Observations are described of the incidence among Caucasians and Negroes of the blood factors RhA, RhB and RhC which occur associated with the Rh0 factor in typical Rh-positive blood. The antiserums used for the tests were derived from Rh-positive patients who had had hemolytic transfusion reactions or erythroblastotic babies. Among a large series of individuals, it was found that only rarely is any of the blood factors RhA, RhB, or RhC lacking from "standard" Rh0-positive blood. On the other hand, about half of the specimens of Rh0 variant blood lack one or more of the factors RhA, RhB, and RhC, which, when present in such blood, are also almost always variants. Judging from the incidence of specimens lacking one or more of these factors, RhA, RhB, and RhB appear to be relatively independent of one another despite their association with blood factor Rh0. Tests for factors RhA, RhB, and RhC distinguish new rare varieties of Rh and ℜh agglutinogens, each genetically determined by corresponding allelic genes.
There is no doubt that more clinical cases will be found in which sensitized Rh-positive individuals have antibodies resembling anti-Rh0 in specificity. Four such cases have already been studied by the present authors, and in each case the antibodies were shown to be different from anti-Rh0 in specificity. Since they were also different from one another, they have been assigned the symbols anti-RhA, anti-RhB, anti-RhC, and anti-RhD, respectively, the first three being the antiserums used in the present study. Obviously, in order to avoid confusion of nomenclature, the specificity of antiserums from other similar cases will have to be compared with anti-RhA, anti-RhB, anti-RhC, and anti-RhD and shown to be different from all four, as well as anti-Rh0, before a distinctive symbol is assigned to them.