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Blank spaces indicate no equivalent term.

LWa (previously Rh25) and Duclos (previously Rh38) are no longer considered to be Rh system antigens since their encoding genes segregate independently of Rh.

Rh13, Rh14, Rh15, Rh16 and Rh24 are considered obsolete since the reagents to define them are no longer available.

Blank spaces indicate no equivalent term.

LWa (previously Rh25) and Duclos (previously Rh38) are no longer considered to be Rh system antigens since their encoding genes segregate independently of Rh.

Rh13, Rh14, Rh15, Rh16 and Rh24 are considered obsolete since the reagents to define them are no longer available.

In about 3% of patients the autoantibodies react with a well-characterized Rh antigen, such as e, c, C or even, on rare occasions, D. More frequently, the causative antibodies have a more complex specificity and react with 'core' Rh antigens that are present on all red cells with a common Rh phenotype, but arc lacking from red cells with 'deleted' Rh phenotypes, when some or all Rh antigens are absent, e.g. Dc-, D— and Rhnu||. There is as yet no immunological explanation of involvement of the Rh system in such a high proportion of persons autoimmunized to red cell antigens.

At the molecular level, much has been learned since the red cell membrane components that express the Rh antigens were first isolated in 1982. In persons with D+ red cells two Rh genes, RHI) and RHCE, are present. The term RHCE includes (at least) the alleles RHcE, RHCe, RHcc and RHCE. In most D- persons, at least those of Caucasian extraction, RHD is deleted. Both RHD and RHCE appear to be organized into 10 exons over 75 kb of DNA. Exons 1-7 each encode 50-60 amino acids, exons 8-10 encode the 58 residues of the C-terminal end of the proteins. The fourth intron of RHD contains a 60 bp deletion as compared to RHCE. Both RHD and RHCE encode production of nonglycosvlated, fatty acid acylated polypeptides comprised of 417 amino acids (the initiating methionine is then cleaved from the mature protein). Hydropathy analysis forecasts that the polypeptides cross the red cell membrane 12 times, thus suggesting an, as yet unidentified, transporter function. There is considerable homology between the RHD- and RHCE-encoded proteins; of the 416 amino acids only 36 differ. The N- and C-termini of the proteins are highly conserved. At the N-terminal end, the first 42 amino acids encoded by RHD and RHCE are identical. At the C-terminal end, only four of the last 84 amino acids differ. Some amino acid differences in the proteins encoded by the various alleles of RHCE have been correlated with red cell Rh antigen expression; such changes are summarized in Table 2. The partial D situation, in which persons with some but not all epitopes of D on their red cells are able to make allo-immune anti-D, is also understood at the molecular level. Table 3 summarizes the situations in which gene conversion (exon swapping), gene deletion and point mutation can result in an RHD gene that fails to encode all epitopes of D.

Isolation of the nonglycosylated Rh polypeptides results in loss of antigen integrity. It is believed that in situ, the Rh polypeptides are part of a complex that includes noncovalently bound Rh-associated glycoproteins (that are coprecipitated with the nonglycosylated polypeptides) CD47, LW glycoprotein.

Table 2 Amino acid changes in the CcEe polypeptide and antigen correlates

Polypeptide Amino acid at position carries

Table 2 Amino acid changes in the CcEe polypeptide and antigen correlates

Polypeptide Amino acid at position carries

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