A highly sensitive and specific sandwich enzyme immunoassay for water soluble A and B substances.

A highly sensitive and specific sandwich enzyme immunoassay for water soluble A and B substances is described. An affinity-purified rabbit anti-A IgG-coated polystyrene ball was incubated with water soluble A substance and subsequently with affinity-purified rabbit anti-A IgG-horseradish peroxidase conjugate. In addition, an affinity-purified goat anti-B IgG-coated polystyrene ball was incubated with water soluble B substance and subsequently with affinity-purified goat anti-B IgG-horseradish peroxidase conjugate. Peroxidase activity bound to the polystyrene balls was assayed by fluorimetry. The detection limits of artificial A and B antigens (synthetic A and B trisaccharides coupled to bovine serum albumin) were both 0.1 fmol/tube, which were 30- and 300-fold lower, respectively, than those by the hemagglutination inhibition method. In addition, A and B substances in secretor saliva could also be measured 3- to 10-fold and 100- to 1,000-fold more sensitively, respectively, by the present method than by the hemagglutination inhibition method.