A highly sensitive enzyme-linked immunosorbent assay (ELISA) method using H-disaccharide (Fucα1, 2 Galβ-BSA) was developed to measure α (1, 3)-N-acetyl-D-galactosaminyltransferase (A-transferase) and α (1, 3)-D-galactosyltransferase (B-transferase) activities in human plasma. Fifty-eight and 43 plasma samples from various subgroups of A and B, respectively, were assayed with UDP-GalNAc or UDP-Gal in microtiter plate wells coated with H-disaccharide covalently attached to BSA, and the products formed by transferases were detected by horse-radish peroxidase-conjugated anti-A or anti-B monoclonal antibody. Transferase activities measured by this method were compared with those by the conventional method based on the conversion of O-type erythrocytes into A- or B-type erythrocytes.
The present method allowed detection of weak enzyme activities from A- and B-type subgroups and variants such as A2, A3, AXB, cisAB (for A-transferase) and AB3, BX, cisAB (for B-transferase). In contrast, these activities could not be detected at all by the conventional method. Further, enzyme activities of all samples (n=101) except one from AX were quantified by this ELISA method, whereas only 21% (12/58) of the A-transferase and 58% (25/43) of B-transferase from the same individuals were determined to be present by conversion of blood types on erythrocytes.
These results demonstrate that the present method was sufficiently sensitive for the assay of weak A- and B-transferase activities and the typing of A and B blood groups.
