The CDe rhesus gene complex; some considerations revealed by a study of a Danish family with an antigen of the Rhesus gene complex (C) D (e) defined by a 'new' antibody

Molecular basis of the LOCR (Rh55) antigen

BACKGROUND

In 1994 during the investigation of a case of hemolytic disease of the newborn, a new low-incidence red cell (RBC) antigen, LOCR, was described. Although the presence of LOCR was associated with altered expression of Rh antigens, its formal assignment to the Rh blood group system did not occur until haplotype and linkage analysis conducted in 2003 provided the necessary proof. The current study was undertaken in an attempt to define the underlying RH mutation in LOCR+ individuals.

STUDY DESIGN AND METHODS

Genomic DNA from five unrelated LOCR+ individuals and three Rh-matched control individuals was amplified by polymerase chain reaction with intronic primers flanking all 10 exons of RH. Amplified products were separated on 1 percent agarose gels and isolated for DNA sequence analysis in both the forward and the reverse directions.

RESULTS

DNA sequence analysis of the three LOCR+ D- individuals revealed a single heterozygous 286G>A nucleotide substitution resulting in a predicted Gly>Ser substitution at amino acid 96. DNA sequence analysis from the two LOCR+ D+ individuals revealed the identical mutation, as well as all of the changes associated with the common RHD gene.

CONCLUSIONS

Based on our results, a Gly96Ser substitution in the Rhce polypeptide defines the low-incidence RBC antigen known as LOCR. This same amino acid change has previously been shown to be involved in the Rh:-26 phenotype, which suggests that LOCR and Rh26 are antithetical. Serologic investigations with various Rh:-26 cells and serum samples, however, reveal that only some c+ Rh:-26 phenotypes are LOCR+.

Molecular background of D(C)(e) haplotypes within the white population

BACKGROUND

D(C)(e) and D(C)e haplotypes may be encountered in the white population. Few data are available on the molecular backgrounds responsible for depressed expression of C and e.

STUDY DESIGN AND METHODS

Individuals of white origin carrying a D(C)(e) genotype resulting in depressed expression of C or both C and e were subdivided into two categories based on the RBC reactivity with the human sera Mol and Hor, which contain antibodies against low-frequency antigens of the Rh (RH) system and other non-Rh low-frequency antigens. Neither Hor+, Mol+ nor Hor+, Mol- RBCs expressed the V (RH10), VS (RH20), and/or Rh32 (RH32) low-frequency antigens. These results suggested that Hor+, Mol+ variants expressed Rh33 (RH33 or Har) and FPTT (RH50), whereas Hor+, Mol- variants might express an undefined low-frequency antigen. Further serologic and molecular analyses were performed.

RESULTS

Molecular analysis of Hor+, Mol+ variants revealed a hybrid gene structure RHCe-D(5)-Ce, in which exon 5 of RHCE (RHCe allele) was replaced by exon 5 of RHD (the so-called RHCeVA allele). The presence of exon 5RHD resulted in several amino acid alterations predicted in the external loop 4 of the CeVA polypeptide. Molecular analysis of Hor+, Mol- variants revealed the presence of a new RHCe allele characterized by a single point mutation C340T within exon 3 (the so-called RHCeMA allele), resulting in a R114W substitution predicted on the external loop 2 of the CeMA polypeptide. A serologic study showed a different pattern of reactivity with C and e MoAbs.

CONCLUSION

Two types of mutations resulted in amino acid substitutions predicted in external loops 4 and 2, respectively, which altered both the C and e reactivity, and indicated conformation changes or defective interaction between nonadjacent loops of the Ce polypeptide. Serologic analysis showed that together with Hor and Mol sera testing, the use of different C and e MoAbs could help to identify these variants within the white population.

MAR, a novel high-incidence Rh antigen revealing the existence of an allelic sub-system including Cw (Rh8) and Cx (Rh9) with exceptional distribution in the Finnish population

We present new genetic evidence obtained from population studies on Finns and from the studies on Finnish blood donors as well as their selected families using an antibody that defines a novel high-incidence Rh antigen MAR. Anti-MAR antibody shows an antithetical relationship to both anti-Cw and anti-Cx. The Rh antigens Cw (RH8) and, more strikingly, Cx (RH9) have each an exceptionally high frequency in Finns. Our studies on their genetic relationship indicate that the three antigens Cw, Cx and MAR behave as if being determined by alleles of the same Rh sub-system. Furthermore, we conclude that this sub-system manifests an inheritance pattern that is distinct from but analogous to that of the two well-known allelic sub-systems of C/c and E/e antigens.

A new, low-incidence red cell antigen (HOFM), associated with depressed C antigen

A case of mild hemolytic disease of the newborn is presented which was caused by an antibody to a hitherto unknown antigen of low incidence. This antigen, now designated as HOFM (ISBT number 700050) was detected in 6 relatives, and in all of them, it was associated with an unusually weakened expression of C antigen. The serological data indicate that HOFM may be part of the Rh system, but the genetic data, although supportive of this interpretation, are inconclusive.

The red cell antigen JAL in the Swiss population: family studies showing that JAL is an Rh antigen (RH48)

The JAL antigen was found to have an overall frequency of 0.004% in the Swiss population and 0.06% in French-speaking Swiss. Family studies of 5 JAL+ individuals have shown that the JAL antigen is not part of the ABO, MNSs, Fy, Jk and Co blood group systems, or the Se system, nor is it X- or Y-linked. JAL is encoded by the RH locus or by a very closely linked locus. The number RH48 (4.48) has been assigned for JAL by the International Society of Blood Transfusion Working Party on Terminology for Red Cell Surface Antigens.

Observations on the number of available C antigen sites on red cells

The number of available C (rh', Rh 2) antigen sites within the Rh system was estimated using trace-labelled antibody. The results, as available sites per red cell, were as follows: CDe/CDe: 45,700-56,400; Cde/Cde: 42,200; CDe/cDE: 25,500-39,700; CwDe/cde: 21,500-40, 000; Cde/cde: 31,100; CDE/cDE: 8,500-9,800; Cde/cde: 7,200. The average equilibrium constant of the anti-C was 0.5 X 10(7) M-1.