![]() The highest homology is within the transmembrane domains, suggesting a conserved functional role for the RhAG protein family. 79 These genes are predicted to encode proteins with remarkably high (respectively, 46%, 39%, and 47%) amino acid identity to human RhAG. These homologs have been found as 2 different RHAG-like genes in Caenorhabditis elegans (a nematode GenBank accession U64 847 and Z74 026) 78 and as at least 1 in Geodia cydonium (a marine sponge GenBank accession Y12 397). ![]() However, the discovery of sequence-related RHAG homologs in invertebrates suggests otherwise. It was thought that Rh proteins were erythroid-specific and confined to higher vertebrates. 20, 28, 31-33, 35, 36 Despite the high degree of homology, the various RhCcEe proteins do not express any D epitopes, and RhD protein does not express C or e antigens. 20, 31-33 and that RhD differs from the common forms of RhCE by only 30 to 35 amino acids along the entire protein. Analysis of the primary amino acid sequences (inferred from cDNAs) shows that the first 41 N-terminal amino acids of RhD and RhCE/e are identical. 19, 28-30 Characteristics of the RhD protein (synonyms: Rh30, Rh30B, Rh30D, D 30, Rh30 polypeptide, RhXIII, Rh13) and of the RhCcEe protein (synonyms: Rh30, Rh30A, Rh30C, Rh30 polypeptide, RhIXb cDNA,, Rh21 cDNA, R6A 32, Rhce, RhCe, RhcE, RhCE, CcEe) are summarized in Table 1 and depicted in Figure 1. The RhD protein expresses the D antigen, while the RhCcEe protein carries either C or c antigens (involving the second extracellular loop) together with E or e antigens (involving the fourth extracellular loop) on the same protein. RBCs with the Rh nullphenotype do not express any of the Rh antigens. RBCs lack E and e antigens, and D−− RBCs lack C, c, E, and e antigens. Rare deletion phentoypes use dashes in the notation to indicate a lack of antithetical antigens eg, Dc−. This notation has practical value in transfusion medicine as a means to communicate the Rh phenotype of a patient or donor. The uppercase “R” is used when the D antigen is expressed, lowercase “r” when it is not. The most frequently occurring forms of RHCE and RHD encode 8 haplotypes: Dce, dce, DCe, dCe, DcE, dcE, DCE, and dCE, known in short, respectively, as R 0, r, R 1, r′, R 2, r″, R z, and r y. Although d antigen, which was thought to be antithetical to D, does not exist, the letter “d” is used to indicate the D-negative phenotype. The common Rh antigens: D, C or c, and E or e, were originally written in alphabetical order (CDE) but later, when it was recognized that C and E antigens are inherited en bloc, the order was changed to DCE. ![]() Because Rh30 and Rh50 also relate to Go a and FPTT antigens, respectively, we will use RH as a generic term for genes encoding either the RhD protein or the RhCcEe (also known as RhCE) protein and use RHAG for the gene encoding the Rh-associated glycoprotein (RhAG). ![]() 6-9 RH30 and RH50 have been used to describe genes encoding Rh proteins (Rh30) and Rh glycoprotein (Rh50), respectively, where the numbers relate to the apparent molecular mass of the proteins on a SDS-polyacrylamide gel. 5 The numeric portion of the ISBT terminology for Rh antigens is based on the nomenclature described by Rosenfield et al. Throughout this review, we will use traditional terminology recommended by the International Society of Blood Transfusion (ISBT) committee for terminology of blood group antigens. Several nomenclatures have been used to describe antigens, proteins, and genes in the Rh system. The heteroantibody was renamed anti-LW (after Landsteiner and Wiener), and the human alloantibody was renamed anti-D. 3 Therefore, the original terms (Rh factor and anti-Rh) coined by Landsteiner and Wiener, although being misnomers, have continued in common usage. It was soon realized that this was not the case. Initially, it was thought that the animal and human antibodies identified a common factor, Rh, on the surface of rhesus and human RBCs. 1 The following year, Landsteiner and Wiener 2 found that sera from rabbits (and later guinea pigs) immunized with RBCs from Macaca mulatta ( Macacus rhesus in the original paper) agglutinated 85% of human RBC samples. Her serum agglutinated red blood cells (RBCs) from her husband and from 80% of Caucasian ABO-compatible donors. A woman had a severe transfusion reaction when she was transfused with blood from her husband following delivery of a stillborn child with erythroblastosis fetalis. The Rh blood group system was first described 60 years ago.
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