d. Family studies very early showed that Rho(D) was genetically determined and
that the gene controlling its production behaved like an autosomal dominant. The Rh
gene has recently been shown to reside on chromosome. With only a few fascinating
exceptions, persons who have the gene for Rho(D) will have the antigen directly
detectable on their cells.
2-18. OTHER MAJOR ANTIGENS
a. Further investigation of patients with transfusion reactions, and more frequent
and sophisticated pretransfusion testing, soon revealed antibodies that identified other
antigens associated with Rho(D). By the mid-1940s, 4 additional antigens had been
recognized as belonging to what we now call the Rh system. Despite the many new
discoveries, these four additional antigens and the original Rh factor, Rho(D), remain the
object of more than 99 percent of clinical work in the Rh field.
b. The four additional antigens are rh'(C), rh"(E), hr'(c), and hr"(e). The association
of these factors suggests that immunologic activity of Rh arises from surface material
with several different determinant areas. Some antigenic associations include Rho(D)
and some do not. Antigenic packages that do not include Rho(D) nonetheless have
activity at the other sites. The constitution of these antigenic groups is genetically
determined. In terms of the five major antigens under discussion, a single gene or gene
complex will determine presence or absence of Rho(D), and the production of rh'(C) or
hr'(c), and rh"(E) or hr"(e). Many variations, combinations, and permutations have been
characterized, but these five antigens, and the readily available antibodies that
characterize them, are the backbone of clinical Rh work.
2-19. INHERITANCE AND NOMENCLATURE
a. General. Certain combinations of Rh antigens are transmitted inseparably.
The chemistry of Rh activity has not been delineated, so it is not clear how genetic
information is translated into serologically demonstrable characteristics. The most
ambitious conceptual model of the Rh system is that of Rosenfield and other people,
but the material that follows is given in terms either through transfusion or pregnancy, to
immunizing red blood cells and concepts far simpler than theirs. A single gene or
complex determines the presence on the red blood cell of a specific combination of
antigens. An individual inherits two such genes or complexes, one from each parent.
These may be the same, in which case the person is homozygous for the gene, or
different, making him heterozygous for each of two genes or gene complexes. Rh genes,
like nearly all other blood group genes, are co-dominant, meaning that all genetic
information is translated into detectable red blood cell antigens. The homozygous
individual will have a single set of antigenic determinants; the heterozygote will have two
sets, although one or more individual antigenic specificities may be common to both