Primary anti-D immunization by weak D type 2 RBCs.
BACKGROUND
D is the most immunogenic blood group antigen. In about 0.4 percent of whites, D is expressed on RBCs in a weak form. Recently, it was found that the weak D phenotypes are caused by a large number of distinct RHD alleles generally encoding altered D proteins. No particular molecular weak D type has yet been shown to induce anti-D. The threshold of D antigen density required for anti-D immunization is not known.


METHODS
A 72-year-old D- white man received apparently D- RBCs. Nineteen days later, he developed a positive DAT, and anti-D was found in his serum and an eluate from his RBCs. One donor was found to be D+ with a weak D type. The weak D type was determined by RHD exon 9-specific nucleotide sequencing from genomic DNA. The transfusion recipient showed alloanti-D. Ten months later, anti-D but no other antibody was detectable; the DAT was negative and the eluate was nonreactive. The donor of the incriminated unit was D+ (ccDEe) with weak D due to the weak D type 2 allele, expressing about 450 D antigens per RBC.


CONCLUSIONS
This case provides formal proof that RBCs of weak D type 2 phenotype may cause alloanti-D immunization. Among the more prevalent weak D types in whites, weak D type 2 has the lowest D antigen density. Thus, units of blood from donors of the weak D type 2 phenotype should be labeled D+; the weak D type 2 phenotype may be useful for quality assurance.
Flegel
W A
WA
Department of Transfusion Medicine, University of Ulm, Germany. waf@ucsd.edu
Khull
S R
SR
Wagner
F F
FF
D000368:Aged; D000911:Antibodies, Monoclonal / Q000097:blood; D001782:Blood Donors; D000939:Epitopes / Q000032:analysis; D004912:Erythrocytes / Q000276:immunology*; D006801:Humans; D007519:Isoantigens / Q000097:blood; D008297:Male; D012203:Rh Isoimmunization / Q000097:blood*
D000911:Antibodies, Monoclonal; D000939:Epitopes; D007519:Isoantigens