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Chapter 2 History of ultrasensitive enzyme immunoassay
CHAPTER 2
History of ultrasensitive enzyme immunoassay
Radioimmunoassay, developed in 1959 (Berson and Yalow, 1959), made it possible to measure femtomole amounts of peptide hormones in the circulation and was almost generally accepted not to be exceeded in sensitivity by any other method. However, in 1968, less than a decade later, the use of enzymes as labels in immunoassay was suggested (Miles and Hales, 1968), and the first attempts of enzyme immunoassay were reported in 1971 (Engvall and Perlmann, 1971; van Weemen and Schuurs, 1971). For many years later, the potential of enzyme immunoassay particularly concerning its sensitivity was a focus of discussion by many investigators. In 1976, a typical view that enzyme immunoassays would replace radioimmunoassays in various fields was published (Editorial, Lancet 1976). One month later, arguments against this view appeared in the same journal. One stated that the suggestion that enzyme-labeling would replace radioisotopic techniques (particularly in assays demanding highest sensitivity) was questionable (Ekins, 1976). The other stated that for analysis of femtomole (1 x 1O-I5 mol) amounts of steroids, hormones, etc., to aid patient diagnosis and treatment there is only radioimmunoassay (Watson, 1976). Less than four months after these arguments, detection by a twosite enzyme immunoassay of one attomole (1 x lo-'* mol; 600,000 molecules as calculated from Avogadro's number) of a macromole5
6
LlLTRASESSlTlVF AND RAPID E S Z Y l l E IMMIl’NOASSAY
cular antigen, ornithine 6-aminotransferase from rat liver with a molecular weight of 170 kDa, was reported (Kato et al., 1977). During the ensuing decade, the two-site enzyme immunoassay was successfully applied in measurements of various antigens at attomole levels, which are below those detectable by radioinimunoassay. The human antigens measured at attomole levels were thyroid-stimulating hormone, IgEb ferritin, a-fetoprotein (Ishikawa et al., 1983a), growth hormone (khikawa et al., 1987), chorionic gonadotropin, insulin (Ishikawa, 1987), atrial natriuretic peptides, interleukin-I and luteinizing hormone (Ishikawa et al., 1989a). For antibodies and haptens, both the assay system and the sensitivity of enzyme immunoassay were fundamentally unchanged for many years after their first reports. In 1987, an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for antibodies was developed (Kohno and Ishikawa, 1987). Later, the sensitivity to antigens was improved to zeptomole (1 x lop2’ mol) levels by the immune complex transfer method (Hashida and Ishikawa, 1990). For some haptens, a noncompetitive method with attomole sensitivity was developed (Tanaka et al., 1989). Recently, the period required for ultrasensitive enzyme immunoassays has been considerably shortened with even further improvement of the sensitivity mt only to antigens (Ishikawa S. et al., 1998b, c) but also to antibobies (Ishikawa S. et al., 1998a, c).
History of ultrasensitive enzyme immunoassay
Radioimmunoassay, developed in 1959 (Berson and Yalow, 1959), made it possible to measure femtomole amounts of peptide hormones in the circulation and was almost generally accepted not to be exceeded in sensitivity by any other method. However, in 1968, less than a decade later, the use of enzymes as labels in immunoassay was suggested (Miles and Hales, 1968), and the first attempts of enzyme immunoassay were reported in 1971 (Engvall and Perlmann, 1971; van Weemen and Schuurs, 1971). For many years later, the potential of enzyme immunoassay particularly concerning its sensitivity was a focus of discussion by many investigators. In 1976, a typical view that enzyme immunoassays would replace radioimmunoassays in various fields was published (Editorial, Lancet 1976). One month later, arguments against this view appeared in the same journal. One stated that the suggestion that enzyme-labeling would replace radioisotopic techniques (particularly in assays demanding highest sensitivity) was questionable (Ekins, 1976). The other stated that for analysis of femtomole (1 x 1O-I5 mol) amounts of steroids, hormones, etc., to aid patient diagnosis and treatment there is only radioimmunoassay (Watson, 1976). Less than four months after these arguments, detection by a twosite enzyme immunoassay of one attomole (1 x lo-'* mol; 600,000 molecules as calculated from Avogadro's number) of a macromole5
6
LlLTRASESSlTlVF AND RAPID E S Z Y l l E IMMIl’NOASSAY
cular antigen, ornithine 6-aminotransferase from rat liver with a molecular weight of 170 kDa, was reported (Kato et al., 1977). During the ensuing decade, the two-site enzyme immunoassay was successfully applied in measurements of various antigens at attomole levels, which are below those detectable by radioinimunoassay. The human antigens measured at attomole levels were thyroid-stimulating hormone, IgEb ferritin, a-fetoprotein (Ishikawa et al., 1983a), growth hormone (khikawa et al., 1987), chorionic gonadotropin, insulin (Ishikawa, 1987), atrial natriuretic peptides, interleukin-I and luteinizing hormone (Ishikawa et al., 1989a). For antibodies and haptens, both the assay system and the sensitivity of enzyme immunoassay were fundamentally unchanged for many years after their first reports. In 1987, an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for antibodies was developed (Kohno and Ishikawa, 1987). Later, the sensitivity to antigens was improved to zeptomole (1 x lop2’ mol) levels by the immune complex transfer method (Hashida and Ishikawa, 1990). For some haptens, a noncompetitive method with attomole sensitivity was developed (Tanaka et al., 1989). Recently, the period required for ultrasensitive enzyme immunoassays has been considerably shortened with even further improvement of the sensitivity mt only to antigens (Ishikawa S. et al., 1998b, c) but also to antibobies (Ishikawa S. et al., 1998a, c).