Some Observations on Blood Factors Rh^A, Rh^B and R^C of the Rh-Hr Blood Group System

The complex serologic behavior of the Rh-Hr agglutinogens has been underlined by the recent discovery that, with very rare exceptions, associated with blood factor Rh_o of Rh-positive blood, there are numerous other blood factors which may be designated Rh^A, Rh^B, Rh^C, etc. Rare Rh-positive individuals exist whose bloods have blood factor Rh_o but lack one or more of the other components. Such individuals can and have become sensitized to the missing blood factor. For example, in the case of an Rh-positive individual lacking blood factor Rh^A, anti-Rh^A may be produced. When Rh^B and/or Rh^C are lacking, anti-Rh^B and anti-Rh^C may be produced. In fact, we have identified all three antibodies. These three antiserums are indistinguishable from "standard" anti-Rh_o serum in parallel tests on a random series of blood specimens unless one of the rare Rh-positive bloods lacking blood factor Rh^A, Rh^B or Rh^C are included.

In the present paper, anti-Rh^A serum from a sensitized type $$Word$$ mother whose child had erythroblastosis was used for studies on the distribution and heredity of the Rh^A blood factor. A total of 2012 blood specimens from Rh_o-positive individuals were tested; 951 from Caucasoids and 918 from Negroids. In tests on blood from Caucasoids, a "standard" Rh_o blood factor was invariably associated with a "standard" Rh^A blood factcr. In no instance where the reactions with anti-Rh_o serums were typical was the Rh^A factor absent or a variant. However, if the Rh_o factor was a variant, three possibilities with regard to factor Rh^A were identified. Either factor Rh^A was "standard," or factor Rh^A was a variant, or factor Rh^A was absent. This last possibility rarely occurs in Caucasoids since in our series only one Caucasoid blood or 0.1 per cent lacked Rh^A blood factor and in that case the Rh_o factor was a variant.

Among the 918 Rh-positive blood specimens from Negroids examined the situation was found to be somewhat different. While a "standard" Rh_o blood factor was almost always associated with a "standard" Rh^A blood factor, in 0.9 per cent the Rh^A factor was absent. Among blood specimens with a Rh_o variant blood factor, just as with Caucasoids, all three possibilities were identified, namely, bloods with "standard" Rh^A blood factor, with Rh^A variant blood factor and also bloods with blood factor Rh^A absent. The incidence of Rh-positive bloods lacking factor Rh^A was considerably higher among Negroids than among Caucasoids, namely, 1.6 per cent in Negroids, as compared with only 0.1 per cent in Caucasoids.

One interesting family was studied. The father’s blood had the "standard" Rh_o blood factor, but lacked the Rh^A component (type $$Word$$). The mother’s blood had the Rh_o variant blood factor, and also lacked blood factor Rh^A (type $$Word$$). The child’s blood was of the same type as its mother, namely, Rh_o variant and lacking blood factor Rh^A (type $$Word$$). Possible genetic explanations for these observations and their clinical significance are discussed.