Abstract: Objective To investigate the possible reasons for the weakened A and/or B antigens in individuals with AB blood type, aiming to facilitate accurate identification of AB blood type. Methods A combined approach of serological testing and molecular biology was employed to identify ten AB-type individuals with weakened ABO antigens. To further explore the potential causes of ABO antigen weakening, the plasma glycosyltransferase activity and antigen expression were compared among individuals with A, B, AB blood types, and those with weakened ABO antigens, aiming to elucidate the underlying reasons for antigen weakening in all AB-type individuals. Results Among the ten AB-type individuals with weakened ABO antigens, five were identified as subtypes, 1 was suspected of leukemia, and the causes of weakening remained unclear in four cases. When compared with normal A and B types, normal AB-type individuals exhibited no significant difference in plasma glycosyltransferase activity (P>0.05), but their A and B antigen expressions were notably weaker. Among the 4 AB-type individuals with unexplained serological B antigen weakening, three showed no change in GTA activity but slightly lower GTB activity, while one exhibited decreased activities of both GTA and GTB. In contrast, individuals with blood type subtypes displayed significantly reduced plasma glycosyltransferase activities. Conclusion The ABO antigen expression in AB-type individuals may be influenced by multiple factors, including age, disease, genetic polymorphisms, epigenetic modifications, and the competitive effects of glycosyltransferases. Therefore, a comprehensive approach that integrates past medical history, case analysis, serological techniques, genotyping, glycosyltransferase activity analysis, and even epigenetic analysis should be adopted during identification to unravel the reasons for ABO antigen weakening.

Key words: AB blood type, ABO antigen weakening, Glycosyltransferase, Competitive effect