Analysis of the optimal conditions for the adsorption of type III pneumococcal polysaccharide to plastic for use in solid-phase ELISA.

An economical, sensitive enzyme-linked immunosorbent assay (ELISA) method for measuring all isotypes of immunoglobulin specific for type III pneumococcal polysaccharide (SSS-III) is described, using 96-well polystyrene microtiter plates coated directly with antigen. To achieve substantial binding of SSS-III to plastic plates, the polysaccharide had to be dissolved in a buffer (0.1 M Hepes) of pH 4.0 or less. Optimal conditions for adsorption of SSS-III to plates were found to be pH 3.5 and a concentration of 1.0 microgram SSS-III/ml (0.1 microgram/well). Under these conditions, murine anti-SSS-III polyclonal or monoclonal antibodies could be detected to a limit of about 5-10 ng/ml. The implications of these findings for assays that use mixtures of polysaccharides adsorbed to plastic plates are discussed.