a good surrogate for clinical protection. Both radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) accurately measure antibody levels to capsular polysaccharide and other antigens, for example, but these assays do not measure functional antibodies, and although useful, care is needed to ascertain that there are strong correlations with an appropriate functional assay. Problems may be encountered with antigen purity (1 ), which may be overcome with the use of highly purified antigens or adsorbing out crossreactive determinants, or low-avidity antibodies overcome by the use of chaotrophs (2 ).