A solid-phase kinetic enzyme-linked immunosorbent assay has been developed to measure binding of antibodies to purified or synthetic blood group antigens and tested in the Lewis blood group system. Chemically synthesized Lewis α antigen is used as the target for the binding of serum antibody in this sandwich-type assay. Kinetic, rather than endpoint, determinations are used to calculate the amount of specific antibody. Data are presented showing the assay to be quantitative, sensitive, and specific. It can separately quantitate the amount of IgG or IgM anti-Lewis a present in patient sera. The assay uses commercially available reagents and is semiautomated. Thus, it will be useful for studies in quantitative immunohematology as other blood group antigens become available in purified form.

Lewis blood group antibodies rarely, if ever, cause hemolytic disease of the newborn. This observation has been attributed to the absence both of Lewis antigens on fetal cells and of maternal IgG Lewis antibody. In the present study, sera from 13 mother-infant pairs were tested for the presence of anti-Lewis (a) by hemagglutination and by a sensitive and specific kinetic enzyme-linked immunosorbent assay. By routine hemagglutination methods, anti-Le^a was present in all maternal samples but absent in all cord samples. By kinetic enzyme-linked immunosorbent assay, IgG anti-Le^a was present in 13 of 13 maternal samples and in 12 of 13 cord samples. These results indicate that IgG anti-Le^a antibodies are common and do cross the placenta. This suggests that they do not cause hemolytic disease of the newborn because of the low levels of Lewis antigens on fetal red cells.