Investigation into A antigen expression on O2 heterozygous group O-labeled red blood cell units

There are two principal types of group O alleles; deletional alleles feature 261delG leading to nonfunctional truncated protein. Nondeletional alleles have the consensus guanosine at residue 261. The major nondeletional allele, O2, encodes full-length protein with Gly268Arg. While reports vary, O2 has been proposed to encode weakly functional A-glycosyltransferase (GTA). The main objective of this study was to evaluate if GTA activity is detectable in O2 donors.

Donor samples from Pittsburgh and Lund were ABO typed by automated methods. DNA was extracted from 779 group O donors whose red blood cells (RBCs) were available for transfusion. ABO genotyping identified those with O2 alleles. The following tests were performed on randomly selected O2 samples (number): adsorption-elution with anti-A (3), flow cytometry (15), plasma enzyme activity (4), and attempts to convert group O RBCs to A (2) with O2 plasma and titration of plasma anti-A/-A1 (3).

Forty O2-heterozygous donors were identified (5.1%). Adsorption-elution and sensitive flow cytometry did not reveal A antigens on O2 RBCs. Plasma enzyme analysis failed to show GTA activity above baseline; O2 plasma was unable to add measurable A antigens to O RBCs. Titers of anti-A/-A1 appeared reduced in O2 plasma but did not cause ABO typing discrepancies. No immediate hemolysis or adverse reactions were reported following transfusion of O2 RBCs to six evaluable group O recipients.

Other than lower plasma anti-A titers, GTA activity was not found in these O2 samples. Neither automated blood grouping discrepancies nor clinical problems related to transfusing these O2 units were observed.