I. CHARACTERIZATION OF A PAIR OF ALLELIC BLOOD GROUP FACTORS AND THEIR SPECIFIC TMMENE ISOANTIBODLES

The hemolytic manifestations of erythroblastosis fetalis have been shown by the studies of Levine (1) mad Wiener (2) to be due to transfer across the pla- centa of maternal isoantibodies that are specific for certain antigens, notably those of the Rh-Hr system, contained in the red blood cells of the fetus. The pathogenesis of other important aspects of this disease process--intrauterine death, kemicterus, and hydrops fetalis, for example--still remain obscure, however, and it is noteworthy in this relation that these manifestations of the disease have not hitherto been reproduced in experimental anlmals. The studies herein reported deal with the recognition of two new allelic blood group antigens in rabbits and with the characteristics of their specific immune iso. antibodies. These blood group factors and their antibodies axe of particular interest because they resemble in many respects those of the Rh-Hr system in man, and also because they provide opportunity for reproducing in a convenient laboratory animal some of the serological and morphological phenomena as- sociated with erythroblastosis fetalis. These phenomena already briefly re- ported 1 will be described in detail in a subsequent paper (4).