Novel weak D types 31 and 32:: adsorption-elution-supported D antigen analysis and comparison to prevalent weak D types

Background: Weak D types are thought to express rather quantitative than qualitative D antigen variants. Distinct type-specific phenotypes and weak D cases with anti-D alloimmunization, however, suggest a variable degree of D antigen alteration. Study Design and Methods: Variant D types were investigated by use of molecular typing, RHD sequencing, extended serologic D antigen investigations, and flow cytometric D antigen density determination. Results: Two novel weak D types were discovered, termed weak D type 31 and 32 with single RHD nucleotide substitutions coding for amino acid exchanges in predicted intracellular RhD polypeptide stretches, with antigen densities of approximately 130 and 50 D sites per red blood cell, respectively. Adsorption-elution technique-supported D epitope mapping of these two weak D types, the recently described weak D type 26, and of the most common Central European weak D types (weak D types 1, 2, 3, 4.0, and 4.1) demonstrated the expression of all tested D epitopes. In contrast, a distinct D epitope loss was detected in weak D type 15 and partial D control samples. Conclusion: All novel and prevalent weak D types expressed all tested D epitopes. Our results indicate that adsorption-elution techniques may be of advantage whenever D epitope loss is suspected in extremely weak D variants.