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Background: KEL1 (K) is the most immunogenic red blood cell antigen of the Kell blood group system. The frequently occurring anti-KEL1 alloantibodies may cause hemolytic transfusion reactions as well as severe hemolytic disease of the fetus and newborn. So far, reports on weak KEL phenotypes are scarce., Study Design and Methods: Blood samples of two unrelated Central European propositi with faint reactions in routine KEL1 typing were analyzed by extended serologic phenotyping, flow cytometry, genotyping by polymerase chain reaction with sequence-specific priming, and genomic DNA sequencing of separated parental KEL alleles., Results: Both propositi exhibited an unusual KEL:1,2,3,4 phenotype: markedly weakened and negative reactions were observed in serologic KEL1 typing in gel and tube technique, respectively. No KEL1 epitope loss was detected using five different monoclonal anti-KEL1 reagents. KEL genotyping confirmed KEL*1/2 and KEL*3/4 (Kpa/Kpb) heterozygosity of both individuals. Importantly, DNA sequencing of the two separated parental alleles of both propositi revealed a KEL*1-specific coding nucleotide T578 and a KEL*3-specific T841 on the same allele. This novel KEL*1,3 (KKpa)allele was associated with an approximately 80 percent reduction in KEL1 expression, compared to KEL:1,2,-3,4 controls. The low KEL1 density was attributed to acis-modifier effect of KEL3, so far only reported in association with weakened expression of KEL2 (k)., Conclusion: This is the first description of the KEL*1,3 allele encoding KEL1 and KEL3 on the same molecule. In individuals with weakened KEL1 because of KEL3 in cis, very sensitive serologic or molecular genetic techniques may be required for reliable Kell typing.

Background and Objectives: RH48 (JAL) is a low-incidence Rh antigen of unknown molecular background associated with weakened expression of RhCE antigens. The objective of this study was to establish the molecular basis of JAL., Materials and Methods: Seventeen JAL+ samples, from seven black (one of them a Brazilian of mixed race: black/Caucasian), nine European Caucasians and one Asian individuals, were typed with anti-D, -C, -c, -E and -e. Some samples were also tested for V/VS and ce (f). Titration studies and flow cytometry were used to analyse the expression of the JAL antigen and genomic DNA sequencing of all RHCE exons was conducted on all samples. Routine genotyping for RHCE was carried out on all samples. Screening of RHD exons 1-10, which included detection of the DAU allele, was carried out on all except one of the black samples. The Caucasian samples and remaining black sample were screened for the DAU mutation 1136C>T (T379M)., Results: Six black individuals had the Dce haplotype with RHCE mutations 340C>T (R114W) and 733C>G (L245V) [V/VS] and the RHD mutation T379M [DAU]. One mixed race individual had the Dce haplotype with the RHCE mutation 340C>T (R114W) but without the V/VS or DAU mutation. Eight Caucasians had the DCe haplotype with the 340C>T mutation. One Caucasian and one Asian had the Dce haplotype with a different mutation in an adjacent nucleotide, 341G>A (R114Q). All Caucasian individuals were negative for the DAU mutation 1136C>T (T379M). Previously described weakness of CE-related Rh antigens when present in single dose on JAL+ samples of DCe and Dce haplotypes was observed. Weak expression of V/VS was observed in the three black samples tested and weakness of JAL was observed in the black samples compared to the Caucasian samples., Conclusion: The same mutation (340C>T, R114W) in two different haplotypes (DCe and Dce) and another mutation (341G>A, R114Q) in one of these haplotypes (Dce) are associated with expression of the JAL antigen. One of the RHCE mutations detected in our samples (340C>T) has been previously described but not in association with the JAL antigen. Our results indicate that the previously described RhCeMA and ce(s)(340) alleles encode the JAL antigen. Expression of V/VS antigen is weakened in the presence of JAL and expression of JAL is usually weaker when associated with the Dce haplotype compared to DCe.