Interference of lysozyme in the sandwich enzyme-linked immunosorbent assay (ELISA)

Lysozyme can cause unreliable results in sandwich ELISA procedures, since it strongly associates with proteins with low isoelectric points. As immunoglobulins have an isoelectric point of about 5, lysozyme may form a bridge between the IgG in the coat and the IgG of the enzyme-labeled antibodies. For reliable ELISA results, it is necessary either to remove lysozyme from samples or to mask it. Both Cu2+ ions and ovalbumin were very effective in masking lysozyme and thus avoiding its linkage to immunoglobulins. Ovalbumin was not always as effective as Cu2+ ions because in test samples other proteins with high isoelectric points may be present which may compete with lysozyme for association with ovalbumin.