Molecular biology analysis of ABO blood group variants caused by natural chimaerism.

Background And Objectives: The chimaerism phenomenon constitutes a significant mechanism underlying ABO phenotype discrepancies; however, its detection has technical challenges. In the current study, we explored different techniques to establish the chimaeric status of ABO blood types.

Materials And Methods: Fifteen individuals with possible chimaeric ABO blood type, as suggested by standard tube or column agglutination method and RBC adsorption-elution test, were enrolled in the study. The red blood cells from 11 investigated subjects showed mix-field agglutination with anti-A or anti-B in blood typing; weak A or B antigens on the other four individuals' RBCs were detected by adsorption-elution tests. The genetic study was conducted with PCR-SSP genotype, DNA sequencing of the ABO gene, STR analysis and ddPCR.

Results: The genetic chimaeric status was confirmed in four (27%) individuals by SSP test alone. The ABO gene sequencing identified an additional ABO allele and enabled chimaerism detection in 10 (67%) subjects. The STR analyses established the chimaerism status in 13 (87%) individuals. In the two cases where neither of the tests mentioned above had positive findings, the ddPCR was adopted, and microchimaerism, with an extremely low degree of chimaerism (0.77% and 0.12%), was revealed. The ddPCR revealed the unequal haplotypes (29.5% B vs. 70.5% O) in one subject and distinguished this B/O-O/O chimaera from certain B subgroups (B/O genotype without any mutation) like B .

Conclusion: The ABO blood type chimaerism can be genetically established by comprehensive molecular methods, including PCR-SSP/DNA sequencing, STR and ddPCR, which is particularly sensitive for the detection of microchimaerism.