Alloanti-c (RH4) revealing that the (C)ces haplotype encodes a partial c antigen

BACKGROUND: In the Rh blood group system, published observations showed that the c antigen has the fewest variant forms of the principal antigens in this system. The partial nature of the c antigen was only reported in c+ Rh:−26 persons and to be associated with the ces(340) allele. This study reports the first case of alloanti-c related to a (C)ces haplotype. STUDY DESIGN AND METHODS: Serologic and genetic studies were performed on blood samples of a multitransfused 40-year-old African patient with sickle cell disease displaying a DCcee phenotype. RESULTS: Red blood cells (RBCs) of the patient displayed normal expression of C, c, e, ce antigens either with routine reagents or with monoclonal antibodies. Analyses of DNA and Rh transcripts showed that the patient carried a (C)ces/DCe genotype. The patient's serum contained anti-D, anti-c, anti-E, anti-e, anti-V, anti-Jsa, and anti-S. Anti-c was isolated from the mixture of antibodies by using absorption and adsorption-elution techniques. Anti-c provided consistent reactions with c+ RBCs. Reactions were stronger with c+ ce+ RBCs than with c+ ce− RBCs. No agglutination of RBCs from individuals carrying a homozygous (C)ces genotype was observed. CONCLUSION: These data provide the evidence that anti-c in our patient was an alloanti-c and, consequently, that (C)ces haplotype encodes a partial c antigen. The clinical significance of anti-c related to this haplotype should be evaluated in the future.