The A and B factors as a possible cause of erythroblastosis.

ECENTLY, isoimmunization of the mother by the Rh factor of the fetus and its mechanism have been clearly demonstrated.” 2 On the other hand, only vague references exist in medical literature regarding sensitization by other blood factors. Considering the fact that when red cells pass into the maternal circulation they carry not only the Rh factor but also the blood factors A and B, the M, N, P, Hr and other as yet unknown factors, it is not surprising that immunization by other than the Rh factor may occur. Pregnancy offers a particularly favourable circumstance to produce isoimmunizaiion, because of the slow administration of antigen during a lengthy period. Therefore, this subject must be carefully studied, because our lack of knowledge of the causes of fetal death is striking.