Distribution of immunoglobulin G subclasses in anti-A and anti-B sera

Sera from 117 immunologically normal subjects, who had been selected for the presence of high titre ABO system antibody on routine screening, were further evaluated for the presence of IgG and its subclasses IgG1, IgG2, IgG3, and IgG4 using an indirect antihuman globulin technique. Subjects of all ABO groups had the capacity to produce IgG antibodies within each subclass, but those of group O produced the broadest spectrum of IgG subclasses and greatest strength of reactions.