Section III. THE Rh SYSTEM
2-16. BACKGROUND
The Rh system is so complex and aspects of its genetics, nomenclature, and
antigenic interactions are so unsettled that any attempt for complete coverage in this
subcourse would be futile. Except for those working in highly specialized laboratories,
however, the body of essential information is relatively compact. This section will
concentrate on commonly encountered observations, problems, and solutions, without
exhaustive theoretical considerations.
2-17. Rh-POSITIVE AND Rh-NEGATIVE
a. The unmodified descriptive terms Rh-positive and Rh-negative refer to the
presence or absence of a single red blood cell antigen. This antigen was first
characterized, in 1939, by Levine and Stetson, who found the identifying antibody in the
serum of a woman whose fetus had fatal hemolytic disease of the newborn. It received
its name in 1940, when Landsteiner and Wiener immunized rabbits with red blood cells
from rhesus monkeys and found that the rabbit antirhesus antibody agglutinated
approximately 85 percent of human red blood cells tested. They gave the name "Rh" to this
determinant present on all rhesus monkey cells and apparently present on 85 percent of
human red blood cells. Levine and his co-workers found several other postpartum
women with similar antibodies, at least one of which gave reactions parallel to rabbit anti-
Rh, and Weiner and Peters observed human examples of anti-Rh in Rh-negative
patients who had received ABO-compatible, Rh-positive transfusions.
b. Now called Rho(D), this antigen is, after A and B, the most important antigen
in transfusion practice. Unlike the situation with ABO, persons whose cells lack the
antigen do not routinely have the antibody in their serum. Formation of the antibody
almost always results from exposure, either through transfusion or pregnancy, to
immunizing red blood cells containing the antigen; and such exposure elicits antibody
production in a high proportion of Rh-negative subjects. As transfusions became more
frequent in the 1940s there were increasing opportunities for immunization to occur and
for the antibody, once developed, to become apparent. Investigation and discoveries
have continued apace.
c. The immunogenicity of Rho(D), that is, its likelihood of provoking an antibody
if transfused into a negative recipient, is greater than that of virtually all other antigens
studied. In routine transfusion practice, Rho(D) is the only antigen for which red blood
cells are tested (outside of A and B), so that Rh-negative recipients can be identified
and given Rh-negative blood. Of the Rh-negative recipients of Rh-positive blood, 50
to 75 percent can be expected to develop the antibody.
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