Enzyme-linked immunosorbent assay. II. Quantitative assay of protein antigen, immunoglobulin G, by means of enzyme-labelled antigen and antibody-coated tubes.

Alkaline phosphatase from calf intestinal mucosa has been conjugated to a protein antigen, rabbit IgG. Such conjugates, prepared by glutardialdehyde, have been used in a competitive solid phase immunoassay. In this test native antigen inhibits the binding of the conjugate to homologous antibodies adsorbed to plastic tubes. Using this assay 1-100 ng/ml of the antigen could be determined.