A comprehensive analysis of DEL types: partial DEL individuals are prone to anti-D alloimmunization

BACKGROUND: The D antigen of the polymorphic Rh blood group system is of particular clinical importance regarding transfusion- and pregnancy-induced alloimmunization. Different RhD variants with specific clinical implications have been characterized. The least expressed D variants collectively called DEL are serologically detectable only by adsorption-elution techniques, with so far only poorly defined antigenic properties. STUDY DESIGN AND METHODS: A comprehensive immunohematologic analysis of five of the six currently known DEL genotypes was performed. DEL phenotypes associated with the RHD(M295I), RHD(IVS3+1g>a), RHD(K409K), RHD(X418L), or RHD(IVS5-38del4) allele were characterized with extended serology and flow cytometry. RESULTS: Epitope mapping with adsorption-elution revealed a prominent D epitope loss in the RHD(IVS3+1g>a)-associated DEL phenotype, whereas in the other four DEL types no signs of qualitative D antigen alteration were detected. The observation of alloanti-D in two RHD(IVS3+1g>a) cases confirmed the partial nature of this DEL phenotype. The RHD(M295I) phenotype exhibited the highest D antigen expression among all investigated DEL types, as determined by a semiquantitative adsorption-elution approach and flow cytometry. CONCLUSION: In conclusion, evidence is provided that different DEL genotypes code either for partial or complete D antigen expression and that this finding is clinically relevant. he Rh blood group system is determined by the highly homologous RHD and RHCE genes encoding the RhD and RhCE polypeptides, respectively. The D antigen (RH1) carried by the RhD polypeptide is of particular clinical importance with respect to transfusion- and pregnancy-induced alloim