Insights into anti-D formation in carriers of RhD variants through studies of 3D intraprotein interactions

A cold case of hemolytic disease of the fetus and newborn resolved by genomic sequencing and population studies to define a new antigen in the Rh system

BACKGROUND

We report an obstetric case involving an RhD-positive woman who had developed a red blood cell (RBC) antibody that was not detected until after delivery of a newborn, who presented with a positive direct antiglobulin test result. Immunohematology studies suggested that the maternal antibody was directed against a low-prevalence antigen on the paternal and newborn RBCs.

RESULTS

Comprehensive blood group profiling by targeted exome sequencing revealed a novel nonsynonymous single nucleotide variant (SNV) RHCE c.486C>G (GenBank MZ326705) on the RHCE*Ce allele, for both the father and newborn. A subsequent genomic-based study to profile blood groups in an Indigenous Australian population revealed the same SNV in 2 of 247 individuals. Serology testing showed that the maternal antibody reacted specifically with RBCs from these two individuals.

DISCUSSION

The maternal antibody was directed against a novel antigen in the Rh blood group system arising from an RHCE c.486C>G variant on the RHCE*Ce allele linked to RHD*01. The variant predicts a p.Asn162Lys change on the RhCE protein and has been registered as the 56th antigen in the Rh system, ISBT RH 004063.

CONCLUSION

This antibody was of clinical significance, resulting in a mild to moderate hemolytic disease of the fetus and newborn (HDFN). In the past, the cause of such HDFN cases may have remained unresolved. Genomic sequencing combined with population studies now assists in resolving such cases. Further population studies have potential to inform the need to design population-specific red cell antibody typing panels for antibody screening in the Australian population.

Molecular dynamics of the human RhD and RhAG blood group proteins

Introduction: Blood group antigens of the RH system (formerly known as "Rhesus") play an important role in transfusion medicine because of the severe haemolytic consequences of antibodies to these antigens. No crystal structure is available for RhD proteins with its partner RhAG, and the precise stoichiometry of the trimer complex remains unknown. Methods: To analyse their structural properties, the trimers formed by RhD and/or RhAG subunits were generated by protein modelling and molecular dynamics simulations were performed. Results: No major differences in structural behaviour were found between trimers of different compositions. The conformation of the subunits is relatively constant during molecular dynamics simulations, except for three large disordered loops. Discussion: This work makes it possible to propose a reasonable stoichiometry and demonstrates the potential of studying the structural behaviour of these proteins to investigate the hundreds of genetic variants relevant to transfusion medicine.

Use of computational biology to compare the theoretical tertiary structures of the most common forms of RhCE and RhD

BACKGROUND AND OBJECTIVES

Computational biology analyses the theoretical tertiary structure of proteins and identifies the 'topological' differences between RhD and RhCE. Our aim was to identify the theoretical structural differences between the four isoforms of RhCE and RhD using computational biological tools.

MATERIALS AND METHODS

Physicochemical profile was determined by hydrophobicity and electrostatic potential analysis. Secondary and tertiary structures were generated using computational biology tools. The structures were evaluated and validated using Ramachandran algorithm, which calculates the single score, p-value and root mean square deviation (RMSD). Structures were overlaid on local refinement of 'RhAG-RhCE-ANK' (PBDID 7uzq) and RhAG to compare their spatial distribution within the membrane.

RESULTS

All proteins differed in surface area and electrostatic distance due to variations in hydrophobicity and electrostatic potential. The RMSD between RhD and RhCE was 0.46 ± 0.04 Å, and the comparison within RhCE was 0.57 ± 0.08 Å. The percentage of amino acids in the hydrophobic thickness was 50.24% for RhD while for RhCE it ranged between 73.08% and 76.68%. The RHAG hydrophobic thickness was 34.2 Å, and RhCE's hydrophobic thickness was 33.83 Å. We suggest that the C/c antigens differ exofacially at loops L1 and L2. For the E/e antigens, the difference lies in L6. By contrast, L4 is the same for all proteins except Rhce.

CONCLUSION

The physicochemical properties of Rh proteins made them different, although their genes are homologous. Using computational biology, we model structures with sufficient precision, similar to those obtained experimentally. An amino acid variation alters the folding of the tertiary structure and the interactions with other proteins, modifying the electrostatic environment, the spatial conformations and therefore the antigenic recognition.

Systematic RHD genotyping in Brazilians reveals a high frequency of partial D in transfused patients serologically typed as weak D

BACKGROUND

The discrimination between weak D types and partial D can be of clinical importance because carriers of partial D antigen may develop anti-D when transfused with D-positive red blood cell units. The aim of this study was to determine by molecular analysis the type of D variants among Brazilian patients requiring transfusions with serologic weak D phenotypes.

