b. Compound Antigens and Spatial Configuration.
(1) The material on the red blood cell surface that displays Rh activity has
numerous possible antigenic subdivisions. Each gene or gene complex determines a
single surface structure, of which some portions are more likely to elicit antibodies than
others. The product of the gene R1 (CDe) has antigenic activity defined as Rho(D),
rh'(C), and hr"(e). It also has Rh:7, rhi(Ce), the "compound" product of rh'(C), and hr"(e)
together in the same gene product. Cells that have rh'(C) and rh"(e) determined by
separate genes (for example, from an Rzr [CDE/cde] person) do not have the antigen
rhi(Ce). Similar compound antigens exist for hr'(c) and hr"(e) determined by the same
gene (the antigen called Rh:6, hr, f, or ce); hr'(c) and rh"(E) determined by the same
gene (Rh:27, cE); and rh'(C) and rh"(E) determined by the same gene (Rh:22, CE).
(2) These compound antigens elicit antibodies less often than the single
specificities. The fact that they are rarely immunogenic does not mean that they are
absent. Antibodies specific for the compound antigen are very useful in determining
genotype. Anti-hr (f,ce) will agglutinate cells from an Rzr (CDE/cde) person but not from
an R1R2 (CDe/cDE) person, even though their phenotypes with the 5 standard
antiserums appear the same.
(3) The existence of compound antigens provides a clue to the structure of
Rh-active material. Whatever the overall configuration of the material produced by each
gene or gene complex, it appears that the rh'/hr' (C/c) and rh"/hr" (E/e) activities are in
close spatial association. No compound antigens have been found that reflect the
presence of the Rho(D) and rh"(E) or hr"(e) determinants on the same gene. Some
workers find it more logical to write the gene product of R1 (CDe) as DCe, or of R2 (cDE)
as DcE to reflect this seeming spatial contiguity.
c. Deletions. Rare genes exist that appear to code for Rh material which lacks
any activity at the rh"/hr" (E/e) site, or at the sites for both rh'/hr'(C/c) and rh"/hr" (E/e).
(See discussion in Race and Sanger, pp 210-216.) It is as if smaller or larger parts of
the surface configuration were lopped off or compressed, leaving Rho(D) as the only
remaining site. Cells which lack any Rh antigens other than Rho(D) have exceptionally
strong Rho(D) activity an observation that may allow such cells to be identified in routine
d. The Antigen rhG and Cross-Reactions. The rhG (or G) antigen cannot be
neatly fitted into the concept of 3 antigenic regions; rather, it appears to be a cross-
reaction between Rho(D) and rh'(C). It almost always accompanies Rho(D) or rh'(C),
and antibodies against rhG superficially appear to be anti-Rho(D) plus anti-rh'C). The
anti-rhG(G) activity cannot, however, be separated into anti-rh'C) and anti-Rho(D). Rare
cells have been found which display rhG but lack Rho(D) and a reasonable expression of
rh'(C); and there are even rarer cells that have at least part of Rho(D) but lack rhG. Such
antibody specificity explains how Rh-negative persons who receive cells positive for