Cationic antigens. Problems associated with measurement by ELISA.

The measurement of the mouse antibody response to cationized bovine serum albumin (cat BSA) and bovine gammaglobulin (cat BGG) was complicated because of the unique properties of these antigens. Cat BGG non-specifically bound rabbit anti-mouse gammaglobulin conjugated to alkaline phosphatase. This was minimized by adding the polyanion, heparin. Cat BSA also reacted non-specifically with some conjugates, but the reaction with specific antibody was enhanced by the addition of the polyanions heparin or dextran sulfate. The non-specific reaction did not appear to be related to the concentration of antigen used to coat the plastic plates. In addition, in ELISA inhibition experiments high concentration of antigens (greater than 100 micrograms/ml) seemed to result in non-specific inhibition of the antibody antigen reaction. A proposed model to explain the problems is based on the polycationic surface formed by coating the plates with the cationized proteins. This cationic surface can be neutralized by polyanions, reducing the non-specific and enhancing the specific reactions. It appears that other polycationic molecules might share these unique properties and these factors must be considered when they are measured.