An antibody chimera technique applied to enzyme immunoassay for human alpha-1-fetoprotein with monoclonal and polyclonal antibodies

A 2-step enzyme immunoassay (EIA) for human alpha-1-fetoprotein (AFP) is proposed, which uses covalently coupled anti-AFP IgG and anti-horseradish peroxidase (HRP) IgG (antibody chimera) binding HRP as the marker enzyme immunologically. The use of polyclonal and monoclonal anti-AFP linked to anti-HRP antibodies was compared with a conventional 2-site binding EIA with HRP covalently bound to anti-AFP IgG. The sensitivity of the conventional EIA is increased by the use of an antibody chimera comprising a molar ratio of anti-AFP IgG: anti-HRP IgG of 1:8, especially if monoclonal antibodies are employed. This improved sensitivity may be achieved by a very simple coupling procedure without purification of conjugate and with very crude HRP preparations.