title: Primary anti-D immunization by weak D type 2 RBCs.
abstract: 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.
authors.affiliation: Department of Transfusion Medicine, University of Ulm, Germany. waf@ucsd.edu
authors.forename: W A
authors.initials: WA
authors.lastname: Flegel
authors.forename: S R
authors.initials: SR
authors.lastname: Khull
authors.forename: F F
authors.initials: FF
authors.lastname: Wagner
mesh_terms: 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*
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D007519:Isoantigens