Naturally occurring ABO antibodies: long-term stable, individually distinct anti-A IgG spectrotypes.

Spectrotypes of naturally occurring IgG antibodies to histo-blood group substance A were analyzed by isoelectric focusing and a newly developed, non-radioactive affinity immunoblotting assay. Specificity was tested by preabsorption of sera on red blood cells and on four different types of blood group substance A. Clonotype-banding patterns of sera from 18 different blood donors were individually distinct, most of them showing an oligoclonal pattern with less than 15 visible bands. To analyze the influence of IgG subclass composition on spectrotype patterns, IgG subclasses were measured by ABO enzyme-linked immunosorbent assay (ELISA) and were shown to be mostly IgG1 and IgG2. Anti-A IgG1 spectrotypes could be detected with four sera and were also individually distinct. A series of six and seven serum samples, respectively from two donors was used to analyze the time-related changes of anti-A IgG spectrotypes. Banding pattern of both individuals remained stable during the whole observation period of 167 and 82 days, respectively, and no differences between follow-up samples could be detected. This long-term stability of individual anti-A IgG spectrotypes is backed by constant serum levels of anti-A IgG and -IgM antibodies during the observation period as measured by ABO ELISA.