MATERIAL AND METHODS

Samples from 87 patients (53 with sickle cell disease, 10 with thalassemia and 24 with myelodysplastic syndrome), serologic typed as weak D by manual tube indirect antiglobulin test or gel test were first RHD genotyped by using the RHD BeadChip Kit (BioArray, Immucor). Sanger sequencing was performed when necessary.

RESULTS

RHD molecular analysis revealed 32 (36.8 %) variant RHD alleles encoding weak D phenotypes and 55 (63.2 %) alleles encoding partial D antigens. RHD variant alleles were present in the homozygous state or as a single RHD allele, one variant RHD allele associated with the RHDΨ allele, or two different variant RHD alleles in compound heterozygosity with each other in 70 patients, 4 patients and 13 patients, respectively. Alloanti-D was found in 9 (16.4 %) cases with RHD alleles predicting a partial D.

DISCUSSION

The frequency of partial D was higher than weak D types in Brazilian patients serologically typed as weak D, showing the importance to differentiate weak D types and partial D in transfused patients to establish a transfusion policy recommendation.

Maternal red blood cell alloimmunisation Working Party, literature review. RH blood group system: Rare specificities

This report is part of a series reporting the GRADE review performed by the 2018-2020 French Working Party on maternal red blood cell alloimmunisation. This report focusses on the clinical significance in obstetrics, as published in the scientific literature, of the rare RH antibodies, variants and antigens (i.e. excluding conventional RH1 trough RH8 antigens, RH12, RH22 and RH27, which are discussed in other reports of this series). Extremely severe or severe haemolytic disease of the fetus and the newborn (HDFN), leading to death or requiring transfusions, have been reported for: anti-RH1 (-D) associated with DVI, DBT and DIVb phenotypes, RHD*12.04 (DOL4), RHD*03.03 (DIIIc), RHD*D-CE(2-5)-D, RHD*01EL.31 (RHD*148+1T), anti-RH9 (-C^X), anti-RH11 (-E^W), anti-RH17 (-Hr⁰), anti-RH18 (-Hr), anti-RH19 (-hr^S), anti-RH23 (-D^W), anti-RH29 ("total" Rh), anti-RH30 (-Go^a), anti-RH32, anti-RH34 (-Hr^B), anti-RH36 (-Be^a), anti-RH40 (-Tar), anti-RH46 (-Sec), anti-RH48 (-JAL), anti-RH54 (DAK), and antibodies to high prevalence antigens such as those associated with RHCE*02.08.02 (RHCE*C^W-RHD(6-10)), RHCE*03N.01 (RHCE*cEMI). HDFN of moderate, mild or undetailed severity have been reported for: anti-RH1 associated with DHar, DIIIa and DIVa phenotypes, RHD*01EL.08 (RHD*486+1A),RHD*01EL.44 (RHD*D-CE(4-9)-D),RHD*25 (DNB), anti-RH20 (-VS), anti-RH31 (-hr^B), anti-RH37 (-Evans), ani-RH42, anti-RH49 (-STEM), anti-RH51 (-MAR), anti-RH55 (-LOCR), anti-RH58 (-CELO). Positive direct antiglobulin test in the newborn but no clinically significant HDFN has been reported for anti-RH1 (-D) associated with RHD*10.05 (DAU5), RHD*12.02 (DOL2). Because so many specificities are associated with severe HDFN in the RH system, all RH antibodies should be considered as potentially able to cause HDFN, even if none has been reported yet.

A Review of the Literature Organized Into a New Database: RHeference

Hundreds of articles containing heterogeneous data describe D variants or add to the knowledge of known alleles. Data can be difficult to find despite existing online blood group resources and genetic and literature databases. We have developed a modern, elaborate database for D variants, thanks to an extensive literature search with meticulous curation of 387 peer-reviewed articles and 80 abstracts from major conferences and other sources. RHeference contains entries for 710 RHD alleles, 11 RHCE alleles, 30 phenotype descriptions (preventing data loss from historical sources), 35 partly characterized alleles, 3 haplotypes, and 16 miscellaneous entries. The entries include molecular, phenotypic, serological, alloimmunization, haplotype, geographical, and other data, detailed for each source. The main characteristics are summarized for each entry. The sources for all information are included and easily accessible through doi and PMID links. Overall, the database contains more than 10,000 individual pieces of data. We have set up the database architecture based on our previous expertise on database setup and biocuration for other topics, using modern technologies such as the Django framework, BioPython, Bootstrap, and Jquery. This architecture allows an easy access to data and enables simple and complex queries: combining multiple mutations, keywords, or any of the characteristics included in the database. RHeference provides a complement to existing resources and will continue to grow as our knowledge expands and new articles are published. The database url is http://www.rheference.org/.