Anti-D immunization by DEL red blood cells.

No data are available on the immunogenicity of extremely weak D variants called DEL. Evaluation of alloanti-D formation in a D- female patient after transfusion of apparently D- blood from an Austrian donor led to discovery of a so far unknown DEL type.Standard blood group serologic methods were applied. Molecular typing, RHD sequencing, and D epitope mapping was performed and the absolute D antigen density determined.After transfusion of RBCs typed D- by routine serology, the recipient developed alloanti-D. Further evaluation with an indirect antiglobulin test confirmed donor RBCs to be D-. Molecular typing, however, demonstrated the presence of the RHD gene in one donor, and RHD sequencing revealed a deletion of four nucleotides in RHD intron 5 (RHD IVS5-38del4) as the only difference compared to the normal RHD gene. Adsorption-elution techniques demonstrated a DEL phenotype without apparent loss of D epitopes.This study documents the clinical significance of the DEL phenotype in blood units that was capable of inducing anti-D in a recipient. Qualitative data are provided on D epitope expression in DEL RBCs.